MSU Extension Fruit & Nuts

Weather update

Over the last few days, weather in the Grand Rapids, Michigan, area cooled off considerably, but hot and dry conditions are expected to resume this week. Temperatures for the past three days included highs in the mid-70s degrees Fahrenheit and overnight lows near 50 F. However, conditions over the past week were fairly similar to seasonal averages and this year continues to be more than a week ahead of normal. The Michigan State University Sparta Enviroweather station has accumulated a total of 2,551.2 degree days base 42 since Jan. 1, indicating the region is approximately eight days earlier than the average for Aug. 2.

Very little rainfall was recorded over the past week, with less than 0.1 inch in most locations. Fortunately, the rainfall we received over the past few weeks significantly replenished soil moisture. According to the U.S. Drought Monitor, less than half the state is now classified as being under any drought conditions; most of the apple production locations in the Grand Rapids, area are currently classified as D0 (abnormally dry) or none (no drought conditions).  

While we hope to have more cool conditions (like the past few days) to help with fruit color and quality, the forecast indicates the opposite. We are expected to have drier and warmer than normal temperatures for most of August. Very little rain is predicted this week, with the best chance of scattered showers over the weekend.

Crop update

Peaches in the region are continuing harvest for early varieties and beginning for Red Haven and others in this series. Some split pits have been observed due to the heavy rain several weeks ago, but this has been greatest in early, more susceptible varieties. Anticipated harvest dates by variety are available on the Enviroweather Peach Harvest Estimate model.

Apples in the Grand Rapids area are continuing to size and beginning to color. Trees have mostly set terminal buds, but some new growth has been observed following the rain over the past few weeks. Due to the early spring heat, early varieties (McIntosh, Gala, Honeycrisp) are expected to begin harvesting a week or more before average picking dates, corresponding to the first week of September this year. See our article on preparing for apple harvest for more detailed information.

Later varieties typically seem to have more stable harvest dates and are expected to be mature nearly the same time as seasonal averages. The lighter than normal crop is likely to mean fruit will be picked and moved more quickly. It is still important to harvest at optimal maturity, as both under and over-ripe fruit are more susceptible to storage disorders, poor quality and bad consumer perception.

A few Paula Red, Ginger Gold and Zestar apples were tested for maturity on Monday, Aug. 2. A few fruit showed a little starch clearing just beginning, but maturity qualities indicate they will still need a few more weeks.

Michigan State University Extension will begin our Apple Maturity Program and weekly reports at the end of August. Samples will be from production areas across the state and will be tested for maturity indicators (starch, soluble solids content, firmness, color and ethylene) to provide guidance on harvest dates and conditions. However, actual harvest date is specific to individual blocks, depending on variety, conditions and specific environment. You can read more about how to check your fruit for maturity.

The 2021 predicted apple harvest dates are available online for all of the Michigan State University Enviroweather Stations. Phenology has been approximately one to two weeks earlier than the 30-year average for the duration of the 2021 season. This is the opposite of the past two years, in which cool late winter climate delayed the development of spring buds. Overall, 2021 predicted harvest dates are earlier than normal. Most of the state is a few days earlier compared to the average and last year. The predicted harvest dates for specific locations can be calculated using the Apple Maturity Model on the Enviroweather Website.

Pest update

August becomes a more relaxed time for insect management in tree fruits, but that doesn’t mean you can become lax in trap or orchard monitoring. There is always something to deal with.

There are a few apple blocks with active fire blight present. As we move to terminal bud set, the risk for continued infection should decline. In young trees where growth continues, stay vigilant with protective sprays and tree removal to get a handle on the problem. Getting trees to shut down active growth is the best thing to slow further blight infection. This includes turning off irrigation, eliminating nitrogen fertilizer and applying copper as a protectant and to shut down growth.

The second generation of codling moth has been active in some higher pressure areas. In general, the Grand Rapids region should be at about 25 to 35% egg hatch and cover sprays are critical in blocks over threshold. A biofix for the Grand Rapids region was set for May 16. The degree day totals for base 50 since that biofix total 1420 base 50.

European red mites are causing visible bronzing in some heavily infested blocks. Continue to monitor; the threshold for European red mites in July is 7.5 mites per leaf. There are twospotted spider mites being found as well. With early harvest predicted for many apples and in blocks with a light crop, if you can hold mites back until mid-August, that should be good enough for this season and not risk fruit size losses. However, keep in mind that in high mite pressure blocks, the late generations will lay eggs in the calyx end of apples.

The summer generation of obliquebanded leafroller adults are flying – numbers seem to be low in most areas. Egg hatch for the overwintering generation should begin any day with visible larvae likely to be found in seven to 10 days. An obliquebanded leafroller biofix for the Grand Rapids region was set for June 7. The degree day totals for base 42 since that biofix total 1519.

Green apple aphids activity is waning as terminal beds set in many apple blocks.

Woolly apple aphid continue to become easier and easier to find each week. Most populations are still small and need to be addressed before they are too out of hand closer to harvest and much more difficult to manage. Because of the waxy coating this aphid exudes, optimum spray coverage is absolutely required to get good control. More water and travelling at a slower speed are needed. There are stories of materials not working well, but for every failure we hear about, we hear from others that the same products work very well for others. Again, good coverage is critical to get the woolly apple aphid management you expect.

San Jose scale males are begin found in traps as the second generation flight is underway. A regional biofix for the general Grand Rapids area was set for May 20 with 1,282 degree days base 51 accumulated since that date. This timing indicates second generation crawlers will likely be present around Aug. 10. We are approaching the timing to manage this next generation of San Jose scale to prevent them from settling on apples where they can make a real mess at harvest.

Oriental fruit moth second generation adult numbers in traps are nearing zero. Egg hatch should be ending for the second generation. A biofix was set for the general Grand Rapids area for May 1. The Sparta MSU Enviroweather station has accumulated 1,911 degree days base 45 since that biofix. In high pressure situations, by this time of year, various generations of oriental fruit moth can be overlapping. Use your trap numbers to help fine-tune your cover spray needs.

Apple maggot adults have been caught in very low numbers for several weeks. In the last week, however, there was a bit of a spike in trap numbers perhaps indicating increased fly activity as apples develop color and aromas attractive to adult females for egglaying. It is important to continue to monitor for apple maggot through the first week of September. 

Japanese beetle adults are still present, and numbers appear to be declining as expected. 

Low numbers of spotted wing Drosophila continue to be caught in traps in many areas of Michigan. Peaches are especially a favorite for spotted wing Drosophila, and cover sprays are necessary where trap numbers continue.

Brown marmorated stink bug are active and so far, numbers are low in traps. Feeding damage in high pressure areas is beginning. Monitoring needs to continue right up to harvest in blocks with a history or damage from this invasive pest.