Diagnosing Plant Problems

I tell people all the time that there are only three things that affect plants: insects, diseases, and everything else. (Simol1407/Shutterstock)

Q: Your answer on a lawn that suddenly appeared dead sounds like what many lawns in our area suffered through. We had army worms. One day the grass was green and the next day it was dead-looking.

A: I tell people all the time that there are only three things that affect plants: insects, diseases, and everything else. Dead grass looks like dead grass, but we often have to be detectives and coroners to figure out the likely cause of the problem.

The key to diagnosing many plant problems is performing regular inspections. If you know what a healthy plant looks like and you are regularly looking at your plants, you can see the problem as it develops.

While the problem is growing, there will be signs and symptoms left by the insect or disease. When looking at plant problems, signs are directly visible evidence of the cause, such as a part of the fungus or insect. Symptoms are visible effects of the problem, such as wilting, yellowing, or branches dying.

Sometimes the problem is hard to diagnose. Take the problem at hand: dying grass. We are looking at only half the plant that is above the ground. It wilts, turns brown, and looks dead. The top can’t survive if the roots are dead, dying, or missing. If grubs ate the roots, then the top will turn brown and die. If a root rotting fungus kills the roots, the top turns brown and dies. If the soil is only a couple inches deep, as in many yards, there aren’t enough roots to supply water in a dry spell, so the top turns brown and dies. So, an insect problem, a disease problem, and an “everything-else category” problem all caused the symptoms of the roots dying first, followed by the top of the grass.

Part of the problem is that few homeowners can tell what is affecting their plants. If someone in the neighborhood says army worms or chinch bugs or some other thing is causing lawns to die, then everyone thinks that is the cause of their lawn problem. So-called professionals may agree with the diagnosis so that they can get a treatment sale out of it. It may be a good idea to get a second opinion. If someone says they know the cause of a problem, ask to see proof. Are there actual army worms or chinch bugs visible?

It may be that the problem pest has already moved on. It is also possible that there may be more than one thing causing the problem. Poor soil can cause slow root growth, which causes the top to wilt; then, insects or disease organisms finish the plant off.

A dry summer this year has harmed a lot of trees that are going to go dormant soon without having stored as much water as usual. If the winter has drying winds and bitter cold, then the tree may have problems growing next spring. The tree may grow in the “survive” range and not the “thrive” range next year. Trees that are not doing well are more susceptible to borer insects. The tree may die in a year or two, but the damage started this summer. When the tree dies, who will blame the dry summer this year?

Did lawns in your area have army worms? No doubt. Did all of the dead lawns have army worms? Maybe. Were army worms the only problem? Probably not. I appreciate your letting me know about the lawns in your area because it is a good reminder that the answers I give may not be complete. I may not have enough information to make a completely accurate diagnosis. Anyway, keep the questions and comments coming.