Northwest Michigan fruit regional report – June 25, 2013

Recent heat has increased insect activity slightly, but fruit continues to size at a slow rate.

Daytime temperatures have been in the high 70s to low 80s since mid-week last week, and humidity levels have been high, but very little rainfall since June 16. The Northwest Michigan Horticultural Research Station (NWMHRS) Enviro-weather station recorded 0.09 inches of rain early Sunday morning (June 23), but conditions are dry across the northwest. We have accumulated 1,113 GDD base 42 and 669 GDD base 50 so far this season.

Although our growing degree days are not far off from our 20-year average, fruit is sizing slowly. Tarts, sweets and Balatons have not gained any size since June 10, and for the past 14 days the fruit is still measuring 11 to 12 millimeters. With the predicted warm conditions this week, we suspect fruit will move along. Some sweet cherry varieties at NWMHRS are showing some color. Birds have moved in to feed on varieties where sugar levels are increasing. Growers have been busy and ensuring proper timing for sprays has been the primary concern with the high humidity. Insect activity has picked up with the warm temperatures.

Apples. The last apple scab infection was on June 16, and although we had a wetting event on June 23, it was not long enough to result in a scab infection. The apple scab model on Enviro-weather says we are at 100 percent spore maturity and 95 percent of our spores have discharged. Although it seems so late, a good rain would ensure a call to end primary scab. There are scab lesions showing up in some blocks across the region; these growers will need to continue their scab program past primary to ensure scab-free fruit at harvest.

Codling moth numbers remain low at NWMHRS, but other growers have reported substantial flight with these warm evenings. Codling moths fly at dusk and they prefer warm temperatures for flight. These last few nights have been excellent conditions for codling moth flight.

Obliquebanded leafroller numbers made a big jump from last week’s zero catches – we caught an average of 19 moths per trap at NWMHRS. Rose chafers have been very problematic in some areas of the northwest and many growers have sprayed for these pests, especially in young apples.

Cherries. Cherry leaf spot is not hard to find in regional blocks, and with these warm and humid conditions, growers need to continue to be diligent about protecting their leaves. Protecting leaves from this disease is particularly important for those trees that have set a lot of fruit; a good, healthy leaf canopy is needed to help ripen trees with a big crop. Additionally, as this season seems to be moving slowly, the harvest season may be a long one, and cherry leaf spot control is key in a drawn-out harvest.

George Sundin’s Michigan State University Extension articles (“European brown rot blossom blight outbreak on Montmorency tart cherries” and “Fungicide protection for ripening tart cherries with European brown rot blossom blight symptoms”) from Friday, June 21, 2013, on European brown rot are worth a second read, particularly for those growers that were hard hit by this somewhat surprise of a disease this season. Although we do not know as much about European brown rot and fruit infection, data from Australia and Eastern Europe have shown this disease to infect fruit. Orchards with substantial European brown rot infections should be applying Gem (3.8 ounces per acre) and captan (1.75 to 2 pounds per acre) for their next spray as Gem has been shown to have anti-sporulant properties, which will help minimize the spread of this disease from dead spurs potentially to the fruit.

American brown rot is also a concern at this time. We have seen the American brown rot fungus move onto fruit that had canker from the freezing conditions earlier in the season. As most fruit is still on the green side, controlling American brown rot now is crucial because this disease is even more problematic when fruits begin to accumulate sugars. We are recommending a Gem application now to minimize the spread of spores and save Indar until we are closer to harvest (see “Scout now for sporulating American brown rot fungus in sweet cherry orchards”).

Obliquebanded leafrollers are also flying in cherries, and we caught an average of 25 moths per trap at NWMHRS. Growers that missed their petal fall insecticide spray targeting overwintering obliquebanded leafrollers should pay close attention to the obliquebanded leafroller model on Enviro-weather to best time a spray to control these summer generation larvae. Larvae that are not controlled can end up as a contaminant pest if larvae are found in tanks at harvest. In past years, we have had more problems with obliquebanded leafroller larvae at harvest if the harvest season is stretched out.

Plum curculio stings are higher in some blocks than in past years, and the current warm and humid conditions are favorable for plum curculio egglaying. Growers that have been using the P.I.T.S model in tart cherries should be putting on an insecticide to protect the fruit as eggs laid in the fruit at this time will be present at harvest. Plum curculio egglaying may go on for a longer period this year due to the cool start to the spring.

Lesser peachtree borers have still been caught in high numbers, and it would be a good time to make trunk applications against this pest. American plum borer numbers remain down, and we caught our first peachtree borer moths this week. We have not caught cherry fruit flies, and now spotted wing Drosophila has been caught in northwest Michigan. Two spotted wing Drosophila were caught in southwest Michigan this week.

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