Common Disease Problems
Bacterial Leaf Spot: Water-soaked brown or black spots appear on the leaves and streaking on stems. The spots are angular or irregular in shape. Burpee Recommends: Avoid planting in the same location in the future, planting in containers can help. This disease may not kill the plant.
Botrytis Blight: Also called gray mold, this causes a brown to gray fungus on plant leaves and stems. Diseased leaves die and fall off. If the infection is severe on the main stem the plant may die. The condition thrives in high humidity and cooler temperatures. Burpee Recommends: Remove infected plants and plant debris and clean tools before working with plants to avoid the spread of the disease and make sure plants have good air circulation.
Downy Mildew: Leaves turn yellow around the middle vein and the disease spreads, eventually turning grayish purple and fuzzy. Burpee Recommends: Make sure the plants have plenty of air circulation, avoid getting water of the foliage when watering, remove infected plant material. Do not plant susceptible plants in the same location next year. Planting in containers can help.
Fusarium Wilt: This soil borne disease causes stunted and wilted plants and yellowish leaves. Brown streaks may occur on the stems and later signs of the disease are twisted stems and leaf drop. The stem tissue is discolored. Burpee Recommends: Because the spores live many years in the soil, do not plant any members of the mint family in the same area. The disease is worse in poorly drained soil. Plant in containers.
Root-Knot Nematodes: Classified as either a disease or pest, nematodes are microscopic worms feeding on the roots and may cause what looks like a nutrient deficiency, wilting and poor growth. Burpee Recommends: Avoid planting in the same area as the nematodes are difficult to eradicate. Plant in containers.
Common Pest and Cultural Problems
Plants die after blooming: Basil is an annual that will stop producing after it blooms. Pinch off the flowers before they set seed to prolong the life of the plant.
Leaves turn black overnight: Basil is very sensitive to cold temperatures and will turn black with any frost.
Aphids: Greenish, red, black or peach colored sucking insects that can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Japanese Beetles: Burpee Recommends: Hand pick early in the morning into a bucket of soapy water.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.
Why does my basil taste bitter? Your plants have probably started to flower in the heat of summer and this will make the leaves taste bitter. At this stage the plants will no longer be productive.
How can I use basil in a vinegar? Take clean leaves of fresh picked basil. Use about ½ cup of fresh herbs to a pint of distilled white vinegar. Pour the vinegar over the basil into a clean glass bottle, cover tightly and place in a sunny location for two weeks to steep. After this time you can strain the liquid and rebottle if you prefer a clearer liquid. Taste the vinegar, and if you prefer it to be stronger add more leaves and steep for another two weeks.
How many plants do I need to make pesto? Six plants of a large leafed variety would be ideal for making pesto.
What is the best basil to use to make pesto? We recommend Genovese for pesto.
Can I grow basil hydroponically? Yes, basil works well as a hydroponic plant.