MSU Extension Fruit & Nuts

Weather crop update

Over the past two weeks, weather in the Grand Rapids, Michigan, area has continued to be very warm and humid, typical of the summer season. Temperatures over the past week were very close to long term averages, with highs in the 70s to 80s degrees Fahrenheit and overnight lows in the 50s and 60s. The Michigan State University Sparta Enviroweather station has accumulated a total of 2,369.2 growing degree days (GDD) base 42 since Jan. 1, indicating the region is still approximately nine days earlier than the average for July 26. Most of this is attributed to early spring heat; GDD accumulation over most of the summer (the past six weeks) has been very close to season averages.

More rainfall over the past week continued to replenish soil moisture deficits. Enviroweather stations across the region recorded between 0.5 and 1 inch of rainfall in most areas overnight Friday, July 23, with some areas receiving more than 2 inches of rain. Rainfall has relieved a considerable amount of the drought we have been experiencing this season. 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).

In the forecast, we are expected to have drier and warmer than normal temperatures today and tomorrow. This will be followed by a significant storm system Wednesday evening into Thursday morning, including heavy rains and possible high winds. Warm summer storm systems are always accompanied by the chance of high winds and hail. The NOAA Storm Prediction Site offers information about predicted and previous storm reports. Medium and long-term forecasts indicate a cooler period over the weekend, with possible scattered showers, followed by a return to warmer and drier than normal conditions for the month of August.

Peaches in the region are beginning harvest for early varieties such as Brightstar. Considerable pit splitting is evident in these varieties due to the heavy rains (6 inches or more) across the region just a couple of weeks before harvest began, following the drought most of the spring. Red Haven series are expected to begin harvesting as early as next week. Anticipated harvest dates are available on the Enviroweather Peach Harvest Estimate model. Earliest varieties are expected to begin harvest in approximately two weeks.

Apples in the Grand Rapids area are continuing to size and beginning to color. Frost damage is becoming more evident from the freeze events in April as frost rings, misshapen fruit and cracking or yellowing of the calyx end of the fruit. Early varieties such as Paula Red, Gingergold and Zestar are beginning to color and put on considerable size. Due to the early spring heat, early varieties like McIntosh, Gala and Honeycrisp are expected to begin harvesting a week or more before average picking dates, corresponding to the first week of September this year. 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.

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 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. Read more about how to check your fruit for maturity.

The 2021 predicted apple harvest dates are available online for all the MSU 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 updates

As we enter the dog days of summer, pest activity tends to become quite routine. We still need to keep in mind that checking traps to make the best timed application decisions is still very important. Routine fungicide cover sprays are also necessary to hold summer diseases and potential fruit rots at bay. You should have at least one summer disease fungicide applied, and some areas might be gaining enough wetting hours for a second application. Check the Summer Disease Model on the nearest MSU Enviroweather station to help time that next spray. You can put in the date of your last spray and it will calculate when that will be reduced by rainfall; add another 200 or so hours of wetting and that’s the time for another summer disease application. When roughly 200 hours of wetting are accumulated, the expression of sooty blotch and flyspeck fungi becomes a possibility and a fungicide will help prevent this.

The second generation of codling moth has been active in some higher pressure areas and early egg hatch is likely happening now. If you did an excellent job managing first generation, hopefully second generation will be lower in pressure. A biofix for the Grand Rapids region was set for May 16. The degree day totals for base 50 since that biofix total 1,295 base 50. The degree day models indicate early egg hatch for second generation is well underway and will continue until mid-August, requiring cover sprays if over threshold in adult traps.

European red mites are causing visible bronzing in some heavily infested blocks. Continue to monitor – the threshold for European red mites in July is five motiles per leaf. There are twospotted spider mites being found as well.

The summer generation of obliquebanded leafroller adults are flying. Egg hatch for the overwintering generation should begin soon with visible larvae likely to be found in ten to fourteen 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 1,340. Continue to monitor traps, knowing cover sprays won’t be needed for at least a couple of weeks when new larvae are again present.

Green apple aphids continue activity on growing terminals in apples. As terminal buds set, these aphids move on to alternate hosts.

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 1,163 degree days base 51 accumulated since that date. This timing indicates second generation crawlers will likely be present 10 to 14 days from now or around Aug. 9 or 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 are declining as expected. Egg hatch continues but should be nearing an end. A biofix was set for the general Grand Rapids area for May 1. The Sparta MSU Enviroweather station has accumulated 1,750 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. This generation usually is not an issue in apples unless trap numbers are extremely high.

Apple maggot adults continue to be caught in very low numbers each week. In the last week, numbers were slightly higher. All traps should be using baited lures to get the best idea of apple maggot activity.

Japanese beetle adults have dramatically increased over the past week or so.

Low numbers of spotted wing Drosophila continue to be caught in traps in many areas of Michigan. If you have susceptible crops nearing harvest, cover sprays for spotted wing Drosophila are recommended.