MSU Extension

Weather and growth stages

All tree fruits are sizing nicely and fruit set appears to be at a normal crop level for most sites.  As usual, there are areas with a heavier than needed fruit set and areas with a lighter crop than desired.

Apples range from 20 to 30 millimeters, depending on variety and site. In many areas around Grand Rapids, Michigan, the apples are a king crop – something we haven’t had in many years.

Peaches continue to grow fast with many in the 23- to 30-millimeters stage and hand-thinning continues. 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 15 to 18 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. There seems to be a higher bird pressure this season in cherries.

Growing degree-day (GDD) totals for the Sparta Enviro-weather station are 1152 GDD base 42, 941 GDD base 45 and 649 GDD base 50. On average, degree-day totals put this area seven to eight days ahead of normal average accumulations.

Diseases

While no primary apple scab spores have been caught in the Grand Rapids, Michigan, area since May 27, you still need to be watching very carefully for scab symptoms. 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.

Fire blight continues to be reported in low pressure here and there on the Ridge – some is from blossom blight infections and some is shoot blight or perhaps trauma blight. In the Hart and areas to the north, more blight is being reported due to blossom 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 egg laying activity should be over for the Ridge. Maybe a few more days of activity to the north – Oceana and Mason Counties. Continue to monitor and reapply cover sprays as rainfall warrants.

Codling moth adult flight continues with over 50 percent of moths emerged. Egg hatch should be around the 25 percent egg mark in most blocks. A Grand Rapids, Michigan, regional biofix was set for May 23 (302 GDD50) and 347 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. Cover sprays are crucial now and need to be reapplied as rain warrants. Traps numbers might have declined with cooler weather, but expect an increase with warmer temperatures this week – adult flight will continue for at least 10 to 14 more days.

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.

First adult flight of obliquebanded leafroller was reported over the weekend. A Grand Rapids, Michigan, regional biofix was set for June 12, 2016 (1132 DD42) and 44 DD42 have been accumulated since that date. Adult flight will increase over the next two weeks with early egg hatch predicted for June 28 – the target for high pressure blocks. Low pressure blocks can be scouted for small larvae and then sprays added as scouting warrants.

A few crawlers of San Jose scale have been reported. Target them now for effective management. Good coverage is key for scale control.

Oriental fruit moth first generation flight and egg hatch should be at an end for the Ridge, and nearly over for Hart and to the north. Second generation flight is underway. A regional biofix was set for May 6, 308 GDD45, and there has been an accumulation of 655 GDD45 since that date. Lures in traps should be changed before second generation flight, if you haven’t’ done so already.

Various species of aphids can be found in all tree fruits, but overall numbers seem to be low this season. Woolly apple aphids started to be found last week under tree wraps and in leaf axils.        

Target woolly aphids right now if you had trouble spots last season. Continue to monitor for all aphid species in all tree fruits as well as the beneficials that attack them.

White apple leafhopper numbers are low overall, but continue to monitor – especially in non-bearing trees.

Lesser peachtree borer and greater peachtree borer flight continues, and trunk sprays in stone fruits need to be applied if not already. No dogwood borer flight has been reported yet, but pupating larvae can be found sticking out of burr knots, so flight will begin any day.

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

Some initial flight of Spotted wing Drosophila is being reported in very low numbers, so traps with lures need to be in place in susceptible crops, including sweet and tart cherries, strawberry, raspberries, etc.

No reports of Brown Marmorated Stinkbug egg hatch or nymphs in Michigan yet, but could begin soon in areas with higher numbers.