Grand Rapids area tree fruit update – April 23, 2019

It’s amazing what a couple of days of warmer weather can do.

Apple buds in the half-inch stage
Temperatures in the high 70s have quickly moved growth along in only a few hours. This is the half-inch stage in apples. Photo by Amy Irish-Brown, MSU Extension.


More seasonable weather has moved in, making tree development begin to move. The past few days have been very warm, and plants have responded with rapid tissue development. All apples have some green tissue showing with stages ranging from green tip on later cultivars and sites to tight cluster on earlier sites and varieties.

Degree day totals for the general west Michigan area took a big leap forward and we are now caught up to near normal totals for this last week of April. As of April 22, the Michigan State University Enviroweather station at Sparta has accumulated 174 degree days base 42, which is three days behind the average for Jan. 1. Degree days base 50 at Sparta are 71, which is exactly the average normal amount from Jan. 1. Forecasted temperatures look to be in the average range for this time of year, so degree day accumulations will move at a normal pace as will tree growth.

Soils have dried out nicely with low rainfall and some rather high winds and a few more blocks have been planted. The big planting push is yet to come. Check out this article for pointers on best practices for apple tree planting for some reminders.

Most blocks have a copper spray already on and many have their first fungicide application on for apple scab as green tissue started to show up late last week.

Tree fruit diseases

With green tissue now present, the first apple scab infections have started for all growing areas around the general Grand Rapids area. I’ve had spore monitoring equipment up for several weeks now. I captured three spores per rod with the April 7 rain and another three per rod with rain on April 11 and 12. No additional spores with the snow on April 14. I found nine spores with the rain on April 16 and zero spores with the rain on April 18.

I think spores are maturing slowly for this season due to the prolonged heavy snow cover and steady cold temperatures from late January until late March. Research indicates that ups and downs with temperature and moisture are needed to mature apple scab spores, and we really didn’t have that until just recently. The recent warm weather will move spore maturity along and any rain events over the next three or four weeks could result in high spore numbers. Rapid tissue growth needs to be covered well as it develops to prevent primary scab.

Tree fruit insects

Adult black stem borer beetles will become active when temperatures get above 70 and it’s time to get traps out.

Green fruitworm adult flight continues in very low numbers for this minor pest in tree fruits.

Redbanded leafroller adult flight began over the past weekend with the warmer weather. Trap numbers are expected to increase over the next two weeks. This is another minor pest in tree fruit in the Grand Rapids area.

Spotted tentiform leafminer adult flight started over the past weekend as expected. Numbers are low to normal. Typically, spotted tentiform leafminer is a minor pest and management is only needed if damage was high the previous growing season.

No activity reported of obliquebanded leafroller overwintering larvae, but they could be found at any time. Pay close attention to blocks with higher pressure in 2018 as this pest seems to be increasing the past two seasons.

The first apple grain aphids were found Monday in very low numbers as a few individuals on terminals. Rosy apple aphids usually appear around pink.

Overwintering San Jose scale are present. Consider management sprays for orchards where scale was present on fruit at harvest last season. Dormant oil is first timing for managing San Jose scale.

Climbing cutworm is a very minor tree fruit pest sometimes seen in cool weather. None have been reported at this time.

Oriental fruit moth first adult flight typically happens around pink in apple. Traps and lures should be in place by approximately May 1. Oriental fruit moth mating disruption pheromone can be put up at any time in stone fruits if pruning is done.

No reports of codling moth adult flight currently. We usually start to catch a few in late bloom. Codling moth mating disruption pheromone can be put up at any time, but before bloom is best. Traps should be placed for codling moth before petal fall.

European red mite is in the egg stage. No activity at this time, but egg hatch could begin at any time. Monitor for overwinter egg mortality; if eggs look pale or clear instead of bright red, they are not viable, and this is likely given the harsh temperatures we experienced in February and March.

No reports of tarnished plant bug activity in this area yet. Continue to monitor.

Pear psylla adults are present in low numbers present with the recent warmer weather. Expect increased adult activity over the next weeks and start management in high pressure blocks.

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