West Michigan tree fruit regional report – July 8, 2014

Summer diseases will thrive in the warm and humid weather.

Posted on July 8, 2014 by Phil Schwallier, and Amy Irish-Brown, Michigan State University Extension

Crop update

Apples in west Michigan are sizing a bit quicker than normal due to the heavy rains. Average fruit size ranges from 30 to 40 millimeters. Fruit is clean and generally blemish-free. Predicted harvest dates are now available for most areas at Michigan State University Enviro-weather. It appears that harvest will be just slightly behind normal dates for 2014.

Tree fruit diseases

Even though many orchards are free of primary apple scab this year, there is still a bit out there. The very wet weather in the past two weeks will encourage fruit scab development and fungicide cover sprays need to be re-applied as rainfall warrants.

With the heavy rainfall and extended wet and humid conditions of late, sooty blotch and flyspeck protective fungicides are really important to have on developing apples. Two inches of rain will remove viable fungicide residues and reapplication will be needed.

Although most blocks are free of fire blight this year, there are hot spots. Unfortunately, some of these hot spot areas also had storms last week with heavy hail damage. Trauma blight is now showing up. When fruits are heavily damaged, copper products are the best defense for active fire blight situations.

Tree fruit insects

Codling moth adult flight is over. Egg hatch is at 75 to 80 percent. A regional biofix was set for May 26, 2014, or 265 growing degree days (GDD) base 50. GDD since biofix is 736. End of first generation is expected for mid-July, approximately July 17-21. Cover sprays are not as critical in low population blocks. High pressure blocks should consider reapplications with heavy rainfall. Second generation flight should begin July 20-30 – new lures will be needed in traps by then.

No apple maggot flight reported in the Grand Rapids, Michigan area. First flight is expected any time on yellow boards, which should be up in known problem areas; heavy rains of late could trigger adult flight at any time. Red sphere traps are best for determining timing of first maggot sprays and should go up by July 15.

Heavy rain should reduce European red mite adults, but eggs are now as easily dislodged. Predator mites are also found. 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.

There are surprisingly high numbers of two-spotted spider mites in some apple blocks, particularly those on sandier soils. Michigan State University Extension advises growers to continue to monitor.

Obliquebanded leafrollers should be at peak egg hatch. Adult moth flight is nearly over. A regional biofix was set for June 15 (1,004 GDD42). GDD since biofix is 600. In general, obliquebanded leafroller larvae are difficult to find. Monitor for larvae feeding in terminals and spray if more than one per tree.

San Jose scale crawlers have settled to permanent feeding locations on stems and possibly fruits. Controls will not work well at this stage. Monitor for scale on stems and fruits.

Some initial spotted wing Drosophila flight was reported in various Michigan locations. This is not an issue for apples, but monitoring should be done in soft fruits including cherries, peaches, plums and berries.

No reports of brown marmorated stinkbug eggs, nymphs or adults in the Grand Rapids, Michigan area.

Green apple aphids are becoming more prevalent in apples, but still very low overall. Once terminal buds set, they may move on to other host plants. Wooly apple aphids were first found on July 2, just the beginning of small colonies. Continue to monitor for all aphid species and the beneficials that often attack them.

Overall there have been very low numbers of white apple leafhoppers and potato leafhoppers. Continue to monitor.

Dogwood borer flight continues. Trunk sprays should be done now in high pressure blocks. Continue to monitor.

Oriental fruit moth second generation adult flight began around June 30, right on target with the GDD model. A regional biofix was set for May 19 (295 GDD45). GDD since biofix is 1,066. Cover sprays in stone fruits will be needed again around 10 percent egg hatch, which is estimated to be near July 10. Second generation is not an issue in bearing apples, but sometimes they infect non-bearing apple terminals.

This article was published by Michigan State University Extension. For more information, visit http://www.cnchemicals.com/. To contact an expert in your area, visit http://www.cnchemicals.com/, or call 888-MSUE4MI (888-678-3464).