West Michigan tree fruit regional report – May 3, 2016

Very cool weather has brought tree and insect development to a standstill.

Weather and growth stages

A week of very cool weather has brought tree growth to a standstill – most orchard sites have been stuck in the general stages of tight cluster to pink for the past five to seven days. Growing degree-day (GDD) totals for the Michigan State University Sparta Enviro-weather station are 879 GDD base 32, 372 GDD base 42, 276 GDD base 45 and 158 GDD base 50. On average, degree-days totals put this area about a week ahead of normal average accumulations.

Growth stages have not changed much from last week. Apples range from the tight cluster to pink stages with a few king blooms opening recently in early varieties and warmer sites. Peaches are in full bloom, European plums are in full bloom, sweet cherries are in full bloom and pears are in the full bloom stage.

Between tight cluster and 20 millimeters, apple fruits are especially sensitive to fruit finish issues. When you add in variables such as temperature, moisture and tank-mixes, it is important to use caution with any spray applications during this sensitive fruit stage.

All tree fruit species are looking a bit deficient in nitrogen due to this extended cold weather. Some heat will green things up nicely, but do consider adding foliar nitrogen to your cover sprays while not overdoing it.

Diseases

Regarding apple scab, there have been several rain events over the past 10 days and depending on the data collection site, some areas had enough wetting hours for scab infections and some did not. The rainfall and hours of wetting have been quite variable and the temperatures have been very cool. Spore numbers have been very high with numbers well over 15,000 spores per rod for the past week’s rain events. Your fungicide coverage program is very important right now and leaves and fruits are very susceptible to possible infections, so keep the fungicide program tight. You can follow the development of apple scab infections and symptoms on MSU Enviro-weather.

Now that bloom is beginning to open, the risk for fire blight becomes a concern, but not with the very cool weather of late. Warm weather in the forecast will bring more open bloom and the fire blight blossom blight risk will need to be on your radar screen. Using prohexadione-calcium (Apogee, Kudos) is highly recommended to prevent potential future spread of blight.

Once bloom is present in sweet cherries and peaches, the need for fungicides to prevent brown rot are important until shuck split.

Insects

Warmer weather has driven some early developing pests forward, but overall insect development is slightly behind crop stages.

The first black stem borer adults were caught over two weeks ago with warm temperatures. Adults have not been very active with cooler weather. MSU Extension suggests growers monitor blocks for burrowing damage and apply trunk sprays in blocks of concern. Pink is a good timing.

Green fruitworm adults are flying and should be just past their peak flight. Mid-size larvae can be found with some very light feeding damage on terminal leaves

Redbanded leafroller flight started about a week ago and continues in low numbers. Expect peak flight in the next five to 10 days. Pink sprays take out small larvae.

The beginning of obliquebanded leafroller activity has been reported in commercial apples in the form of light terminal feeding. A few larvae are being found.

Apple grain aphids continue to be reported in very low numbers. A few rosy apple aphids have been reported in the last few days. Continue monitoring for all aphid species in all tree fruits.

Overwintering San Jose scale are present. Pink is the next timing for San Jose scale management.

Spotted tentiform leafminer adult flight continues in light numbers. Monitor for it if you have had high leaf damage recently.

No sustained oriental fruit moth flight has been reported in the Grand Rapids, Michigan, area. First adult flight typically happens around pink stage in apples; average first flight is 330 GDD 45. As soon as warmer weather moves back in, traps will jump.

European red mites are mostly in the egg stage with some first hatch being reported in the last day or two.

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