| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control |
|---|---|---|---|
| Black root rot * (Thielaviopsis basicola) |
Poor top growth. Black lesions on roots and root rot. Seedlings may be killed. | Fungus is soilborne. Favored by cool, wet soils and any condition that weakens the plant. | Avoid fields previously planted in legumes. Avoid overirrigation and overfertilization. Plant on raised beds. |
| Powdery mildew * (Erysiphe trifolii) |
White powdery growth on surface of leaves and stems. Older infected leaves yellow and wither. Growth of heavily infected plants is diminished. | Favored by moderate temperatures. Spores (conidia) are produced in great abundance and they are airborne. Moisture is not necessary for germination and infection and is detrimental to the fungus. | Several powdery mildew fungicides are effective if applied in a regular preventative program commencing with the first signs of the fungus. Check product label for registration. |
| Ramularia leaf spot (Ramularia deusta) |
Large, irregular or circular tan spots without definite margins. Lower leaves are first affected. Infected leaves often drop. | Fungus is specific to sweet pea and survives in sweet pea refuse. Favored by wet conditions. | Rotate with other crops for 2 years. A fungicide may be necessary in some severe cases. Avoid overhead irrigation. |
| Seed decay (Pythium spp. and other fungi) |
Seeds rot in soil. Seedlings do not emerge. | Favored by wet soil and poor aeration. | Provide better drainage. Grow on raised beds. |
| Virus or viruslike disease | Symptoms | Host range and natural spread | Comments on control |
| Enation mosaic (Pea enation mosaic virus) |
Leaves contain scattered translucent areas ("windows"). Foliage may be crumbled and stunted. There may be "windows" in the flowers. | Virus is spread by aphids. Host plants include many legumes. | Control nearby weeds, especially legumes. Control aphids. |
| Mosaic (Pea mosaic virus) |
Mottling and chlorosis of the foliage. Dark green areas interspersed with yellow-green portions of leaves. Flowers have "broken" colors. | Virus is spread by aphids. Host plants include many legumes. | Control nearby weeds, especially legumes. Control aphids. |
| Spotted wilt (Tomato spotted wilt virus) |
Reddish brown streaks on stems. Leaves with circular spots that are yellow at first and later turn brown. Plant may die. | Spread by thrips. Virus has a wide host range, including many weeds. Juvenile thrips (nymphs) acquire the virus and transmit it as adults. | Control nearby weeds including grasses. Control thrips. |
| Sweet peas are also susceptible to Ascochyta blight (Ascochyta lathyri), bacterial streak (Pantoea agglomerans, formerly Erwinia herbicola), fasciation (Rhodococcus fascians), Pythium root rot * (Pythium spp.), cottony rot * (Sclerotinia sclerotiorum), downy mildew * (Peronospora trifoliorum), and damping-off * (Rhizoctonia solani, Fusarium spp., and Pythium spp.) | |||
| * For additional information, see section on Key Diseases. |