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Schmidt: Fall webworm starting to appear

By Staff | Aug 15, 2014

Fall webworms are beginning to emerge. Although the silken nests that are appearing in the trees of yards and public grounds this time of year can be very unsightly, fall webworms cause more of a nuisance than a threat to tree health.

Fall webworm (Hyphantria cunea) will eat the foliage of many trees and shrubs. There are a number of trees that are likely hosts for fall webworm including: alder, aspen, birch, chokecherry, cottonwood, elm, fruit trees, maple, pin cherry, poplar, willow and other hardwood trees, but chokecherry, cherry, birch and elm leaves seem to be preferred.

There is no need to worry about the defoliation caused by the feeding of fall webworms. The leaves have pretty much done their job for the year and you can let the webworms eat. When they get full, they will leave the nest and find a sheltered place to form a cocoon and spend the winter. The trees will be fine. Often times the defoliation is more distressing to the homeowner than it is to the tree.

Since the caterpillars do their feeding within the web, control with insecticidal sprays is difficult as the pesticide must contact the webworm larvae. This can be achieved by opening the nest – a tedious task – before applying the insecticide.

Insecticides containing the active ingredients: carbaryl (Sevin), malathion, bifenthrin and permethrin can kill fall webworms. Safer insecticides like Bacillus thuringiensis var. kurstaki, horticultural oils and insecticidal soaps can also be used, but are most effective before the worms become enclosed inside their webs.

It is justifiable to spray young trees to protect them from webworms since these trees don’t have a lot of leaves and they need them to overcome transplanting shock and to prepare for winter. It is hard to justify killing webworms in tall trees such as elms and birches. These mature trees are under minimal stress due to the feeding of webworms and you are more likely to get the toxic insecticide on you when spraying.

Some gardeners choose to prune out nests as soon as they appear, but it is not totally necessary and can cause more harm to the tree in terms of the open pruning wound being an entry point for other infections. The use of propane blowtorches to “fry” the worms is not recommended for obvious fire-risk potential and can also cause more damage to the tree than the webworms themselves.

– A previous version of Schmidt’s article ran in 2013

Master gardener course starts Sept. 19

Do you love gardening and sharing your knowledge with others? Consider becoming a North Dakota Master Gardener volunteer in collaboration with the NDSU Extension Service.

Master Gardener training is convenient and flexible. The course will be offered both online and in a traditional classroom setting. “If weekday morning classes conflict with your schedule, watch online lectures in the comfort of your home on your own schedule,” said Esther McGinnis, director of North Dakota Master Gardener Program. For those who prefer traditional learning, classroom training will be conducted in Bismarck, Devils Lake, Dickinson, Fargo, Forman, Grand Forks, Minot, Napoleon, Rugby and Williston.

Online and classroom sessions will run for 10 weeks beginning September 19 and ending November 21. Classroom training will be held every Friday from 8:30 a.m. to 12:30 p.m. (CDT) during this time.

Course topics will include annual and perennial flowers, tree selection and maintenance, soil health, composting, fertilizers, plant diseases and pests, vegetable and fruit production and so much more. Classes are taught by NDSU faculty and by Extension personnel.

Once training is completed, interns will volunteer 48 hours over two years on horticultural projects in their home counties before earning the title of Master Gardener. Projects include answering questions at county fairs, organizing horticultural workshops, and managing school and community gardens.

Tuition for the 2014 class is $150 for volunteers or $400 for non-volunteers. Computer knowledge, internet access and an email account are required.

Class size is limited and filled on a first-come, first-served basis. The registration deadline is September 2. Registration is online at ag.ndsu.edu/mastergardener/ For more information, contact your local NDSU County Extension office or Esther McGinnis at 231-7406.

– Esther McGinnis

– Column compiled by Yolanda Schmidt

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