Weed Control in Grapes

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1 Weed Control in Grapes Scott Guiser, Extension Educator, Penn State Extension, Bucks County Weed control in grapes, as in most perennial horticultural crops, involves a weed free strip beneath the crop row and an aisle between rows that is maintained in some kind of permanent cover crop. This system allows for maximum crop growth while preserving good soil quality. Many research studies have documented the benefits of weed control in perennial cropping systems, especially in the first few years after planting. Here, we ll focus on the weed free strip but it is worth considering the covered aisle in detail as well. Proper establishment of a perennial grass sod has great advantages. More detailed information about the herbicides described here can be obtained from two excellent Extension publications: 2011 New York and Pennsylvania Pest Management Guidelines for Grapes ( and Commercial Grape Pest Control Recommendations for New Jersey, 2011 ( Both are available on-line or through your state Cooperative Extension system. Labels for all of the herbicides mentioned here can be seen by going to Important detailed precautions are found there. Always read the label before use and follow its instructions, regardless of what you read or hear elsewhere! Weed control in perennial systems such as grapes is best thought of as a three part approach: Step 1 - Eliminate perennial weeds prior to establishment; Step 2 - Control weeds that attempt to establish by seed; Step 3- Manage the weeds that escape steps 1 and 2. Step 1 Eliminate perennial weeds before planting Canada thistle, quackgrass, yellow nutsedge, bindweed and many other perennial weeds are best tackled before establishing the vineyard. These species have underground storage structures such as roots, rhizomes and tubers that allow the weed to regenerate. Generally, perennial weeds are not controlled by pre-emergence herbicides. One very effective and efficient method to control perennials is to grow a competitive row crop the year before grape planting. Corn and soybeans are especially good choices because glyphosate tolerant varieties may be used and no impact from herbicide carry over is involved. These same crops, and others, may be grown with residual herbicides for weed control. Be sure to check the plant-back restrictions on all herbicides used in the crop preceding grapes because some have long soil residual activity that may impact grape growth. Perennial weeds can also be controlled the year before planting grapes with a timely application of glyphosate or other translocated herbicides. Late summer or early fall applications of translocated

2 herbicides such as glyphosate and 2, 4-D are especially effective on most broadleaved perennial weeds. Spring applications in the year of grape planting are ineffective because perennial weeds have not made sufficient growth to absorb and translocate the herbicide. If crop rotation for perennial weed control is not employed, carefully assess the planting site the summer before vineyard establishment and apply the necessary controls. Step 2 Control weeds that attempt to establish by seed If perennial weeds are controlled prior to planting, the only way weeds can infest the vineyard is via weed seedling establishment. Step 2 is aimed at preventing this. While mulches and cultivation are possible techniques for weed control, we will focus on the herbicide option here. Sprayer calibration is essential when applying pre-emergence herbicides! Proper application rates are critical. Also, soil type will dictate what herbicide rates are used. Lighter soils get lower rates (or preclude certain uses), heavy soils require higher rates. Thirteen pre-emergence herbicides are labeled for grape weed control. Using a combination of two herbicides, one with strength on grassy weeds and one with strength on broadleaved weed is an excellent approach. A fact of life in weed management is that no single herbicide controls all weeds and the weeds that are not controlled will dominate the space available to them. For example, if Princep alone were used, excellent broadleaf weed control would be achieved but grass control would be weak. Grasses would probably completely fill the treated area and weed control would effectively be a failure, even though control of broadleaved species was achieved. On the other hand, If Surflan alone was used, excellent grass control would be achieved but broadleaves would break thru and dominate the space. A combination of these two herbicides covers all bases. From this we can see that it is useful to think of herbicides as those with strengths for grasses and those with strengths for broadleaves. Note that we are talking about weed seedlings, not established perennials. With few exceptions, preemerge herbicides have little effect on established perennial weeds. Use Tank Mixes Broadleaf Control Gallery Princep Goal Karmex Grass Control Devrinol Prowl Solicam Surflan Chateau

3 Sample tank mixes Gallery + Prowl H2O Ok for first year plantings Karmex + Solicam Princep + Surflan Moderate rates of two herbicides = effective, safe weed control An important consideration is whether the herbicides can be used on newly established vines. Many preemerge herbicides can be used safely. Exceptions are Princep, Karmex, Solicam, Goal, Matrix, and Casoron. These must not be used until vines are established one or more growing seasons. See the labels for details. In addition, attention must be paid to which herbicides may be used on bearing vines. Gallery and some formulations of pendimethalin cannot be used on bearing vines. Chateau is a relatively new pre-emergence herbicide that provides relatively good control of both broadleaved and grassy weeds although season-long grass control may not be achieved. Chateau is often best applied in a split application in mid and late spring along with glyphosate, glufosinate or paraquat. Step 3 Control weeds that escape steps 1 and 2 Post-emerge herbicides can be used to clean up weeds that escape the site prep and preemerge steps. Glyphosate (Roundup, etc) is unique in that it is translocated and will provide good control of perennial weeds, both broadleaves and grasses. While translocation is a good thing for weed control it poses a potential hazard to the vines as well. Follow precautions to prevent glyphosate contact with green stems, leaves and fresh pruning cuts. This is a critical concern in young vineyards. A benefit of a good preemerge program is that it minimizes the need to apply post emerge herbicides such as glyphosate.

4 Rely (glufosinate)and Gramoxone (paraquat)are two additional postemerge herbicides that are useful in cleaning up escaped weeds. These differ from glyphosate in that they are primarily contact or burndown herbicides. Contact with green stems and leaves of grapes must be avoided to prevent localized, but significant injury. A few specialty herbicides can be quite useful. Kerb provides excellent control of established perennial grasses such as tall and fine fescues. It must be applied in the fall when soil temperatures are below 55 degrees. Casoron, another fall applied herbicide, can provide some control of established perennials. Poast, Select and Fusilade are three post-emerge grass control products. They are especially useful for eliminating annual grass breakthroughs but provide no residual weed control. Only Poast is labeled for bearing vineyards. Ok, let s try to put together an example from start to finish, assuming perennial weeds were well controlled prior to vineyard establishment. Year 1 Plant vines and irrigate or allow rainfall to settle soil around the roots. Apply Gallery plus Prowl H 2 0 at rates appropriate for your soil type. Do this as soon as possible after soil is settled and before weed seedling emergence! Do not wait until weeds have emerged. Pre-emergence herbicides will not control emerged weeds. If weeds have emerged, a burndown herbicide such as Gramoxone or Rely can be added to the preemerge mix but care must be used so that these materials do not contact the leaves and green stems of young plants. Grow tubes can provide this insurance. Use Gramoxone or Rely to control escaped weeds as necessary throughout the year. Year 2 Repeat year one treatments. Spot treat perennial weed patches with glyphosate as needed. Year 3 Apply Chateau plus glyphosate in a split application in April and May, using 6 ounces of Chateau per application. After year 3 Consider all herbicide options and rotate herbicide tank mixes periodically to reduce the potential for herbicide resistance or shifts in weed populations that result in problems. Tank mixes such as Goal plus Solicam or Karmex plus Surflan are examples of Spring preemerge treatments that should provide excellent broad-spectrum weed control. Assess the weed situation each fall and consider a cleanup spray at this time. Fall applications may include Princep, Chateau or Karmex plus a burndown herbicide. Certain winter annual weed species such as horseweed require special attention. Where specific weed problems such as yellow nutsedge occur, consult the current references for solutions. For instance, Matrix is a relatively new herbicide labeled for grapes that addresses the nutsedge problem. Glyphosate is an excellent tool for spot treating perennial weed hot spots.

5 In summary, grape growers have many herbicide tools to manage weeds in vineyards. Think about weed control as a three step program: Eliminate perennials before planting, control seedling weeds with preemerge herbicides and then follow up as needed with postemerge products suited to the task. Sprayer calibration is critical. Adjust preemerge rates to suit your soil type. Read herbicide labels carefully considering the limitations and precautions of each herbicide in the program. If in doubt, consult with a knowledgeable person who can guide you. Ounces to Gallons Sprayer Calibration Sprayer calibration is made easy with the ounces to gallons method. This technique works because we will use a 340 square foot calibration area. Since 340 square feet is 1/128 th of an acre and there are 128 ounces of water in a gallon, the ounces of spray solution we apply to 340 square feet is equivalent to the same number of gallons per acre. Let s say we want a 4 foot wide weed free strip under the vines. We ll spray a band 2 feet wide on each side to achieve this. Select a nozzle (wide angle nozzles are available) and adjust the height to achieve this band width. Practice on a gravel area (where the pattern will be easily visible) until you achieve the band with you want. Dividing 340 by the 2 foot band width, we see that a 170 foot calibration length would result in the 340 square foot total (340/2 = 170). If band with was 1.5 feet, the calibration distance would be 227 (340/1.5). If 3 feet, then a 113 foot length works (340/3). The key is to divide your band width into 340 to determine the calibration length. Next, measure the number of seconds it takes to travel the calibration length. Use a consistent speed over terrain that is similar to the area you will spray. Select a gear and RPM that is safe and reasonable for the actual herbicide application. Do this step in the vineyard. Repeat until you are comfortable with the tractor operation and are getting relatively consistent times. Record the number of seconds it takes to travel the calibration distance. Now, with the sprayer stationary and operating at the same pressure you will use when making the application, collect the output of the nozzle (water only) for the same number of seconds that you needed for the calibration run. The number of ounces collected is equivalent to the sprayer s output in gallons per acre. Example: For the two foot band width you travel 170 feet in 40 seconds. You collect 25 ounces in 40 seconds. Your system is applying at a rate of 25 gallons per acre. If your tank capacity is 50 gallons, each tank treats 2 acres (50/25 = 2). So, if you intended to apply 6 ounces of Chateau plus 2 quarts of Roundup per acre, you would put 12 ounces of Chateau (6 ounces x 2 acres )and four quarts of Roundup (2 quarts x 2 acres) in the tank. If using a boom with multiple nozzles, substitute nozzle spacing for band width. For example, using a 20 inch nozzle spacing we d calibrate over 205 feet (340 /1.6 feet). Collect the output of each nozzle, then determine the average number of ounces delivered. So, if nozzle 1 put out 28 ounces

6 and nozzle 2, 30 ounces, the average output would be 29 ounces =58/2 =29. The boom is delivering at 29 GPA. Below is a step by step process of the ounces to gallons method taken from Controlling Weeds in Nursery and Landscape Plantings, a Penn State publication. Calibrating a sprayer ounces to gallons method. After a tractor-mounted or backpack sprayer has been customized to meet particular needs, it should be calibrated according to the following instructions: 1. On an area that best represents the average topography for the area to be sprayed, measure and mark off the calibration distance that coincides with the band width, if band applying, or with the nozzle spacing (width covered by a single nozzle) if broadcast applying (see Table). Calibration distance feet 2. Fill the sprayer with water only and record the number of seconds required to travel the calibration distance at a comfortable, steady speed. With a tractor-mounted sprayer, note and record the engine rpm and the gear selection so that the same speed is used during calibration and application. For backpack sprayers, it is important that the person making the application is the person that calibrates the sprayer, because the calibration is based on that person s pace. Gear rpm time in seconds 3. While maintaining the selected application pressure, collect the spray output from one nozzle for the same number of seconds needed to travel the calibration distance. Collected water in fluid ounces. The number of fluid ounces collected equals the gallons per acre (GPA) output of the spraying system. Example 1: With a 32-inch band, if it took 28 seconds to travel 127 feet, collect the nozzle discharge for 28 seconds. 16 ounces collected equals a system output of 16 GPA. Example 2: With 20-inch nozzle spacing, if it took 35 seconds to travel 204 feet, collect the discharge of one nozzle for 35 seconds. 20 ounces collected equals a system output of 20 GPA. 4. If using a boom, repeat step 3 twice more, collecting water from a different nozzle each time. The average number of ounces collected for each of the three nozzles is equal to the gallons of water applied per acre for that boom, speed, and pressure. If the difference in output of any of the nozzles tested varies more than 10% from the others, check all of the nozzles on the boom and replace as needed. 5. To determine the amount of chemical to add to the spray tank, divide the capacity of the tank by the number of gallons of water applied per acre to determine the area that can be covered with a tankful of spray. Example 1: 3 gal tank 16 GPA = acres covered per tank. Example 2: 200 gal tank 20 GPA = 10 acres covered per tank. 6. Multiply the application rate of the product per acre times the area covered per tank. Add that amount of chemical to

7 the sprayer tank. Example 1: 2 qt per acre = 64 fl oz per acre x.188 acre per tank = 12 fl oz per tank. Example 2: 2 qt per acre x 10 acres per tank = 20 qt, or 5 gal per tank. Calibration distance based on nozzle spacing or band width. Band width calibration nozzle spacing distance 10 inches 408 feet 12 inches 340 feet 16 inches 255 feet 18 inches 227 feet 20 inches 204 feet 24 inches 170 feet 28 inches 146 feet 32 inches 127 feet 36 inches 113 feet 40 inches 102 feet Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.