Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
5/14/01
Contacts:
Barbara Ambruzs, Extension Plant Pathology, (515) 294-0581,
ambruzsb@iastate.edu
Elaine Edwards, Continuing Education and Communication
Systems, (515) 294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning May 18
Protecting Your Plant Investments
By Barbara Ambruzs
Extension plant diagnostician
Iowa State University Extension
Debris has been raked up and removed, the ground has been cultivated, pages in garden catalogs have been turned and money has been spent. Everything is clean and plants are ready to be planted. What are some ways to protect these valuable investments?
Before thinking of ways to prevent or manage a disease, it is helpful to first understand how and why plants become "sick." An interaction of three factors is required for a plant to become diseased: 1) a plant capable of being infected (host), 2) an organism that can infect the plant (pathogen) and 3) the right environmental conditions. If any one of these is missing, no disease will occur.
Let's take Fusarium wilt of tomato as an example. This disease is caused by a common soil-dwelling fungus, called Fusarium oxysporum, which can remain in the soil for several years. Does this mean that you can never grow tomatoes in your garden? Remember the three things necessary for disease to occur: a host, a pathogen and the right environmental conditions. We can't do much about the fungal pathogen once it's present. So, let's concentrate on the other two factors, the host and environment, and see if we can manage this disease.
Fusarium resistant tomatoes are available for this exact scenario. They were bred to grow in areas infested with the Fusarium fungus. However, altering the environmental conditions for management of Fusarium wilt is difficult because the fungus usually enters plants below the ground and is protected by the soil.
For leaf diseases such as Septoria leaf spot, another fungal disease of tomato, it's much easier to change the local environment. In fact, using this strategy is important since there aren't any cultivars available right now with resistance to Septoria leaf spot. Some ways to adjust the environment are to minimize the length of time the leaves are wet, avoid splashing water and soil particles when watering, adequately space and stake plants to aid with air circulation and keep leaves up off the soil. This same strategy can work with most leaf diseases.
As the saying goes, " An ounce of prevention is worth a pound of cure." This statement is certainly true where plant diseases are concerned. It's much easier to prevent a disease than eliminate it once it is established. Curing a plant of a disease is difficult, if not impossible. Examine plant material before purchasing it. Does it look healthy? Are there leaf spots or wounded stems? Can you see any mold growing on the plant or soil?
Is last year's debris removed? Some weed species are a place for disease-causing organisms to hide, so weed control can be an important tool for disease management. Weed control practices can help you avoid, eliminate or reduce a good portion of the organisms that could get the disease ball rolling. Rotation is another way to take the host plant out of the picture; for example, plant corn or spinach where there is a history of Septoria leaf spot.
A plant that has balanced nutrition, adequate water and is planted in an appropriate location (keeping in mind factors such as sunlight, zone, soil type, drainage and wind exposure) can tolerate some disease pressure.
If a plant disease challenge makes its way into your garden, remember there are several strategies that you can use to, at least, slow down disease progression. Fungicides are available for protection against some diseases, but if used as the only pest management tool, usually are ineffective.
ml: isugarden
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