Vegetable Fungus Disease

I'm not discussing IF it's coming, I telling you that if you grow plants in Texas IT IS COMING!

The "it" to which I am referring is fungus disease. Vegetables can and will be infected by disease-causing organisms. In plants, these organisms may produce leaf spots, wilt, yellow leaves, stem, fruit and root rots. The symptoms expressed by the plant are a signal that either an organism is infecting the plant and causing disease or other factors in the environment have injured the plant. Few gardeners in Texas have escaped the disastrous symptoms on tomato plants universally described as "the leaves on my tomato plants are turning yellow and dying from the bottom of the plant moving upward. Last year this "blight" killed my entire plant!"

Plant disease is the result of living organisms such as fungi or bacteria infecting the plant tissue and disrupting normal functions carried on in the plant. The organisms infecting the plant can multiply and spread the disease within the plant and/or to other healthy plants.

Damage caused by non-living factors such as weather, air pollution and chemicals is not contagious and does not spread unless the source of the problem persists in the area of the plants.

Three things MUST be present for plant disease to occur: 1) a disease-causing organism, 2) a susceptible plant and 3) an environment suitable for the organism to infect the plant and multiply in.

What are these organisms that cause plant disease?

Fungi are actually simple plants without true leaves, stems or roots. They grow in thread-like forms and produce minute 'seeds' called spores. These spores can be carried by wind, water, animals, tools or machinery (even clothing) to other parts of the same plant, as well as to healthy plants. Under favorable conditions, the spores infect plant tissue and produce new fungus structures.

Plants react to fungi and other disease-causing organisms in much the same way the human body does. The infected tissue may release substances to ward off the organisms or to kill the plant tissue itself, leaving no food for the organism to live on. In some instances, plants produce swollen 'bubbles' inside their vessels to stop the spread of the fungus.

These defense reactions, in addition to toxic substances secreted by the fungi itself, cause the brown spots, yellow tissues, wilting and other symptoms of disease. When the fungus is able to produce spores and spread to other parts of the plant, the damage it causes begins to interfere with normal plant functions and death or production losses occur.

A number of diseases attack the foliage and fruit of vegetables. Controlling diseases that are caused by fungi differ from insect control techniques in that fungus problems must be prevented rather than cured. Prophylactic remedies are justified. When a gardener sees a fungus problem, irreversible damage already has been done. Cloudy, damp mornings encourage the growth of fungus spores.

Each spring, gardeners become extremely disturbed about leaves on tomato plants dying. Every year, it’s the same old story. Plants are beautiful, loaded with fruit and growing like mad. Then, disaster! The leaves begin turning yellow and dying at the bottom of the plant. The sickening disorder slowly moves up the plant until nothing remains except the green frame of stems with small, green shriveling fruit. This is not a horror story; this is an annual reality for Texas gardeners.

There are two main diseases which cause this disaster every spring. Early blight (Alternaria) and Septoria leaf spot are the culprits. Early blight is characterized by irregular brown spots appear first on older foliage. With age, the spots show concentric rings forming a target pattern. A yellow, diffuse zone is formed around each spot. Although this fungus disease can be observed throughout the year, it is most common during the fruiting period. The more tomatoes a plant produces, the more susceptible to and disastrous are the effects of an early blight infection. The fungus is susceptible to high humidity and high temperatures. Even if rainy weather is not prevalent, morning dews provide sufficient moisture to support the occurrence of the fungus. The only control is prevention, which begins when the plant begins setting fruit. During periods of high humidity, which includes most of the spring, apply a fungicide weekly. The best fungicide to use is one containing chlorothalonil (Ortho Daconil, Fertilome Broad Spectrum Liquid Fungicide, HiYield Daconil, or Rigo Lawn & Garden Fungicide).

Another destructive foliage disease of tomato plants is Septoria leaf spot. It may attack tomatoes at any time. However, it generally causes problems after the fruit begins maturing. When you check plants for this disease, look at the older foliage. The fungus is characterized by circular lesions with gray centers surrounded by dark margins. With age, the spots become covered with tiny, black specks from which spores grow. Lesions are smaller and more numerous than the early blight organism.

The fruit is rarely affected, but stems and blossoms are attacked. The disease overwinters on old tomato vines and wild relatives of the tomato family. The fungus is most active when temperatures are between 60 and 80 degrees F., and during periods of high humidity. Apply a fungicide containing Topsin M (Greenlight Systemic Fungicide, Fertilome Halt Systemic Fungicide or Rigo Rose & Ornamental Fungicide). Because bayleton is a systemic fungicide that goes into the plant, it lasts longer and does not have to be applied as often. To provide complete fungus protection from Septoria and early blight during spring periods of high humidity, mix Topsin M with every second weekly chlorothalonil spray application, i.e., apply a Topsin M spray every 10 to 14 days.

Peppers and potatoes can be destroyed by the same diseases, so when you are spraying your tomatoes, share a little protection with your peppers and potatoes. Peppers also suffer from bacterial diseases that cause rapid leaf drop if infection occurs. As a preventive measure, streptomycin (1 teaspoon per gallon of Agri-Strep) or Kocide 101 can be added to the previously mentioned products. These can be applied to most vegetables. Follow label instructions.