Why Hasn't My Sweet Potato Developed Well?

Are there any brown lesions with concentric rings on older leaves, lesions may be surrounded by a yellow halo?

Are there any small gray-black oval lesions with lighter centers on stems and leaf petioles and occasionally on leaves?

Are there any circular brown-black patches of rot on tubers, plants may be stunted, wilting and yellowing?

Is the base of the stem swollen and distorted, tubers have deep, dark rot that forms an elliptical cavity?

Are there any water-soaked, brown lesions on the stems and petioles, the stem may collapse causing several vines to wilt?

Are there any small brown lesions on leaf veins that become corky in texture and cause veins to shrink which in turn causes leaves to curl?

Are there any circular dark brown, corky lesions on tubers that are V-shaped in cross-section, plant growth is poor and the yield is reduced?

Are there any holes in the stem, plants are wilting, yellowing and dying?

These symptoms indicate Alternaria leaf spot. Warm, wet conditions favor this fungal disease. Spray infected plants with copper and/or sulfur to prevent further disease development.

These symptoms indicate Alternaria leaf and stem blight, a much more destructive disease than Alternaria leaf spot. It doesn't usually appear in North America. Destroy all sweet potato crop residue immediately following harvest. Plant only disease-free seed material from a reputable nursery.

Only disease-free seed material should be planted. Sweet potato should not be planted in sites where it has been grown during the previous 3-4 years. Seed material should be treated with an appropriate fungicide before planting.

These symptoms indicate Fusarium root and stem rot. The disease is generally not a problem if good sanitation is implemented. If it does occur, do not replant sweet potatoes or any susceptible crop in that soil for 3-4 years. Select only disease-free roots for seed. Practice crop rotation.

Bacterial soft rot is caused by a bacterium that is common in most soils, particularly if the area is frequently planted with susceptible crops. Remove and destroy infected plants. Avoid planting in poorly draining soil. Rotate crops with corn, small grains, or grasses where possible. Plant sweet potato varieties that are resistant to the disease.

Leaf and stem scab is one of the most severe diseases of sweet potato. You can prevent scab by keeping soil pH below 5.5. Avoid the use of overhead irrigation. Rotate sweet potato with other crops. Destroy sweet potato crop residue immediately after harvest. Good control of the disease can be achieved with benomyl and chlorothalonil but only where they are licensed for use.

Streptomyces soil rot or pox is a widespread disease of sweet potato that results in a reduction in plant growth and severe yield losses. Plant resistant varieties of sweet potato. Maintain the soil at a low pH which is unfavorable to the pathogen. Sweet potato should be rotated with other crops that are non-hosts to prevent the build-up of the pathogen in the soil.

Sweet Potato stem borer larva is light-purple and/or yellowish-white. Keep the field free from weeds especially Ipomoea spp. Fallow the land for a few seasons if the infestation is severe. Use pheromone traps to monitor and control the insect.

If there are thick, soft grubs curled in C-shape in the soil and feeding on tubers, the culprits are larvae of scarab beetles called White grubs. Apply parasitic nematodes to the soil before planting to control soil-dwelling pests. Prevent adults from laying eggs on or near seedbed by covering it with a large piece of row cover after planting. Follow crop rotation with soybean to reduce the grub population.