Although Michigan’s apple harvest is now in full swing for many varieties, abnormally warm temperatures could pose a challenge for apple farmers throughout the western growing region of the state, according to Michigan Farm Bureau Horticultural Specialist Kevin Robson, particularly for more sensitive varieties like Honeycrisp, Sweet Tango, and Goldens, all of which are popular varieties with consumers.
“Some areas in northern Michigan will hit 90+ degrees, for the first time this summer, ironically on the first day of fall,” Robson said. “This just goes to show how much our fruit industry depends on the mood of Mother Nature. Farmers can do everything right from a crop management point of view for pest and disease control, pruning, mowing, maintaining, and protecting, but it isn’t over until the apples are in the hands of a hungry consumer.”
MSU Extension Specialists concur with Robson’s assessment, stressing that it will to be difficult to get the latent heat out of apples over the next several days with daytime highs predicted in the upper 80s and even 90s, and nighttime temperatures in the 60s.
They suggest that apple producers consider these additional steps before moving apples into storage:
- Don’t close up storage rooms until the heat is out of the fruit.
- Carbon dioxide levels will be very elevated, even in open-air storage like a pole building. Some varieties, such as Honeycrisp, are very sensitive to CO2. Adding a half skid of lime in the room will help reduce CO2.
- Get the heat out of fruit before putting them in rooms—take advantage of slightly cooler nights by leaving fruit outdoors and then fill rooms in the morning hours.
- Storage cooling units are going to have to work overtime to get latent heat out of apples. Consider scattering fruit in different rooms to not tax any room’s system too much and then consolidate as needed once cooled down.
- Don’t stack bins tight in a room until fruit is cooled.
- Using 1-MCP products (Harvista and SmartFresh) might be more important than usual to prevent excess ethylene production in stored apples over this hot spell. Be aware of issues when applying 1-MCP in the room with warm fruit. For instance, Golden Delicious will get a “ghosting” on the surface if 1-MCP is used on warm fruit.
See more discussion in this 2016 article from MSU‘s Randy Beaudry, “Apple storage advice for 2016 - a warm year at harvest.”
- Very warm temperatures in September could lead to higher incidence of superficial (storage) scald in susceptible varieties. Treat fruit rapidly after harvest with DPA or 1-MCP to minimize risk.
- The predicted hot weather for later this week will advance apple maturity, including increased tendency for pre-harvest drop, increasing the need for effective stop-drop and ripening inhibitor treatments.
Last, but not least, MSU Extension Specialist recommend considering the impact to harvest crews and advise putting heat prevention at the top of your human resources list for the next several days. People working outdoors might not take the extra time to drink enough water and dehydration can happen quickly, as we are just not used to this kind of heat in late September. Have water readily available to workers and encourage all steps to prevent dehydration, heat stroke and sunburn. “This is nothing our state’s fruit growers haven’t seen before” Robson said. “There’s no doubt they’ll be taking the proper precautions, and following their well-established protocols, to ensure a safe, quality product to the marketplace.”