Pea plants are fairly simple to grow, but they are susceptible to a number of infections that are carried from plant to plant by insects and to fungal infections. These infections not only stunt the growth of the plants and deform the foliage, but they also impact the yield of veggies at the end of the season. The best way to prevent diseases of pea plants from having a negative effect on your pea harvest is to make sure that you are familiar with the signs, symptoms and treatments so that you can avert disaster early on.
Fusarium, which is also called "True Wilt," causes the lower leaves of the pea plant to turn yellow while the growth of the plant slows to a halt or becomes deformed. Near the soil line, there may be thickened, brittle stems on the plants. Often infected plants will produce no pods at all, or flat and deformed ones. The disease spreads in oval patterns from plant to plant. Fusarium will spread in wider and wider ovals from year to year, so you need to remove affected plants from the area as soon as you spot them and replace the soil in the impacted area if possible. The only sure-fire preventative is to plant fusarium-resistant cultivars or to rotate the pea plants out of the affected area for at least five years.
Powdery mildew can grow on any part of the pea plant. It looks like a thick coating of black, gray, white or pinkish chalk dust. Left unchecked, powdery mildew can overrun a pea plant and render the pods inedible, although it generally will not actually kill the plant. You can control this disease by removing affected parts of the plant and disposing of them in a sealed bag rather than dropping them to the ground, where they will simply lead to reinfection or spread the infection.
Pea Plant Viruses
Pea plants often fall prey to a variety of viruses carried by aphids from plant to plant. In this scenario, you will need to control the aphids and treat the virus in order to halt the spread of the infection. Aphids can be controlled by pesticides or using horticultural oils that make the pea plants taste unpleasant to these bugs. Carefully watch for the appearance of virus symptoms, which can range from purple streaks and pitting of pods to mottling in the cases of mosaic viruses, and remove any affected plants from the area immediately and dispose of them by burning or in sealed bags.