Q: What are the bumps on my tree leaves, and how do I get rid of them? — Scott Langemo.
A: The round, protruding bump-like growths on tree leaves are called galls. Tree types commonly affected include maple, hackberry, poplar, oak and linden. The galls are caused by several types of insects and mites.
This from North Dakota State University: “Galls are produced by the trees in response to early-season feeding from these pests. Then, the insect or mite will generally use the gall as protection — a sort of home — while it completes its life cycle. The time to use a pesticide to prevent new damage was when leaves were opening and the pests were still exposed. Once the galls form, they provide protection for the insect, so applying a pesticide now will have very limited effectiveness at controlling what’s there, or for preventing new infestations. The good news is that damage is generally minimal. Trees can lose up to 25% of their leaf tissue without causing any major damage to the trees.”
Many gall-forming pests survive winter in the rough bark and crevices of the trunk and larger branches. Populations may be reduced by applying horticultural oil liberally to the trunk and branches in early spring just as the tree buds are beginning to open.
Q: It appears that many ash trees are having a very slow start this spring. On a bike ride in late May, I noticed thousands of small ash leaves falling from many trees. What's going on? — Carl Eidbo, Fargo.
A: I’ve had many questions about ash leaves falling from communities all around the region. In most cases it’s ash anthracnose, which is a fungus disease that is prevalent following cool, moist springs. It usually doesn’t have lasting impact on the trees, unless a large portion of the leaves are lost several years in a row.
Fallen leaves might be distorted with brown spots and leaves sometimes turn yellow, but often leaves look normal and drop off green. There is no practical treatment for the disease once a tree is affected, as it’s difficult to spray large trees with adequate fungicide coverage. To reduce future infections, remove fallen leaves either by raking, or by mowing with a bagger attachment.
Q: Is it safe to spray Roundup under my evergreen trees? It’s so much easier to mow and keep it looking good with the areas killed below. At one time, someone told me it was okay. — Sheri Stoeckel Friederichs, Foxhome, Minn.
A: Roundup glyphosate or other brands of glyphosate can be used under evergreens, as long as the product does not contact or drift onto the needles and branches. Also, although some sources say it's okay if glyphosate contacts the trunks of trees, I don't believe that’s a safe practice. I believe the trunks have the possibility of absorbing the product and may result in delayed-reaction long-term damage. I would err on the side of caution, and shield the trunks with cardboard. Around the yard and garden, it’s wise to avoid getting glyphosate on anything you don’t want dead.
If you have a gardening or lawn care question, email Don Kinzler at ForumGrowingTogether@hotmail.com. All questions will be answered, and those with broad appeal may be published, so please include your name, city and state for appropriate advice.