The Three-Legged Stool of Disease

Three Legged Stool


Plant diseases can be a serious problem in fruit and vegetable crops. Diseases can stunt plant growth, reduce yields, and sometimes even kill the plant. There are many methods for keeping fruit and vegetable plants free of disease, but they all boil down to one concept. In order for plants to be infected with a disease, three things must be present – the disease causing organism, a susceptible plant, and favorable conditions for the disease agent to develop. You can think of each factor as one leg of a three-legged stool. All three legs must be present for a successful disease infestation to occur. If just one of these factors is missing, then the stool collapses and no infestation occurs.

Diseases are caused by a variety of agents – bacteria, fungi, mycoplasma, nematodes, and viruses. These can be carried by insects, weeds, or plant debris. Some diseases like verticillium wilt of tomatoes can live in the soil for as long as ten years. So one good garden practice to prevent disease infestation of your plants is to clean up all the plant debris at the end of the season. This will remove a potential source of contamination. No disease-causing agent, no disease, and the stool collapses.

Keeping plants well-watered and well-fed will insure that they are healthy and strong. Healthy and strong plants are better able to survive a disease infestation than stressed and weak plants. The disease agent may be present and the conditions may be favorable to it, but plants that are well-cared for are better able to resist the disease. No susceptible plant, no disease, and the stool collapses.

Some diseases can be transmitted by insect pests. Cucumber beetles and leaf hoppers, for example, can carry the organisms that carry bacterial wilt and yellows, respectively. Controlling these insects can remove a source of transmission of these diseases. The conditions for development may be present and the plants may be susceptible, but if the organism is not present, then infestation cannot occur. No disease-causing agent, no disease, and the stool collapses once again.

Buying disease-resistant cultivars is an excellent way of insuring that your plants aren’t felled by an infestation. Better Boy tomatoes, for example, are bred to be resistant to verticillium wilt, fusarium wilt, and nematodes. That means that the organisms may be present and conditions for development may be present, but if the plant is bred to resist these organisms, then the plant is not susceptible t0 the disease. The stool collapses yet again.

Many weeds can act as hosts for disease-carrying organisms. Keeping the garden free of weeds, whether through handpicking or hoeing, or laying down mulch to prevent them from growing in the first place, can remove an agent of disease transmission. Conditions may be right for the disease to develop and the plants may be stressed. But if the organism isn’t present, the disease cannot develop. Crash goes the stool!

Watering your plants in the early morning gives them a chance to dry out before nightfall. As a result, the plants will be dry instead of cold and wet. Cold and wet plants are breeding grounds for disease- carrying fungus. Fungus, however, is less likely to breed on dry plants. The fungus may be present and the plants may be a bit stressed, but conditions aren’t right, so the fungus cannot grow, so no disease occurs. The stool collapses once more.

In conclusion, keeping plants healthy and strong and your garden dry, clean, and free of weeds will go a long way towards keeping the stool of disease infestation in a permanent state of disrepair.

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