Thursday, October 31, 2013

Some late season reminders

A late season scab build-up would increase inoculum levels for 2014
Fall urea spray to reduce overwintering disease inoculum.
The scabby leaf pictured above indicates a potential build-up of late season scab. It was on a tree that had been treated with protectant fungicides every two weeks through Aug 30. Harvest season in the Winchester area was relatively dry-- until October 10-14 when we got 3.6 in. of rain. By that time most commercial orchards were unprotected and the cool temperatures during those rains were optimal for scab development on the underside of leaves after the fungicides were gone. Such infection will overwinter and increase ascospore levels next spring.

A foliar urea spray is recommended as a supplemental application at early leaf drop to encourage more rapid leaf breakdown and reduce overwintering of leaves with apple scab, Glomerella leaf spot and Alternaria leaf blotch inoculum. The recommended rate is 40 lbs of urea per acre, applied to wet the remaining leaves on the tree and with nozzles also directed to cover leaves already on the orchard floor, under the trees and in the adjacent row middles. This practice has been shown to reduce scab inoculum by as much as 95%, thereby reducing the threat of heavy early season infection next spring. Special consideration should be given to this approach where resistance to strobilurin (QoI) and sterol-inhibiting (SI) fungicides is suspected. Glomerella leaf spot was a new problem in the Winchester area in 2012 but not as much of a problem in area orchards this year; however this year it remained a serious problem east of the Blue Ridge, in southern Virginia and western North Carolina.

Bacterial spot on Galaxy "flat" peach
Bacterial spot- Note angular lesions

Bacterial leaf spot of peach: The leaf spot bacteria overwinters in small twig cankers caused by infections at the leaf abscission scars soon after leaf drop. Where bacterial leaf spot has been a problem, apply a copper spray at early leaf drop to protect those leaf abscission scars thereby reducing the potential for infection next year. A copper spray in the fall (or any time before bud swell in the spring) also serves as the peach leaf curl spray.

Pay attention to abnormal foliage color of trees in a planting: Early, reddish/purplish coloring of foliage often signals a problem with the lower trunk or crown area of that tree. This year we saw some increase in collar rot problems, but such symptoms could also be caused by voles, dogwood borers, or more than one of these problems. All have specific treatments that improve control and reduce tree loss but need correct diagnosis and treatment to expect effective results. It could also be fire blight in the rootstock of M.9, M.26 or Mark rootstock if there was earlier infection in the planting. There isn't much that can be done for a tree dying from fire blight in the rootstock but it should be recognized and noted for improving control measures for next year. This includes thoroughly cutting out overwintering inoculum cankers during the winter and by being ready to protect the planting with copper at early green-tip and with streptomycin as needed at bloom.

A final reminder for the year: As usual, make notes, based on harvested crop, of disease or insect problems that affected quality yield in individual orchard blocks this year, and develop management strategies to address these problems at appropriate times next year.