Apple fruit maturity for early varieties in 2020

Harvest the best looking fruit from early varieties in the next few days and delay additional harvest for a week or two.

Growth of McIntosh apple fruit and ethylene production
Figure 1. Growth of McIntosh apple fruit and ethylene production. Arrow indicated target harvest date for long-term storage.

I have been a little surprised by the mixed messages I am getting from our various fruit maturity indices for Gala, McIntosh and Honeycrisp this year. Fruit are tending to be a little on the small size but with good color despite the generally warm season. That is a bit surprising and contrary to most years, but I am happy to see the nice color development.

What is even more unusual this year is that the fruit are coming in with advanced starch clearing and fully brown seeds, and yet the firmness is unusually high. We are also finding relatively variable but high levels of ethylene for fruit harvested so early in the season. These conflicting signals from the apple trees make it difficult to estimate the maturity of the fruit and, by extrapolation, estimate fruit storability.

However, we have seen this before and there is no serious cause of concern.

My suggestion is to hedge bets a little at this point and not jump into full harvest too quickly. The high firmness—some of our Gala are at 24 to 26 pounds, and Honeycrisp at about 20 pounds or so—means we have some flexibility in our harvest date. The fruit will not lose firmness too quickly with the upcoming cool weather. So, for the moment we can reduce our reliance on starch index, which would suggest getting all the fruit in from the orchard very soon and focus more on the advantage given by high fruit firmness.

Harvest high color fruit at this point and give the remaining fruit some time to catch up in terms of color and size. Recall that apple fruit continue to grow even at this late stage in development—about 0.5% to 1% per day—and rain will accentuate this (Figure 1).

The high ethylene and low starch may be effects of this season's relatively high temperatures and low rainfall during the growing season. I have seen this before. There have been years where Gala show relatively high ethylene levels (similar to what we are finding this year, about 1 ppm), and yet ripening does not really engage for some weeks. I worry a bit more about Honeycrisp, which can drop easily in response to ethylene.

Keep a close eye on the fruit and their propensity to drop. Again, pulling off the most highly colored and most advanced fruit should help reduce this issue. However, if the fruit are loose, NAA application may be in order. If ReTain has been applied, the little data I have seen so far suggests it has been effective at reducing ethylene formation in the fruit, so you should be in good shape to delay harvest of treated fruit.

The take-home message is get the best looking fruit out of the orchard from these early varieties in the next few days and, as long as firmness and fruit attachment hold up, delay additional harvest for a week or two, depending on your situation.

Did you find this article useful?