West Michigan tree fruit regional report – June 24, 2014
Codling moth cover sprays need to be re-applied with heavy rainfall.
Traditional chemical thinners will have little effect in the Grand Rapids, Michigan area and south. In Hart and farther north, the carbohydrate model is indicating some stress that might allow chemical thinners to work in the next few days, but that window is quickly closing as fruits gain size.
Tree fruit diseases
Primary apple scab is over for the general West Michigan areas including Hart and Ludington. There is very little scab on leaves this year, but continue to monitor closely with all the rain of late.
Sooty blotch and flyspeck are nearing the time when they will begin to sporulate and cause fruit blemishes. The very wet conditions over the past two weeks will increase the likelihood of summer diseases in apples, so Michigan State University Extension highly recommends adding fungicides in your cover sprays in the next week or two.
There appears to be a higher level of nectria canker appearing in some orchards this year. Or, some of the shoot collapse could be from winter damage to the shoot base without disease present. It is easy to confuse this damage or disease with fire blight, so be sure to look closely to identify it correctly. Rome and Gala are commonly infected with nectria, but this year I have also seen it in Paula Red.
Tree fruit insects
Codling moth adult flight continues but seems to be declining. Egg hatch is at 30 to 40 percent. A regional biofix was set for May 26, 2014 for 265 growing degree days (GDD) base 50; GDD since biofix is 482. Continue coverage for blocks that are over threshold: five moths per trap accumulated or one to two moths per trap in disrupted blocks. Be sure to reapply as needed with rainfall. Peak egg hatch is expected this weekend, June 28, 2014.
Some blocks are reporting building or static numbers of European red mite. Heavy rain should reduce adults. Continue to assess mites per leaf; they are beginning to build again in some blocks. Threshold is five mites per leaf for July. Monitor for beneficials. One per leaf indicates wait a week and count again.
We should be at peak obliquebanded leafroller adult moth flight. A regional biofix was set for June 15, 2014 for 1,004 GDD42; GDD since biofix is 242. The start of egg hatch is estimated for June 30 or so. Use this early date to spray in problem blocks. In all other blocks, scout for small larvae and spray if there is more than one per tree. San Jose scale crawlers should be present. Monitor closely in known hot spots. Targeting crawlers is the next control window for San Jose scale.
Some initial flight of spotted wing Drosophila has been reported in various Michigan locations. They are not an issue for apples, but monitoring should be done in soft fruits, i.e. cherries, peaches, plums and berries. No reports of brown marmorated stinkbug egg hatch or nymphs in West Michigan yet. They overwinter as eggs, so monitor for nymphs.
Very low numbers of spotted tentiform leafminer this season. Green apple aphids are beginning to be found in apple. Continue to monitor for all aphid species and the beneficials that often attack them. Wooly apple aphid should begin to show up soon. Very low overall numbers of white apple leafhopper and potato leafhoppers.
Some suspect damage in small apples from plant bugs, but not exactly typical plant bug damage; seems to be weeping of lenticels and a small spot of brown sap. Borers in stone fruits are at peak flight and egg hatch; trunk sprays should be started. Some initial dogwood borer flight began last week. Dogwood borer trunk sprays are best timed for peak egg hatch, typically around July 4.
First generation oriental fruit moth adult flight and egg hatch should be ending. A little flagging reported. A regional biofix was set for May 19, 2014 for 295 GDD45; GDD since biofix is 747. Cover sprays in stone fruits are less important for a few weeks until second generation begins. This is a good time to change out lures if needed.