Tomato Early Blight

 

I have noticed that several of the plots in the garden have early tomato blight.  I have attached a couple of photos that show what it looks like. The disease is a fungus that starts on the lower parts of the plants and spreads upward.  As the disease progresses, leaves turn yellow, wither and drop from the plant. Affected plants produce a low yield of undersized fruit. The tomatoes also suffer from sun scald as their leaves are no longer available to protect the fruit from direct sunlight.  

Factors favorable to the spread of the disease are wet weather and humidity.  While crop rotation is a recommended practice to avoid plant disease, this is not always practical – especially in our 40 square foot plots.  So, we have to rely on other practices, some cultural and some chemical.  

Tomatoes should be staked and mulched to keep leaves and fruit from contacting the soil surface.  Soil particles contain the fungal spores that cause the disease. Organic mulch, pine straw and newspapers are good ways to keep the surface of the soil from contacting the plant.  Remember – mulch, mulch, mulch! Good air flow is also critical to reduce the level of humidity as much as possible.

Fertilize your plants.  Green healthy plants are better able to protect themselves and ward off diseases and pests. 

If you think you have blight, remove the affected leaves and throw them in the trash.  Do not leave them in the garden and never put tomatoes in the compost. If you use a scissor to cut affected plant parts, you should use a mild bleach solution to clean the scissors between cuttings to avoid spreading the fungus.  At the end of the season, remove all plant debris and place it in the trash.  

Unfortunately, the use of fungicides will be unavoidable.  You do not have to/should not wait until your plant shows sign of infection before you start a regimen of fungicidal treatment.  I have read in some scientific publications that “Serenade” is NOT a useful fungicide. If other garden members have used it with success, let me know.  The following fungicidal chemicals are recommended: chlorothalonil (Daconil, Bravo, Echo), maneb (Dithane, Manex, Nereb) and mancozeb (Manzeb). Ortho Garden Disease Control is recommended by the Forsyth County Extension Service (contains clorothalonil).  They are sold in all garden and big box stores under various trade names. Look for the active ingredient on the label. And remember – Read and Follow all Label Instructions to get best results and minimize impact to the environment. These fungicides require re-application every 7 to 10 days and after rain.  You are coating and protecting leaves that have not been infected with the fungus. Nothing can save leaves that are already infected. Follow label instructions about how long to wait before harvesting fruit after fungicide application.

 

Tomato Early Blight - Steps for Control

 

Attention home gardeners -- it's not too early to start your control program for tomato early blight. This fungus disease is generally one of the most severe tomato problems faced by home gardeners each season. 

For top yields of high quality fruit, early blight control is essential. Since early blight-resistant tomato varieties aren't available, gardeners have to use a combination of practices to keep this disease in check. 

Early blight shows up as a leaf blight on the lower part of plants. The disease moves upward, and by early to mid-summer, early blight has caused a "firing-up" of foliage over most of the tomato plants in the garden. 

As the disease progresses, leaves turn yellow, wither, and drop from plants. Tomato plant severely infected by early blight produce low yields of undersized fruit. Generally, fruit are also show signs of sun-scald since leaves aren't present to protect fruit from direct sunlight. 

Early blight tends to get off to an early start in the spring when wet weather is experienced soon after transplants are set. These type conditions are ideal for infection of young tomato plants by the early blight fungus. But probably the most important reason this disease is so common has to do with the tremendous popularity of tomatoes in Southern gardens. 

What does popularity of the crop have to do with early blight? It's just difficult for most home gardeners to find a spot where tomatoes haven't been grown for awhile. As experienced gardeners know, growing a crop in the same area for several years often leads to increased disease problems. 

Early blight control is based on crop rotation, removal and destruction of crop debris from previous crops, staking, mulching, and timely application of fungicides. 

Staking and mulching are important in an early blight control program, since staking keeps foliage and fruit from contacting the soil surface, and mulching cuts down on "soil splash" onto lower parts of the plant. Since soil particles often contain the early blight fungus, this is a good way of keeping the fungus from invading plants. Plastic, or organic mulches (pine straw or even newspapers) are equally effective. 

Application of fungicides is also generally needed for early blight control. Field tests have shown that chlorothalonil, maneb, and mancozeb fungicides --- all available at gardening supply stores under a variety of trade names --- provide effective early blight control when used according to label directions and applications are started early in the season. 

As an added plus, any of these fungicides may be "tank mixed" with an insecticide such as malathion or sevin, thus allowing a single application for control of disease and insects. 

Begin fungicide applications as soon as possible after transplants are set out and continue at 7 to 10-day intervals throughout the season. Also, applications should be made after a rain. Other leaf diseases such as leaf mold, gray leaf spot, and Septoria leaf spot are controlled by these fungicides. 

Make sure to read and follow label directions concerning rates, application intervals, and the number of days required from the last application until fruit can be harvested. 

For additional information on early blight and other disease problems, check with your county Extension office.