My Basil Leaves Are Drying Up: What Is Wrong?

Fungal Diseases of Basil

• Basil plants are susceptible to a number of diseases that can cause leaves to dry and wilt. The most common disease that causes leaves to dry up is fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. basilicum. The leaves on infected plants 6 to 12 inches tall will become dry and wilted, and eventually drop off. You may also notice brown streaking on basil plant stems. Curiously, only sweet basil is affected by this disease. Less popular varieties like purple basil and lemon basil show strong resistance to the fungus.

Cultural Problems

• In addition to fusarium wilt, dried leaves can be an indication of other, potentially less serious problems with your basil plants as well. Simple drought stress due to under-watering or competition from invasive weeds or other plants nearby can quickly cause wilting and drying of leaves. Over-fertilization can encourage plant growth to the degree that plant nutrients and moisture are diverted away from leaf production into stem and flower production, in extreme cases also leading to leaf drying and wilting.

Treatment for Non-Fungal Problems

• Drought stress should be treated by simply adopting a more frequent watering schedule to provide the basil plants with the moisture they are lacking. If your plants show signs of over-fertilizing, adjust your fertilization schedule to one recommended for basil plants and for your geographic area (consult local university extension services for advice).

  Weed and invasive crops should be treated with biological methods first; resort to herbicides and other chemical control methods only as a last resort and only use ones that are safe for use on or near food plants.

Fusarium Wilt Control

• Control options for fusarium wilt are unfortunately limited. Growers should immediately remove and discard all diseased parts of the plants to prevent the spread of the disease to other basil plants. As much as is possible, keep basil leaves dry after you water them since wet leaves are more prone to fungal infections. Depending on your geographic area, there may be few or no fungicides approved for fusarium wilt treatment, since chemical fungicides are regulated on a state by state basis.

  In cases of extreme infection, simply remove the plants and consider planting a more disease-resistant cultivar such as purple or lemon basil. Also consider planting basil crops in a new location away from where the diseased basil grew to avoid infection from fungi that live in the soil underneath the plants.