MSU Extension Fruit & Nuts

Weather update

Weather conditions in the Grand Rapids, Michigan, area over the last week have included a major shift in precipitation and temperatures. Overall, the week was much closer to normal for the area than most of the rest of the season has been. The Michigan State University Sparta Enviroweather station has accumulated a total of 1,415.1 degree days base 42 since Jan. 1, indicating the region is still approximately 11 days earlier than the average for June 22. Temperatures at the end of last week and over the weekend included highs in the 70s and low 80s degrees Fahrenheit. This was followed by a considerable cooling trend beginning Sunday evening, with low temperatures Sunday and Monday evenings in the 40s and 50s, and highs on Monday only in the mid-60s.

Considerable widespread rainfall occurred at the end of the week as storm systems moved through the area. The greatest precipitation occurred on Friday evening into Saturday, with 0.7-1 inches recorded in most locations, and another 0.1 inch in many places on Sunday evening. This much-needed rainfall has alleviated some of the dryness. However, soil moisture estimates indicate that long term deficits are still present and irrigation will continue to be necessary.

The beginning of this week is expected to be much cooler than normal. However, warm conditions are expected to return late in the week, including highs in the low- to mid-80s. The forecast includes another precipitation event, with a slow moving weather system expected to bring extended showers and storms on Friday and Saturday. Warm summer storm systems are always accompanied by the chance of high winds and hail, although specific predictions do not offer very much accuracy at this time. The NOAA Storm Prediction Site offers information about predicted and previous storm reports, including yesterday’s storms in southwest Michigan, which included 2-inch hail and wind gusts over 60 mph. Another useful site is Hail.org, which offers a variety of hail reports including predictions and maps throughout the country.

The long lead outlook includes a return to warmer than normal temperatures, beginning in the first week of July. Forecasts indicate warmer than normal conditions are expected for the remainder of the summer and the fall.

Apples in the Grand Rapids area are continuing to size, with most varieties approximately 1.5 inches in diameter. Some frost damage is now evident, from the freeze events in April, as frost rings, misshapen fruit, and cracking or yellowing of the calyx end of the fruit. Growth will continue rapidly in light of the precipitation over the past week and the return to warmer temperatures this week.

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 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 overall 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

Primary apple scab is finally over for the general Grand Rapids area. Spore monitoring was done over a three-month period of time in 2021 – it’s been a long primary scab season. Dry conditions dragged the primary scab season out longer than usual, and careful scouting is needed to make sure no scab lesions snuck through in the last few infection events.

Powdery mildew seems to be more of an issue in 2021 than usual and it will continue to spread until terminal bud set occurs.

Fire blight symptoms in the general Grand Rapids area are not too common due to diligent cover sprays during bloom and the use of Apogee and Actigard in this area. If blocks are clean of blight, the risk is so much less if any summer storms occur. If trauma conditions occur, preventative applications will be needed until we get to terminal bud set.

Some collapsing of trees is beginning to show from the heat and drought stress a couple of weeks ago. At first glance, one might think this to be fire blight, but be sure to look closely and use a pocket knife to check the rootstock and trunk for other symptoms. In the picture below, this collapsing tree had winter injury from two winters ago in the rootstock and the trunk.

Sooty blotch and flyspeck fungicides might be needed in some areas that received rain over the past few weeks. The rainfall and wetting hours for the various MSU Enviroweather stations has been highly variable – this has led to high variability in the summer disease model results across the region. Be sure you are watching the weather station nearest you for the proper timing to begin adding summer disease fungicides as needed.

Adult codling moth numbers are still being caught in traps in low numbers for the most part. There are a few blocks with reports of higher than normal numbers. A biofix for the Grand Rapids region was set for May 16. The degree day totals for base 50 since that biofix total 616 base 50. The degree day models indicate the general Grand Rapids area is past peak egg hatch for codling moth. The end of first generation egg hatch is likely to be in mid-July and cover sprays continue to be necessary next two weeks in blocks over threshold (five moths accumulated per trap or one moth per 1X trap in disrupted apple blocks).

European red mites continue to do well. Recent rain events and cover sprays have reduced them somewhat. Continue to monitor – the threshold for European red mites in June is 2.5 motiles per leaf. Beneficials are beginning to be found in European red mite populations and should be considered. Twospotted spider mites can be found in Grand Rapids orchards too.

Obliquebanded leafroller adults are being regularly caught in pheromone traps. It is likely the Grand Rapids area in general is past peak flight. 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 382. In blocks with higher populations, first treatments should be timed for 400 to 450 GDD42 post-biofix or around June 22-23. In blocks with lighter numbers and no damage to fruits in 2020, scout for larvae and spray as needed if over threshold (i.e., one larva per tree/block). It’s’ likely the first larvae will become easier to find with the naked eye around July 2 or 3.

A few rosy apple aphid are still present in apple terminals but seem to be moving on to alternate hosts. Green apple aphids (also known as Spirea aphid) are now building quickly on growing terminals in apples. It’s easier to also find several species of aphid predators in aphid colonies.

Woolly apple aphid is now starting to be reported in blocks with high numbers in 2020. They are extremely hard to find, but early management is important to keep woolly apple aphid at bay in late summer and early fall. If you had high populations in fall 2020, scout for their presence now.

San Jose scale male flight is declining. First crawlers started to be found in the past week. A regional biofix for the general Grand Rapids area was set for May 20, with 518 degree days base 51 accumulated since that date. Cover sprays to target San Jose crawlers need to be considered where populations were high in 2020. Systemic materials need time to be taken up by trees and we are quickly moving out of that ideal timing. If using contact insecticides targeting crawlers recommended between 600 and 700 degree days base 51 post biofix of male flight. This is guesstimated for June 28 or 29 using Sparta weather station data. The recent cooler weather has slowed this model by a few days.

Oriental fruit moth adult flight is down considerably. A biofix was set for the general Grand Rapids area for May 1. The Sparta MSU Enviroweather station has accumulated 899 degree days base 45 since that biofix. Change out lures in traps if not already done the start of second generation adult flight is likely this week. The expected early egg hatch for second generation will fall in the first week of July when cover sprays will again be critical in stone fruits.

White apple leafhopper nymphs and adults can be found in apples in rather low numbers. Keep an eye on non-bearing trees where insecticide covers are not used as much – a smaller than normal level of white apple leafhoppers could shut down shoot growth in drought condition.

Dogwood borer adult flight is in its second week in the Grand Rapids area – numbers are low. Lesser peach tree borers, American plum borer and peach tree borer are all flying now in low to normal numbers. Borer sprays are usually timed for peak adult flight. For peach tree and lesser peach tree borers, this is usually late June. For dogwood borer timing is usually around July 4.