Why Is the Base of My Pea Stem Black and Rotted?

A blackened, soft, or water-soaked stem base at or just below soil level — with the plant above initially appearing to wilt and then collapsing — is the classic presentation of pea foot rot. This term covers several soil-borne pathogens that attack the stem base and root crown: Fusarium solani, Pythium ultimum, and the ascochyta complex can all produce foot rot symptoms. The condition is most common in cold, wet soil conditions at sowing time and in ground that has grown peas in recent years.

Identifying foot rot

Examine the stem base at soil level. A healthy pea stem is firm, cream-green, and intact at the base. Foot rot produces a dark brown to black discolouration that is usually soft or water-soaked, often girdling the stem completely. The tissue may be sunken or collapsed. Above the infected zone, the plant wilts — at first recovering at night but then permanently collapsing as the constriction cuts off water and nutrient flow. The roots may also be brown and rotted. This pattern of stem-base girdling distinguishes foot rot from above-ground diseases that cause leaf symptoms without stem-base damage.

Conditions that favour foot rot

Cold, wet, compacted soil significantly increases the risk. Waterlogged soil deprives roots of oxygen, weakening them and creating ideal conditions for Pythium (a water mould that moves through saturated soil). Cold soil slows plant growth but does not slow pathogen activity proportionally, leaving seedlings exposed for extended periods. Heavy clay soils in wet springs are the highest-risk situation. Improving drainage through raised beds or incorporating organic matter reduces water-holding and aerates the root zone.

Rotation and resistant varieties

Foot rot pathogens accumulate in soil with repeated pea crops. A minimum three to four year rotation — not growing peas or other legumes in the same ground — allows pathogen populations to decline. In small gardens where this is not possible, growing peas in raised beds with fresh compost effectively bypasses the soil pathogen problem. Some pea varieties have improved tolerance to foot and root rots — check catalogue descriptions when choosing seed. Avoid saved seed from diseased crops, as seed-borne infection (particularly the ascochyta complex) contributes to foot rot in the following season.