Thai Basil Plant Diseases
No herb garden is complete without at least one variety of basil (Ocimum basilicum). If you enjoy Asian cuisine, such as curries, you might want to grow Thai basil, which has smaller leaves and a more intense licorice flavor than sweet basil. Although basil is typically easy to grow, all varieties, including Thai basil, are susceptible to diseases if the ideal conditions aren't provided or if the seeds or plants are infected.
Several types of disease caused by fungi affect Thai basil and other varieties. A common type of fungal infection is fusarium wilt of basil, caused by Fusarium oxysporum f. sp. basilicum. The fungus is soilborne and can live in the soil for several years. Fusarium wilt causes the plant's leaves to turn brown and the entire plant to wilt. Downy mildew is another fungal infection that affects basil, although Thai basil varieties seem to be less affected than other types. The mildew causes the basil leaves to yellow. Fuzzy gray spores also develop on the underside of the leaves. Other fungal diseases that can affect Thai basil include leaf spots and fungal root rot.
Bacteria can cause some of the diseases that plaque Thai basil. Ralstonia solanacearum causes bacterial wilt of the plant's stems. The bacteria are found in the soil and enter the plant through the roots. While the stem turns mushy, the leaves remain healthy looking. Pseudomonas cichorii bacteria cause leaf spots on basil plants. Areas of brown or black spotting appear on infected plants. The bacteria can be spread easily from plant to plant by touch.
Your reaction if you notice disease on your Thai basil plant depends on the type of disease. Plants that are infected with fusarium wilt or bacterial wilt should be pulled out and thrown out as soon as the symptoms are noticed. Also remove soil from the area, because the fungi or bacteria live in the soil. Plants infected with leaf spot should also be removed from the garden. Spraying the basil with fungicide regularly and before the appearance of symptoms can help control downy mildew.
Avoid planting Thai basil in a spot that has had any type of disease in the past few years. Rotate the location of the basil plants each season to reduce the risk of disease. To keep disease under control, give each plant an ample amount of space to encourage good air circulation. Avoid watering the leaves of the plants, which can encourage fungal or bacterial infections. Choose seeds or plants that have been tested and found to be free of diseases such as fusarium wilt.
Based in Pennsylvania, Emily Weller has been writing professionally since 2007, when she began writing theater reviews Off-Off Broadway productions. Since then, she has written for TheNest, ModernMom and Rhode Island Home and Design magazine, among others. Weller attended CUNY/Brooklyn college and Temple University.