Aster yellows can harm more than 300 types of plants
Question: I have two feverfew plants. One is blooming beautifully and the other has light green, hard and lumpy flowers that never turn white. What’s wrong?
Answer: From your description, it sounds like aster yellows. This plant disease attacks more than 300 species of plants, including feverfew. The symptoms displayed may be malformed flowers, brush-like shoots, yellowing and stunting of leaves, wilt and dieback.
This disease is spread by aster leafhoppers from infected to healthy plants. The plants usually survive the disease but serve as a source of infection for healthy plants. Remove infected plants as soon as they are observed to reduce the risk to other susceptible plants. Eliminate weeds in the garden like dandelions that can serve as a host for this disease. Replace susceptible plants with those known to be resistant in areas where this disease has become a yearly problem.
Q: I am looking for groundcovers that will grow under the canopy of an oak tree. Any suggestions?
A: A lack of sunlight and moisture make it challenging to grow groundcovers under oaks, maples, spruce and other trees. The dense canopy not only shades the plants, but also prevents rainfall from reaching the groundcovers below. Plus, the extensive tree roots absorb most of the water, leaving little for the groundcovers. Mulch may be the easiest solution and good for the trees. A 2-to-3-inch layer of wood chips under the canopy and pulled away from the trunk of the tree helps suppress weeds, conserve moisture, moderate soil temperatures and improve the soil as they break down.
If you opt for plants, consider Canadian ginger, Pennsylvania sedge and Christmas fern that are native to Wisconsin. Barrenwort (epimedium), shade tolerant coral bells, foam flower (tiarella), lungwort (pulmonaria), hostas, brunnera and variegated Solomon seal are a few other plants to consider. Do not cultivate deeply or add soil when planting under the tree. As little as an inch of soil placed over the roots can cause some trees to decline and even die.
You can add a bit of seasonal color with a few potted flowering plants set on the mulch or among the groundcover surrounding the tree. Or permanently sink a few pots in the ground. Then set pots of annual flowers inside the buried pots. You’ll only dig these holes once, making it easier on your back and the tree.
Q: I saw you at Energy Park at the Wisconsin State Fair. You mentioned a product for managing fungus gnats and I can’t remember the name.
A: Fungus gnats certainly are annoying as they fly in your face, computer screen and windows. They feed on the organic matter in the soil but usually do not develop large enough populations to harm our plants.
I mentioned using Summit Mosquito Bits made from a naturally occurring soil bacteria, bacillus thuingiensis israelensis (Bti), to control this insect. It kills the larvae of fungus gnats as well as mosquitoes and black flies but is safe for people, pets, birds and wildlife. You will need to make several applications as there may be eggs and larvae in the soil and adults laying more eggs. As always, read and follow label directions for the most effective control.
Post questions at melindamyers. com, or write P.O. Box 798, Mukwonago, WI 53149