Apple Disease Update: Week of June 21, 2021
At this point in the season in North Carolina, you should be well into boring summer fungicide cover programs, regardless if you have a full crop this year or not. As has been the norm for my posts this season, please do not let your sprayers sit lonely in the shed. While in the absence of fruit a Cadillac fungicide program to completely eliminate disease may not be imperative, it’s important to remember that many of the pathogens that infect your fruit will also infect foliage, which can lead to reduced photosynthetic capacity and perhaps reduced winter hardiness and return budset due to premature defoliation. Furthermore, infection of leaf tissue will allow inoculum (populations) to build within your orchard, making management that much more difficult next year.
As a brief review, here are the simplified spray intervals I am suggesting this year when on a captan rotation for Glomerella leaf spot and bitter rot control.
Marketable fruit on tree: 7 to 10 day interval-possibly less if severe rain and rain is predicted in forecast before interval is up
None to few marketable fruit on cultivar susceptible to GLS: No greater than 14 day interval
None to few marketable fruit on cultivar NOT susceptible to GLS: No greater than 21 day interval
Looking at the forecast, if you applied Captan or another fungicide for GLS/bitter rot management a few days prior to yesterday’s/today’s rain, I would consider another application on Friday or Saturday, as rain is predicted on Sunday. If more than 10 days has passed since your last Captan application, consider an application of a FRAC 11 (strobilurin fungicide such as Merivon, Flint, or Luna Sensation) plus a half rate of captan no later than tomorrow morning on trees in which you plan on harvesting a crop.
Now is also a good time for my yearly PSA about June drops and hand thinning fruit. Fruit drops, even at this stage of development, can and will get bitter rot. Applications of herbicides to try to destroy fruit tissue or the bitter rot fungus will actually encourage the development of symptoms so please refrain from trying that. In blocks where bitter rot or GLS has historically been an issue, at the very least sweep apples to row middles. Better yet is to remove the drops and get them away from your trees.