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Lettuce pests and diseases

Published: 09.04.2023
pest/disease type symptoms on lettuce control/prevention
Aphids Pest Tiny insects that cluster on new growth or under leaves, often covered in a sticky substance called honeydew Regularly check for aphids and remove them with a strong stream of water, insecticidal soap or neem oil spray
Armyworms Pest Green or brown caterpillars that feed on lettuce leaves, leaving large holes Handpick and remove armyworms, use Bacillus thuringiensis (Bt) spray
Cabbage loopers Pest Green caterpillars that move in a loop-like motion, feed on lettuce leaves Use row covers to prevent infestation, handpick and remove cabbage loopers, use Bt spray
Cutworms Pest Brown or gray caterpillars that feed on stems of young lettuce plants, causing them to fall over Use cardboard or plastic collars around stems of young plants, handpick and remove cutworms, use Bt spray
Leaf miners Pest Larvae tunnel into lettuce leaves and create discolored trails or blotches Remove affected leaves, use sticky traps or parasitic wasps to control adult leaf miners
Slugs and snails Pest Slimy mollusks that feed on lettuce leaves, leaving irregular holes Handpick slugs and snails, use copper tape or diatomaceous earth to create a barrier around plants, use iron phosphate bait
Powdery mildew Disease White powdery spots on lettuce leaves, can cause leaves to become distorted and stunted Improve air circulation around plants, avoid overhead watering, use fungicidal soap or neem oil spray
Downy mildew Disease Yellow or pale green spots on lettuce leaves, fluffy white growth on underside of leaves Remove affected leaves, improve air circulation, avoid overhead watering, use fungicidal soap or copper-based fungicides.
Bacterial leaf spot Disease Water-soaked lesions on lettuce leaves, which turn brown or black and may have yellow halos Avoid overhead watering, remove affected leaves, use copper-based fungicides
Fusarium wilt Disease Yellowing and wilting of lower leaves, brown discoloration of stem Remove infected plants and soil, avoid planting lettuce in the affected soil, use resistant lettuce varieties.


Aphids are tiny, soft-bodied insects that are commonly found on lettuce plants. They are pear-shaped and can be green, yellow, brown, or black in color. Aphids suck the sap from the leaves, causing them to wilt and become distorted. They also excrete a sticky substance called honeydew, which can attract other pests and cause fungal diseases to develop on the plant.

Symptoms of aphid infestation include curling leaves, stunted growth, and yellowing of leaves. If left untreated, aphids can quickly reproduce and spread to other plants in the garden.

To control or prevent aphids, you can use insecticidal soap or neem oil. These natural remedies will kill the aphids without harming beneficial insects like ladybugs and lacewings. You can also use a strong jet of water to wash them off the plant.

To prevent aphids from infesting your lettuce plants in the first place, make sure to keep your garden clean and free of weeds. Remove any plant debris or weeds that could provide a habitat for aphids. You can also introduce beneficial insects like ladybugs or lacewings to your garden to help control aphid populations.


Armyworms are one of the most destructive pests that can infest a lettuce garden. These caterpillars are voracious eaters and can cause extensive damage to your lettuce crop if left unchecked.


The first sign of armyworm infestation is usually the appearance of ragged holes in the leaves of your lettuce plants. As the infestation progresses, you may notice that entire leaves have been stripped of their foliage. You may also see clusters of small green or brown caterpillars on the undersides of the leaves.

Control and Prevention

The best way to control armyworms is to catch the infestation early. Inspect your lettuce plants regularly and remove any caterpillars that you find. If the infestation is more severe, you may need to use an insecticide to control the population.

To prevent future infestations, keep your garden clean and free of debris, as armyworms can overwinter in plant debris. You can also use floating row covers to protect your lettuce plants from adult moths, which are the source of armyworm eggs.

In conclusion, armyworms can be a serious threat to your lettuce garden, but with vigilant monitoring and proper control measures, you can keep them at bay and enjoy a healthy crop.

Cabbage Loopers

Cabbage loopers are a common pest that can damage not only cabbage but also lettuce plants. These pests are the larvae of a small, brownish-gray moth with a distinctive white mark on each of its wings. The larvae are light green in color with white stripes running down their backs, giving them a distinctive looping motion as they move.


Cabbage loopers can cause serious damage to lettuce plants by chewing on leaves, causing large ragged holes. The larvae will also leave behind dark green or black droppings on the leaves, which can lead to fungal diseases.

Control and Prevention

The best way to control cabbage loopers is to prevent them from laying eggs on your plants. You can do this by using row covers or insect netting to keep the moths away from your plants. If you do find cabbage loopers on your lettuce plants, you can use Bacillus thuringiensis (Bt) as a natural insecticide. Bt is a bacteria that targets only the larvae of moths and butterflies, leaving beneficial insects unharmed.

Another effective method is to spray the leaves of your lettuce plants with a mixture of water and dish soap. This will kill the cabbage loopers on contact without harming your plants. If you prefer an organic solution, you can use neem oil or pyrethrin-based insecticides.

In summary, cabbage loopers can cause serious damage to your lettuce plants if left untreated. By using preventive measures and natural insecticides, you can keep these pests at bay and enjoy healthy, delicious lettuce all season long.


Cutworms are a common pest that can devastate a lettuce crop in a matter of days. These caterpillars can be found hiding in the soil during the day and feeding on the lettuce leaves at night. They are most active in the early spring and late fall.

Symptoms of cutworm damage include plants that have been cut off at the base, or wilted leaves with ragged edges. You may also notice small brown pellets near the base of the plant, which are a telltale sign of cutworms.

To prevent cutworm damage, use row covers to protect young lettuce plants. You can also sprinkle diatomaceous earth around the base of your plants, which will kill any cutworms that come in contact with it. If you do find cutworms in your garden, handpicking them off your plants is an effective control method.

If you prefer a more hands-off approach, you can use a biological control such as Bacillus thuringiensis (Bt) or Steinernema feltiae nematodes to kill cutworms. These methods are safe for both humans and pets and will not harm beneficial insects. By taking these preventative measures, you can keep your lettuce crop healthy and free from cutworm damage.

Leaf Miners

Leaf miners are pests that can attack lettuce and other plants in your garden. They are tiny insects that lay eggs on the leaves of plants, and when the eggs hatch, the larvae burrow into the leaves and start to feed on the plant tissue. This can cause damage to the leaves and can even kill the plant if left untreated.


The most common symptom of leaf miner infestation is a series of small, winding tunnels on the surface of the leaves. These tunnels can be seen by holding the leaf up to the light, as they will appear as dark lines. The tunnels themselves are not harmful to the plant, but they weaken it and make it more susceptible to disease.

Control or Prevention

The best way to prevent leaf miners is to keep your garden clean and free of debris. This will reduce the chances of the insects finding a place to lay their eggs. You can also use sticky traps or insecticidal sprays to control the population of leaf miners in your garden.

If you do find leaf miners in your garden, it is important to act quickly. Remove any affected leaves and dispose of them properly. You can also try using neem oil or insecticidal soap to control the population. Be sure to follow the instructions on the label carefully, as these products can be harmful if used incorrectly.

In conclusion, leaf miners are a common pest that can be found in lettuce and other plants in your garden. By keeping your garden clean and using insecticidal sprays or sticky traps, you can prevent or control their population and keep your plants healthy.

Slugs and Snails

Slugs and snails are common pests that can wreak havoc on lettuce and other leafy vegetables. These slimy creatures feed on the tender leaves, leaving behind large holes and unsightly trails of slime.


Signs of a slug or snail infestation include irregular holes in the leaves, slime trails on the ground or plants, and damage to young seedlings. These pests are most active at night, so it may be difficult to spot them during the day.

Control or Prevention

Preventing slug and snail infestations is key to keeping your lettuce crop healthy. One way to do this is by keeping your garden area clean and free of debris, which can provide hiding places for these pests. You can also create a physical barrier around your lettuce plants using copper tape or mesh.

Another effective method is to use beer traps. Simply bury a small container of beer in the soil near your plants, and slugs and snails will be attracted to it and drown. There are also organic slug and snail baits available that use iron phosphate as the active ingredient.

In conclusion, slugs and snails can be a frustrating pest to deal with in your lettuce garden, but with proper prevention and control methods, you can keep these slimy creatures at bay and enjoy a healthy harvest.

Powdery Mildew

Powdery mildew is a common fungal disease that can affect a wide range of plants, including lettuce. This disease is caused by various species of fungi that produce a white, powdery growth on the leaves, stems, and flowers of infected plants.


The initial symptoms of powdery mildew include the appearance of small, white spots on the leaves. As the disease progresses, these spots will grow and merge, forming a white or grayish powdery coating on the leaves. Infected leaves may also become distorted or stunted, and in severe cases, the plant may die.

Control and Prevention

Preventing powdery mildew from spreading to your lettuce plants is key to controlling this disease. Some effective prevention measures include ensuring proper air circulation around plants by spacing them out properly and avoiding overcrowding. Additionally, avoid watering your plants from above as this can create a moist environment that promotes fungal growth.

If you do spot signs of powdery mildew on your lettuce plants, you can try removing infected leaves or using organic fungicides to control the disease. Organic fungicides like sulfur or neem oil can be effective in controlling powdery mildew without harming beneficial insects.

In conclusion, early detection and prevention are critical in controlling powdery mildew in lettuce plants. Proper cultural practices like maintaining good air circulation and avoiding overhead watering can go a long way in preventing this disease from taking hold in your garden.

Downy Mildew

Downy mildew is a common disease that affects lettuce plants. It is caused by the fungal pathogen Peronospora farinosa f. sp. lactucae and can cause significant damage to lettuce crops.

Symptoms: The symptoms of downy mildew include yellowing and browning of leaves, white or grayish-blue fungal growth on the undersides of leaves, and stunted growth. The fungus can also cause the leaves to become distorted, making it difficult for the plant to photosynthesize.

Control or Prevention: To prevent downy mildew, it's important to maintain good hygiene in your garden. Ensure proper spacing between plants to promote good air circulation and avoid overcrowding. Water the plants early in the day to give them enough time to dry before nightfall. Use a fungicide specifically designed for downy mildew control, following the manufacturer's instructions carefully.

If downy mildew has already affected your lettuce plants, remove any infected plant parts and destroy them. Do not compost them as the fungus can survive in compost. Also, consider rotating your crops to prevent a recurrence of downy mildew in the same area.

In conclusion, downy mildew can be devastating to lettuce plants, but with proper prevention and control measures, it can be managed effectively.

Bacterial Leaf Spot

Bacterial leaf spot is a common disease that affects lettuce plants. It is caused by the bacterium Xanthomonas campestris, which thrives in warm and humid conditions. This disease can cause severe damage to the lettuce crop, making it important to identify and control it early.


The first symptoms of bacterial leaf spot are small, water-soaked spots on the leaves. These spots may be yellow or brown in color and may appear greasy or oily. As the disease progresses, the spots may become larger and more numerous, causing the leaves to turn brown and wilt. In severe cases, the entire plant may die.

Control and Prevention

Preventing bacterial leaf spot is easier than controlling it once it has infected your plants. You should start by planting disease-resistant varieties of lettuce and ensuring that your garden has good air circulation. Additionally, you should avoid overhead watering, as this can spread the bacteria.

If you do notice symptoms of bacterial leaf spot, you should remove any infected plants immediately to prevent the disease from spreading. You can also apply copper-based fungicides to help control the spread of the bacteria.

In conclusion, bacterial leaf spot can be a devastating disease for your lettuce plants. However, with proper prevention and control measures, you can ensure that your garden remains healthy and productive.

Fusarium Wilt

Fusarium wilt is a soil-borne fungal disease that affects a wide range of plants, including lettuce. The fungus enters the plant through the roots and blocks the water-conducting vessels, causing wilting, yellowing, and eventual death of the plant. Fusarium wilt can survive in the soil for many years, making it difficult to control once it becomes established.

Symptoms of Fusarium wilt in lettuce include yellowing and wilting of the leaves, starting from the bottom of the plant and moving upwards. The leaves may also appear stunted and twisted, and the veins may turn brown. Eventually, the entire plant will wilt and die.

Preventing Fusarium wilt is the best approach since there are no effective treatments for infected plants. To prevent Fusarium wilt in lettuce, use disease-resistant varieties, rotate crops regularly, avoid overwatering, and keep the soil well-drained. If you suspect your soil is contaminated with Fusarium wilt, avoid planting susceptible crops in that area for several years.

In summary, Fusarium wilt is a serious disease that can affect lettuce and other plants. Prevention is key to avoiding this disease since there are no effective treatments once a plant is infected. Regular crop rotation, proper watering, and use of disease-resistant varieties can help to prevent Fusarium wilt in lettuce.

Author: Michael Chen
Bio: I'm gardening specialist with a mission to empower people to grow their own fruits and vegetables. With my background in Plant Science from the University of California and experience working with farmers and community gardens, I'm dedicated to promoting sustainable agriculture practices and helping individuals achieve bountiful harvests. Let's get growing!