Tom Glasgow: Buying locally may slow pest movement

The likely, future arrival of crapemyrtle bark scale to North Carolina will increase our needs for diversity in tree and shrub selection.

Crapemyrtles and cucurbits (squash, watermelon, cucumbers, etc.) are among our more familiar horticultural topics of conversation during the summer months. Currently, one group has a potentially serious problem on the way, and another has a serious problem already here. Well start with the problem thats on the way.

In a May 15 posting on his entomology website (see http://ecoipm.com/), Steven Frank of N.C. State addresses the introduced crapemyrtle bark scale (Eriococcus lagerstroemia) and its progress since being found outside Dallas in 2004. Since 2004 it has spread throughout much of Texas, and has also moved into Arkansas, Louisiana, Oklahoma and Tennessee. In early May of this year it was detected in Georgia. Frank concludes that even though crapemyrtle bark scale isnt yet known to occur in North Carolina, it is probably coming.

The consequences for infested crapemyrtle are quite serious. Frank relates a visit to Dallas in the fall of 2013, where he found the crapemyrtle trees in residential areas and along downtown streets in terrible condition. Infested trees were black and crusted with scales, and stumps indicated that many had already been removed.

Control will be difficult, in part because this is a relatively new pest for the U.S. and we dont yet have a good idea of how to manage it; and in part because many scale insects are by nature exceedingly difficult to control.

One strategy for now is to buy crapemyrtles locally, so as to slow movement of this pest into our state. Another is to get more serious about diversifying our tree species selection. Crapemyrtles have been relied upon heavily in the southeastern U.S. because they are exceptionally attractive in flower, and exceptionally tough and persistent under difficult landscape conditions. A much greater diversity of plant species will be needed in the future, and not just in response to the crapemyrtle bark scale.

Our second plant problem for today is cucurbit downy mildew, which was reported on June 9 in a commercial cucumber field in Duplin County, and subsequently confirmed by the Quesada Lab at N.C. State. Symptoms include angular chlorotic lesions on the upper leaf surface and a grayish-brown downy appearance on the leaf underside. Cucurbit downy mildew can result in exceptional damage and economic loss to commercial plantings, so its a disease that is carefully monitored. If you suspect cucurbit downy mildew in your garden, bring leaf samples to your local Extension office.

For the home garden, chlorothalonil products such as Daconil can provide limited control of cucurbit downy mildew, but youll also be locking yourself into a weekly spray schedule. A better strategy might be to remove infected leaves when the disease first shows up, and then remove infected plants if it begins to spread. Among the various cucurbits affected, cucumbers, watermelons and melons are more susceptible than squash and pumpkin, with cucumbers being the most susceptible of all. NCSU plant pathologist Lina Quesada-Ocampo tells me that there are a couple of slicing cucumbers with resistance to the pathogen, but resistant cultivars arent available for the other cucurbits.

Visit http://fsg.ces.ncsu.edu/publication/cucurbit-downy-mildew/ for excellent photographs and detailed information on this disease.

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Tom Glasgow: Buying locally may slow pest movement