West Michigan tree fruit regional report – May 10, 2016

Apples are in full bloom and growers need to consider some diseases.

Weather and growth stages

The rollercoaster of weather continues, but on average temperatures have been cooler than normal. Some warmer weather over the past weekend helped green up trees that were looking a little nitrogen deprived due to the cold conditions. In general, most apple varieties are in the full bloom stage with some early petal fall beginning. Growing degree-day (GDD) totals for the Michigan State University Sparta Enviro-weather station are 1,024 GDD base 32, 449 GDD base 42, 337 GDD base 45 and 198 GDD base 50. On average, degree-day totals put this area five or six days ahead of normal average accumulations.


On May 4, 2016, widespread rain settled in for nearly 24 hours of wetting with cool temperatures, resulting in some areas with enough wetting for apple scab and others fell short by only an hour or two – close enough that it needed to be taken seriously as a major scab infection potential. Overall, for the 2016 season there has been very few rain events that have resulted in enough wetting to become scab infections. Spore discharge numbers have been very high as is expected around bloom. Your fungicide coverage program continues to be very important to maintain as leaves and fruits are very susceptible. Rain is again moving through the area today, May 10, and you can follow the development of apple scab infections and symptoms on MSU Enviro-weather for the most up-to-date information.

With most apples in full bloom, the risk for fire blight is on the radar screen. The cool weather is keeping the MaryBlyt model in the low to moderate risk category for the early part of this week. Warmer temperatures and thunderstorms forecasted for Thursday, May 12, spike the blossom blight risk up to high and MaryBlyt does call for sprays to be made for the high risk category. The only piece of the blossom blight puzzle missing for a full out infection is if the Epiphytic Infection Potential (EIP) is below 100. EIP is an estimated level of fire blight bacterial presence on apple flowers. Growers will want to consider something in the tank for blossom blight ahead of or just after the rain on Thursday. Using prohexadione-calcium (Apogee, Kudos) is highly recommended to prevent potential future spread of blight and second applications might be needed, depending on when you started with the first.


Warmer weather has driven some early developing pests forward, but overall insect development is slightly behind crop stages. There should be no insecticides used during tree fruit bloom when pollinators are present.

Redbanded leafroller flight is declining and egg hatch is well underway. This is a minor pest in apples.

A few overwintering obliquebanded leafroller larvae have been reported feeding in terminals – numbers are very low in general, but problem blocks need to be monitored closely for activity.

Apple grain aphids continue to be reported in very low numbers. Rosy apple aphids continue being found with some leaf curling found in unsprayed trees. Michigan State University Extension suggests monitoring for green peach aphids and black sweet cherry aphids as they should begin to become active in peaches and cherries respectively. Scouts should also be taking note of beneficial insects that might be present and feeding on aphid populations.

Overwintering San Jose scale are present with no activity being reported. Males typically fly during bloom and crawlers emerge 10 to 14 days after. Traps should be in place for males in problem areas.

Spotted tentiform leafminer adult flight continues and seems to be declining as first generation ends. No sap feeders have been reported, and they should be found at any time.

There have been no reports of white apple leafhopper activity. They overwinter as eggs and typically egg hatch begins at petal fall. The earliest nymphs are often found on the underside of older leaves.

Oriental fruit moth flight has been a bit erratic with the up and down temperatures, but a definite sustained flight occurred late last week in many areas and a regional biofix was set for May 6, 2016 (308 GDD45). Since that date, there has been an accumulation of 30 GDD45 using Sparta Enviro-weather station data. Oriental fruit moth mating disruption needs to be up now in stone fruits to be most effective. Peak egg hatch is at least 10-14 days away – target this timing for first management in stone fruits.

European red mite eggs and early instars nymphs can be found. No adult mites have been reported. Petal fall is the next timing for targeting mites.

There have been no reports of codling moth adult flight. Traps and disruption should be up before now. First flight usually begins at petal fall, but could be delayed in low population blocks and due to cooler night temperatures.

There have been no reports of plum curculio activity in any tree fruit crops in the general Grand Rapids, Michigan, area. The target for first management is petal fall and cooler weather will depress plum curculio activity.           

A few adult tarnished plant bugs can be found feeding on broadleaf weeds in the orchard floor, with no activity of note in tree fruits.

No mullein bugs have been reported in the Grand Rapids, Michigan, area.

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