Q: I have some black cankers or growths on a tree in my yard. What is this, and is there anything I need to do about it now? — Tom Frappier.

A: The disease is called black knot, which is caused by a fungus. It is very common on Canada red cherry, chokecherry and other members of the plum family of trees, and is very visible during the dormant season, when trees are bare of leaves.

The disease causes blackened, distorted growths along branches, and can progress throughout the tree, eventually invading large, main trunks. If left unchecked, branches eventually die beyond the point of the cancerlike growths.

Control is admittedly difficult and the disease spread can be reduced, but often not eliminated totally. To control the disease, prune out the black knots in late winter, which is the preferred time, when the disease isn’t active. Pruning during the growing season can spread the disease.

Plant pathologist Jim Walla, with Northern Tree Specialties, describes the recommendations well: “Effective pruning is best done before leaves form on the trees. The galls are easiest to find and new infections can already be happening by the time leaves are present.

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“The galls should be pruned at least 4 inches below the gall, or down to the next crotch, without leaving a branch stub. The fungus is within the branch, so if you don’t prune far enough below the gall, the infection may remain.

“If the galls are left on the ground or in an area near the susceptible trees, spores can spread back to the tree. Collect all galls, place in a closed container, bury or move at least 600 feet away.”

Trees can be protected with a fungicide containing active ingredients such as captan or chlorothalonil following the label directions. Fungicides can help, but spraying alone is ineffective without proper pruning, and spraying won’t make the existing galls go away.

Q: Is it really true Epsom salts are a good fertilizer for tomatoes and other vegetables? — Teri Hall Smith, Fargo.

A: North Dakota State University, in a past summary written by horticulturist Tom Kalb, describes it well: “Many of us have a few tricks we’ve developed in growing a great garden. One trick is to put a scoop of Epsom salts into each hole when planting tomatoes. Some gardeners swear it prevents blossom end rot. It’s time to debunk that myth.

“Epsom salts don't stop blossom end rot — it leads to more of it. Blossom end rot is caused by a deficiency of calcium. Epsom salts contain magnesium sulfate — no calcium at all.

“Adding Epsom salts to the soil may create more rot since magnesium and calcium ions compete for uptake into the plant. The more magnesium in the soil, the less chance that calcium will be absorbed.

“What can we do to prevent blossom end rot? Don’t focus on the soil. Most soils in (North Dakota) have plenty of calcium. Focus on watering. The uptake of calcium depends on the uptake of water. Irrigate regularly. Avoid the extremes of waterlogged soil and droughty soil. Mulch to maintain consistent levels of moisture in the soil. Cultivate shallowly. Don’t damage the roots of your vines. We need these roots to absorb calcium.”

Q: When is it safe to plant bare-root shrubs in Fargo? — Arielle Windham, Fargo.

A: Bare-root trees and shrubs can be planted starting in mid- to late April. Because they normally do not have leaves yet, they are not injured by the freezing temps still likely until mid-May.

Potted shrubs and trees, on the other hand, that were started in greenhouses or warmer climates and brought here in full leaf, should not be planted until the likelihood of frost is past, usually mid-May, because freezing temperatures would likely injure the leaves.

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.