Problems with pests, diseased leaves? Here's what the Master Gardener recommends
The Springfield News-Leader in Springfield, Missouri, partners with the Master Gardeners of Green County each week to bring readers a question-and-answer column with some of the expert horticulturists in the region.
Colleges and universities in the U.S. typically offer Master Gardener programs, which provide "intensive horticultural training," according to the American Horticultural Society. The certified Master Gardeners then volunteer as lecturers, researchers and gardeners in their communities. For more information about Master Gardener programs in your community, the American Horticultural Society created this page with local resources.
Here's a sample of some of the recent questions amateur gardeners had for the masters of the craft.
My basil plants have dark spots on them. What causes this and what can I do?
There are several things that could cause this problem, but the most likely culprit is overwatering and/or poor drainage, which can in turn lead to fungal disease. In light of our recent heavy rains, this would be my first guess. Making sure the plants are properly drained, especially if in a container, and allowing the soil to dry out between watering is a good start. I would also trim off any affected leaves, discarding rather than composting. Improving air circulation by light pruning is also a good idea. Fungal disease can be identified by concentric circles on the leaves, often with a yellow halo around the spots. Bacterial leaf spot is characterized by angular brown or black spots. You should also check the underside of the leaves for any pests such as aphids or spider mites. Environmental stress such as too much sun or high temperatures can also cause dark spots on basil.
My hostas have large holes all over. What is eating my plants and what can be done to stop this?
Slugs and/or snails are the mostly likely suspects here. Since they do come out at night, they are seldom seen, but the damage they leave is quite evident! Some people recommend setting out trays of beer to trap and drown them and while this may have limited success, it has not worked well for me in the past. Other recommendations include sprinkling Epsom salts or crushed eggshells around the plants, which may or may not work. The roughness and grittiness of the crushed eggshells may deter these soft-bodied pests and the addition of calcium couldn't hurt. I am also not sure what Epsom salts would do, but it would be a plus for the soil. Diatomaceous earth is often used to deter slugs or snails, again due to the gritty and course nature of this product.
One of my two Alberta Spruce has turned a reddish color and seems to be doing poorly in general. What is the problem? Can this tree be saved?
This is most likely due to spider mites, although overwatering or herbicide drift is also possible. There are treatments for spider mites, such as neem oil, insecticidal soaps, or a chemical miticide, but those will also harm beneficial insects. Any chemical treatments should be used carefully and as a last resort. A brisk spray of water will dislodge many of the mites. Making sure the tree is as healthy as possible by proper irrigation and fertilization will also help the tree resist pests and disease. In addition, any heavily damaged/infested areas should be pruned off and disposed of or burned. It is important to remember that even with treatment, the damaged areas will not regrow and the tree may not recover. Spruce trees simply don't do well in Missouri due to the climate, they are from a cooler climate and most of Missouri just doesn't suit these trees well.
Readers can pose questions or get more information by calling 417-874-2963 and talking to one of the trained volunteers staffing the Master Gardener Hotline at the University of Missouri Extension Center in Greene County located inside the Botanical Center, 2400 S. Scenic Ave., Springfield, MO 65807.