Sweet Pea (Lathyrus)

Plant Health Problems
See Perennials for a detailed discussion of problems that may occur and are common to most herbaceous ornamentals. 

Diseases caused by Fungi:

Anthracnose, Glomerella cingulata.Symptoms first appear as whitish lesions on leaves, shoots, and flower stalks. Heavy infection results in extensive loss of leaves and shoot tips may wilt and die. Infected tissues are frequently covered with salmon-colored spore masses after periods of wet weather. This is the same fungus that causes bitter rot of apples.

Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. It is also helpful to pick and remove symptomatic leaves as soon as they develop and after the tops have been killed by frost. This disease may also be prevented by using healthy seed and by planting in clean soil. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut are maneb and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Root rot, Rhizoctonia solani.
The above-ground symptoms of this disease are usually nonspecific and include a general wilting, decline, and collapse of the foliage and the entire plant. This general droopiness or flaccid appearance is often accompanied by browning and rotting of the roots and the crown. Darkened or discolored lesions can develop on the main stem near the soil line. Yellowing and death of the outer leaves follows, until finally the entire plant is dead.

Control can be difficult once plants are infected so prevention is important. It is helpful to avoid overwatering, especially in heavy soils, and to avoid watering directly into the crown area of the plant. Highly symptomatic plants can be rogued and removed since recovery is unlikely.

Powdery mildew, Microsphaera.
White powdery spots or patches develop on leaves and occasionally on stems. Symptoms often first appear on the upper surfaces of the leaves and are usually most pronounced during hot, humid weather. Heavily infected leaves turn brown and shrivel.

Disease can be minimized by avoiding overcrowded spacing of plants and by carefully picking off affected leaves as soon as symptoms are evident. Symptomatic leaves can be placed into a plastic bag in order to avoid spreading the spores of the fungus to other plants. Use of fungicides is usually not necessary. However, applications can be made as soon as symptoms are visible. Among the compounds registered for use in Connecticut are horticultural oil, sulfur, potassium bicarbonate, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Diseases caused by Viruses:

Spotted wilt, virus, Impatiens Necrotic Spot Virus (INSV).
Initial symptoms of infection appear as a mottling of the leaves. Purple spots then develop on these leaves and stems. This virus is transmitted by the western flower thrips.

Control of this disease is focused on prevention since once plants are infected, they cannot be cured. It is important to eliminate and remove infected plants as soon as they are recognized and to eliminate other symptomatic plants since this virus has a very broad host range. It is also critical to manage the thrips population.

Diseases caused by Physiological/Environmental Factors:

Bud drop, physiological.
This problem is attributed to a number of cultural factors such as overwatering, overfertilizing, low light levels, and high temperatures.

Bud drop can be minimized by careful attention to cultural care.

Insect Problems:

The common aphid on sweet pea is the pea aphid, but the potato aphid sometimes infests sweet pea. Spraying with insecticidal soap, ultrafine horticultural oil or malathion, which are among the compounds registered for control of this pest in Connecticut, will control this pest. Imidacloprid may also be useful as a systemic to be taken up by the roots. Consult the label for dosage rates and safety precautions.

Corn earworm, Helicoverpa zea.
The larvae, when abundant, feed upon sweet pea and many other plants. The moths, with a wingspread of about 1.5 inches, are tan with darker markings. They arrive in Connecticut each season from more southern areas after which they lay eggs singly on various plants. After hatching, the caterpillars feed on the leaves, eventually reaching a length of up to 2". Their color varies from brown, tan, green, or pink with light and dark longitudinal stripes. The head is golden brown and the body has small bumps and spines, giving it a rough texture. There can be two or three generations in a year, depending on when the adults arrive on winds from the south. Bacillus thuringiensis var. kurstaki (Bt) and spinosad are registered for control of this pest in Connecticut. Consult the label for dosage rates, safety precautions, and preharvest intervals.

Celery leaftier.
This insect feeds upon sweet pea. See Celery.