Q: What's eating my pea leaves? Ron Boe, Fargo.

A: When leaves develop neat, circular holes on the margins of a leaf, it's the work of leafcutter bees, who use the material for nesting. They're good little pollinators, and plants usually don't suffer greatly from missing a few leaf pieces, and so no control measures are usually advised. I think your pea vines will still produce normally.

Leafcutter bee holes are also frequently seen on rose leaves.

From North Dakota State University: “A leafcutter bee is an impressive pollinator and our friend in the garden. The bee carries its golden pollen loosely on the underside of its abdomen. Since they keep the pollen dry, it falls off easily when the bee flies from flower to flower, making them a much more efficient pollinator than a honeybee, who tucks pollen in ‘baskets’ in its hind legs. A honeybee does a great job of gathering pollen, but not in spreading it.

“Leafcutter bees are solitary and busy. They nest in small cavities found in rotted wood or hollow stems. They are non-aggressive and only sting when handled or trapped, and its effect is no more painful than a mosquito bite.”

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Q: My raspberry fruits have been infested with those tiny white worms the past several years. Is there anything that can be done? John H., Harwood, N.D.

A: The tiny white worms are the larvae of the spotted winged Drosophila fly, abbreviated SWD, and have become a plague in raspberries and other small fruits. Besides being unpalatable, the worms cause mushy berries.

Control is aimed at the adult fruit fly, which lays eggs in developing fruit. The eggs hatch into larvae which feed inside the fruit.

Jim Walla, of Northern Tree Specialties, has a long history of addressing insects and diseases of fruit, and has developed a spray regimen that has worked well for his raspberry harvest. Jim says:

“I have chosen two insecticides that I alternate to control SWD on raspberries. They are spinosad and malathion. Both are rated by the EPA as having a one-day pre-harvest interval on raspberries. That is, wait one day (24 hours) after spraying before harvesting the fruit for consumption. I wait two days after application of these insecticides on raspberries, just to play it a little safer. Spinosad is effective for five to six days, while malathion is effective for six to seven days.”

Alternating between the two insecticides helps prevent resistance to the products by the flies. To summarize the schedule, Jim sprays the raspberries, waits two days, then harvests until the seventh day, on which he sprays the alternate insecticide. Then he waits two days, harvests until the seventh day and sprays the other insecticide, in an ongoing cycle.

This and other good information can be found on Jim’s Facebook page, Northern Tree Specialties w/ Jim Walla — Tree Doctor.


Q: I’m tired of the struggles with Autumn Blaze maple. Is there a tree that is better adapted to our conditions, but still has nice fall color? Dave N., Fargo.

A: Autumn Blaze maple, and similar hybrid maples, are a roll of the dice in the alkaline soils of the Red River Valley and westward. Some survive to adulthood, many do not. They are better adapted to the naturally forested areas of Minnesota and eastward.

A better choice for regions that were once prairie grassland, such as most of North Dakota and western Minnesota, is Ohio Buckeye. They become large shade trees, well-adapted to the soil conditions and winter-hardiness requirements. The autumn color is an outstanding shade of bright orange.

You’ll find several named cultivars of Ohio Buckeye at locally owned garden centers, such as Autumn Splendor, Prairie Torch and LavaBurst. The latter two were developed by NDSU.

ARCHIVE: Read more of Don Kinzler's Fielding Questions columns

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at kinzlerd@casscountynd.gov or call 701-241-5707. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.