Basil is one of the easiest herbs to grow at home and is far less susceptible to pests and disease than some other herbs. That said, problems can always arise and it’s best to diagnose them right away in order to treat them before they get out of hand. Here’s a list of some common problems when growing basil.
Damping-off is a name given to a condition that attacks the seeds or the roots of young plants during wet, cool conditions. Seedlings may look healthy and then suddenly topple over and die. This is caused by a number of different fungal agents, but if your basil is planted in soil with poor drainage and fertility, it is all the more susceptible. Do not over water. Basil can’t stand sitting in damp conditions. Sterilizing containers before planting basil is also a must, since diseases can hang around for a while even after the previous plant is long gone.
Usually caused by poor drainage and over watering, root rot is another type of fungal disease that will stunt your plants and eventually kill them. They may lose color and begin to die. Roots may appear dark and slimy. Lay off watering. If your soil is poor and your basil does not recover, you may need to replant.
Leaf Spot Disease
Leaf spot is caused by a bacterial infection that causes spots on the leaves and streaks on the stems. Remove any infected leaves as soon as you see them so this disease does not spread. Overhead watering and damp foliage can contribute to leaf spot. Water at the base of the plant and try to water in the morning so the foliage has adequate time to dry throughout the day.
Sweet basil is most susceptible to fusarium wilt, which causes stunted plants, wilted yellow leaves, twisted stems, brown spots and streaks on the stems, and the leaves to drop. This fungus grows in the soil and can be transmitted through infected leaves. Destroy infected plants and avoid planting in that area for 3 years.
Downy mildew is any number of microbes that can attack basil plants. Look for yellow leaves with fuzzy, grey growth on the underside. Good air circulation and keeping the foliage dry is the best way to avoid downy mildew. Remove infected leaves and stems to prevent it from spreading.
Root Knot Nematodes
Nematodes are worm-like creatures that live in the soil and cause your basil to wilt and turn yellow. The roots may be swollen and disfigured when nematodes are present. Till your soil deeply to disturb any possible nematode presence but crop rotation is the best way to avoid them. Otherwise, try growing basil in pots and replanting every year.
Aphids suck plant juice and leave behind a sticky substance called honeydew. They can be found on the undersides of the leaves. They are usually semi-green or yellow (but can be red, black or other colors too), with almost transparent bodies. Blast them off with water. If let be they can do serious damage to your basil plant.
Flea beetles chew tiny holes in the basil leaves. They can usually be blasted off with water. Spray them with insecticidal soap if that doesn’t do the trick.
When you shake your basil plant and a ‘cloud’ of insects rise up and then settle back down, you have whiteflies. Much like aphids, they suck the life out of plants if left unhindered. Spray them with water or insecticidal soap.
Snails and Slugs
Chewed leaves accompanied by silver streaks is likely the work of snails or slugs. Pick them off if you see them. Use beer traps or copper fencing if they are a real problem.
Wilting, yellow leaves and poor growth may be a symptom of nitrogen and other nutrient deficiency. Feed your plants with a liquid organic fertilizer that is high in nitrogen to reverse the problem. Disease can also cause these symptoms. So if fertilizing doesn’t correct it, look to nematodes or another problem listed above.
Always plant basil in fertile soil that drains really well.
Water wisely. Poor drainage combined with too much water is one of the fastest ways to see fungus and other diseases settle in your basil.
Harvest regularly. Even if you aren’t using all that much basil, picking leaves often will encourage new growth and keep air circulation good.
Feed or replant container basil to ensure they have all the nutrients they need.
Do not plant too early. Basil does well indoors, so avoid putting it outside before it’s time.