Biology and management of Botrytis and Anthracnose fruit and crown rots of strawberry

Transcription

1 Biology and management of Botrytis and Anthracnose fruit and crown rots of strawberry Dr. Cassandra Swett Grape and small fruit pathologist University of Maryland, College Park Dept. of Plant Science and Landscape Architecture Located on College Park campus

2 Questions--ask at any time

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4 Botrytis diseases on strawberry Caused by one species: Botrytis cinerea Botrytis crown rot Botrytis fruit rot

5 Pathogen inoculum: spores Produced when it has been persistently wet (rainfall, heavy dew), above 65F

6 When is infection occurring? Figure credit: Frank Louws Feb-June = critical control period

7 Leaf and petiole infections in fall provide spring inoculum Infected plant tissue appears healthy FALL INOCULUM FROM: Nursery stock HOW TO CONTROL FALL INFECTION: Fall fungicide application (pre-row cover) Sclerotia Remove infected fruit Plastic mulch Soil treatments? General methods: Avoid dense spacing Avoid over applying fertilizer--nutrient tests

8 Diseases develop in the spring CROWN ROT Pathogen grows down into petioles at plant base; Dead leaves and petioles but no inner crown discoloration Figure credit: Frank Louws

9 Diseases develop in the spring FRUIT ROT DEVELOPMENT Pathogen infects flowers Inoculum produced on infected fruit spread to nearby fruit uncontrolled, will lead to a disease epidemic Figure credit: Frank Louws

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11 Spring infections that lead to crown rot SPORE PRODUCTION ON: Dead leaves and petioles Early-bloom frost-killed flowers Occurs on Swett Charlie and other early blooming varieties Sclerotia produced on fruit, petioles, (matted row, carry over, organic) Figure credit: Frank Louws

12 Cultural practices to control Botrytis crown rot in the spring Remove infected leaves and petioles, and flowers (organic or min. spray) Est. $300 / A

13 Cultural practices to control Botrytis crown rot in the spring Avoid early blooming varieties Use row covers to prevent frost damage Avoid excess nitrogen (increases susceptibility) Avoid dense plantings (reduce humidity and spread)?

14 Fungicide control of Botrytis crown rot Monitor for infected flowers and petioles immediately after row cover removal Apply as soon as you see spore production Figure credit: Frank Louws

15 Fungicide control of Botrytis crown rot Recommended spray program: Rovral: single pre-bloom application Systemic action Note: resistance is developing Captan: use post-bloom Switch and other Botryicidesare effective but not recommended save for bloom

16 Spring FLOWER infections that lead to fruit rot FLOWERS GET INFECTED BY SPORES PRODUCED ON: Crowns (crown rot infected plants) And, as for crown rot: Dead leaves and petioles Early-bloom frost-killed flowers Sclerotia (infected fruit, petioles)

17 Controlling flower infections that lead to fruit rot relies on preventative management Reduce inoculum load in fall and spring Cultural management strategies as described for crown rot Prevent crown rot as described Protect flowers in spring Fungicide applications starting at 10% bloom Continue up to harvest for optimal production

18 Chemical control to prevent flower infection Rotate reduced risk and broad spectrum fungicides Avoid repeat application on reduced risk compounds See the Southeastern strawberry IPM guideline for compound recommendations and rates

19 The risk of reduced risk compounds Reduced risk compounds are single mode of action They kill the fungus by damaging a single metabolic pathway It only takes a single adaption in the fungus to no longer be affected by single mode of action fungicides By chance, a small part of the pathogen population (a group) develops this adaption The more times the fungicide is used, the more common the resistant group can become The fungicide is killing the competing, susceptible group of fungi

20 Fungicide resistant populations of Botrytis in this region, based on 2015 testing

21 Managing fungicide resistance: Spray reduced risk (single mode of action) compounds as infrequently as possible 1-2 times / season Very hard to do with a calendar-based program One solution: only apply fungicide when spores are being produced

22 Pathogen inoculum: spores Spores are produced and the pathogen infects when it is persistently wet (rainfall, heavy dew) for at least 12 hours, above 65F Figure credit: Frank Louws

23 Disease forecasting Predicts spore dispersal and infection based on weather data Only apply fungicide when conditions are conducive Disease forecasting in action in Florida, South Carolina, North Carolina, Iowa, and Ohio

24 Disease forecasting is being used by 20-50% of strawberry growers in Florida, South Carolina, North Carolina, Iowa, and Ohio Reduces fungicide applications by up to 50% No yield reduction

25 Number of sprays needed in Maryland, based on weather data collected in Spring 2015 Number of sprays / year Calendar SAS-based % Reduction Eastern Shore, MD (2015) % Western MD (2015) %

26 2016 disease forecasting trials in the mid-atlantic Goals Build weather station network in MD and VA (PA in 2017) Run trials at WMREC in Maryland and participating grower fields Evaluate feasibility: labor demands, efficacy (yields) Botrytis fruit rot Anthracnose fruit rot Maryland: Cassandra Swett, Bryan Butler, Emmi Koivunen Virginia: Cassandra Swett, Roy Flannagan and Chuck Johnson Florida (weather station netrwork): Natalia Peres Support from: NIFA-CARE grant, Baugher sorchard (plants), Butlers Orchard and Larriland Farm (consulting)

27 Do you have fungicide resistant Botrytis populations? The Berry pathology lab will help you test for fungicide resistance! We will collect samples from your farm and send them to Dr. Guido Schnabel at Clemson for fungicide resistance testing Free if you are in MD: The Maryland State Horticulture Society supports the Clemson program $120 / sample if you are in DE, PA, or WV.

28 Better understanding the importance of managing sclerotia and infected tissue in the soil Botrytis inoculum loads in soil Current estimates ~ 200 1,200 viable spores / gram soil Botrytis sclerotia loads in soil Current estimates ~ 1 sclerotia in 1 gram soil

29 Better understanding the importance of soil management Can soil management strategies that improve soil health also accelerate sclerotia break down? Applications: Matted row build up soil populations over time Carry over as above, but in shorter time frame Organic high disease pressure

30 Efficacy of compost and cover crop green manures in reducing sclerotia survival Emmi Koivunen and Cassandra Swett

31 Questions? Next: Anthracnose crown rot and ripe fruit rot

32 Anthracnose crown rot and ripe fruit rot Unlike Botrytis, these diseases are caused by different species CROWN ROT C. gloeosporoioides RIPE FRUIT ROT C. acutatum Figure credit: Frank Louws

33 Anthracnose crown rot (C. gloeosporioides) symptoms Most diagnostic symptom = red and whit marbling of the crown Figure credit: Frank Louws

34 Anthracnose crown rot (C. gloeosporioides) symptoms Initial symptoms: stunting, flagging of young leaves, premature wilting in mid-day

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37 Distinguishing from Phytophthora crown rot Phytophthora: Dull brown crown rot, Roots are black below crown If you have crown rot and require a diagnosis, contact your local farm adviser to send samples to the Plant diagnostic clinic at either the University of Delaware (Nancy Gregory) or University of Maryland (Karen Rane) Services are FREE

38 Biology and control of Anthracnose crown rot Clean nursery stock Most CROWN ROT infections occur in the nursery: when you get the plants, they are already infected No anthracnose certification program at present Reduced risk if micropropagated, with strict plant certification program Figure credit: Frank Louws

39 Biology and control of Anthracnose crown rot Disease resistant varieties Primarily a problem in plasticulturevarieties, such as Chandler

40 C. gloeosporoioidesspreads from infected to healthy tissue as spores Spores are produced from infected petioles, runner and upper crown tissue in the fall and spring Spore production and infection occurs when it is persistently wet at above 65F Movement of spores occurs by rain splash and wind driven rain Figure credit: Frank Louws

41 Controlling spread of Anthracnose crown rot Fungicide management is important to control spread If nursery stock is known to be infected: Whole plant dip in Switch reduces disease by 1/3 or more See SmallFruits.org IPM guide for rates Fall application targeting the crown in the fall, when warm weather is forecasted Similar strategies in early to mid-spring Rates and resistance management outlined in the Southeast Strawberry IPM guide

42 Controlling spread of Anthracnose crown rot Manage alternate hosts which may provide an in-field inoculum source Ex. Virginia creeper, oak, wax myrtle, smilax Wild and cultivated grape (bitter rot)

43 Symptoms of Anthracnose ripe fruit rot caused by Colletotrichum acutatum

44 Colletotrichum acutaumalso causes petiole rot, flower blight and green fruit rot Figure credit: Frank Louws

45 C. acutatum disperses to plants as spores Figure credit: Frank Louws

46 C. acutatum disperses to plants as spores Spore production and infection occurs when it is persistently wet at above 65F Movement of spores occurs by rain splash and wind driven rain Machines and people can also spread spores

47 Figure credit: Frank Louws C. acutatum is a widespread problem in plug and transplant nursery stock production Infected, healthy looking stock is sold to fruit farms

48 Nursery stock is not the only source of C. acutatum spores in fruit farms Plants also get infected from spores produced on: Infected fruit (mummies) left in the field Other infected tissue left in the field Alternate hosts Other crops that are infected by C. acutatum Blueberries = anthracnose Apples= bitter rot Grapes = ripe rot Cover crops? Weeds

49 FALL: Petiole and runners become infected; these infections produce spores in the spring Figure credit: Frank Louws

50 SPRING: spores from infected plants, soil and alternative hosts infect fruit starting at fruit set Green fruit can develop lesions or remain symptomless until ripening Figure credit: Frank Louws

51 Use resistant cultivars to reduce Anthracnose ripe fruit rot losses USDA-ARS Beltsville breeding trials select for Anthracnose fruit rot resistance under this regions high inoculum loads Popular resistant varieties: Flavorfest(new ARS Beltsville release) Near 0% infectionin 2015 ratings of organic Flavorfest(50% in Chandler) Swett Charlie (susceptible to crown rot) Bish(NCSU release) Susceptible varieties Chandler

52 Effective cultural practices to control Anthracnose fruit rot Use disease free plants No anthracnose certification program Reduced risk: micropropagated, with strict plant certification program Do not work plants when wet or perform hand sanitation work in the spring, to minimize spread Suppress survival on infected fruit and other tissue Soil management strategies? Hand removal? Rotate out of strawberries 2-3 years (or longer)

53 Fungicides are critical for Anthracnose fruit rot control Very important to protect during early and full bloomin problem fields Prevent inoculum build up Takes days to slow down an epidemic once disease starts on fruit For rates and resistance management recommendations, see the Southeastern Strawberry IPM Guide Reduced risk compounds: Strobilurins Broad specrum: Captan, Thiram

54 Figure credit: Frank Louws

55 Fungicide schedules for Botrytis fruit rot focused and combined Botrytis and Anthracnose fruit rot combined control

56 Schedule 1. Botrytis-focused control, when there is no risk of Anthracnose (e.g. matted row) For a conservative (low risk) fungicide program, apply every 7-10 days Application #1: At 10% bloom apply captan+ Thiram24/7 or Thiram Granuflo Application #2: 7-10 days later apply Elevate OR Pristine OR Switch Application #3: same, if in full bloom Application #4, and weekly : Rotate two or more of captan, Thiram products, Elevate, Captevate, Switch, or Pristine

57 Schedule 1. Botrytis and Anthracnose fruit rot control For a conservative (low risk) fungicide program, apply every 7-10 days Application #1: At 10% bloom apply captan+ Thiram24/7 or Thiram Granuflo Application #2: 7-10 days later apply Captivate OR Pristine Application #3: same, if in full bloom Application #4, and weekly : Rotate two or more of captan, Elevate, Captevate, or Pristine

58 *This year* it will be critical to monitor for petiole and flower infections for Botrytis, Anthracnose crown rot and Anthracnose fruit rot infections Mild winter has been highly conducive to inoculum build up: Petiole infections Winter blooms that will be frost killed

59 As with Botrytis: fungicide resistance management is important Recent resistance detected to Cabrio and Abound Disease forecasting programming in the mid- Atlantic includes Anthracnose fruit rot

60 Trials in North Carolina, using weather prediction-based fungicide trial to control Anthracnose fruit rot (Louws) Figure credit: Frank Louws

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62 Questions?

63 Dr. Cassandra Swett contact information: Berry Pathology Extension Program: Twitter: Dr. Cassandra Located on College Park campus