As we're facing the home stretch of the season, the biggest disease concern this time of year is keeping fruit free of rots. Fruit rots still seem to be prevailing in the orchard despite the dry conditions and folks should not let their guard down. Not only a headache in the field, but the fungi causing fruit rots can be quite stealth since spores will land on the fruit and cause symptoms only after the fruit have been in storage. This is especially significant if your apples are headed for a packinghouse or even fresh market.
Options for final sprays (be mindful of the maximum limit for sprays for each product/FRAC Group):
- Merivon (FRAC Groups 7 + 11; 0 day PHI)
- Luna Sensation (FRAC Groups 7 + 11; 14 day PHI)
- Flint (FRAC Group 11; 14 day PHI)
- Indar (FRAC Grop 3; 14 day PHI)
- Topsin M (FRAC Group 1; 1 day PHI)
- Captan (FRAC Group M4; 0 day PHI - used alone or tank mixed with a single mode of action product)
- Serenade Optimum (biofungicide - B. subtilus; 0 PHI)
- Double Nickel (biofungicide - Bacillus amyloliquefaciens; 0 PHI)
For folks seeking alternatives, we are in the midst of evaluating Serenade Optimum (again) and Double Nickel for summer disease control. For the last two seasons, we used Serenade Optimum (16 oz/A) as the last two cover sprays (with a conventional program up to these sprays). We observed minimal fruit rot diseases in the field and storage, at least on Golden Delicious. These results may vary with other cultivars, depending on their susceptibility to certain rot diseases. This year we are expanding our evaluation to Red Delicious, which appears to be especially rot-susceptible.
Minimizing postharvest fruit rots this season
As you're getting your orchards ready for harvest, some general management techniques to keep in mind to reduce postharvest fruit rots:
- Bruised or wounded fruit are susceptible to blue mold and gray mold. While harvesting, handle fruit carefully when picking and transferring fruit from bag to bin to avoid bruising or wounding.
- The more mature a fruit, the more susceptible it is to storage diseases. Harvest fruit at proper maturity.
- Inoculum sources for rot pathogens causing disease in storage (if already not hitching a ride on the fruit) come from plant and soil debris. Use clean bins and minimize the amount of soil and plant debris brought in on bins.
- Warm temperatures encourage pathogens to grow. Keep fruit cool after harvest, i.e. keep bins in shade.
- If delivering to a packinghouse, minimize time between harvest and delivery of fruit.
For commercial growers: When controlling for disease, weather and tree growth conditions need to be monitored at a local level within one's own orchard. Before chemical products are applied, be sure to be in compliance by obtaining the current usage regulations and examining the product label. Product information can be easily obtained from CDMS.