West central Michigan tree fruit regional report – May 26, 2015

Apple thinning needs to be done soon.

On the Ridge, apples are mostly in the 10 to 15 millimeter stage with a few varieties holding onto rag tag bloom on one-year-old wood. If you are starting to think about apple thinning, keep in mind there might be less pollination and fertilization of bloom due to rainy and cool weather during the peak bloom period for many varieties. So go easy on thinning until you have a better sense of your crop set. See the latest Carbohydrate Model graphics below.


The Carbohydrate Thinning Model for Sparta, Michigan, as of May 25, 2015.


The Carbohydrate Thinning Model for Hart, Michigan, as of May 25, 2015.

Phil Schwallier states the carbohydrate models for all of Michigan are very similar. Sparta and Hart weather data indicates we are in a stage of moderate stress and moving towards no stress with cooler weather at the end of the week and fruit size increasing quickly. Thinning now requires normal to aggressive rates of thinners.

Apple scab

Scattered rains moved through west Michigan over the holiday weekend. Some sites had none and others had several hours of wetting that resulted in apple scab infections. We are nearing the end of primary scab season, but we are not quite there yet. Don’t back off on your primary fungicide rates. We are still catching primary scab spores – numbers are decreasing, but they are still there. We are very close to having 100 percent of primary ascospores mature. It typically takes two or three decent daytime rain events to discharge all spores once we get to 100 percent maturity.

Fire blight

With a little rag tag bloom on one-year-old wood still present in some apples, we keep the alert up for possible blossom blight situations. There were some rather high winds over this past weekend too, which could cause a concern for trauma blight if wetting occurred with the wind. This wasn’t an all-out infection risk – only blocks with a history of recent fire blight would have needed to be covered. Symptoms from the blossom blight infections back on May 7, 8 and 9 could begin to show up at any time – the cooler weather has slowed the disease progress. Watch closely for first wilting symptoms and fresh ooze.

Powdery mildew

Powdery mildew is just beginning to be seen in unmanaged apples. The warmer and drier periods of weather this spring will favor mildew establishment. Scouts should be looking carefully for mildew.

Tree fruit insects

Many growers on the Ridge have applied their petal fall insecticide cover spray, but if you haven’t, it needs to be done soon. Be sure your neighbors’ bees are removed before you apply any insecticides.

Black stem borer first adults were trapped May 8. A few were in traps last week. Initial sawdust toothpicks were present May 18. Expect adult flight to continue. Trunk sprays can go on now if you have sites with this sporadic pest.

Codling moth first adult flight in high pressure blocks began May 16. First flight in low to moderate pressure blocks began over this past weekend. Use an early biofix on problem blocks and later for all others. Problem blocks are 100 growing degree days (GDD) since May 16 biofix, also the start of egglaying and time for egg IGR sprays. Normal trap number blocks is the start of egglaying estimated for June 2 or 3.

European red mite egg hatch continues near Grand Rapids, Michigan. No new eggs have been reported. Michigan State University Extension advises growers to continue monitoring. Petal fall applications are an important European red mite management timing.

Plum curculio first sightings were reported in near Grand Rapids, Michigan. They will be quite active with this warm weather pattern. Petal fall sprays should not be delayed in blocks with known plum curculio history.

Obliquebanded leafroller larvae are now pupating and controls will not have any effect. Adult flight usually begins in mid-June on the Ridge. None have been reported in Michigan yet. Traps should be set. Expect first flight approximately 1,000 to 1,100 GDD42 from Jan. 1

Spotted tentiform leafminer adult flight should be complete for first generation. Larvae are mostly in the sap feeding stage with some tissue feeding now being found.

White apple leafhoppers have not been reported, but growers should expect young nymphs any day. They overwinter as eggs and typically egg hatch starts at petal fall. There are a few adult potato leafhoppers to be found. White apple leafhopper peak egg hatch typically occurs around first cover. The earliest nymphs are often found on the underside of older leaves.

Various species of aphids are found in all tree fruits, but overall numbers appear to be much lower than expected. Continue to monitor for all aphid species and the beneficials that often attack them.

San Jose scale overwintering are present and adult male flight has begun in near Grand Rapids, Michigan. Growers should closely monitor known hot spots. Crawlers typically appear about 10 to 14 days after adult males are first trapped or around mid-June.

Oriental fruit moth first generation flight continues and may be at a peak. Egg hatch is approximately at 30 percent. A regional biofix was set for May 6 (256 GDD45) – GDD since biofix is 288. First sprays to target small larvae should have been applied a week ago in stone fruits to prevent flagging of shoot tips. Expect peak egg hatch around June 1 or 2 on the Ridge. Continue to cover as needed.

Apple rust mites should be present now. They overwinter as an adult female. Monitoring should begin as soon as possible in blocks with a history of apple rust mites. Red Delicious is a favorite variety for rust mites.

American plum borer flight is beginning. Lesser peachtree borers and greater peachtree borers should begin to fly at any time. Dogwood borer flight has not begun.

Redbanded leafroller larvae, small to mid-sized, are present in light numbers in managed blocks, but very high numbers in unsprayed trees. These are a minor pest in apples, but a few more than usual are being reported around the state this year.

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