Grand Rapids area tree fruit update – June 25, 2019

Summer weather is finally here.

Winter injury

June drop of apples is well underway and will most likely end this week. Early indications are that apples are setting up nicely – a little heavy in some place and a little light in others, but overall, a nice crop seems to be in place for the Grand Rapids area. All tree fruits are sizing nicely and tree growth has been tremendous given the recent rainfall.

Degree day totals for the general west Michigan area are about five or six days behind normal averages through May 27. From January 1 through June 24, the MSU Enviroweather station at Sparta has accumulated 1133 degree days base 42 and 617 degree days base 50.

The predicted apple harvest dates are now available on MSU Enviroweather for all weather stations in the Grand Rapids area, including Sparta.

Tree fruit diseases

There were finally zero primary apple scab spores with the most recent rain event. That puts an official end to primary scab for the growing areas around Grand Rapids. The last several weeks have been very challenging to stay ahead of all the rain events and there is some primary scab showing up in commercial apple blocks, so take the time to carefully scout for scab before you reduce fungicide rates to summer levels.

If fire blight got established either through blossoms or shoots or related to a trauma event, you should be able to easily see it by now. Like apple scab, this is a good time to scout very carefully for fire blight to be sure you are clean. There is some very unsettled weather moving in for this week as temperatures rise and convection brings the possibility of storms. Be sure you have a plan in place for how you might deal with potential trauma blight situations if we get any high wind or hail events. Leaves and shoots are still very tender – we usually need to get to mid-July and terminal bud set before the risk for trauma blight is reduced.

Tree fruit insects

There continues to be quite a bit of variability in codling moth activity this season. Adult males have been flying in high pressure blocks for several weeks, while some low pressure blocks are just beginning to catch a few. I set a regional biofix for moderate pressure blocks for May 25, 2019 (237 DD50), and there have been 399 degree days base 50 accumulated since then. Expect trap numbers in many blocks to increase this week and 250 DD50 from now will be a key timing for good covers in place.

Various sizes of leafrollers are present – are they all obliquebanded leafroller (OBLR) larvae? Be sure they are being identified correctly. Adults of OBLR for the summer generation are now flying. I set a regional biofix for June 17, 2019 (970 DD42) and there have been 399 DD base 42 accumulated since that date. Continue to monitor trap activity. Some small overwintering larvae might be managed with codling moth sprays if you need to. Early egg hatch is predicted for July 3 or 4. First summer larvae might be visible around July 13 or so.

Our MSU trapping network for spotted wing Drosophila has caught very low to no adults in traps this past week. As cherries move to straw color or red stages, cover sprays should be considered as fruit might ripen quickly. Continue to trap for flies in ripening crops – cherries especially. Earlier than normal trap numbers are leading to a concern for strawberries for 2019. Watch PHI’s as you plan out SWD management.

Warmer weather and rapidly expanding shoot growth will likely be favorable for aphids to get established. Keep an eye on non-bearing trees where routine cover sprays are lower – aphid populations can get out of hand in these blocks quickly. Wooly apple aphids are now present in apple canopies and they are extremely hard to find – even in blocks with known high pressure in fall 2018. Management of wooly apple aphids should be considered now in blocks with high pressure in 2018.

Overwintering San Jose scale are present. Adult male flight continues and is declining somewhat. A regional biofix was set for May 25, 2019 (211 DD51) with 370 degree days base 51 accumulated since that date. Crawlers emerge around 400 DD51 after biofix – estimated for June 26 in the Grand Rapids area with normal temperatures.

Adult activity of Oriental fruit moth is down and should start to increase as second generation begins flying. Very little flagging from first generation is being reported – perhaps due to a lower population overall of first generation due to cooler weather. A regional biofix was set for May 17, 2019 (288 DD45) with 656 degree days base 42 accumulated since. Egg hatch for first generation should be complete. Change lures now to be sure to get good trap numbers for second generation adults. Cover sprays are not as critical at this time. Second generation egg hatch will start around July 14 and cover sprays will again become important around that time.

Nymphs and adult European red mite can be found, but numbers are on the low side due to cooler temperatures and petal fall applications. New eggs are now starting to be found. Continue to monitor. Twospotted spider mites should also be present at this time. Threshold for all mites is 2.5 mites per leaf for June. It goes up to five mites per leaf for July.

Black stem borer damage composite
Black stem borer sawdust “toothpick” and damage.

Activity of adult black stem borer continues to be reported in the Grand Rapids area.  Higher numbers of winter injured trees in the area could lead to higher infestation of black stem borers – trunk sprays should be going on now if not already. Monitor blocks along wooded areas for infestation.

Numbers of nymphs of white apple leafhopper are building slowly. Continue to monitor - remembering to keep an eye on non-bearing trees for leafhoppers and aphids that can limit shoot growth.

Brown marmorated stink bug adults seem to be active sooner this spring and we are catching them in traps, which is unusual. There are no reports of nymphs in traps at this time. Continue to monitor.

Several species of borers are now active in tree fruit crops. Dogwood borer is now flying in low numbers. Greater and lesser peachtree borers and American plum borer have been flying for several weeks now. Borer sprays are usually timed for peak adult flight. For greater peachtree borer and lesser peachtree borer, it’s usually late June. For dogwood borer, it is usually around July 4.

No Japanese beetle activity in the Grand Rapids area as of yet. Rose chafer started to become active about a week ago primarily on sandy sites. Continue to monitor.

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