MSU Extension

Fruit development continues and all tree fruits are beginning to size with the warmer weather that moved in last week. It is still much too early to have a full handle on the status of tree fruit crops in the Grand Rapids, Michigan, area after the cold snap on May 8 and 9. There will be apples, peaches and sweet cherries to harvest in the area—it’s simply too early to determine at this time.

Disease update

Most Michigan State University Enviroweather stations in the area have or are near 1,000 growing degree-days (GDD) base 32 accumulated from first apple scab spore catch in late March. This indicates roughly that 99–100 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. This is estimated to be perhaps by the end of May, which is earlier than normal. In the last few rain events, we have continued to catch primary apple scab spores.

It has not been a particularly harsh spring for apple scab, but if some escaped your fungicide program, you would most likely be seeing scab present in your orchards from rain events back in April. Scout closely to make sure you are free from scab before reducing fungicide rates any time soon.

Powdery mildew risk returned with the hot and humid weather last week, but overall this spring has not been ideal to promote mildew.

Much warmer weather last week, with highs in the 80s and lows in the 60s, really pushed the fire blight blossom blight risk well over threshold and any blocks with open, viable bloom were at risk for blossom blight infections with rain events on May 15–18. Winds were rather gusty, too, on some days, which could result in trauma blight infections. Symptoms from last week’s high risk for fire blight will likely show up right around Memorial Day.

Insect update

First plum curculio adult egglaying activity has been reported in all tree fruits around the state in the past few days. Monitor for egglaying activity.

Codling moth trap numbers jumped in the first week of flight around the Grand Rapids, Michigan, area. A regional biofix was set for May 15 (250 GDD50). GDD since biofix are 100. Monitor trap numbers and set biofix for individual blocks as needed. Materials for egg activity need to be applied right away. Materials for early hatch and larval activity should be applied in 10 to 14 days.

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

All stages of European red mite can now be found. Predator mites are also present. Continue to monitor. Petal fall sprays target European red mites.

Apple rust mites should be present now and are very difficult to find. 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.

Various aphid species 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 make an appearance soon in blocks with high pressure in 2016.

Oriental fruit moth first generation flight has increased with warmer weather, but flight is steady. Egg hatch should be near 15 to 20 percent and cover sprays are crucial in stone fruits. A regional biofix was set for April 28 (307 GDD45). GDD since biofix is 230. Continue to monitor traps and maintain cover sprays as rainfall warrants. This is a key time for good coverage.

Male San Jose scale flight began over the past few days; trap numbers are normal to slightly high in high pressure blocks. Monitor known hot spots for activity. Expect crawlers to emerge in seven to 14 days—begin monitoring for them in a week with black tape near infestations.

Very few tarnished plant bug adults can be found. No mullein bugs have been reported this season. Continue to monitor. They often become more active after petal fall.

Initial reports of newly hatched white apple leafhopper nymphs started last week and more can be found now. Numbers continue to be low overall. Adult leafhoppers you might see are potato leafhopper. Peak egg hatch is expected around the Grand Rapids area in seven to 10 days. Watch non-bearing trees for high populations of leafhoppers and aphids and manage where necessary to maximize shoot growth.

Spotted tentiform leafminer sap feeders can be found in low numbers in unsprayed trees. They will move to the tissue feeding stage with warmer weather. Minor pest in cared for blocks.

American plum borer flight is ongoing in low numbers. Lesser peachtree borer and peachtree borers should begin flying at any time. No dogwood borer flight yet. ]

Be on the lookout for black stem borer in sick trees. Monitor with traps for adult activity. Look for dogwood borer frass and pupal cases in burr knots. Mating disruption for all borer species can start to be placed now.