We are well into the growing season and by now you have probably run into a few problems with your plants and trees. Diagnosing the malady is often tricky, but you need to know the cause before determining what, if anything, to do about it. A plant problem falls into one of three categories: insects, disease, or environmental.
You will either see the actual insects (Japanese beetles chewing away on a rose leaf) or find evidence of their presence even if they are not currently present or visible. Besides the obvious damage of eaten leaves or blooms, look for their waste. I usually notice the dark round pellets scattered on the light-colored mulch under a tomato plant before I see the tomato hornworm and the damage it has done. Other signs to look for include sticky honeydew, dark fungus growing on the honeydew or ants attracted to the sweet honeydew. They all indicate the presence of aphids, scale, or mealybugs. Cocoons, webbing, and exit holes on tree branches all point to an insect problem.
Diseases are caused by bacteria, viruses, and fungi, with fungi being the front runner. Things to look for are fruiting bodies like conks and mushrooms, molds, scabs, mildews, cankers, galls, wilts, rusts, and the list goes on. The causal agent can be present in the soil, the air, on other plants, or carried in on insects. Sometimes the damage is cosmetic with the plant recovering, and other times it is more serious. Think of hollyhock rust. In the first half of the summer, the plant looks great and flowers well. The second half, not so much, but the cycle repeats next year with you still getting some wonderful flowers in the beginning.
Once you’ve ruled out insects and disease, the fault is probably environmental. Standing in water after a flood, extended drought, losing a shade tree in a storm exposing the shade-loving plants underneath the canopy to full sun, and salt spray from snowplows to name a few. Don’t forget about humans as part of the environmental damage. We get too close to tree trunks with our string trimmers. We park cars on the lawn and top of plant roots, compacting the soil, or we treat a plant with a concoction somebody on social media recommended which has no testing, no safe dosage, and no labeling for use on plants.
There is one final way to determine if the problem is environmental instead of insects or disease. Environmental injuries may occur on multiple species while insect and disease problems are often species-specific. Using the hollyhock rust example again, it usually only infects plants in the hollyhock and mallow families but doesn’t cross over to mums or petunias, etc.
Even though the Illinois Extension offices are closed to the public at this time, the Master Gardeners of Edgar County can help you with a gardening question. Please leave a message at 217-465-8585 or email us at firstname.lastname@example.org.