Grand Rapids area tree fruit update

Heavy rainfall a challenge for adequate fungicide coverage for apple scab.

Tree fruit growth stages

Degree day totals continue to run behind normal averages and tree growth continues to move very slowly. In general, the degree day totals in the Grand Rapids area are 7 to 10 days later than normal averages for this date. Apple growth is from silver tip to half-inch green depending on variety and site.

Tree fruit pests

Apple scab ascospores have been trapped since just before green tip this year. Even with the slow tissue movement due to the cold, many growers have two or even three cover sprays on for apple scab so far this year due to the rains. This week will be a challenging one to stay ahead of the rainfall with scab covers. The latest rain event started in the early morning hours of Tuesday, April 26 and, already, some stations have recorded nearly or over an inch of rain. As of 9:00 AM, April 26, 2011, rainfall totals at area weather stations are: Belding = 0.8; Fremont = 0.81; Kent City = 0.94; Sparta = 1.27 (measured in inches).

The warmer weather predicted for today will push tissue development quickly. With the heavy rains and potentially new growth, there is a high potential for apple scab infections to get started. It’s going to be tough to get cover sprays re-applied again over the next several days.

In blocks with powdery mildew problems in 2010, you are encouraged to add mildewcides earlier to the tank than in a normal year.

Everything on the insect front is at a standstill from the cold. The warmer forecasted temperatures for this week would encourage insect activity, but the heavy rain will probably curb it somewhat.

For those with sweet cherries, this weather pattern we’ve been in – cold and wet – is perfect for bacterial canker development. You should avoid all pruning or tree manipulation at this time so you’re not creating wounds for the Pseudomonas bacteria to get into the tree.

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