MSU Extension

Weather and growth stages

As all tree fruit size quickly with the much warmer than normal temperatures, the fruit set appears to be very nice for much of the Grand Rapids, Michigan, area. As usual, there are areas with a heavier than needed fruit set and areas with a lighter crop than desired.

Apples range from 12 to 28 millimeters, depending on variety and site. Some areas are reporting apples thinning down very nicely and while there are a few reports of less crop set than desired, we all know this will change in the next few weeks as fruit becomes easier to see.

Peaches continue to grow fast with many in the 20- to 25-millimeters stage and hand-thinning is beginning. Estimated harvest dates for some peach varieties are available on the Michigan State University Enviro-weather website in the fruit tools section.

Sweet cherries are 12 to 15 millimeters and also sizing quickly – some sites have a very nice crop and others are a bit light. Sweet cherries with lighter crops are sizing faster with some straw-colored fruits apparent in early varieties.

Growing degree-day (GDD) totals for the Sparta Enviro-weather station are 1,009 GDD base 42, 819 GDD base 45 and 558 GDD base 50. On average, degree-day totals put this area seven to eight days ahead of normal average accumulations.

Diseases

With heavy rains in the Grand Rapids, Michigan, area compared to other apple producing areas in Michigan, our primary apple scab season has come to an end, at least according to the capture of primary scab spores. No spores have been caught since the May 27 rain event. Growers need to be very sure their blocks are free of primary scab before cutting back on primary scab fungicide rates – we trap for spores and monitor degree-days as a guide to the end of primary scab, but MSU Extension advises following up with good scouting. There are potential lesions to show up from the last few infections in May, so keep scouting carefully.

There is a little fire blight showing up here and there – some is from blossom blight infections and some is shoot blight or perhaps trauma blight. As long as trees are still actively growing, fire blight can progress. If you have active blight in blocks, keep on it with copper until terminal bud set.

Insects

Plum curculio adult egglaying activity continues to be reported in all tree fruits over the last week with warmer weather. Cool weather will slow their activity. Continue to monitor and reapply cover sprays as rainfall warrants. Plum curculio risk should be declining soon in apples as fruits are getting too large for egglaying. They seem to be more active in the stone fruit crops this year.

Codling moth adult flight continues. Early egg hatch should be starting in higher pressure blocks and cover sprays are crucial now. A Grand Rapids, Michigan, regional biofix was set for May 23 (302 GDD50) and 263 GDD50 have accumulated since that date. You can track degree-days for your own biofix date in the Enviro-weather codling moth model. Continue monitoring all blocks. Growers could consider adding virus in to general cover sprays as insurance in low pressure blocks or blocks below threshold.

All stages of European red mite are found in commercial apple blocks. All stages can now be found. The warmer weather really got their development moving and they should be monitored closely for potential exploding populations.

Many obliquebanded leafroller larvae are now pupating and controls won’t work in this stage.

Traps with lures should be in place now to catch first flight. First adult flight could begin at any time, most likely after warmer weather returns and in the next week.

Male flight of San Jose scale continues. No crawlers have been reported, and they should emerge at any time. Targeting crawlers is the next timing for good management, most likely in the next seven days.

Oriental fruit moth first generation flight should be over. Some areas report an increase in trap numbers which could be the beginning of second generation – this is a good time to change out lures. First generation egg hatch should be past the peak, and cover sprays in stone fruits will be needed for another week as egg hatch winds down, especially in high pressure blocks and areas to the north. A regional biofix was set for May 6, 308 GDD45, and there has been an accumulation of 523 GDD45 since that date.

The following are minor apple insect pests to keep an eye on.

Various species of aphids can be found in all tree fruits, but overall numbers seem to be low this season. Predators are starting to be found in aphid populations. Woolly apple aphids are likely to be present and should be targeted in the next week in blocks that had high numbers late last year.

White apple leafhopper nymph numbers continue to be low overall, and we should be at peak egg hatch now. No adult white apple leafhoppers have been reported. Adult leafhoppers present are likely potato leafhoppers that tracked here with the southern based storms of last week. Continue monitoring and watching non-bearing trees for high populations of leafhoppers and aphids and manage where necessary to maximize shoot growth.

Lesser peachtree borer and greater peachtree borer flight continues, and trunk sprays in stone fruits need to begin. No dogwood borer flight has been reported and it should begin at any time.

The first reports of rose chafer in stone fruits in sandy sites are coming in.

Spotted wing Drosophila will soon begin and traps with lures should be in place in susceptible crops, including sweet and tart cherries, strawberry, raspberries, etc. Some initial flight has been reported in very low numbers. Spotted wing Drosophila is not a pest of apples or pears.