July 26, 2017
Trap catches of spotted wing drosophila will increase in post-harvest orchards. We expect SWD populations to continue to rise as they begin to infest fruit left in the trees and on the ground. There is no advantage to making control applications at this time. In fact, any controls applied now would likely speed up the development of resistance. The presence of high populations, with the short generation times occurring now, will expose larger numbers of individuals to any materials applied resulting in greater selection pressure and a greater probability of resistant population development.
This past week may be the first of the season where we did not record multiple disease infection events. Most weather stations recorded only a single apple scab and cherry leaf spot infection period, the exception was in West Jacksonport which recorded none. Cherry leafspot continues to be an issue in most orchards and post harvest fungicide application will be very important in maintaining tree health.
INSECT & DISEASE CONTROL
Disease Pressure – Growers that have had an issue with sooty blotch and/or fly speck in the last year or two will want to consider an appropriate fungicide application to keep these diseases from developing. Coverage now, and then again in 3-4 weeks, of a higher rate of Captan 80 WDG (6lb/A) or either Pristine, Flint or Sovran would help to reduce this pair of diseases.
Apple scab control is less of a concern as we are out of the primary infection season. Length of fungicide intervals can now be between 2-3 weeks if scab lesions are not present on leaves or fruit. Apple growers who have scab lesions present in their orchards should be applying protectant fungicides on a shorter 10-14 day schedule.
Insect Pressure – Codling moth adult catches continue to remain above treatment threshold in many scouted orchards. Control applications to reduce damage from 1st generation should be continued on a 10 -14 day schedule as long as catches remain above threshold. Apple maggot have also started to be caught in some scouted orchards. The choice of control materials at this time should rate good to excellent for both codling moth and apple maggot as they continue to be the main pest concern for the next month. These include Imidan, Assail, Exirel, Delegate, Voliam Xpress and Voliam flexi.
The August threshold for European red mites rises to 7-10 mites per leaf. The frequent and heavy rains have kept this pest below threshold levels for much of the season so far.
Disease Pressure – Leaf spot continues to be seen in scouted orchards. Post harvest fungicide applications will be extremely critical this season because of the numerous infection events and the high level of infected leaves seen throughout the season. Chlorothalonil containing products (Bravo, Echo Equus, etc.) are the best choice for post harvest control applications. Copper fungicides may also be considered where infected leaves were high and a second post harvest application is needed. It would be best to use the copper compounds in a second application 3-4 weeks after chlorolthalonil when temperatures are not has warm to avoid phytotoxicity.
Insect Pressure – In the remaining unharvested commercial orchards, spotted wing drosophila catches are increasing. Few effective options, with short pre-harvest intervals, are available for control of this pest.
Spotted Wing Drosophila Control Options
|Trade Name||Class||PHI||Effectiveness Rating|
|Imidan||Organophosphate||7 Day||Excellent (7 days)|
|Pounce (permethrin)||Pyrethroid||3 Day||Fair (3-5 days)|
|Exirel||Diamide||3 Day||Excellent (7 days)|
|Danitol||Pyrethroid||3 Days||Excellent (7 days)|
Links to individual Enviro-Weather stations: