MSU Extension

Very hot weather moved in for the Memorial Day weekend and the insects all appeared. Tree growth also moved forward quickly with all tree fruits putting on size quite quickly. All apples are now in petal fall with early developing varieties quickly gaining size with 6 to 10 millimeters being the average right now. All stone fruits are out of the shuck and gaining size quickly as well.

Apple thinning needs to be done as soon as possible. The warm weather will push apple development very quickly and fruits will grow fast. There are some reports of large amounts of apple fruitlets shucking off, but there was an overabundance of flowers and fruit this year, making the shedding look pretty dramatic. While there might be some issues with flower health due to the very cold temperatures we had way back in December 2017, this should be the exception and not the rule for apples. You will need to thin and thin soon before the window closes and all you will be left with is hand-thinning.

See "PGR’s and Thinning Strategies 2018" by Phil Schwallier for 10 pages of guidance for thinning this season.

Tree fruit diseases

After a stretch of very rainy weather last week, warm and dry was the pattern for the past five days. Primary apple scab spores are not all mature yet, so be ready for the next rain event as we are still in primary scab mode. I expect we are at 90 percent mature spores right now and will reach 100 percent in a week or 10 days. Then, we will need a good rain or two to discharge all remaining spores, so plan on full fungicide rates for at least two more weeks to get you through primary scab. Lesions from earlier infections are now showing up quite readily in unsprayed trees and even in a few sprayed blocks. For the latest information for all MSU Enviroweather stations in our area, check out the regional disease report.

Recent warm weather will greatly favor powdery mildew, so stay covered well for it.

Rains last week were too cool to pose much risk for fire blight blossom blight, but the very hot temperatures over the weekend brought predicted EIP levels to over 500 for a couple of days. There ended up being no rain recorded anywhere near Grand Rapids, Michigan, so we snuck through the tail end of bloom with no big blossom blight scenarios.

For blocks with rag tag bloom still present, and for newly planted trees blooming out of sequence, we ready to cover for blossom blight with the heavy rains predicted for Wednesday and Thursday this week, May 30 and 31—MaryBlyt is calling for blossom infections with the upcoming rain left over from tropical Storm Alberto. You can track fire blight 24/7 with the MSU Enviroweather Fire Blight model.

Tree fruit insects

I think most growers got their petal fall sprays on ahead of the very hot weather late last week which was a wise move given the huge spike in activity of plum curculio reported from various places. First, plum curculio adult egglaying activity was found in the Grand Rapids area last Friday, May 25, in plums and sweet cherries, and apples are now in the size range where they are ideal for egglaying as well. This warm weather is ideal for plum curcuolio activity. Monitor for egg laying activity and don’t delay Petal fall sprays.

Codling moth trap numbers jumped late last week with warm nights around the Grand Rapids area. A regional biofix was set for May 25 (313 GDD50), with 104 GDD base 50 accumulated as of midnight May 29. Warm weather will push codling moth development quickly and early egg hatch will occur around June 7, faster than one might expect.

Obliquebanded leafroller large larvae are present and should be pupating soon. Monitor known problem blocks closely for larval activity. Adult flight usually begins at roughly 1030 GDD42, or around June 10 for this year. Traps with lures should be in place by late next week.

Apple grain aphids and rosy apple aphids can be found. Woolly apple aphids are also being seen on roots. Continue to scout for all aphid species and be on the lookout for predators.

San Jose scale male flight began with the warmer weather and numbers are quite high in high pressure spots. A regional biofix was set for May 25 (286 GDD51) with 100 GDD accumulated since. Crawlers emerge 10 to 14 days after first male flight or around June 14 this year.

All stages of European red mite are now present in apple orchards. Continue to monitor.

More white apple leafhopper nymphs can now be found, but numbers are very low overall. Peak egg hatch typically occurs around first cover. The earliest nymphs are often found on the underside of older leaves

Spotted tentiform leafminer adult flight is declining as first generation comes to an end. Egg hatch is past the peak and sap feeders are more readily found along with a few tissue feeders. No pupating larvae yet. Numbers are very low for this minor pest of apple. Adult numbers will increase in the next 10 days as second generation flight starts.

A few more tarnished plant bug adults can be found. No mullein bugs have been reported this season. Continue to monitor. They often become more active after petal fall or move to apples from nearby weedy areas or after mowing.

Oriental fruit moth first generation adult flight continues with good numbers still being reported. We should be nearly the end of first generation flight. A regional biofix was set for May 10 (272 GDD45) and there have been 331 GDD base 24 accumulated since. We are approaching peak egg hatch for first generation and cover sprays are critical in stone fruits to prevent shoot flagging from first generation.

American plum borer flight is beginning in low numbers. Lesser peachtree borer started flying in the last few days. Peachtree borer should begin to fly at any time. No dogwood borer flight yet. Look for dogwood borer frass and pupal cases in burr knots. Mating disruption for all borer species can start to be placed now.

There has been an uptick of black stem borer activity in traps around the state with the recent warm temperatures. Monitor blocks for burrowing damage.