Cucumber Anthracnose Treatment: Tips For Anthracnose Control In Cucumbers

Cucumber Anthracnose Treatment: Tips For Anthracnose Control In Cucumbers

By: Amy Grant

Anthracnose in cucumber crops can cause serious economic losses to commercial growers. This disease also afflicts most other cucurbits as well as many non-cucurbit species. The symptoms of cucumbers with anthracnose disease are often confused with other foliar diseases, which makes anthracnose control in cucumbers difficult. The following article discusses how to identify this disease and cucumber anthracnose treatment.

What is Cucumber Anthracnose Disease?

Anthracnose in cucumbers is a fungal disease caused by the fungus Colletotrichum orbiculare (C. lagenarium). It afflicts most cucurbits, other vine crops, and cucurbit weeds. Squash and pumpkins, however, are primarily immune to the disease.

In cucumbers, this disease is fostered by seasons of warm temperatures combined with frequent rain. When anthracnose control in cucumbers is not implemented, losses of 30% or more may be realized.

Symptoms of Cucumbers with Anthracnose

The symptoms of anthracnose vary somewhat from host to host. All aboveground parts of the plant may become infected. The first signs in cucumber crops appear on the leaves. Small water-soaked lesions appear, enlarging rapidly as the disease advances and becoming irregular in shape and darker in color.

The centers of older leaf lesions may fall out, giving the leaf a “shot hole” appearance. Lesions begin to appear on stems as well as fruit if present. On fruit, the pinkish spore masses are clearly visible.

As mentioned, anthracnose in cucumber crops may be confused with other diseases. Correct identification can be made using a hand lens or microscope. Anthracnose disease will appear as pink spore masses marred by hair-like structures.

Cucumber Anthracnose Control

Controlling anthracnose is a multi-tiered approach. First, plant only disease-free certified seed and sow only in well-draining soil free of runoff water.

Be sure to rotate with a crop other than another cucurbit every three years or longer. Control all weeds surrounding the cucumber crop and avoid handling the crop when it is wet, which can further spread the disease.

Fungicides can aid in controlling this fungal disease affecting cucumber crops. They will need to be applied more frequently during rainy periods. Those available are both chemical and organic. Organic options include potassium bicarbonate, coppers, Bacillus subtilis, and some horticultural oils. Follow the instructions provided by the manufacturer.

If a field has been infected with cucumber anthracnose disease, burn or cleanly plow down any infected plant debris.

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Anthracnose of Cucurbits

We have recently received several cucurbit samples in the Plant Disease Clinic with anthracnose. Anthracnose is a common fungal disease of cucurbits, including watermelons, muskmelons, and cucumbers. Squash and pumpkins are rarely affected by anthracnose.

Anthracnose causes small, yellow, water soaked lesions to appear on the leaves near the veins. Over time these lesions enlarge and turn brown and the dead tissue may fall out, creating holes in the leaves. Spots on watermelon leaves are irregular in shape and turn dark brown or black. Lesions on cucumber and muskmelon leaves tend to be round, brown, and quite large. When lesions occur on the stems, they may cause wilting of the foliage when the stems are girdled. Round, sunken, water soaked lesions also may appear on the fruits. In moist weather, the center of these spots may be covered by slimy, salmon-colored spore masses.

Anthracnose is caused by a fungus, Colletotrichum lagenarium. It is favored by warm, wet conditions. Although initial infection usually occurs in the spring, the disease typically does not become established until mid-season when the canopy is fully developed.

The fungus that causes anthracnose can survive the winter on cucurbit residue therefore, all diseased debris should be removed or plowed under at the end of the season. Growing cucurbits in a three-year rotation with other types of crops can help prevent disease. Anthracnose can enter the garden on diseased seed, so only disease-free seed should be used. Resistant varieties of watermelons and cucumbers are available. Fungicide sprays also may be used.

More information on cucurbit diseases can be found in PM 1049, Curcurbit Diseases An Aid to Identification and Control (PDF).

This article originally appeared in the 8/13/2004 issue.

Anthracnose is a fungal disease of corn, cucumber, beans, peppers, squash and tomato. It can spread very quickly in warm (80 degrees F), wet weather, especially if air circulation is poor. Fortunately for California gardeners it doesn’t thrive in our hot dry summers.

This disease first appears as small, variously colored, circular spots (those on watermelon are angular) on the older leaves, though it eventually spreads to younger leaves, stems, pods and fruit. The spots enlarge and merge, getting darker until the leaves drop off and the plant is defoliated (or the stem is girdled) and dies. Sunken, round, water-soaked spots appear on fruit.

Anthracnose prevention is easier than cure. Remove diseased plants promptly to minimize its spread. Keep the plants off of the ground on stakes or cages to provide good air circulation. The spores overwinter on volunteers and crop debris, so clear up the beds in fall and rotate your crops. The spores are most often spread via water, when soil containing spores are splashed onto the plants by rain or irrigation. You can reduce this by mulching around the plants and by using drip irrigation. They may also be spread on the hands if the gardener, so don’t touch wet plants (especially not after removing infected plants). Some crop varieties are resistant to Anthracnose.

Anthracnose can also be carried on the surface of the seed, in which case treat them with hot water (127 degrees F for 25 minutes) or bleach solution (1 part bleach to 10 parts water for 30 minutes) to kill the spores.

Image: David B. Langston, University of Georgia,

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The symptoms of anthracnose vary somewhat on different hosts. On cucumber leaves the spots start as water soaked areas and expand into brown spots which are roughly circular, reaching about 1 ⁄4 to 1 ⁄2 inch in diameter (Figure 3 & Figure 5). Small, growing leaves may be distorted and severe spotting may cause entire leaves to blight (Figure 4). Lesions on watermelon leaves can also appear circular at first, but later coalesce into more irregular necrotic areas (Figure 6).

Leaf petiole and stem lesions are shallow, elongate and tan. Lesions on fruit are roughly circular, sunken and contain pinkish spore masses in moist weather. Spots on watermelon foliage are black, and a foliar blight may develop giving a scorched appearance to the planting. The lesions on stem and fruit are similar to cucumber.

Figure 3. Cucumber leaf with lesions caused by the anthracnose fungus.

Figure 3. Cucumber leaf with lesions caused by the anthracnose fungus.

Figure 4. Cucumber seedling with anthracnose symptoms.

Figure 4. Cucumber seedling with anthracnose symptoms.

Figure 5. Anthracnose on cucumber leaf.

Dr. Lina Quesada, NC State Vegetable Pathology Lab

Figure 5. Anthracnose on cucumber leaf.

Dr. Lina Quesada, NC State Vegetable Pathology Lab

Figure 6. Anthracnose on watermelon leaf.

Dr. Lina Quesada, NC State Vegetable Pathology Lab

Figure 6. Anthracnose on watermelon leaf.

Dr. Lina Quesada, NC State Vegetable Pathology Lab

Resistant Varieties Key Against Anthracnose

UGA Extension photo/Shows anthracnose disease in pepper.

It is never too early to start thinking about cucurbit disease management in Alabama. In the case of anthracnose, producers who are planting their crops are best served by utilizing resistant varieties, according to Ed Sikora, professor and Extension plant pathologist in the Department of Entomology and Plant Pathology at Auburn University.

“I was just looking through the Southeast Handbook for 2021 and we do have a lot of anthracnose-resistant varieties for a number of different crops for watermelon, cantaloupe and cucumber. That’s the best control practice we have if you have a history of this disease in your field,” Sikora said.

It’s important to avoid overhead irrigation if you are not using disease-resistant varieties. It just promotes the disease and provides conditions for its development.

Follow a fungicide spray program when there are warm and wet conditions. These conditions will favor the disease’s development.

Sikora said anthracnose is probably the most common cucurbit disease every year.

“Cantaloupe, cucumber and watermelon are all sensitive to it, more susceptible. You’ll see these tan to brown spots on the leaves, fairly small and conspicuous. Often times, you’ll see shallow elongated tan spots on the stems as well,” Sikora said. “On the fruit, you might see sunken areas on the fruit with pink discoloration to them, which is the disease-producing fungal spores.”

Watch the video: Cucumber. Fungi. Diseases. Symptoms. Management