Grand Rapids area tree fruit update – May 26, 2020

Our region has gone from cool and dry to hot and humid in a few short days.

Apple flowers blooming
Photo by Amy Irish-Brown, MSU Extension

Weather update

After a cool spring, it seems summer has arrived, and hot and humid weather is in place this week. The warmer than average temperatures have pushed degree day totals forward, but overall, we are still behind the normal through May 25 when compared to a 40-year average. The Michigan State University Sparta Enviroweather station has accumulated 527 growing degree days (GDD) base 42, which is five days behind the average for Jan. 1 to May 25. Growing degree days base 50 at Sparta are 233, which is seven days behind normal from Jan. 1.

Crop update

Apple growth stage ranges from full bloom on later varieties to petal fall on early varieties. Most apples in the main Ridge growing area are the early petal fall stage. The bloom stage moved very quickly with very warm days and nights in the past few days.

Tree fruit pests

There has been very little rainfall in the last week and no additional apple scab infections since May 19. Models estimate much of the Grand Rapids, Michigan, area has over 90% mature ascospores and primary scab is still very much on and will be for at least three more weeks.

Cool and dry weather reduced the risk for normal powdery mildew applications from tight cluster to bloom, but with the warm and humid weather now in place, that risk is very high. Adding something in for mildew over the next few cover sprays is highly recommended.

With bloom present, the risk for fire blight increases, and with the favorable warm temperatures moving in just in time for bloom, that risk is extreme. Current EIP (Epiphytic Infection Potential) is very high and all that is needed is a light rain, heavy dew or even a spray application to create a blossom blight infection according to the MaryBlyt model. You can track the predictions on the Enviroweather Fire Blight model, or you can use the Fire Blight Interactive model on Enviroweather to change parameters to better fit your local weather data.

Insect activity has increased with the warmer weather. We are quickly moving towards petal fall applications. Of course, you will get your bees out before you spray, but make sure your neighbors have their bees out as well before petal fall insecticides are applied.

No plum curculio adult activity reported in Grand Rapids, but it is expected at any time. Be ready to move with petal fall apps when your bees are out. Plum curculio needs night temperatures over 60 degrees Fahrenheit for egglaying and we certainly have that going on this week.

Codling moth is just beginning to fly in high pressure blocks. No regional biofix is set at this time. First catch is typically between 250 to 370 base 50 (average of 300 base 50) in the Grand Rapids area. Mating disruption pheromone and traps with lures should be in place now.

I can now find various species of aphids in various tree fruits. No beneficials to note yet but they will appear soon. Warmer weather and rapidly expanding shoot growth will likely be favorable for aphids to get established.

Small to medium sized obliquebanded leafroller larvae are present. Monitor known problem blocks closely for larval activity. There are a few small redbanded leafroller larvae present as well. Scout for their presence and add management sprays at petal fall for blocks with high numbers—one per tree. Traps go up in early June (1,000 GDD42) for summer adults.

San Jose scale adult male flight expected soon. Traps need to be in place now. Target sprays are only needed in blocks with known hot spots—this is a slow-moving pest and orchard wide sprays are seldom needed if good scouting is in place.

Oriental fruit moth adult males made a definite flight for biofix over the weekend.  A regional biofix was set for May 22 (323 GDD45) with 75 GDD45 since. We should reach the 10% egg hatch threshold (150-170 GDD45) by May 28 or 29 and cover sprays to prevent shoot tip damage should be applied in stone fruits.

Some European red mite egg hatch on the Ridge is beginning. Warm weather this week will very much encourage development. Petal fall miticides are likely to be very important in 2020.

There is some black stem borer adult activity in the Grand Rapids area in the last week with warmer temperatures. Begin monitoring for evidence of trunk and limb boring.

First hatch of white apple leafhopper is occurring and nymphs are present in very low numbers. Continue to monitor, particularly in non-bearing trees where pesticide covers are minimal.

Very few tarnished plant bugs are in this area yet. No reports of mullein bug/campylomma but continue to monitor.

Spotted tentiform leafminer adult numbers are low to normal. Egg hatch should be nearing a peak. Sap feeders should appear at any time. This is a minor pest where management is only needed if damage was high the previous growing season.

Green fruitworm adult flight continues in very low numbers and seems to be a longer flight than in recent years. This is a minor pest in tree fruits but there have been more reports of fruit damage in last few years, so it warrants monitoring.

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