How do diseases in the soil affect pea plant growth? Some soils carry pathogens (organisms that cause disease) that attack roots and stems. This project tests which diseases appear most often in Central Washington pea plants. You collect 14 soil samples from different locations. You plant pea seeds in each sample and water them over several weeks. Then you check for three common diseases: - Fusarium wilt - Aphanomyces root rot - Rhizoctonia root rot Fusarium wilt turned out to be the most common. It appeared in 37 percent of the plants. Rhizoctonia followed at 32 percent.