Grand Rapids area tree fruit update – Aug. 10, 2021

The first apple maturity report of the season is out this week.

Entry holes from black stem borer.
Tree collapse from black stem borer. Photo by Amy Irish-Brown, MSU Extension.

Weather update

Over the few days, weather in the Grand Rapids, Michigan, area has been very hot, with highs in the 80s and lows only down to the 60s. The Michigan State University Sparta Enviroweather station has accumulated a total of 2,742.0 degree days base 42 since Jan. 1, indicating the region is approximately eight days earlier than the average for Aug. 9.

Last week saw mostly dry conditions, including heat advisories in Kent County similar to many locations in the eastern part of the country, but storms yesterday and today are expected to bring a total accumulation of 1-2 inches of precipitation. Fortunately, since the drought earlier this season, rainfall has significantly replenished soil moisture, and the lush growth is evidence of this. According to the U.S. Drought Monitor, less than half of 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).

Over the next few days, forecasts indicate hot, humid conditions with continued rainfall. Severe thunderstorms are possible across the region Tuesday and Wednesday night, including heavy rain and high winds. More information can be found on the NOAA Storm Prediction Center. By the end of the week, a cold front moving in Thursday night into Friday will lead to fair, dry, cooler conditions. Dewpoints will move from the 70s down to the 50s.

Highs over the weekend and into next week will be much cooler, with highs in the 70s and lows in the 50s. 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.

Crop update

Peaches in the region are continuing harvest 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 “Preparing for apple harvest in the Grand Rapids area” 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. But 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.

The first apple maturity report for the Grand Rapids region from MSU Extension is available today. Weekly reports will continue for the duration of harvest. Samples 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 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 pest management in tree fruits, but that doesn’t mean you can become lax in trap or orchard monitoring or pesticide cover sprays. It’s common to hear, “I haven’t put a spray on since….” While that’s great if you know there aren’t any pest issues present, some insects and diseases are still active and need to be addressed if numbers warrant.

Here’s a rundown to consider.

Some heavy rainfall totals over the past few days could lead to stretching of fungicide cover sprays and allow summer diseases and fruit rots to get established. Keep your fungicide covers fresh as rainfall demands. This week of hot and humid weather is great for summer diseases and fruit rot fungi. There have been reports of light hail with some storms – small knicks can be just the spot where fruit rot fungi can get established if you aren’t keeping those fungicide covers renewed.

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, you need to 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.

In the past few weeks, reports of collapsing trees have been coming in. At first glance, it appears to be fire blight. Upon closer inspection, it’s not quite right for fire blight, however, it is getting late in the growing season, so it could still be blight. Some of these collapsing trees also have black stem borer (BSB) present. This presents the question of which comes first, tree stress or black stem borer? We know black stem borer is attracted to injured trees that give off ethanol, but there is some discussion that sound trees can be infested. Trees under stress can look fine until some other pest or event comes along to stress even further, so perhaps we will never know for sure. If you do see tree that look like these pictures, look closely for the black stem borer holes – they are very tiny. It is best to cut out the infested section and burn it to destroy the insects.

The second generation of codling moth has been active in some higher pressure areas. In general, the Grand Rapids region should be nearing peak adult activity and peak egg hatch this week. Cover sprays are critical in blocks over threshold and should be continued for at least two more weeks as warranted. A biofix for the Grand Rapids region was set for May 16. The degree day totals for base 50 since that biofix total 1,566 base 50. The end of second generation codling moth activity is predicted for Aug. 24 or 25 for the general Grand Rapids area. With heavy rain events recently, pest management covers could be less than desired.

European red mites and twospotted spider mites continue to be found in some apple blocks. Now that we are in August, management is typically not necessary. Also, with no drought in place, any mite populations at this time should not compromise potential fruit sizing.

The summer generation of obliquebanded leafroller adults continue to fly in low to moderate numbers. Egg hatch should be underway and tiny larvae should become visible any day now in high pressure blocks. Obliquebanded leafroller late season larvae always seem to be tied well to the first pickings of Paula Reds in the Grand Rapids area. A biofix for the Grand Rapids region was set for June 7. The degree day totals for base 42 since that biofix total 1,721.

Woolly apple aphid continue to become easier and easier to find each week where they are not being addressed. With good spray coverage, populations appear to be declining.

San Jose scale males are still being found in traps and are declining as expected. A regional biofix for the general Grand Rapids area was set for May 20, with 1,420 degree days base 51 accumulated since that date. This model indicates second generation crawlers will likely be visible this week and the timing to manage this next generation of San Jose scale is fast approaching. This generation will settle on new shoots as well as on apples where they can cause defects on apples leading to culls.

Oriental fruit moth second generation adults trap numbers are greatly reduced. Egg hatch should also come to an end for the second generation. A biofix was set for the general Grand Rapids area for May 1. The Sparta MSU Enviroweather station has accumulated 2,091 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. The later generations of oriental fruit moth can infect apple fruits when codling moth covers get stretched out at the end of that insect’s life cycle.

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, but there are still some present and doing light feeding on various tree fruit species.

Spotted wing Drosophila continue to be caught in traps in many areas of Michigan and there seems to be a bit of an uptick in some areas. 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 in the general Grand Rapids area. We are approaching the time where we could begin to see an increase in brown marmorated stink bug activity in apple blocks along woodlands or other crop borders. As neighboring crops (soybeans, in particular) begin to dry down, this can trigger brown marmorated stink bug to seek other food sources. At this time, soybeans and corn look great, but will likely show the start of senescence in the next two to three weeks. Monitoring for brown marmorated stink bug needs to continue right up to harvest in blocks with a history or damage from this invasive pest.

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