INTEGRATED PEST MANAGEMENT MANUAL FOR MINNESOTA STRAWBERRY FIELDS. A Scouting and Management Guide for Key Strawberry Pests

Transcription

1 INTEGRATED PEST MANAGEMENT MANUAL FOR MINNESOTA STRAWBERRY FIELDS A Scouting and Management Guide for Key Strawberry Pests Minnesota Department of Agriculture September, 2007

2 Integrated Pest Management Manual for Min ne so ta Strawberry Fields, 2nd Edition 2007 Revised and rewritten by Thaddeus McCamant, Northland Community & Technical College, Detroit Lakes, MN. Acknowledgements The 2007 Manual was developed and published by the Minnesota Department of Agriculture. Funding for the revised 2007 Manual is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association (MFVGA) and the United States Department of Agriculture Risk Management Agency (RMA). These institutions are equal opportunity providers. The following persons helped review and/or contributed to the 2nd Edition: Emily Hoover, University of Minnesota, Horticulture Department, St. Paul, MN Bill Jacobson, Pine Tree Apple Orchard, White Bear Lake, MN John Luhman, Minnesota Department of Agriculture, St. Paul, MN Steven Poppe, University of Minnesota, West Central Research and Outreach Center, Morris, MN Edited by: Jeanne Ciborowski, Minnesota Department of Agriculture [The following individuals were contributing authors to the 1 st Edition: Henry Fadamiro, formerly Minnesota Department of Agriculture; Thaddeus McCamant, Northland Community and Technical College, Detroit Lakes, MN; Suzanne Wold- Burkness, formerly University of Minnesota, St. Paul, MN; Terrance Nennich, University of Minnesota Extension, Crookston, MN; Jill MacKenzie, formerly University of Minnesota Extension.] For additional copies of this manual, contact: Minnesota Department of Agriculture Agricultural Development and Financial Assistance Division 625 Robert Street North St. Paul, MN Phone: In accordance with the Americans with Disablities Act, an alternative form of communication is available upon request. TTY:

3 Table of Contents 1. Introduction Pest Management Concepts and Definitions... 6 Pest Classification Beneficials and Biological Control Integrated Pest Management Cultural Practices Resistant Varieties Economic/Action Thresholds Pesticide Resistance Degree Days and Insect Pest Forecasting Forecasting Disease Infection Periods Forecasting Weed Emergence 3. Using Pesticides Safely Pest Scouting Pest Scouting Equipment Scouting Techniques 5. Strawberry Developmental Stages and Associated Pests Planting Year Planting to First Runners First Daughter Plants to Full Canopy Full Canopy to Dormancy Bearing Fields Early Spring Pre-bloom Full Bloom Green Fruit Ripe Fruit Post-harvest 6. Biology and Management of Select Insect Pests and Diseases of Strawberry INSECTS Tarnished Plant Bug Strawberry Bud Weevil Flower Thrips Twospotted Spider Mite Cyclamen Mite Slugs White Grubs DISEASES Gray Mold Anthracnose Leather Rot Root Diseases

4 7. Weed Management in Minnesota Strawberry Fields Problem Weeds in Minnesota Strawberry Fields Site Preparation/Rotation Out of Strawberries Weed Control During the Establishment Year Weed Control in Bearing Fields 8. IPM in Day Neutral Strawberries Tarnished Plant Bug Other Insect Pests Diseases Organic Options 9. Organic Systems for June Bearing Strawberries The Finke System - Single Year Cropping Organic Production Using Long Rotations 10. Red Raspberries Appendix 1: Pesticide Options for Strawberries - Overview Appendix 2: Herbicide Options for Strawberries - Planting Year (Establishment) Appendix 3: Herbicide Options for Stawberries - Production Years (Bearing) Appendix 4: Insecticides for Strawberries Appendix 5: Fungicides for Strawberries Appendix 6: References and Suggested Readings Appendix 7: Sources of Pest Management Supplies DISCLAIMER Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current manufacturer directions. 4

5 1. Introduction STRAWBERRIES can be grown in all parts of Minnesota, from Lake of the Woods in the north to the bluffs of the Mississippi in the south. Demand for locally grown strawberries is high and increasing. Dozens of small farms throughout the state supplement their incomes while meeting the demand for healthy, locally grown berries. A well managed strawberry farm in a good location can gross more than $10,000 an acre. As a high value crop, strawberries also require high inputs. Production costs average $5,000 an acre, with the highest cost being weed control. Growers must also spend hundreds of dollars per acre on insect and disease control, or risk losing their crop. In conventional strawberry production, growers sprayed fungicides weekly from bloom through harvest. With Integrated Pest Management (IPM), growers use cultural practices to lower the pest pressure in their fields and spray when the insects or diseases are present at high enough levels to lower yield. In an IPM program, a grower must spend time monitoring his/her field, but the higher costs in labor and time are offset by lower pesticide costs, fewer environmental concerns and better control of some pests. Strawberry growers interested in adopting IPM can use the information in this manual to improve their skills on their own farms. Minnesota has a unique climate, with warm, humid summers, long, cold winters, and short springs. The developmental phenology of many pests is different than in places with milder winters or longer springs. The current manual is intended for use as a tool to aid Minnesota strawberry growers and growers from other Upper Midwest states in sampling, monitoring, and managing key insect, mite, disease, and weed pests. This publication incorporates research data collected in Minnesota during the past few years as well as tested IPM concepts and information from other sources. In dealing with pesticide information throughout this manual, our goal is not to endorse a particular product or trade name, but to merely indicate possible options to the grower or user. It is our hope that growers, academics, scientists, extension agents, industry representatives, private consultants, and other members of the fruit production community will find this manual useful and informative. Kendall Lorenz helping with the strawberry harvest. 5

6 2. Pest Management Concepts and Definitions Pest Classification Insects: Strawberry pests can be classified according to the part of the plant they infest or by their economic importance. Fruit and flower feeders include tarnished plant bugs, slugs, sap beetles, thrips, and strawberry bud weevils. Fruit feeders directly lower yields by reducing the number of fruit, reducing fruit size or making the fruit unmarketable. Leaf feeders such as leafrollers, leafhoppers, aphids, and mites reduce the plant s leaf area and reduce yields by lowering a plant s photosynthetic capacity. Root-feeding insects such as strawberry rootworm, root weevils, and white grubs attack and damage strawberry roots and either stunt or kill plants. Insect pests can also be classified in terms of the seriousness of their infestation. Key pests cause major damage on a regular basis unless controlled. Occasional pests become intolerable only irregularly due to climate or a change in environment. Secondary pests can be tolerated in small numbers and do not need to be controlled every year. Secondary pests can become important after broad spectrum insecticides kill beneficial insects. Diseases: Strawberry diseases can also be classified according to the part of the plant infected. Fruit diseases include gray mold, anthracnose, and leather rot. Leaf spot, leaf scorch, and leaf blight lower yields by reducing leaf area. Diseases such as red stele, black root rot, and verticillium wilt damage root systems, causing stunted or dead plants. Beneficials and Biological Control Most insects, mites, fungi and bacteria living in a strawberry field are either benign or beneficial. Benign organisms neither directly help nor harm berry plants, like the fungi that break down the straw each summer. Beneficial insects include insects that feed on insect pests or bees that aid pollination and assure fruit set. Beneficial fungi and bacteria help strawberry plants absorb nutrients from the soil and protect plants from diseases. Two important groups of beneficials are the predators, and parasitoids. Predators attack or kill a pest (e.g. lady beetles, syrphid flies, lacewings, ants, spiders, and predator mites). Parasitoids are small wasps that lay their eggs in insect eggs, larvae, pupae or in aphids. The larvae hatch in the host, feed and grow inside the host and eventually kill it. Many insects do not fit neatly into the categories of beneficial, benign or pest. Some insects can be beneficial at one time of year and turn into a pest at another time of year, such as yellow jackets which eat caterpillars in midsummer, but feed on fruit in late summer. Others, such as the Polydrosus beetle, are benign at low levels, but can harm a strawberry field if the plants are weak and the beetle population is high. Scientists have yet to assign a role to most of the insects and mites living in a strawberry field. Strawberry growers should try to increase the population of natural enemies to common pests through introduction, augmentation, or conservation techniques. Introduction is releasing predators or parasites that are not living in the field. Augmentation is releasing natural enemies to boost existing populations. Conservation is manipulating habitat and resources to conserve or enhance natural enemy numbers. Beneficials will thrive if growers spray insecticides only when needed, time their sprays accurately, or select pesticides that are least toxic to beneficials. Many broad spectrum insecticides kill minor pests, secondary pests and beneficials. Under an integrated pest management program, broad spectrum insecticides are used sparingly and secondary pests are carefully monitored and managed to preserve beneficials. 6

7 Integrated Pest Management Integrated pest management (IPM) coordinates the use of pest biology, environmental information and available technology to prevent unacceptable levels of pest damage by the most economical means, while posing the least possible risk to people and the environment. IPM strategies include planting pest-resistant varieties, pest scouting, pest forecasting, cultural control, physical control, biological control, and judicious pesticide use. Synthetic pesticides can be used in an IPM program when no other options are available and the pesticides do not eradicate benign or beneficial organisms. By using multiple control strategies, pests are less likely to develop resistance to one particular strategy. The goal of IPM is to produce high quality, safe fruit in a cost-effective manner without significant adverse effects on the environment. IPM began when growers and scientists realized that most insect problems did not disappear under conventional pest control. Growers who practice IPM don t try to eliminate all pests, but rather try to suppress pest populations to levels that do not cause economic damage rather than eradicate all insects. IPM requires a knowledge of pests and the coordination of all fruit production components. Growers who want to develop an IPM program should develop the following skills and knowledge: Learn to identify insect and disease pests and their associated damage on your farm. Know the biology and ecology of key pests in your planting. Know how climate and location influence pest infestation in your field. Learn to differentiate between beneficial organisms and pests. Assess the potential of beneficials to control pests. Find accurate information on appropriate pest control options, their use, efficacy, and potential adverse effects. Most of the skills listed above can be acquired through training, short-courses, or from appropriate and relevant publications such as field guides and IPM manuals. Cultural Practices Cultural practices form the foundation of a good IPM program that reduce pest populations and minimize diseases. By choosing the right site to grow strawberries, you can lower disease and insect pest pressure. Strawberries should be planted in well-drained soil that does not have standing water following a heavy summer rainstorm. Planting on higher ground minimizes frost damage, while increasing air circulation around the strawberry plants. Good air circulation allows the berries to dry out faster, reducing gray mold and anthracnose outbreaks. Strawberries should be rotated to different fields at regular intervals. Land that has been in strawberries for four years should be planted to another crop or a series of cover crops for one to two years to reduce root diseases. Solanaceous crops like tomatoes, potatoes and peppers carry verticillium wilt and should be avoided as rotation crops. By rotating crops, growers can reduce the number of weeds and weed seeds in a field. Perennial weeds like quackgrass, white clover and Canada thistle expand through existing fields. Fields with quackgrass, white clover or Canada thistle should be plowed and replaced with a cover crop. Slow moving pests like strawberry bud weevil and cyclamen mites build up gradually each year, and many strawberry growers have eliminated sprays for both pests by plowing their strawberry fields under after one or two harvest seasons (Chapter 8). Straw mulch can reduce fruit diseases better than fungicides. Straw mulch reduces winter injury, and plants that have less winter injury have fewer diseases. Straw mulch is equally important in the spring and summer, when it reduces fruit diseases by keeping fungi from moving from the soil or dead leaves to the strawberry fruit. When possible, chop the straw when applying straw in the fall. Many people use straw choppers developed specifically for strawberries, but straw choppers developed for animal bedding or road construction work well too. Finely chopped straw falls between the plants and protects the developing fruit better than unchopped straw. When removing straw in spring, ½ to 1 of straw should be left over the row to keep fruit off the soil. 7

8 Most strawberry growers renovate their fields after harvest, which helps control many diseases and insect pests. During renovation, growers mow the leaves off the strawberry plants and till between the rows, narrowing the rows to a specified width. Mowing interrupts the disease cycle of leaf diseases, resulting in healthier leaves during late summer. Mowing should be done before August 1, so that plants can develop a new canopy by the middle of August. Growers who remove mowed leaves during renovation have found fewer leaf diseases. Mowing reduces the number of plants in the rows and improves air circulation. Rows should be narrowed to 12 to 20 at the end of the growing season. Narrow rows dry faster and expose the fruit to more sun, thereby reducing the chance for fungi to infect fruit. Resistant Varieties Plant breeders have enhanced disease resistance to leaf spot, red stele (rare in Minnesota) and verticillium wilt. Many popular varieties in Minnesota are resistant to diseases and insect pests. Honeoye shows some resistance to tarnished plant bug. Glooscap, Cavendish, Annapolis and Honeoye rarely get leaf spot or leaf scorch above economic thresholds. New strawberry varieties are being introduced faster than scientists can evaluate their resistance to secondary diseases and pests, and new pests and diseases are constantly moving into Minnesota. Strawberry growers are finding that some varieties are more resistant to the new diseases than others. Before planting, always talk to other strawberry growers in your area to determine which varieties are most resistant to diseases. Economic/Action Thresholds In conventional pest control, growers tried to eradicate pests. In IPM, growers try to manage pests and keep their populations below a level that will cause economic damage. The term economic threshold refers to the point when the economic losses caused by a pest exceed the cost of the pesticide application. In most cases, the insect pests must be controlled long before any damage is seen, and growers must follow thresholds that have been experimentally determined by scientists. By spraying at economic thresholds, growers can save money, reduce pesticide use and achieve better pest control. The published thresholds serve as mere guidelines or recommendations for making treatment decisions. Growers are encouraged to use these guidelines in combination with past experience and the history of their strawberry plantings to make treatment decisions. Pesticide Resistance Growers, who use the same pesticide over and over for a decade or longer, notice that the pesticide begins to lose its effectiveness. Pests that survive the sprays reproduce and pass genes with resistance to the pesticide on to the next generation. After a while resistant pests multiply. Growers must either increase the rates of the pesticide or change pesticides. Scientists have documented pesticide resistance in all types of pests, including weeds, insects, fungi, bacteria and mites. Many new fungicides and insecticides are highly effective and cause little environment damage, but fungi and insects will develop resistance to the new products if steps are not taken to slow resistance. Pesticide resistance develops slower when growers rely on alternative methods of control such as cultural practices and resistant varieties. Pests that move between strawberry fields and other host plants, such as tarnished plant bug, are less likely to develop pesticide resistance than pests that primarily live in strawberry plants, like cyclamen mites. 8 Growers should alternate one pesticide with another pesticide with a different mode of action to slow the development of pesticide resistance. The alternate pesticides should have different modes of action. For example, two sprays for controlling anthracnose in strawberries, Cabrio and Quadris, have identical modes of action, and the anthracnose fungi will develop resistance to both fungicides if the two fungicides are alternated. Many pesticides with the same active ingredient and mode of action are marketed by different manufacturers under different trade names, so growers should know the name of the active ingredients of pesticides they are spraying. Table 1 groups fungicides with different modes of action.

9 A group of scientists have classified fungicides into 43 specific groups or codes based on their mode of action. Only a few of those groups have fungicides labeled for strawberry producers (Table 1). In addition, there are several fungicides that have multiple modes of action (multi-site fungicides). Fungicides with the same numbered code cannot be alternated, or the fungi can develop resistance to both fungicides. Fungal diseases cannot develop resistance to multi-site fungicides like Captan. Mixing a single site fungicide like Topsin M with Captan will reduce the chance of resistance developing to Topsin M. Table 1. Strawberry Fungicides Grouped by Code for Resistance Development. Never spray fungicides from the same code two times in a row. Information from the Fungicide Resistance and Action Committee (FRAC, Code Group Name Common Name Brand Names 1 Benzimidazols Thiophanate Methyl Topsin M 7 Carboxamides Boscalid Pristine 9 Anilino-Pyrimidines Cyprodinil Switch 11 Strobilurins Azoxystrobin, Pyraclostrobin 12 Phenyl Pyrroles Fudioxonil Switch 17 Hydroxyanalides fenhexamide Elevate Quadris (Abound), Cabrio, Pristine Degree Days and Insect Pest Forecasting In conventional fruit production, most growers used a calendar or a phenological schedule to time pest control in their plantings. With the calendar method, growers sprayed on a weekly schedule without monitoring fruit or pest development. With the phenological schedule, growers sprayed according to the developmental stage of the plant, such as 10% bloom or green fruit. The calendar method is grossly inaccurate, since insect and strawberry development occurs at different calendar dates each year. The phenological method is more accurate, but insects, weeds and fungi have different optimum temperatures for growth than strawberry plants and peak at different stages of crop development each year. Insect life cycles are primarily regulated by temperature. The date that insects emerge each spring depends on factors such as soil temperature, daily highs and overnight lows. The most accurate way to track insect pest maturity and predict when specific pests are most likely to cause economic losses is by calculating degree days. Degree days are a measurement of the cumulative heat for the growing season. Growers can calculate degree days by obtaining the high and low temperature from local climate websites (www. climate.umn.edu), by high/low thermometers at their own farms or by using computerized weather stations. In order to calculate degree-day (DD) accumulations, take the day s maximum temperature (Tmax) and add the day s minimum temperature (Tmin), then divide the result by two and subtract the base temperature. The base temperature is the lowest temperature the insect remains active and varies according to pest. An insect active at cool temperatures will have a lower base temperature than one that needs heat to grow and reproduce. Tarnished plant bugs emerge as soon as the ground thaws and have a base temperature of 50ºF. Clipper weevils emerge later and have a base temperature of 55ºF. To calculate degree days, use the formula: DD = (Tmax + Tmin)/2 - base temperature. The first part of the formula, (Tmax + Tmin)/2, gives an estimate of the average temperature for the day. The second part of the formula subtracts the base temperature specific to the pest. 9

10 Example: The lowest and highest temperatures recorded at a farm were 50ºF and 80ºF. The DD accumulation for that day, with a base 50ºF is: DD = ( ) 2 ) - 50 = = 15 DD This calculation should be done every day, and the degree day totals of each day added together. Figure 1. Weather data logger. A portable weather data logger, such as the one manufactured by Spectrum Technologies Inc. (Fig. 1) automatically calculates accumulated degree-days. This logger has the ability to collect site-specific weather data, including temperature and leaf wetness. The equipment has a long-life battery and can be placed in the field on a stand. Data accumulated by the logger can be downloaded once or twice per week directly to a computer hard drive. A computer software program automatically calculates degree days and can forecast diseases. Forecasting Disease Infection Periods Fungi and bacteria only infect plants when certain temperature and moisture conditions are present. Weather stations such as the instruments shown in Figure 1, tell growers when weather conditions are right for major diseases to develop. Each disease has a specific optimum temperature for infection. For example, botrytis fungi can only infect strawberry flowers if the leaves are wet for 12 hours and the temperature is 70ºF. If weather conditions are not met, the disease will not develop, even if the fungi are present. If the temperature is 50ºF, botrytis fungi do not infect strawberry flowers, even if the leaves are wet for two days. Leaf wetness can be measured with special instruments that are about the size of a thick playing card and attached to dataloggers that record data every ten or fifteen minutes. Leaf wetness monitors record wetness from dew and rain. Dataloggers also record temperature at the same time as leaf wetness. More expensive dataloggers record humidity and rainfall in addition to leaf wetness and temperature. When the data is downloaded into a computer, special programs on the computer tell the grower if an infection period has occurred. Currently, the only disease model available for strawberry growers is for gray mold or botrytis. Even without the disease models, weather stations can guide growers who want to time fungicide sprays. Weather conditions for each major disease are found in the section on specific diseases and pests. 10

11 Forecasting Weed Emergence The date that weeds emerge in the spring is regulated by a combination of soil moisture and temperature. Each species of weed has a different optimum temperature for germination. For example, wild buckwheat can sprout when soil temperatures are 45ºF, and the first wild buckwheat seedlings can be seen shortly after straw is removed from the field. Redroot pigweed seedlings look similar to wild buckwheat, but can only germinate in warm soils. In Minnesota, growers don t see pigweed in their fields until June, when the wild buckwheat is already 2 long. Computer models have been developed for weed emergence which use soil moisture and temperature to predict weed emergence ( Growers should know the worst weeds in their fields, so that they can time their weed control around those weeds. If a new field has wild buckwheat seedlings, a grower can let the buckwheat germinate in early spring, then till the soil before planting in early May. If a field is full of pigweed seeds, the weeds will not germinate until long after an early May planting. Some weeds are also affected by daylength in addition to moisture and temperature. The best time to kill Canada thistles by tillage or herbicides is when they start to form flower buds. Bloom in Canada thistles is triggered by photoperiod, or daylength, so they bloom at almost the same time every year, which is about June 20, in Morris, Minnesota. Pigweed is also affected by daylength. Pigweed that grow in early June grow 3 tall before starting to set seeds, but pigweed that germinate in late August rarely grow more than 6 tall. Late season pigweed rarely causes crop losses in berry fields, but they can still add to the seedbank. 11

12 3. Using Pesticides Safely PESTICIDES are categorized as either restricted use or non-restricted use. A pesticide is classified as restricted use if it meets certain toxicity or environmental impact criteria. Growers who use restricted use pesticides must obtain a pesticide applicator s license or private pesticide applicator certification by passing a test and submitting a completed application form and fee. Most berry growers do not have a license/certification because most pesticides used in strawberry production are not restricted use pesticides. All growers who spray pesticides must observe: 1) The re-entry interval (REI) - the minimum number of days (or hours) before an orchard or property can be re-entered after a pesticide application. 2) The Pre-harvest Interval the minimum number of days required between final spray and harvest. Nearly all strawberry growers must comply with worker protection standards (WPS) to protect agricultural workers. The WPS is in effect when workers enter a field within thirty days after spraying, so most berry growers must comply with some part of the WPS. There are, however, different rules depending on the type of employee hired. Agriculture Owners: If the only people working on your farm are yourself and your immediate family, you must comply with the following rules: 1) Use proper personal protective equipment (PPE) such as gloves, eyewear, clothes, or aprons when mixing or applying pesticides; (the required PPE for each pesticide is found on the pesticide label). 2) Apply pesticides in a manner so as not to contact workers or other persons either directly or through drift. 3) Keep family members out of areas being treated with pesticides. 4) Keep records of all Restricted Use Pesticide applications. (This is not a requirement of the WPS, but it is still the law). It is also recommended that you keep records of any pesticide applications you make. Employers: Employers who hire workers outside the family and within thirty days of a pesticide application with a REI, must comply with all WPS requirements. Employees can be classified as either workers or handlers. Workers work with plants and do tasks such as watering, weeding, and harvesting. Handlers work with pesticides and do tasks such as: a) Mix, load, transfer, or apply pesticides. b) Handle opened pesticide containers. c) Act as flaggers. d) Clean, handle, adjust or repair the parts of equipment that may contain pesticide residues. e) Assist with pesticide applications. Handlers require more extensive training than workers. 12

13 All employers must do the following in order to comply with the WPS, regardless of whether they hire handlers or workers: 1) Display the following information at a central location. a. Maintain a 30-day pesticide application record. The record should include the location of the field sprayed, product name, EPA registration number, date and time the pesticide was applied and the restricted-entry interval of the pesticide. b. Emergency medical information, which includes the name, telephone number and address of the nearest emergency medical facility. c. An EPA approved pesticide safety poster. 2) Provide WPS pesticide safety training for new employees. a. Workers must be trained within five days of employment. b. Handlers must be trained immediately. (Minnesota Licensed pesticide applicators are exempt from the training requirement.) c. Workers and handlers must be provided safety training once every five years. 3) Have a decontamination site that contains: a. Water for routine washing and emergency eyeflush. i. Recommended - one gallon per worker. ii. Recommended - three gallons per handler. b. Soap and single use towels. c. Decontaminations sites should be located within ¼ mile of where employees are working. 4) Provide emergency assistance to any worker or handler who has been injured or poisoned by a pesticide as a result of that employment. Specific for pesticide handlers: a. Have pesticide labels and Material Safety Data Sheet (MSDS) available for handlers to review. b. Provide decontamination supplies at the pesticide mixing and loading area. c. Include an emergency change of clothing (example: coveralls) at all handler decontamination sites. d. Provide at least one pint of emergency eye flush when the pesticide label requires that protective eyewear be worn. e. Provide all required PPE for pesticide handler when mixing, loading, applying pesticides or conducting other handler tasks. f. Provide an area separate from pesticide storage or mixing area for handlers to change and store clothing. Warning Signs All workers need to be notified when a field is to be sprayed, either verbally or by posting the area with EPA approved warning signs. If you spray in the evening with a pesticide that has a 12 hour or less REI, employees do not need to be notified if the REI will have expired by the time the employees return. Spills All pesticide spills must be reported to the Minnesota Department of Agriculture by calling the Minnesota Duty Officer (MDO) at The MDA provides a 24 hour/7 day a week point of contact service for reporting spills. The MDO will forward your call to staff who will provide you with cleanup and disposal guidance. Personal Protective Equipment When mixing pesticides the applicator should use the appropriate clothing and equipment, which is usually listed on the front page of the pesticide label. 13

14 4. Pest Scouting PEST SCOUTING enables a grower to determine if pest numbers are large enough to require treatment and to time sprays that coincide with the most susceptible stage of the pest. Scouting usually involves checking for eggs, larvae or adults of a given pest in berry leaves, fruits, or flowers. Most pests can be seen with the naked eye, but for small specimens such as mites and insect eggs, a hand lens may be needed. Aphids, plant bugs, thrips, and populations of natural enemies are commonly sampled with beating-trays. Knowing how to correctly identify pests at all life stages is critical, and growers should be able to distinguish pests from closely related or look-alike species. For this purpose, growers are encouraged to use this manual hand-in-hand with the Field Guide for Identifi cation of Pest Insects, Diseases, and Benefi cial Organisms in Minnesota Strawberry Fields. Growers need to record weekly or daily pest scouting data for proper and timely decision-making. Accurate records include a map of all the fields, a list of insect pests found in those fields, the numbers of insects recorded on each sampling date and control measures taken on those fields. In Minnesota, scouting should begin in early spring and continue until strawberry renovation. Pest Scouting Equipment The following equipment and tools are necessary for pest scouting: Notebook (or clipboard with data sheet) for record-keeping. Hand lens (10X or stronger), for small insects, eggs, and mites. Sweep net to scout ground cover or capture flying insects. Beating-tray (preferably white in color) to scout pests and beneficials on the fruit and foliage. A copy of the Field Guide for Identifi cation of Pest Insects, Diseases, and Benefi cial Organisms in Minnesota Strawberry Fields. Alcohol vials, plastic bags, and capsules for insect collection. Scouting Techniques Different scouting techniques are available and can be used depending on the pest or pest stage being scouted. The following are suggested as general guidelines for scouting: Divide a large planting into blocks of 1-2 acres of similar age, variety, and soil type. Major pests like tarnished plant bug should be scouted at least twice a week. Leaf pests can be monitored once a week. To scout plants within a block, make a random selection based on a pre-determined selection pattern (e.g. diagonal, V-shaped pattern, etc). Figure 2. Hand lens Figure 3. Sweep net Figure 4. Beating-tray 14

15 5. Strawberry Developmental Stages and Associated Pests - Planting Year Plant Stage Pests Damage Planting to First Runners White Grubs Soil Insect Eats roots and kills plants Potato Leafhopper Leaf Insect Causes yellow leaves Root Weevils Soil Insect - Stunt plants Black Root Rot Root Disease Stunts plants Deer Defoliate plants Verticillium Wilt Soil Disease Kills plants First Daughter Plants to Full Canopy White Grubs Black Root Rot Powdery Mildew Leaf Spot Deer Soil Insect Kills plants Root Disease Stunts plants Leaf Disease Sunts plants Leaf Disease Stunts plants Defoliate and stunt plants Full Canopy to Dormancy Powdery Mildew Leaf Disease Twospotted Spider Mites Leaf Feeder Stunts plants Deer Stunts or kills plants Strawberry Developmental Stages and Associated Pests Bearing Fields Plant Stage Early Spring Pre-bloom Full Bloom Green Fruit Ripe Fruit Post-harvest Pests of Concern Deer Cyclamen Mite Strawberry Bud Weevil Tarnished Plant Bug Leafrollers Botrytis Thrips Strawberry Root Aphid Tarnished Plant Bugs Botrytis Leaf Spot Thrips Meadow Spittlebug Botrytis Leather Rot Slugs Meadow Spittlebug Sap Beetles Anthracnose Leather Rot Potato Leafhopper Powdery Mildew Leaf Spot Leaf Scorch Anthracnose Black Root Rot Cyclamen Mites Deer 15

16 6. Biology and Management of Select Insect Pests and Diseases of Strawberry JUNE-BEARING strawberries are a good crop for Minnesota, with its warm summers, large cities and vacation areas. However, not only do people like strawberries, but many pests like to eat them as well. Some insects eat the seeds while others prefer fruit. In order to protect their crop from the many pests, strawberry growers should learn how to identify and control the major pests. By using an integrated approach, berry growers can save money while achieving better pest control and producing more berries. In this section, the biology, ecology, monitoring and management strategies for key pests of strawberry in Minnesota are discussed so that growers can learn to identify the pests on their farms and develop management plans for each pest. A detailed description and identification of each pest as well as other strawberry pests is provided in the Field Guide for Identifi cation of Pest Insects, Diseases, and Beneficial Organisms in Minnesota Strawberry Fields. For each pest, we describe available pest management strategies, and the Minnesota Department of Agriculture does not endorse particular products. We have attempted to leave out specific pesticide information or recommendations in this chapter. Information on pesticide options is given in the Appendices. INSECTS Tarnished Plant Bug (Lygus lineolaris) Tarnished plant bug (TPB) has one of the broadest host ranges of any major insect pest, feeding on alfalfa and grasses in addition to strawberry blossoms. Biology TPB live in the tall grasses and plants in alfalfa fields and pastures, and they avoid forests and fields with shortly mown grass. TPB overwinter as adults in vegetation and plant debris and emerge in the spring when temperatures reach and remain around 50 F (early April). Emerging adults feed upon actively growing plant tissue such as leaves, stems, and flower buds. When strawberries bloom, TPB adults can fly over 50 yards looking for flowers. Females mate and insert their eggs in blossoms in April and early May. Nymphs emerge 7-10 days later (early-mid May) and feed upon the developing tissue. There are several generations each year, so adults and nymphs can be found from April or May until a heavy frost in the fall. Damage Tarnished plant bugs eat parts of the blossom by piercing and sucking out plant juices with their beak-like mouthparts. TPB kill developing seeds, which prevents the fruit tissue from expanding, leading to small seedy strawberries with a woody texture called button berry, or cat-faced berry. Moderate damage is unnoticeable, but severely damaged fruits are unmarketable (Fig. 5). Lower yields are due to a combination of smaller and unmarketable fruit. Nymphs appear to cause most of the damage during bloom. Growers who time their control to small nymphs in the first or second instar have achieved good control. If a field has a high population of fourth and fifth instar nymphs, some of the crop has already been lost. 16

17 Figure 5. Different levels of TPB damage in strawberry. The fi eld was sprayed after TPB damaged the king bloom (center). The secondary fruit (top left) had minor, but marketable damage. The tertiary fruit (white) have almost no damage. Without spray, the damage would have been least in the fi rst fruit and worst in the last fruit. Monitoring TPB monitoring should start in early April to detect migrating adults and continue until harvest. Both adults and nymphs can be monitored, but thresholds for nymphs are better understood than adults. TPB should be monitored every two days before and during bloom if a grower is considering reducing pesticide applications. Adults: Adult TPB can be monitored by walking the fields and looking for bugs that are feeding on strawberry flowers or flying above the strawberry canopy. There is currently no suggested threshold for adults. If adults are seen at bloom, the threshold for nymphs can be lowered to less than 1 nymph per four clusters. Nymphs: Begin sampling for nymphs at 5% bloom. Nymphs should be monitored at least every two days if a grower wants to reduce sprays. Walking through a field in a V-shaped sampling pattern, tap blossom clusters against a white pan and look for small, green nymphs that move rapidly across the pan. Sample at least 20 blossom clusters per field. The suggested action threshold is 1 out of 4 blossom clusters infested with one or more TPB nymphs. If nymphs are very small, a lower threshold can be used. Control Roughly 20% of all Minnesota strawberry farms have TPB under threshold numbers each spring and do not need insecticides. Growers interested in reducing or skipping sprays should be educated in by a professional on how to identify all stages of the TPB. Biological and Cultural Control: Innundative releases of the parasitic wasps, Anaphes iole and Peristenus digoneutis have been effective in California and New England. Row covers can cause strawberries to bloom before the TPB adults emerge. Weed control in the berry field is important because weeds may attract TPB into the strawberry planting and allow adults to overwinter in the strawberry field. Grass driveways and parking lots should be mown on a weekly basis so that the lawn does not become TPB habitat. Avoid mowing nearby hayfields when berries are blooming. Mowing will drive the adult TPB from the hayfields into strawberry plantings. As a rule, TPB prefer blooming alfalfa to strawberries, and they will not fly from a blooming alfalfa field to a strawberry field unless the field is mown. Although no strawberry variety is known to be resistant to TPB, Honeoye is less susceptible to feeding injury than other varieties. Avoid planting day neutral varieties (Chapter 9). TPB levels sharply rise throughout the summer. Varieties that bloom in July or August are especially vulnerable to injury. Chemical Control: TPB can be killed with soft and organically approved insecticides. Insecticide rates and options are mentioned in Appendix 4. Sprays applied just before bloom kill overwintered adults and do not harm bees and other pollinators. 17

18 Strawberry Bud Weevil (Anthonomous signatus) Strawberry bud weevil or clipper weevil (SBW) reduces the number of blossoms in the field. Clipper weevils are rare in the southern three tiers of counties in Minnesota, but in the rest of Minnesota, they can cause large economic losses in fields in their second or third year of picking. Biology SBW overwinter as adult weevils in fence-rows, wooded areas, and berry fields. Once temperatures reach 60 F, females search for flower buds where they can lay their eggs. Adults have chewing mouthparts at the end of a long snout. Adults feed on petals, pollen and the developing flower receptacle. The females deposit eggs in the buds (Fig. 6). After depositing the egg, the female SBW girdles the bud and clips the stem, causing the bud to hang down or fall to the ground. Egg laying usually peaks in early bloom (approximately 300 DD base 50 F). A week later, the egg hatches into a white, legless grub. The larva develops inside the bud, reaching maturity in 3-4 weeks. Larvae exit the buds and pupate in the soil, emerging as adults in late June through July. After feeding on the pollen from various flowers for a short time, the new adults seek hibernating sites and remain until the next spring. Only one generation of clipper occurs per year in Minnesota. Clipper weevils rarely fly or walk more than 30 while looking for food or places to lay eggs. Damage When the female clips the bud, the fruit is lost. In severe infestations, 75% of the buds are killed. If the weevils emerge early, the majority of the clipped buds will be king bloom, which typically produce the largest fruit. Injury is most common along edges of fields near woodlots. Monitoring Clipper weevils are difficult to see because they are small and hide in the strawberry canopy. Most people monitor clipped buds or damaged flowers. Monitoring should begin just before bloom. Clipper weevils are unevenly distributed across fields, with some sections having severe damage and others having no weevils. Following a V-shaped sampling pattern, walk across the field. If the plants are not in bloom, look for clipped buds. If plants are blooming, look for holes in the petals (Fig. 7). If you find flowers with holes in the petals, check for clipped buds. If weevils are actively feeding on flower petals and laying eggs, the treatment threshold is 1 clipped bud per 2 of row. If clippers are finishing laying eggs, and have stopped feeding a higher threshold of 6 clipped buds per 3 of row can be used. Cultural and Biological Control: Clipper weevils in strawberry fields in their first year of picking are usually below economic thresholds, and therefore do not need to be sprayed. Immediately plowing under old beds following harvest and removal of leaves and mulch may help by reducing the overwintering habitat of the weevil. Regularly rotate fields out of production so that there are few fields in production for more than three picking seasons. 18 Chemical Control: Insecticides labeled for SBW tend to be harsh, with long pre-harvest intervals. Rates are higher than required for TPB. In fields with a history of clipper damage, growers can use a preventative spray prior to bloom, after buds have emerged from the crown and when temperatures have reached 65ºF. Insecticide options are mentioned in Appendix 4. Complete field treatment is recommended for older plantings with a history of high SBW pressure.

19 Flower Thrips (Frankliniella tritici) Flower thrips are extremely small insects that damage strawberry fields once every three or four years. Although thrip damage is rare, when it does occur, entire fields can be unmarketable. Biology Flower thrips winter in the southern region of the United States and are carried northward on frontal systems in early summer. Female thrips lay their eggs under the surface of leaves. Eggs hatch in about 2-4 days. There are two larval instars. Development from egg to adult can be completed within a week or two during hot weather. Because of this short generation cycle, the thrips can increase rapidly during hot spells. Damage Thrips have rasping, sucking mouthparts that cut the skin cells of strawberry fruit, causing the fruit to turn bronze colored or to cause a slight russetting. The skin cannot properly stretch as it ripens, and the seeds stick out of the skin. In some cases, large numbers of thrips have been counted in fields, with little or no damaged fruit. In other cases, fields have been ruined when small numbers of insects were counted. Severe thrip damage may be caused by a combination of insects and high temperatures in late bloom. Monitoring Thrips can be monitored at the same time as tarnished plant bug nymphs. When tapping blossom clusters for tarnished plant bug nymphs, always count thrips. Thrips are very small insects, about the size and shape of the strawberry stamens that fall off blossoms in late bloom. The most accurate method of monitoring is outlined below. Collect ten flower buds from a field (use a V-shaped sampling pattern to determine sampling locations). Place the flower buds in a clear plastic ziplock bag, close and put the bag in a hot place for a few minutes to kill the thrips. Due to their small size, it may be useful to use a hand lens to identify thrips. The popular threshold is more than 10 thrips per flower bud. Biological and Cultural Control: During the 2006 growing season, strawberry growers noticed large differences in damage severity between cultivars. Jewel and Glooscap were damaged, but had normal tasting fruit. Cavendish and Honeoye in the same fields had a bitter taste and were unmarketable. Naturally occurring minute pirate bugs (Orius spp.) feed on thrips. Orius are also available commercially and have proven successful in greenhouses. Chemical Control: In general, treatments applied to control TPB will offer some protection against thrips, although Endosulfan is only moderately effective against thrips. Sprays targeted against thrips may disrupt biological control of other pests such as the twospotted spider mite. Consider treating only if populations reach over 10 thrips per blossom cluster. If hot weather is predicted, use a lower threshold. 19

20 Twospotted Spider Mite (Tetranychus urticae) Twospotted spider mite (TSSM) feeds on the leaves of many fruit crops. TSSM is more common in states south of Minnesota, but during hot, dry summers the mites can build up in local fields. Biology Adult spider mites feed and deposit eggs on the underside of the leaf starting in early spring. In a heavy infestation, a tangle of fine, silken threads can be found on the leaves. TSSM mature two weeks after hatching, and new broods are produced continuously from early spring to late fall. Mite populations increase rapidly in hot, dry weather. Spider mites disperse into plantings on the silken threads in the wind. TSSM overwinter as mature fertile females in protected areas in the fields. Damage Mites have piercing, sucking mouthparts. They feed by sucking the chlorophyll from leaf cells, causing the characteristic whitish spotting, eventually turning the leaves a coppery-bronze color. TSSM damage usually occurs during hot, dry weather, and is first noticed in areas of the field that are dry. Heavily infested plants are stunted. Monitoring Plants with bronzed, dusty leaves should be inspected for TSSM. Using a hand lens, inspect the underside of leaflets for TSSM and the quicker predatory mites, which are either clear or orange in color. An acceptable threshold is 5 mites per leaflet. Biological and Cultural Control: Plants that are healthy and properly watered are more likely to fight off mite infestations than sick, poorly watered plants. In healthy fields, mites are kept under control by predatory mites, such as Amblyseius fallacis. Pyrethroids and several broad spectrum insecticides, such as Sevin can kill predators and cause spider mite populations to flare up. Predatory mites can be introduced to fields when damage is starting to show on the plants. Avoid using broad spectrum insecticides that kill predatory mites. 20

21 Cyclamen Mite (Steneotarsonemus pallidus) Cyclamen mites are significantly smaller than spider mites, but are more common, infecting roughly 20% of the strawberry fields in Minnesota. Cyclamen mites have few other hosts than strawberry plants. Biology Cyclamen mites live in the crown of the plants and feed on developing leaves by piercing and sucking nutrients from the leaves. As the leaf unfolds, the mites move onto smaller leaves in the center of the plant. Cyclamen mites overwinter in the strawberry crown and start to feed as soon as the plant begins to grow in early spring. Cyclamen mites multiply rapidly in hot weather. Damage Cyclamen mite damage can be seen as leaves unfold. Damaged leaves are small, crinkled, twisted and a yellow color. In early stages of an infestation, older leaves are healthy while the young leaves in the center are small and crinkled. In older infestations, the canopy is 25-50% smaller than surrounding uninfested plants. During spring, cyclamen mites feed on flowers, producing symptoms similar to thrips. Often the damage is not seen until the end of picking, when they spread during hot weather. Management Monitoring: Plants showing symptoms of cyclamen mite should be carefully inspected in order to assure the grower that the mites are causing the observed damage. Nutrient deficiencies and diseases can cause similar symptoms. Collect leaves from the center of the crown, less than 1 in diameter Place leaves under a dissecting microscope or inspect with a hand lens. Cyclamen mites are much smaller than TSSM and difficult to see even with a good microscope. Mature mites are pinkish-red, while immature mites are a translucent white. If plants show cyclamen mite symptoms and if mites are observed, take control measures. Cultural Control: Cyclamen mites usually come into fields through nursery planting stock. Always buy certified, disease-free plants. If a few plants show signs of cyclamen mites the first year, remove plants from fields Cyclamen mites almost never damage fields until after their first year of production. If fields are only picked one year, cyclamen mites remain below threshold. Certain varieties, such as Cavendish and Annapolis appear to be very susceptible. Jewel is most tolerant. Chemical control: Because cyclamen mites live in the center of the crown, they are protected from insecticides by the leaf canopy. Insecticides should only be sprayed when there are few or no leaves, either after renovation or in early spring, as the first buds are emerging from the crown. Spray volume should be at least 200 gallons per acre to make sure the insecticides penetrate the crown. Cyclamen mite infestations are usually limited to small sections of each field and many growers only need to spot spray infested areas. 21