West central Michigan tree fruit regional report – June 30, 2015
Tree fruit crops are setting nicely.
All tree fruit crops in the Grand Rapids, Michigan, area have completed June drop, and the fruit set level appears to be good to be very good. There are a few apple sites with a heavier set and hand-thinning is ongoing. There are also sites with a less than optimal crop set. The peach crop is variable with some varieties with a decent crop set and others that are on the light side due to winter cold temperatures. Sweet cherries have a good set, but not quite excellent and harvest for fresh sweets is happening now.
Tree fruit diseases
Primary apple scab was over with the last heavy rain a week ago. It was a longer than usual primary scab season this year as spores seemed to be more drawn out in their release. While there are a few blocks around west Michigan with apple scab, the majority of blocks are clean. Often, I find scab on the ends of rows, tops of big trees or low on trees where coverage was not ideal. When looking for samples yesterday, June 29, I noticed a trend in some blocks where scab was only on leaves of the lowest branches, with lesions concentrated at the leaf tips. This tells me a fungicide cover got stretched too far and the leaves at the bottom of the trees took longer to dry off with spores perhaps concentrated there.
Fire blight symptoms are low overall for the west Michigan area, which is great. Michigan State University Extension advises growers watch hot spots carefully and continue to be ready for any situations that could kick up a trauma blight risk such as hail or high winds. Until we get to terminal bud set and trees slow down their growth, they are still very susceptible to trauma blight. Terminal bud set is starting, but recent heavy rains seemed to have pushed growth a bit longer, which extends the fire blight risk.
Powdery mildew continues to spread in some blocks. It will continue to spread with no management and as long as shoots are actively growing.
Regarding summer diseases in apples, we are approaching the timing when fungicides for sooty blotch and fly speck need to be added in to prevent these diseases on apple fruits. There is an excellent decision-making model for summer diseases on MSU Enviro-weather.
Tree fruit insects
Codling moth adult flight is at or just past peak, and egg hatch is most likely at peak as well. Cover sprays are crucial to maintain at this time in blocks that are over thresholds. Expect larval activity for two more weeks.
Continue to assess European red mites per leaf as they are beginning to build again in some blocks. The threshold is five mites per leaf for July. Monitor for beneficials – one per leaf indicates to wait a week and count again.
Obliquebanded leafroller adult flight seems to be declining as expected. Initial early egg hatch should just be beginning and cover sprays should be applied in blocks with a history of high obliquebanded leafroller pressure. The majority of apple blocks continue to have low pressure from obliquebanded leafrollers and cover sprays in those blocks can be applied when small larvae are visually found.
Oriental fruit moth second generation adult flight continues to increase as expected. Oriental fruit moths are following the degree day models very closely this season. Expect second generation flight to increase over the week or so before it hits peak in mid-July. Egg hatch should begin soon with cover sprays needed again in stone fruits around July 4 in blocks with high numbers. In apples with trap numbers over 40 moths per week, cover sprays should be considered to prevent shoot tip infestation.