MSU Extension Fruit & Nuts

Weather update

Over the past two weeks, the Grand Rapids, Michigan, area has experienced very warm, humid conditions, typical of the summer season. Temperatures over the past week were very close to or slightly lower than long term averages, with highs in the 70s to 80s degrees Fahrenheit and overnight lows in the 50s and 60s. Overall heat accumulation this season continues to be ahead of normal. The Michigan State University Sparta Enviroweather station has accumulated a total of 1,964.2 degree days base 42 since Jan. 1, indicating the region is still approximately eight days earlier than the average for July 12.

Rainfall over the past week contributed significantly to replenishing precipitation and soil moisture deficits. Enviroweather stations across the region recorded between 0.40-1.53 inches of rainfall, primarily in the middle of last week. This is important as we move into the period of the season with most intensive water demands. 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 of the state is now classified as being under D1 (moderate) drought conditions, including.

Rain and storms are expected over the next few days as two cold fronts move through the region, with possible accumulation of 0.25 to 0.5 inches. The highest probability of storms will be Tuesday afternoon and again on Wednesday evening into Thursday morning. There is a possibility of thunderstorms each afternoon. 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.

The medium and long lead outlook includes a return to warmer than normal temperatures, beginning at the end of the week. Temperatures will include highs in the 80s and lows in the upper 50s-60s F. Forecasts indicate warmer than normal conditions are expected for the remainder of the summer and the fall.

Crop update

Apples in the Grand Rapids area are continuing to size and beginning to color, with most varieties approximately 1.5 inches or 50-60 grams in size. 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.

Peaches in the region are approaching harvest, with pit hardening well underway final swell beginning for early varieties such as Brightstar. Anticipated harvest dates are available on the Enviroweather Peach Harvest Estimate model. Earliest varieties are expected to begin harvest in approximately two weeks.

Now is a good time for apple growers to begin taking leaf samples for tissue analysis for monitoring fruit nutrition. Results of foliar analyses are an excellent indication of which nutrients the trees are taking up and utilizing. They can be used to determine if the fertilizer program is meeting the needs of the trees in the orchard, diagnose nutritional problems, and identify developing problems before growth or yield is affected. The best time for sample collection is mid-summer, after shoot growth has stopped. In Honeycrisp, this timing is slightly earlier before “zonal or marginal chlorosis,” the mottled yellowed appearance of leaves common in this variety, becomes too pronounced. More information on Apple Nutrition is available from MSU’s Eric Hanson.

The 2021 predicted apple harvest dates are now available online for all of 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 update

Many of the weather stations around the general grand Rapids area have accumulated enough hours of wetting and rainfall to warrant fungicides for summer disease suppression. The rainfall and wetting have been variable this season, so some areas met the 200 hours of wetting several weeks ago and a few have yet to get there. When roughly 200 hours of wetting are accumulated, the expression of sooty blotch and flyspeck fungi becomes a possibility. Summer fungicides help suppress the bloom of various fungi that reside on the apple surface. These fungicides will also help curb any early start of fruit rots.

We are in between first and second generation of codling moth this week. This is a great time to change lures ahead of second generation flight. Adult numbers in traps should begin to increase over the next week. A biofix for the Grand Rapids region was set for May 16. The degree day totals for base 50 since that biofix total 1,001 base 50. The degree day models indicate early egg hatch for second generation is likely to begin around July 22 in blocks with populations over threshold.

European red mites continue to do well. Heavy rain events helped to reduce adult numbers on leaves a bit, but they seem to be recovering. Continue to monitor; the threshold for European red mites in July is five motiles per leaf.

Obliquebanded leafroller larvae are active in apple terminals, and they are starting to pupate. The start of second generation adult flight is likely to begin over the next week or so. 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 932. Continue to monitor and knock back populations to reduce the potential overwintering larvae which will not be present until early to mid-August.

Green apple aphids continue activity on growing terminals in apples. It is easier to also find several species of aphid predators in aphid colonies.

Woolly apple aphid are becoming 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. They can be found in leaf axils and on pruning wounds.

San Jose scale is in between generations and second generation male flight should begin this week. Areas to the south of Grand Rapids are reporting males in traps again. A regional biofix for the general Grand Rapids area was set for May 20, with 883 degree days base 51 accumulated since that date. This timing indicates second generation flight should begin very soon with second generation crawlers present again in the first week of August. Careful scouting is important for second generation as crawlers will settle on apples near harvest and make a mess.

Oriental fruit moth second generation adult numbers are declining as expected. Egg hatch is well underway and cover sprays are critical in stone fruits. In apples, second generation can sometimes be an issue where long-time codling moth mating disruption is in place or if there is a poorly managed peach block next door, or recently removed. A biofix was set for the general Grand Rapids area for May 1. The Sparta MSU Enviroweather station has accumulated 1,386 degree days base 45 since that biofix.

Apple maggot adults continue to be caught on yellow board traps and some on red sphere traps. All traps should be using baited lures to get the best idea of apple maggot activity.

First reports of Japanese beetle adults started about a week ago.

Spotted wing Drosophila (SWD) continue to be caught in traps in many areas of Michigan. Numbers are still on the low side, but if you have susceptible crops nearing harvest, cover sprays for SWD are recommended.