Why are my tomato leaves turning yellow?

Last updated: October 2026

Yellow tomato leaves usually mean a leaf spot disease, a nutrient shortage or a wilt. Yellowing that starts on the lower leaves with brown spots points to early blight or Septoria leaf spot^2,3. Even, pale yellowing of older leaves suggests nitrogen deficiency⁶. V-shaped yellow wedges or yellowing on one side of the plant point to Verticillium or Fusarium wilt^5,1.

What does the yellowing pattern on tomato leaves tell you?

Where the yellow starts, and whether it comes with spots, narrows the cause quickly. On tomato (Solanum lycopersicum), the common leaf spot diseases begin on the lower leaves and move upward^2,3, while tomato yellow leaf curl virus yellows the margins and the tissue between the veins of young leaves first⁸. Nutrient deficiencies tend to look uniform across a whole planting, whereas plants infected with that virus appear in patches⁸.

In North America, yellow tomato leaves are searched most in June, as canopies close and early blight and Septoria leaf spot take hold in warm, wet weather; Septoria usually follows the start of fruit set. In the Southern Hemisphere, the same window falls around December.

Why are my tomato leaves yellow at the bottom?

Bottom-up yellowing has three common causes. The first is nitrogen deficiency: nitrogen is a mobile nutrient that moves to new growth when supplies run short, so older, lower leaves turn pale green to yellow first, and over time more of the plant yellows⁶. Stems may be thin, and a severe or prolonged shortage can cause leaf drop and lower yields⁶.

The second is leaf spot disease. Early blight lesions first develop on the lower leaves, the area around them may turn yellow, and as the disease progresses the whole leaf may yellow². Septoria leaf spot usually infects the lower leaves near the ground after plants begin to set fruit, and severely spotted leaves turn yellow, die and fall off¹. Both diseases tend to start as plant canopies close, because denser foliage keeps leaves wet longer⁴.

The third is a wilt disease. Verticillium wilt starts with yellowing of the lower leaves, wilting and stunting, and lower leaves die and drop as it advances⁵. Check the leaves for spots or V-shaped wedges before you fertilize, because those signs point to disease rather than a nutrient shortage^2,5.

Why are my tomato leaves yellow with brown spots?

Brown spots on yellowing leaves point to a fungal or bacterial leaf spot disease^2,1. Early blight, caused by Alternaria linariae (formerly A. solani), produces brownish-black spots of about 1/4 to 1/2 inch with characteristic concentric rings, a bull's-eye pattern^2,1. It is favored by temperatures above 80°F and moderate to heavy rain, and in later stages it can strip the lower plant, leaving fruit exposed to sunscald².

Septoria leaf spot produces smaller spots, under 1/8 inch, that are round with tan to gray centers, dark brown borders and sometimes a yellow halo³. Tiny black specks in the center are the spore-producing bodies of the fungus³. It is most active between 68°F and 77°F in high humidity, and it rarely infects the fruit^1,3.

Bacterial spot causes numerous small, angular to irregular, water-soaked spots that may have a yellow halo and whose centers dry out and tear¹. Compared with early blight, bacterial spot lesions are smaller, about 1/16 inch, and may look water-soaked on the leaf underside². Late blight is different again: its lesions are lighter tan with a light green halo, and it appears all over the plant, including young leaves².

Could a nutrient shortage be turning tomato leaves yellow?

Yes, and the leaf position tells you which nutrient. Nitrogen deficiency yellows older leaves evenly⁶. Magnesium deficiency gives older leaves yellow tissue between green veins, sometimes with leaf curling, sudden browning between the veins and early leaf drop⁷. Potassium deficiency usually yellows and scorches the margins of older leaves⁷. Iron deficiency, by contrast, affects young leaves first⁷, and shortages of micronutrients such as iron, zinc, manganese and boron can cause yellowing and deformed young leaves⁸.

Do not guess with fertilizer. Avoid adding magnesium unless a recent soil test shows a deficiency, because excess magnesium and potassium compete with calcium uptake and raise the risk of blossom end rot¹. A soil test also guides liming, which Clemson Extension recommends to bring garden soil to about pH 6.5 for tomatoes¹.

How do you tell Fusarium wilt from Verticillium wilt?

Both are soil-borne fungi that attack the water-conducting tissue, and both brown the inside of the lower stem^1,5. Fusarium wilt, a warm-weather disease, often turns the leaves on only one side of the stem golden yellow first, followed by wilting and death of the plant¹. Verticillium wilt prefers cooler weather, around 75°F to 85°F, and neutral to alkaline soil; its V-shaped leaf lesions are its distinguishing sign, and plants often wilt in the afternoon and seem to recover by morning⁵.

Neither can be cured once a plant is infected^1,5. Grow cultivars with resistance, shown by letters after the cultivar name such as FF for Fusarium races 1 and 2¹. Raising soil pH to 6.5 to 7.0 and using nitrate nitrogen rather than ammonium nitrogen slows Fusarium wilt¹. Verticillium can survive in soil for up to 10 years, so rotate away from susceptible crops for 4 to 5 years and remove infected plants promptly⁵.

How do you stop tomato leaves turning yellow from disease?

Prevention matters most, because control is difficult once leaf spot symptoms appear⁴. For early blight, use resistant or tolerant cultivars, rotate crops, remove weeds and volunteer tomatoes, space and mulch plants, avoid wetting the foliage when watering, and trim off infected lower branches and leaves¹. Volunteer tomatoes can carry early blight between seasons, so removing them reduces disease².

For Septoria leaf spot, rotate away from tomato for 2 or more years, remove crop debris, stake plants so leaves dry faster, use mulch to keep leaves off the soil, avoid working among wet plants and clean tools afterward³. Thinning plants or removing selected branches improves airflow and shortens the time leaves stay wet⁴. Where a fungicide is needed, use one labeled for vegetables, start early, before symptoms if possible, and follow the product label⁴.