Grand Rapids, Mich., area tree fruit regional report – May 7, 2013

The region is off to a great start to the 2013 apple growing season.

Growth stage update

Warmer weather has finally made a debut in west Michigan and fruit trees are responding with rapid expansion of leaves and fruit buds. Apples in the Grand Rapids, Mich., area are mostly in a pink stage with the first king blooms expected in the earliest cultivars today or tomorrow, May 7 or 8. The majority of apple blossoms should begin to open by mid- to later in the week. Sweet cherry and pears are in full bloom.

Apple scab update

There were two light rain events in the last week. On April 30 there was a short wetting event with four to six hours of wetting, depending on the area. This did not result in an apple scab infection according to any west Michigan Enviro-weather station data, but there was a discharge of an average of 283 spores per rod.

Another wetting event occurred on May 2 and was a marginal infection risk for the Sparta Enviro-weather station data due to very light rain and the hours of wetting being mostly from high relative humidity. Hopefully growers had fungicide covers on just in case. There were no spores caught on the May 2 rain, but only 0.01 inches was recorded, so perhaps the equipment only ran for a very brief time.

On May 2 there was a light scab infection according to the Fremont Enviro-weather station data. There have been no significant wetting events since May 3 in any areas in west Michigan. Ascospore maturity should be near 25 percent and there are many lush new leaves present that need to be protected for the next rain event, most likely coming Thursday into Friday (May 9-10).

Powdery mildew

Even though the weather in the past several days has not been conducive for powdery mildew development due to extremely low relative humidity levels, we are coming into the season with a very high inoculum load and mildew preventative fungicides are recommended by Michigan State University Extension. Relative humidity levels have been low, but the nights are still a bit dewy and mildew does not need actual rainfall to get started, so it’s best to add mildewcides in the tank now as a preventative measure. It’s often the case that in low pressure apple scab years we see more mildew.

Fire blight

As we approach bloom time in apples, blossom blight situations need to be considered. You can use the two models on the Enviro-weather website to monitor possible blossom blight situations and the fire blight interactive predictor model allows you to put your own data in or create mock scenarios to help you decide how to manage fire blight during bloom. It takes about 24 hours once a blossom opens for it to be colonized by fire blight bacteria in the most ideal conditions (high temperatures). Then, rainfall or heavy dew is needed to move that bacteria into the natural openings in the flowers to cause an infection. Use the fire blight model to help you make decisions – it works.

Insect update

There is still little activity in the insect world. Green fruitworm adults are flying. Spotted tentiform leafminer adult flight is ongoing. Scouts should be watching for overwintering obliquebanded leafroller larvae in apple terminals, especially in 2012 problem blocks. There are a few apple grain aphids around and rosy apple aphids are most likely present, but very hard to find this early.

Pink sprays for aphid, scale and leafminer management are being made now on the Ridge. No reports of oriental fruit moth flight yet, but it is expected soon. No flight of codling moth yet, but mating disruption can be applied now and traps should be set during bloom to capture that potential first flight.

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