Q: The leaves on two of the maple trees in our backyard have growths that almost look like eggs of some kind. Can you identify what this is? - Jim McEvers, West Fargo
A: Thanks for the great photo. These growths are called leaf galls, and certain insects and mites cause them to be formed on different leaf types, including maple. These reddish-green growths are generally harmless to trees, unless they are extremely numerous.
Leaves produce these galls in response to feeding from mites early in the growing season. The pest then uses the gall as protection, harboring safely inside while it completes its life cycle. The time to use a pesticide to prevent damage is in spring as leaves are just opening and the pests are still exposed. After the galls are formed, the mites are well shielded inside, so applying a pesticide is ineffective for eliminating the current galls or killing the pests. By the time we see the gall, the damage is done, and it can’t be reversed for this growing season.
The good news is that damage is generally minimal. Trees can lose up to 25 percent of their leaf tissue without experiencing any stress. Unless the galls cover more than a quarter of the leaf surface, they won’t cause any major damage to the trees.
Many of these gall mites overwinter in cracks and crevices of the bark on the trunk and major branches. As the buds swell in the early spring, they migrate onto developing leaves, which is when mites are most vulnerable. Horticultural oil, available at garden centers, can greatly reduce the pest population if applied to trunk and major branches just prior to spring bud swell.
Q: We have a well-established row of lilacs, and I noticed the leaves are getting this chalky white stuff on them. I can rub it off a little, but not entirely. We have had several rains, could it be too much moisture? – Matt Maresh
A: You’ve described well the fungus disease called powdery mildew, which commonly effects lilacs, ninebark, peony foliage, zinnias, and many perennial flowers. It’s one of the most widespread and easily recognized plant diseases, characterized by spots or patches of white to grayish, talcum-powder-like growth on leaf surfaces, and sometimes undersides.
The humidity of the air needs to be high for germination of the disease spores. The disease is even more common in crowded plantings where air circulation is poor and in damp, shaded areas. Incidence of infection increases as humidity rises in summer.
As you mentioned, the powdery substance is well attached to the leaf surface and once affected, the leaves won’t revert to normal appearance for the rest of the season. To prevent the disease in future years, fungicides containing the active ingredient chlorothalonil can be applied to the foliage as a preventative, before the disease is evident, or at its earliest signs.
Q: I wanted to pass along a tip about weeding. I’ve always had success with the type of hoe called a scuffle hoe. The cutting blade at the end of the handle looks a little bit like a horseshoe, but squarer on the bottom, and you pull the hoe back and forth, while the blade cuts right below the soil surface. It makes quick work while the weeds are small. – Albert Fischer, Frazee, Minn.
A: Thanks, Albert, for the great tip. Scuffle hoes are among my favorites for weeding. Albert, who is 98 years old, continues with the following: “You can get right next to the garden rows, removing the weeds without disturbing the vegetables.” Thanks for passing along a great tip, Albert.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at firstname.lastname@example.org or call 701-241-5707. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.