MANAGING DISEASES DURING A WET YEAR

Transcription

1 MANAGING DISEASES DURING A WET YEAR Kari Peter, Ph.D. Department of Plant Pathology and Environmental Microbiology Penn State University Fruit Research and Extension Center Biglerville, PA

2 Diseases influenced by wet weather. Apple scab Fire blight Cherry leaf spot Bacterial spot Cedar apple rust Others to consider and keep in mind: Moldy core Late season fruit rots (peach and apple) Root rots

3 APPLE SCAB Disease cycle Scab infection conditions Management strategies

4 APPLE SCAB Disease cycle of Venturia inaequalis: polycyclic Ascospores: Mature at GT Discharged by early spring rains Peaks: Bloom - PF Primary infection can last until mid- June Spring: primary inoculum Secondary inoculum MUST get control of the disease early! Spores overwinter

5 Predicting apple scab infection: Mills Table Severe: rainy spring Little: hot and dry Temperature ( F) Wetness hours Lesion appearance (days)

6 Managing Apple Scab GOAL: Controlling the disease early Dormant (Before the growing season starts) Silver Tip to Green Tip ½ Green Tip to 1 st Cover Additional considerations Fungicide resistance?

7 Management Before the growing season kicks off! Cultural Control: Sanitation = Free from pathogens When it comes to scab, orchards are self-infecting! Approach inoculum reduction in the same way you think about fire insurance: You hope you never need it, but if you do need it and haven t got it in place, you ve really dug yourself into a hole Dr. David Rosenberger Focus attention on blocks with scab last year/history of scab and blocks with highly susceptible cultivars** Reducing the number of available spores for the coming season: leaf removal Urea sprays (fall or spring) Leaf chopping (after pulling leaves from beneath trees) Spreading lime after leaf drop (especially if you will be applying lime for horticultural reasons) Calibrate sprayers!

8 Management Silver Tip to Green Tip Be sure your sprayers are calibrated to ensure good coverage! Copper Sprays Apply at silver tip to green tip Reduces scab spores and suppresses fire blight bacteria colonizing bark and bud surfaces 2 lbs/a of metallic copper at green tip Example: Kocide 3000 metallic Cu Equivalent 30% Kocide metallic Cu 2 lbs/a = Applying 6 lbs/a (6 lbs/a x 0.30 metallic Cu = 2 lbs/a metallic Cu) Be careful during dry years (no rain between ½ GT to Pink) = Russetting on sensitive cultivars

9 Management ½ Green Tip to 1 st Cover Be sure your sprayers are calibrated to ensure good coverage! Rule of thumb: Use contact fungicides in combination with at least 3 different chemistries/modes of action (SPRAY BY THE NUMBERS) Dodine (Syllit, FRAC Group Code U12) DMIs (FRAC Group Code 3) QoIs (Strobilurins, FRAC Group Code 11) SDHIs (FRAC Group Code 7) NOTE: Starting in 2015, the Syllit label has changed; it can no longer be applied after pink bud

10 Management ½ Green Tip to 1 st Cover Be sure your sprayers are calibrated to ensure good coverage! 1/2 Green Tip and Tight Cluster: Syllit + mancozeb Pink and Bloom: Fontelis + mancozeb Petal Fall and 1 st cover: Flint + mancozeb Other products can be substituted: Examples: Inspire Super + mancozeb Luna Tranquility + mancozeb Indar + mancozeb Primary infection can last until mid- June Adding several pounds of sulfur = For powdery mildew suppression Rusts controlled with EBDCs (mancozeb/manzate/penncozeb etc.)

11 Management Additional considerations Be sure your sprayers are calibrated to ensure good coverage! In very wet weather: ABSOLUTELY MUST RE-APPLY FUNGICIDES IN THE RAIN Mancozeb, captan, and sulfur will all provide several days of protection if applied in the rain Assume all fungicide protection, regardless of product, will be removed after 2 inches of rain If extended warm rains occur over the next few days: AN ABSOLUTE MUST to get out and renew coverage by spraying a protectant (mancozeb, captan, or sulfur) in the rain Duration of product: Avoid spraying in pouring rain = product washes off Duration of product: Applied during a drizzle = Uncertain about duration, but could expect 2 3 days

12 Management Additional considerations Be sure your sprayers are calibrated to ensure good coverage! Biggest problem: Poor coverage Right equipment Set up properly Ideal: Able to cover acreage in 3 days (or less) if needed to recover during a 2 week wetting period in a wet scab year Alternate Row Middle sprays good for wet years PRIORITIZE COVERAGE MOST SCAB SUSCEPTIBLE CULTIVARS Getting back through blocks quickly if rain removes all protection and continued wetting is predicted

13 Fungicide Failure! Is Resistance to Blame? Fungicide failures may not be due to resistance 1 st : Eliminate other possible causes Fungicide application: Was your sprayer calibrated? Environmental and plant growth conditions Is the orchard in a low-lying area? Near a pond/body of water? Not drying completely? When other possible causes have been eliminated, ask: Does the field have a history of extensive at-risk fungicide use? Has little to no nonchemical control methods been used?

14 FIRE BLIGHT Disease cycle Bacterial dispersal and colonization Blossom blight Canker blight Management strategies

15 Bacteria Dispersal and Colonization Canker oozing bacteria: Attracts insects insects disperse bacteria Insects move the bacteria to flowers Other modes of dispersal: Rain (splashing or aerosols) Wind Stigmas: Bacteria grows epiphytically does not cause disease (yet)

16 **Rain **Heavy dew Washes bacteria from stigma to nectaries Blossom blight 5 30 days postinfection Nectaries: Bacteria enters the plant

17 Symptoms occur after bloom Canker blight** Develops because of Renewed activity by the pathogen at the margins of overwintering cankers from previous season Occurs regularly every year where the disease is established MaryBlyt 7.1 Manual ***Bacteria invades systemically from canker: Alternative bacteria source for initiating summer shoot blight epidemics in years when blossom blight is scarce (think back to the summer of 2013 ) Can serve as primary source of bacteria for a continuing epidemic of secondary shoot infections major losses

18 Management Dormant Prune blighted limbs, shoots, cankers to reduce bacteria sources Remove wild or neglected fruit trees, susceptible host plants from fencerows and areas nearby Green Tip/Pre-Bloom Fertility: avoid excessive nitrogen Minimize tree stress Copper spray: 2 lb/a metallic Cu Bloom Terminal Bud Set Monitor weather conditions: Average temp >60 F and wetting event (rain, heavy dew) Antibiotics complete, + adjuvant or surfactant 4 spray max Plant growth regulator: Apogee, 6-12 oz/100 gal dilute + adjuv. Monitor regularly for infections if there were blossom blight conditions prune as necessary (NOT DURING WET WEATHER) Control piercing-sucking insects

19 CHERRY LEAF SPOT

20 Cherry leaf spot (very similar to apple scab for infection periods ) Fungus overwinters in fallen leaves Ascospores discharged into air during rainy weather Optimal: 61 F and higher Spread by wind and splashing raindrops Management Remove overwintering leaves G. Sundin MSU Proper pruning to open up canopy Increase air circulation Sunlight penetration Apply fungicide sprays early Bract leaves of tart cherry = very susceptible Monitoring conditions at bloom Chlorothalonil Luna Sensation Merivon Postharvest applications necessary

21 Take home messages: Good disease management programs during wet years Reduce the amount of overwintering sources of inoculum Practice good sanitation! Calibrate sprayers for good coverage ( Copper sprays at silver tip through green tip 2 lbs/a of metallic Copper Helps both apple scab, fire blight, bacterial spot Monitor orchard conditions and infection events (NEWA, SkyBit) Apply control before infection event Apple Scab: Rotate chemistries and tank mix with protectants from ½ GT through first cover MUST RE-APPLY FUNGICIDES IN THE RAIN Important to control diseases on nonbearing fruit trees during wet years

22 MANAGING DISEASES DURING A WET YEAR QUESTIONS? Kari Peter, Ph.D. Department of Plant Pathology and Environmental Microbiology Penn State University Fruit Research and Extension Center Biglerville, PA