Check these first
- Does the yellowing start at the bottom of the plant or at the tips?
- Are the veins still green while the rest of the leaf fades? That points to a nutrient deficiency.
- Look under the leaves for tiny insects or white specks.
Most likely causes
From the pests and diseases recorded for this plant, the ones whose symptoms match, most serious first. Symptoms alone rarely confirm a cause, so use the linked page to check the signs and treatment.
Downy Mildew
Pale yellow to yellow-brown angular lesions form on the upper leaf surface with a gray-purple mold in the matching spot underneath. Lesions merge, the leaves die back and the plant declines early.
How to identify and treat: Downy MildewFusarium Wilt
Lower leaves wilt during the day and recover morning and evening, and this cycle repeats as the plant dies back. Cutting the stem reveals characteristic browning of the vascular tissue.
How to identify and treat: Fusarium WiltEtiolation
Internodes stretch long, stems are thin and leaf color is pale. The plant topples easily and becomes vulnerable to pests and disease.
How to identify and treat: EtiolationOther possible causes
- Waterlogging Root Decay — The plant wilts even though the soil never dries, and the lower leaves yellow. Pull it up …
- Root Rot — Fine roots rot brown to blackish brown, growth stops and the lower leaves yellow. The plan…
Other symptoms on this plant
What other growers did about it
A page like this one can tell you what basil leaves turning yellow is and what to try. What it cannot tell you is what actually happened to someone who had it on the same plant, at the same point in the season, and what they did next.
Gadenin is a free garden journal built around that. You photograph the plant, tag what you are seeing, and the entries line up by date for each plant you grow.
- Tag the problem and the app tells you how many other growers have logged the same thing on the same plant.
- Growers who make their records public can be followed, so you can read what they did and how it turned out.
- Next season your own entries come back at the same point in the year, so you check the plant before it starts.
Free on iPhone. Recording, tagging and reading public records cost nothing.