Whatever the deficiency, the liquid fertilizer should take care of it. But if you want to know exactly which nutrient is deficient, you might be able to figure it out by looking at the specific pattern of yellowing.

If you notice your young leaves (those at the top of the plant) are yellow with green veins, suspect iron deficiency. Check your soil pH to make sure it is between 6 and 6.8. If it’s too high, your tomato can’t take up necessary nutrients including iron.

If you notice older leaves (those at the bottom of the plant) are yellow with green veins, suspect potassium deficiency.

If you notice dark spots within the yellow areas and the leaves are small and narrow, you might have a zinc deficiency.

If young leaves are pale and the growing tips of your tomato plant die, suspect calcium deficiency.

Stunted plants with general yellowing of the leaves is an indication of nitrogen deficiency.

It’s best practice to have your soil tested to confirm nutrient deficiencies before adding anything other than organic fertilizer and compost.

Adding too much synthetic fertilizer can burn your plants, and overuse of lime and wood ash can alter your soil pH causing more problems with nutrients than they prevent.

Learn about using fertilizer in your veggie garden.

YELLOW TOMATO LEAVES DUE TO PESTS

Pests are a common cause of tomato leaf problems. They are often carriers of tomato diseases as well, so it’s prudent to keep an eye out for any insects on your tomatoes. Read about some of the bugs I’ve found in my tomatoes.

Aphids love tomato plants and cause yellow, misshapen, and sticky leaves. Look for tiny insects on the undersides of leaves and on the stem. These pests will suck the sap from your tomato plant and can be a real problem in any garden.

If you notice dark spots within the yellow areas and the leaves are small and narrow, you might have a zinc deficiency.

If young leaves are pale and the growing tips of your tomato plant die, suspect calcium deficiency.

Stunted plants with general yellowing of the leaves is an indication of nitrogen deficiency.

It’s best practice to have your soil tested to confirm nutrient deficiencies before adding anything other than organic fertilizer and compost.

Adding too much synthetic fertilizer can burn your plants, and overuse of lime and wood ash can alter your soil pH causing more problems with nutrients than they prevent.

Learn about using fertilizer in your veggie garden.

YELLOW TOMATO LEAVES DUE TO PESTS

Pests are a common cause of tomato leaf problems. They are often carriers of tomato diseases as well, so it’s prudent to keep an eye out for any insects on your tomatoes. Read about some of the bugs I’ve found in my tomatoes.

Aphids love tomato plants and cause yellow, misshapen, and sticky leaves. Look for tiny insects on the undersides of leaves and on the stem. These pests will suck the sap from your tomato plant and can be a real problem in any garden.

They can be many colors, but we often see the red/pink ones. Ants love the sticky substance they excrete, and you may have an issue with both insects at the same time.

Treat aphids organically by dusting them with diatomaceous earth.

Brownish, finely dotted leaves with thin webs are an indication of spider mites. Look for tiny spider-like insects on your leaves that make fine webs between and below the leaves. Infested leaves will dry up and fall off.

Spider mites and aphids can be treated with diatomaceous earth (DE). DE is a natural substance that is readily available at local garden centers.

We use a plant duster like this one to apply diatomaceous earth to affected plants. This powder will cut through the aphids’ soft exoskeletons and cause them to dehydrate and die.

Rain and watering will negate the effect of the DE so reapply as needed. Be careful to use DE in well-ventilated areas as inhaling this powder can cause damage to your lungs. And the lungs of kids, pets, and chickens, too!

If they get really bad, other forms of organic pest control including insecticidal soaps and spinosad sprayscan also help.

YELLOW LEAVES WITH HOLES

Whenever you see holes in your tomato leaves, you should suspect insect damage. Colorado potato beetles, tomato hornworms, grasshoppers, and flea beetles are all common culprits. Remove and squish these pests when you see them and utilize organic pest control practices to manage them.

YELLOW LEAVES AND PLANTS THAT WILT

There are several kinds of wilt caused by bacteria, fungi, nematodes, and toxins that can affect tomatoes. Regardless of the cause of the wilt, it’s best to remove severely affected plants from your garden and destroy them.

For mild infections, remove affected leaves (usually the lower leaves) and send them to the landfill or burn them in an area well removed from your garden. Do not compost diseased plants or leaves.

Fusarium and Verticillium wilt cause yellowing and wilting beginning with the lower leaves.

Tomatoes planted within about 50 feet of a black walnut tree, may suddenly wilt and die. This is caused a toxin secreted from the roots of black walnut trees and tree stumps.

Nematodes in the soil can infect the roots of your plants and cause wilt. If you pull up wilted plants and notice swollen sections in the root balls, nematodes may be the problem. Choose resistant varieties and/or add parasitic nematodes to decrease the incidence of disease.

There are many varieties of tomatoes that are documented to be resistant to various types of wilt. Look for resistance codes BFNV (Bacterial, Fusarium, Nematodes, Verticillium).

A note about resistance: don’t expect resistant varieties not to be affected by these diseases. Expect them to tolerate the disease. Remove and destroy affected leaves as they appear, and the plant should continue to produce fruit for you.

YELLOW LEAVES WITH BROWN SPOTS, MOTTLED, OR DAPPLED APPEARANCE

Pale thin spots like the ones below are due to leaf burn. Leaves will experience sunburn when they haven’t been properly hardened off or when water droplets concentrate light on the leaves. If the burn is not too extensive, your plants will heal on their own and are not cause for concern.

LEAF PROBLEMS DUE TO TOMATO PLANT DISEASES

Tobacco Mosaic Virus

Dappled yellow leaves with twisty new growth are common with tobacco mosaic virus. This virus is often transmitted by insects and especially aphids.

Do not try to treat these plants. Destroy them and remove them from your property, and be sure to wash your hands after touching any plant you suspect could be infected with this virus.

When choosing tomato varieties for future gardening seasons, look for the TMV resistant label.

Bacterial Speck and Bacterial Leaf Spot

Small dark spots on leaves that then turn brown and fall off are a symptom of bacterial speck and bacterial leaf spot. These diseases thrive in hot, humid environments and can be transmitted by your hands and garden tools.

Be careful working with plants suspected to be infected with this disease. To prevent future issues, remove and destroy severely infected plants and choose varieties with BLS and PST resistance in the future.

Late Blight on tomatoes

Leaves develop brown patches that turn dry and papery when they become infected with late blight. Sometimes a white mold grows along the edges of the brown patches. If your tomato plants have late blight you will also notice blackened areas along the stems and the tomatoes develop hard brown lesions.

Late blight will wipe out your tomato crop, and there is no treatment for infected plants. So try to prevent this disease by removing and destroying infected plants. Don’t compost them. Send them to the landfill and clean and remove all remnants of the infected crops from your garden.

Here’s a video from the University of Maine about late blight:

For future crops, try applying a preventative copper fungicide or Bacillus subtilis spray, make sure to water your plants at the base as wet conditions favor the spread of this disease, and look for resistant varieties labeled LB.

Septoria Leaf Spot

Septoria leaf spot has a similar appearance, but the brown patches are circular with light centers and dark specks. And the disease will start with the older leaves. Trim off infected leaves and remove them from your garden. Sanitize your hands after dealing with infected plants.

Early Blight on tomato plants

Early blight causes spots of dark concentric rings on leaves and stem of the lower plant first.

Early blight tends to strike your tomato plants when they’re loaded with fruit and days are humid and warm.

Preventative sprays may help slow the onset and spread of the disease, but infected plants should be removed and destroyed. Look for resistant varieties labeled AB (A for Alternaria fungal species) for future gardens.

Tomato Spotted Wilt Virus

Dark brown rings on the leaves can also be caused by tomato spotted wilt virus. In this disease process, you’ll also notice brown streaks on the stems, stunted or one-sided growth, and green rings on immature fruit.

This disease is spread by tiny flying insects called thrips. Check purchase plants carefully for signs of thrips and disease before bringing them home to your garden.

Practice good pest control and remove infected plants to control the spread of this disease. Resistant varieties are labeled TSWV.

Bacterial Canker disease on tomato plant leaves

Leaves with brown edges may be caused by bacterial canker. Lower leaves will also curl up and you may see light brown streaks on the stems of your plant. This disease often shows up after plants have been injured, so be careful when trimming your plants not to leave open wounds.

A note about disease resistance:

Don’t expect resistant varieties not to be affected by these diseases. Expect them to tolerate the disease. Remove and destroy affected leaves as they appear, and the plant should continue to produce fruit for you.

TOMATO LEAF PROBLEMS YOU SHOULD NOT WORRY ABOUT

Tomato leaf curl is often an environmental change due to stress. With no other symptoms of disease, no treatment is necessary.

Purple leaves are caused by expression of anthocyanin due to light exposure. Often appearing on plants grown under intense light, there is no cause for concern or need for treatment of purple tomato leaves.

QUICK TIPS FOR DEALING WITH TOMATO LEAF PROBLEMS.

1. Make sure your plants have adequate nutrients. Try an organic liquid fertilizer first.
2. Check for pests on the stems and undersides of your tomato leaves. Remove them by hand and use organic pest control sprays retreating as needed.
3. If you do find leaves that are yellow, wilted, or spotty. Remove them immediately and dispose of them in your trash. Wash your hands after you handle any plants you suspect may be infected with fungal, bacterial, or viral diseases.
4. Plant resistant varieties remembering that even resistant plants can be affected by tomato plant diseases but will often continue to produce if cared for properly (remove infected leaves, water, fertilize).
5. Severely affected plants should be removed from the garden and disposed of as soon as possible.