Sweet basil is the herb synonymous with tomatoes, pesto, Italian dishes, and summer time. One of the biggest disappointments for herb gardeners is when the plants are about six to twelve inches tall, brown streaking appears on stems, and whole plants suddenly wilt and die. This disease is caused by a soil borne fungus, Fusarium oxysporum f. sp. basilicum, which was presumably introduced to North America on infected seeds from Italy in 1991 (Figure 1).
Many sweet basil (Ocimum basilicum) varieties, including the Genovese types, are susceptible to fusarium. Other species, such as camphor (O. kilamandscharicum) or lemon (O. americanum do not exhibit the characteristic wilting symptom of this disease, but they are hosts for the disease. Other plants in the mint family, such as rosemary and thyme also appear symptomless, but are fusarium hosts. In 199, Nufar was selected as the first Genovese basil resistant to fusarium wilt. Aroma 1 and 2 are also Genovese basil types resistant to this disease. Fusarium-resistant varieties are available from several mail order seed companies.
Fusarium is introduced into the growing medium (soil, potting mix, hydroponic systems) from contaminated seed and can persist in the soil for eight to twelve years. Asymptomatic plants, such as mints, will also carry over the inoculum from year to year. Currently there are no products registered to control this disease. Thus, the use of disease-resistant seed is recommended to prevent this disease. If susceptible basil varieties are planted, annual replacement of the growing medium is recommended for container grown plants. In the garden, rotate basil to a different part of the site each year and remove all plant debris after the final harvest.
REVISED: September 29, 2015