Do Insects or Diseases Affect Basil Plants?

Foliar Fungal Disease

• Basil plants are at risk of developing fungal disease if the soil remains too moist. Basil requires water to grow, but to prevent diseases such as foliar fungal disease, avoid dousing the basil's leaves with water. Instead, water the ground around the basil plant. If you typically water the plant from above, splashing the leaves, do so in warm weather so the water evaporates quickly, recommends the North Carolina State University Extension.

Fusarium Oxysporum

• Fusarium oxysporum is a devastating soil-borne disease that can easily wipe out your basil crop and spread to other herbs in your garden. Symptoms of this disease include discoloration of the leaves and stem of the basil, which will die quickly. Sweet basil is most at risk of this disease; other varieties are more resistant.

Slugs and Caterpillars

• Slugs and caterpillars will frequently eat holes in the leaves of basil plants. While this problem doesn't necessarily kill plants, it does stunt growth, affecting yield. Select herbicides such as Javelin work to kill caterpillars in your garden. If you see slugs frequently, dig a hole in the garden and place a cup filled with beer in the hole. Slugs will be attracted to the sweet, yeast flavor of the beer, fall in and drown.

Other

• Beetles, especially Japanese beetles, can quickly eat through the leaves of your basil plant, giving them a skeleton-like appearance. Other insects that frequently target basil plants include whiteflies, aphids, spider mites and even grasshoppers. Garden centers offer insecticide treatments to deter these pests. You can sprinkle soap shavings around your garden to deter some insects.