West Michigan tree fruit update – May 30, 2017

Cooler than normal weather has slowed many insects.

Fruit development continues and all tree fruits are beginning to size with many apple now in the 10 to 15 millimeter stage. Some blocks were thinned last week for the first time. No June drop has been noticed in the general Grand Rapids, Michigan, area yet.

Disease update

All Michigan State University Enviroweather stations in the area accumulated more than 1,000 growing degree-days (GDD) base 32 accumulated from first apple scab spore catch in late March. This indicates 100 percent of primary scab spores are mature and all that’s needed are a few rains to completely discharge those mature spores. Primary scab fungicide rates and protection levels need to be maintained until all spores are released. The rains predicted for the past weekend never materialized but I did catch 5 spores per rod with only 0.01 inch of rain, so I do think there are a few more to be released yet. Keep primary scab fungicide rates maintained.

According to MSU Enviroweather’s Maryblyt prediction model, there were blossom fire blight infections with rain events on May 15 through 18. Symptoms from these infections could show up any day now, so be on the lookout for that initial wilting of shoot tips in blight susceptible blocks. If there are any blocks with open bloom present later this week, the risk for blossom blight gets pretty high again with rain predicted at the end of the week. Newly planted blocks and one year old trees are usually out of sync with established trees.

Insect update

Plum curculio adults can be found in trees, but egg laying is minimal. Continue to monitor for egg laying activity.

Trap numbers have been low overall due to cooler weather for codling moth. A slight blip with the warm weekend weather. A regional biofix was set for May 15, 2017 (250 DD50). DD since biofix are 160 for the ridge. Monitor trap numbers and set biofix for individual blocks as needed. Materials for early hatch and larval activity should be applied near 250 DD 50 post biofix – around June 5 for the May 15 biofix near Sparta.

Large obliquebanded leafroller larvae are still present as well as a few pupal cases. No management needed in this stage. Traps need to be up to catch first adults which could begin flying in one or two weeks.

All stages of European red mite can now be found and predator mites are also present. Continue to monitor both European red mite and beneficial mite populations. The threshold for June is 2.5 mites per leaf.

Various species of aphids can be found in all tree fruits, but overall numbers seem to be low this season. Continue to monitor for all aphid species in all tree fruits as well as the beneficials that attack them. Woolly apple aphids could start to be found at this time as well.

The first generation flight of oriental fruit moth has increased with warmer weather, but flight is steady. Egg hatch should be near 45 to 50 percent and cover sprays are crucial in stone fruits. A regional biofix was set for April 28, 2017 (307 DD45). DD since biofix are 350. Continue to monitor traps and maintain cover sprays as rainfall warrants. This is a key time for good coverage in stone fruits. Apples with 70+ moths/trap/week also need cover sprays.

Male San Jose scale flight began during the past few days and pheromone trap numbers are normal to slightly high in high pressure blocks. A regional biofix was set for May 21 (317.9 DD50), DD50 since biofix are 105. Yellowish crawlers generally are present 300-350 DD base 50 after the first adult catch of either generation. Crawlers’ emergence is estimated from June 13 to 17 for the Ridge.

White apple leafhopper nymphs are present in low numbers. We should be nearing peak hatch, but they seem to be hard to find. Adult leafhoppers you might see are potato leafhopper. Watch non-bearing trees for high populations of leafhopper and aphids and manage where necessary to maximize shoot growth.

Spotted tentiform leafminer tissue feeders can be found in low numbers in unsprayed trees. They are a minor pest in cared for blocks.

The American plum borer flight continues. Both species of peach tree borer flight is beginning. There has been no dogwood borer flight yet. Be on the lookout for black stem borer in sick trees or top-worked trees. Monitor with traps for adult activity. Trunk sprays in stone fruits should be applied in the next seven to 10 days.

There are no reports yet of rose chafer but they typically show up the first week of June in sandy sites (apples, stone fruits). Continue to monitor for them.

Traps with lures need to be in place in susceptible crops for spotted wing Drosophila – sweet and tart cherry, strawberry, raspberries, etc. Some initial flight has been reported in very low numbers. Continue to monitor. Spotted wing Drosophila is not a pest of apple or pear.

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