Apple Harvest Time: Managing pre-harvest and postharvest rots

The biggest disease concern this time of year is keeping fruit free of rots as they are nearing the home stretch of the season. The recent bouts of rain and prolonged warm weather are ideal conditions for fruit rot issues.

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.

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)
• 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)
• Oso 5% SC (biofungicide – Polyoxin D zinc salt; 0 PHI)

We are in the midst of evaluating Serenade Optimum and Oso 5% SC for summer disease control; we hope to evaluate Double Nickel next year. Last year when Serenade Optimum (16 oz/A) was used as the last two cover sprays, we observed good results for controlling rots in the field and during storage. We are repeating the trial again this year. Pome fruits were added to the Oso 5% SC label last year, specifically for control of summer diseases. We are in the process of putting the product (6.5 oz/A plus LI-700 1 pt/100 gal) through its paces under PA conditions this year.

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.

— Penn State University