Early Blight of Tomato Plants

Tomato plants are common for growth in home gardens because of their ease of growth and quality of fruit. There are hundreds of tomato plant varieties. Growing location, climate and soil conditions are all important factors to consider when choosing a tomato cultivator. Early blight of tomato plants is an important and devastating disease that affects many tomato plant species.

Causes and Favorable Conditions

Alternaria solani is the fungus that causes early blight of tomato plants. The fungus germinates during periods of free moisture and temperatures ranging from 80 to 85 degrees F, according to The University of Maine Cooperative Extension. However, the fungus can still germinate during cooler temperatures, but the process takes longer. Once the fungus germinates on the tomato plant, it requires 3 to 12 hours to penetrate and infect the plant, according to The University of Maine Cooperative Extension. However, infection typically occurs on stressed tomato plants that have reduced natural defenses.

Symptoms

Symptoms of early blight on tomato plants vary as the disease develops on the plant tissue. Early symptoms appear on older, susceptible leaves, consisting of dark brown to black spots on leaves and dead spots on the leaf surface up to one half of an inch in diameter, according to the Ohio State University Fact Sheet Extension. As the fungus develops, it can cause stem legions, collar rot, blossom rot, and spotting on fruits, according to the Ohio State University Factsheet Extension. Identifying early symptoms are important for controlling the disease before infection spreads to nearby tomato plants and damages fruit production.

Prevention and Control

Because Alternaria solani requires free moisture and high temperatures to infect tomato plants, it is important to increase airflow and reduce excess moisture on the plant surface. The Michigan State University recommends staking tomato plants to reduce foliage from coming in contact with the ground, thus reducing free moisture and preventing an early blight infection. To prevent infection, use early blight resistant tomato plant species. However, maintaining proper fertilization and reducing stress can prevent infection in disease susceptible varieties. Control for early blight consists of fungicidal spray early in the growing season during initial infection, according to the Michigan State University. The Ohio State University Extension Fact Sheet reports that fungicidal control is also an effective method of preventing disease in susceptible tomato crops if done 2 to 3 weeks after emergence.

Sources:

http://urbanext.illinois.edu/veggies/tomato.cfm

http://pmo.umext.maine.edu/factsht/earlytom.htm

http://ohioline.osu.edu/hyg-fact/3000/3101.html