Prevention is best way to control plant disease

Angela O'Callaghan

Thursday, Nov. 13, 2008 | midnight

Angela O'Callaghan

When we deal with garden pests ­— whether they are insects, weeds or diseases — we are often surprised by their appearance and the amount of damage they can do in a short period. A plant that looks healthy and happy one week appears to fall into a steep decline the next.

Of course, problem development is not literally so quick, but early symptoms of problems can be missed easily unless the intrepid gardener is ready to keep a close eye on everything that is growing in the landscape. That is the essence of horticultural scouting (just as the Girl Scouts used to say: "Scouting makes the difference!")

Early detection of any problem is the critical first step to control it, especially with garden pests.

A number of factors need to coexist in order for a nuisance to become a crisis. The collection of these factors is often assembled into a triangle. Each of the factors sits at one of the legs of this triangle.

Take for instance, a disease problem.

There can be a great deal of specificity between plants and the organisms that sicken them. One of the most exciting developments of modern years has been the production of plants that can resist many of the diseases that once could wipe out an entire crop. Still, there remain diseases caused by fungi or bacteria that can kill or injure susceptible plants.

Therefore, one leg of the triangle is the plant vulnerable to the second leg — the disease-causing organism.

Prevention is the great element of disease control. When you are planning to install an element in the landscape, find out if it is immune to most of the diseases that might otherwise plague it. This cuts the connection between the two legs of the triangle.

Another form of prevention is keeping gardening equipment clean so that it does not spread disease organisms.

Even if a plant is a potential victim of a disease, and the disease is present, there are ways to avoid problems.

The proper environment for disease is the third leg of the pest triangle.

In much the same way that a plant has an optimum level of humidity, temperature and light for growth, a disease-causing organism often has a preferred environment. Rarely do the plant and pest thrive under the same circumstances. In other words, if a plant is growing under optimal conditions, it is probably going to be strong enough to resist disease, and it is unlikely that it will fall victim to a pest. At the same time, when the environment is insufficient for the disease bacteria or fungus, it will not propagate rapidly enough to become pestilential.

The situation is similar for problems caused by insects.

The hardy gardener has a number of ways to help plants escape disease or infestation problems. Using resistant plants is an important first step. Cleaning equipment is another. Finally, keeping the humidity, temperature and light levels optimum for the plant and not for the disease organism will prevent the disease triangle from forming.

Angela O’Callaghan is the area specialist in social horticulture for the University of Nevada Cooperative Extension. She can be reached c/o the Home News, 2360 Corporate Circle, Third Floor, Henderson, NV 89074, or TheNews@hbcpub.com.