Northwest Michigan fruit regional report – April 28, 2015

Growers have kicked off their insect and disease management programs for this season and predicted warm temperatures will accelerate crop development this week.

Mature lecanium scale empty shells on the top branch, and overwintering fertilized female lecanium scales on the bottom branch.
Mature lecanium scale empty shells on the top branch, and overwintering fertilized female lecanium scales on the bottom branch.

Weather report

The weather has remained cool over the past week and trees have moved very little since we examined the growth stages last week. However, temperatures are predicted to rise toward the end of the week and rain is in the forecast for next Monday, May 4. Growers will need to protect new tissue as these predicted warm temperatures would certainly accelerate growth.

Growing degree day (GDD) accumulations have not changed much in the past week. We have accumulated 143 GDD base 42 and 50 GDD base 50; we are now slightly behind our 20-plus-year average. If temperatures do warm during the latter part of the week, we will catch back up and be on par with our past GDD accumulations. Conditions have been dry across the region and we have had little rainfall since April 20. As mentioned above, the next chance for rain will be on Monday, May 4.

We had some cold overnight temperatures across the region last week. Temperatures dipped into the mid-20s last Wednesday and Thursday, April 22 and 23. Friday, April 24, was the coldest night, and overnight temperatures dipped into the low to mid-20s at many of the northwest Michigan Enviro-weather stations.

We cut buds Friday afternoon and we had little to no damage in sweet cherries at the Northwest Michigan Horticulture Research Center (NWMHRC). In our tart cherries, we cut 100 buds and 33 of them were damaged. However, the location from where we cut these buds was a lower site on the station. Most growers feel like they have come through these cold temperatures with little damage. Predicted overnight temperatures for the remainder of the week are expected to be in the upper 30s and low 40s, so the forecast looks favorable for minimal freeze events.

Crop report

There has been little movement in crop development with the cool temperatures last week. However, with the predicted warm up in the forecast, many growers will be spraying this week and into next week. Conditions are also predicted to be warm and dry, which will be optimal for wrapping up sweet cherry pruning for the season. Tree planting continues and sprayers are gearing up for the season.

Pest report

At the NWMHRC, McIntosh, Gala, Red Delicious and Golden Delicious are showing 0.25 inch green tissue and many growers in the region have begun their insect and disease spray programs. Some growers made copper applications last week to reduce fire blight inoculum. These copper sprays would have also provided protection from apple scab infection, particularly if green tissue was present on susceptible varieties during last week’s potential infection periods. Chances for scab infection periods are low for the remainder of the week as conditions are predicted to be warm and dry. However, there is a 48 percent chance of rain Monday, May 4, and new green tissue will be susceptible to scab ascospores and should be protected prior to this rain event.

Growers are also spraying oil targeting overwintering scales and mite eggs at this time. Michigan State University Extension would like to remind growers that oil can have phytotoxic effects on green tissue, buds and blossoms if it is applied in or around below freezing temperatures. Oil should not be used 48 hours before or after a frost.

We have had reports that lecanium scale populations are high in some sweet cherry and peach orchards, and growers with high populations should make an application to control this species of scale. In the past, lecanium scale has been a concern in sweet cherries near wooded areas as this pest has a broad host range and feeds on forest trees such as maples and oaks. Mature lecanium scale is a larger scale species, 3-5 millimeters long, and dark brown. Mature scales are oval, evident raised bumps on branches. The shells of last year’s lecanium scales are visible on trees at this time. However, these large shells are empty and dead.

The scales that are a concern this spring are the fertilized female scales that are overwintering on branches. Overwintering scales are brown and oval, but more flattened and not as large or obvious on branches. Lecanium scale is present and more susceptible to control earlier in the season than other scale pests, such as San Jose scale. A dormant oil will help control Lecanium scale, but if populations are high or if growers missed the opportunity for this early oil spray, we recommend other materials to minimize the populations.

Very little work has been done on Lecanium scale, but Centaur and Esteem have this pest on their labels. Esteem applied at delay-dormant could suppress egg hatch from treated adults. Unlike San Jose scale, lecanium scale is not on the Movento label. 

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