First Apple Bitter Rot Symptoms in 2024 Visible in Winchester, VA (14 June 2024)

Apple bitter rot is caused by six Colletotrichum species of fungi in Virginia: C. fructicola , C. chrysophilum, C. siamense, C. theobromicola, C. fioriniae and C. nymphaeae. First symptoms of bitter rot disease on fruit of apple cultivar ‘Gala’ have been found on 14 June in Winchester at AREC’s experimental Block 30W (Figures 1-4). These trees were not sprayed with any fungicides so far. The rot started on the sun exposed fruit side (Fig. 1). We found these bitter rot lesions on fruit on the Eastern side of the tree crown, most likely indicating on the conducive moisture was keeping longer on this side of the trees (Fig. 1 ). Bitter rot fungi can infect any areas not covered with an effective fungicide on fruit, especially when warm wetting events occur, and we had more than several of these weather periods in the last 30 days. The oncoming extreme heat and rainy weather will favor infections by this disease from now until the harvest. Start scouting for bitter rot symptoms to make sure your trees are free of this disease and to determine how good was your fungicide coverage during the first cover sprays.

We hope you will NOT see any bitter rot in your blocks and that your fungicide coverage was satisfactory. However, if you see bitter rot on some fruit, especially on highly valuable crop like ‘Honeycrisp’, our recommendation is to protect the whole block by immediately spray applying the full rate of captan plus higher rate of Pristine or Merivon or other QoI containing fungicides such as Flint Extra or Luna Sensation (keep in mind the Pre-Harvest Interval /PHI/ though). We would also recommend to include a surfactant such as LI-700 to enhance fruit coverage (use low rate for coverage only). This will help both to inactivate spores on the decay lesions and to protect the remaining healthy fruit from infection until they can be harvested. We warn that if fruit will be sold for pick-your-own, then the full rate of captan close to harvest may be a problem and one might get by with a half-rate of Captan 80 plus a full rate of either Pristine or Merivon (read the labels and PHI limits of these fungicides). After harvest, strive to pick all of the decayed fruit from the orchard floor before winter and destroy it by burying the fruit. If the bitter rot affected block was a block that had fire blight last year or this year, it will also be important to cut out and remove all of the dead fire blight wood because bitter rot likes to colonize old fire blight strikes.

I would recommend the following effective fungicides at this time of the year: Aprovia 5.5 – 7 fl oz (30 PHI) + Captan 80 WDG 3 lb, or Omega 13.8 fl oz (28 PHI) + Captan 80 WDG 3 lb. Alternate these fungicides with strobilurins: Flint Extra, Luna Sensation, Pristine and Merivon which should be combined in a tank with captan or ziram or ferbam. Use Merivon or Pristine plus captan for your last two cover sprays before harvest.