NCLC Plant Problems Diagnosis Practice Test

Phytophthora root and crown rot is driven by consistently wet, poorly drained soils. The pathogen sends motile zoospores through free soil water, so standing water or poor drainage creates the ideal medium for movement and infection. When the root zone stays waterlogged, oxygen in the soil drops, stressing roots and weakening defenses, which lets Phytophthora colonize root and crown tissues more easily. In contrast, well-drained, drier conditions keep roots oxygenated and limit the pathogen’s ability to spread, reducing disease risk. While soil pH can influence some plant–pathogen interactions, moisture status is the dominant factor here, and sandy soils that drain quickly generally don’t support prolonged waterlogged conditions.