What is the problem when pea plants turn yellow?

Pea plants are popular garden vegetables throughout much of the country. These cool-weather crops usually grow in the early spring, depending upon location. Pea plants are fairly quick and easy to grow and will germinate within approximately two weeks of planting. Pea plants are susceptible to a number of diseases that often result in wilting and yellowing of the leaves.

Several different fungi cause root rot in pea plants, with Aphanomyces euteiches and Pythium ultimum being most common. Symptoms vary somewhat in order and time of onset depending on the type of fungus causing the root rot. In general, expect to see yellowing, wilting leaves which may start at the bottom of the plant and move upwards. The stem of the pea plant may turn brown or yellow, eventually turning black as it becomes infected and dies. Plants affected by root rot pull from the ground easily and thus are differentiated from those suffering from wilt. Root rot occurs more often in cool and wet weather. Early planting in fertile soil with adequate drainage helps prevent root rot. Fungicides and crop rotation are useful as well.

Pea mosaic is a viral disease which infects pea plants. Infection occurs early in the season and kills plants. Pea mosaic symptoms including stunted growth, mottled leaves and yellowing stems. This virus can be best controlled through the use of crop rotation in the planting area.

Technically known as Peronospora pisi, downy mildew is a fungal disease. Once a plant with downy mildew dies, this fungus remains on the dead plant particles in the soil, waiting to infect future plants. Pea plants infected with downy mildew show yellow lesions on the top of leaves. Leaves turn yellow and die, pods develop black or brown spots and the plant's growth is stunted. Crop rotation and treatment with a fungicide help prevent downy mildew.

Wet and cool weather cause pea plants to appear yellow in colour in early spring. This is not caused by any type of disease and is normal under such conditions. These yellow pea plants will darken and turn green as temperatures rise and the soil dries out. Pea plants grown in this type of weather are at greater risk of developing other conditions, especially fungal diseases. Observe your plants closely, looking for other signs of disease such as wilting, curling of leaves or stunted growth to determine if the yellow discolouration is due simply to weather conditions.

To prevent yellowing and disease, avoid planting pea plants in areas with poor drainage and take care not to water pea plants excessively. Research pea plant varieties before planting to ensure the best match for the weather and conditions in your area. Fertilise and use fungicides and herbicides to prevent conditions encouraging disease development.