Many home gardeners enjoy growing tomato plants, which flourish without much maintenance if planted in sunny locations with plenty of water. However, tomatoes tend to succumb to several types of fungal infections. Many of these first appear on the lower, or oldest, leaves of the plant, where the sun doesn't always hit to dry them quickly after watering or a rain shower.
Fungal infections
Fungal infections are the most likely culprits if your tomato plants have lower leaves that are beginning to wilt and die. The fungus typically flourishes in the moist heat of summer, just as the tomato plants are starting to fruit. Possible fungal infections include Fusarium wilt, early blight, late blight or Septoria leaf spot. Although these each present with different symptoms, all tend to affect the lower leaves first.
Fungi symptoms
Look closely at the wilting leaves for signs of fungal infection. With Fusarium wilt, the leaf veins turn lighter than the rest of the leaves, called vein clearing. Entire stems of leaves begin to yellow and wilt quickly, often along one side of the plant. Early leaf blight appears as dark spots of concentric circles that grow and multiply, causing leaves to wilt. In late blight infections, the leaves develop light green spots along the edges that grow inward and turn dark, causing the leaves to wilt from the outside in. You might see white, downy fungus growth on the leaves' undersides. Septoria leaf spot causes gray or tan spots with dark edges to appear on the leaves. Infected leaves turn yellow and die.
What to do?
When your tomatoes become infected with a fungus, there's no way to cure them. Remove the infected plants immediately to stop the spread to healthy plants and don't plant in infected soil the next year, if possible. In smaller gardens where there's not room to rotate the tomato plants each year, treat the soil with a fungicide such as mancozeb or benomyl. To help keep the fungus from spreading, treat uninfected plants nearby by mixing the fungicide according to the manufacturer's directions and spraying the plant leaves and the soil underneath the plants. For benomyl, for example, mix 1/2 ounce with 5 gallons of water for the spray. Mix 1 to 3 ounces of mancozeb with 5 gallons of water. The best type of fungicide for your problem might vary, so check the label carefully to ensure the fungicide you choose works with the fungus you suspect.
How to prevent infections?
The best way to address fungal infections is to prevent them. Space your plants at least 24 inches apart to allow proper airflow around the leaves. Water the plants from the base when possible, using either a drip irrigation system or a watering can. If you water using regular sprinklers that wet the entire plant, water in the morning so the plants can dry out before nightfall. Choosing the right type of tomato can also prevent infections; many are resistant to certain fungal infections. Resistance is shown on the seedling labels with letter codes such as "F" for Fusarium wilt.
Fungal infections are the most likely culprits if your tomato plants have lower leaves that are beginning to wilt and die. The fungus typically flourishes in the moist heat of summer, just as the tomato plants are starting to fruit. Possible fungal infections include Fusarium wilt, early blight, late blight or Septoria leaf spot. Although these each present with different symptoms, all tend to affect the lower leaves first.
Fungi symptoms
Look closely at the wilting leaves for signs of fungal infection. With Fusarium wilt, the leaf veins turn lighter than the rest of the leaves, called vein clearing. Entire stems of leaves begin to yellow and wilt quickly, often along one side of the plant. Early leaf blight appears as dark spots of concentric circles that grow and multiply, causing leaves to wilt. In late blight infections, the leaves develop light green spots along the edges that grow inward and turn dark, causing the leaves to wilt from the outside in. You might see white, downy fungus growth on the leaves' undersides. Septoria leaf spot causes gray or tan spots with dark edges to appear on the leaves. Infected leaves turn yellow and die.
What to do?
When your tomatoes become infected with a fungus, there's no way to cure them. Remove the infected plants immediately to stop the spread to healthy plants and don't plant in infected soil the next year, if possible. In smaller gardens where there's not room to rotate the tomato plants each year, treat the soil with a fungicide such as mancozeb or benomyl. To help keep the fungus from spreading, treat uninfected plants nearby by mixing the fungicide according to the manufacturer's directions and spraying the plant leaves and the soil underneath the plants. For benomyl, for example, mix 1/2 ounce with 5 gallons of water for the spray. Mix 1 to 3 ounces of mancozeb with 5 gallons of water. The best type of fungicide for your problem might vary, so check the label carefully to ensure the fungicide you choose works with the fungus you suspect.
How to prevent infections?
The best way to address fungal infections is to prevent them. Space your plants at least 24 inches apart to allow proper airflow around the leaves. Water the plants from the base when possible, using either a drip irrigation system or a watering can. If you water using regular sprinklers that wet the entire plant, water in the morning so the plants can dry out before nightfall. Choosing the right type of tomato can also prevent infections; many are resistant to certain fungal infections. Resistance is shown on the seedling labels with letter codes such as "F" for Fusarium wilt.
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