Hot, hot apple harvest concerns

Unusual heat wave in late September calls for special concerns to apples.

It’s going 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. Consider these special concerns during this unusual situation.

  • Don’t close up 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, like 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 your fruits. 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, keep your harvesting humans in mind and put 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.

For more information on heat stress prevention in humans, see these Michigan State University Extension articles:

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