Grand Rapids, Mich., area tree fruit regional report – May 21, 2013

Fire blight is of utmost concern this week around Grand Rapids, Mich.

Growth stage update

Tree development has moved along quickly with the very warm weather. Many apple varieties were in full bloom coming into the weekend. With rain that moved through the area Monday night (May 20), many petals have fallen. Growers are starting to remove bees from apples.

Fire blight

Temperatures over the weekend and into the beginning of the week of May 19 have been near or over 80 degrees Fahrenheit for highs and in the 60s for lows. With open bloom still present and the chance for rain for several days early this week, fire blight of blossoms is of the utmost concern this week. Growers are encouraged to keep cover sprays for blossom blight on a tight schedule – every two to three days with bloom present is recommended.

Michigan State University Extension says an inch of rain requires a reapplication of fire blight prevention materials. The epiphytic infection potential (EIP) according to the MaryBlyt model on Enviro-weather has been predicted to be well over 200 and close to 300 according to some weather station data. We haven’t seen EIP’s this high in many years and this is not the time to cut any corners with your fire blight management. It is highly recommended that you add Apogee into your spray program this year to help with shoot growth management, but even more so, for fire blight.

Apple scab update

So far, 2013 has not been a favorable season for apple scab with light or no rains of late. Most of west Michigan saw some widespread rain move across the state early Tuesday morning (May 21). There were 478 spores per rod from this overnight rain, which is a moderate spore release. For the Ridge and Belding, Mich., areas, it is estimated that about 90 percent of ascospores for apple scab should be mature, and in 10 days (about June 1), 100 percent should be mature. Then we need rain to discharge them.

The next few rain events will most likely release a high number of spores and good cover sprays of fungicides will be important for at least two more weeks and perhaps longer if rain continues to be sparse. For areas farther north (Hart, Mich., and Ludington, Mich.), spore maturity is estimated to be around 75 percent or about four or five days behind the Ridge.

Powdery mildew

Continue to monitor for mildew in all tree fruits. With higher relative humidity levels this week, mildew could be active and should be covered for with mildew preventative fungicides.

Tree fruit insects

The main focus early this week for apple growers should be management of fire blight, apple scab and powdery mildew, and as we move towards the end of the week and into next week, your attention should turn to petal fall management for the key insects controlled at that timing. In particular plum curculio, which is already out and active in stone fruits in the general west Michigan fruit growing regions. Even with a no crop or small crop situation in 2012, plum curculio has many alternate hosts and the lack of apples most likely would not lessen its numbers as it would with other pests that are more specific to apples such at codling moth.

Some growers are already moving bees out of blocks, but some are still present. Please be aware of your neighbor’s bees if you are thinking of applying petal fall insecticides soon. Bees have had a rough time with their own pests and diseases that we don’t want to tax them further with accidental insecticide sprays.

A few first codling moths have been trapped late last week, but a regional biofix has not been set. All codling moth traps should be in place now in west Michigan and you should be monitoring them closely to determine your own biofix. Oriental fruit moth also started flying last week and a regional biofix was set for May 14.

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