Yellow Leaves on a Sweet Pea Plant

sweet pea image by Alison Bowden from

Sweet pea plants (Lathryus odoratus) are commonly grown in commercial and residential landscapes for their ornamental value. This annual plant is a member of the Fabaceae family and was traditionally used in old-fashioned English gardens.

In the spring and summer months, this ornamental plant can be damaged by root rot.


Sweet pea plants thrive in locations where they receive full sunlight. This low-maintenance plant can grow as a vine or a bush, and is commonly used to adorn fences and trellises. For healthy growth, plant pea-plant seeds in soil with a temperature of 12.7 to 18.3 degrees C until germination. Once the plants have germinated, soil temperatures should ideally be 21.1 to 26.6 degrees C.

Root Rot

Sweet pea plants commonly develop root rot, a disease caused by any one of several types of fungi, including Aphanomyces euteiches, Phythium ultimum, Fusarium solani and Rhizoctonia solani. These fungi overwinter in the soil and infect the plant as spring and summer temperatures reach warmer temperatures.

Life Cycle

The fungi that causes root rot lies dormant in the soil throughout the cold winter months. When soil temperatures reach 18.3 degrees C, this disease starts to enter the root system of the sweet pea plant. Each type of fungi thrives in slightly different temperatures, but they are all within the range of 17.7 to 30.5 degrees C. As the fungi spreads throughout the plant, it produces spores which aid in the spread of the disease. These spores reinfect the soil, and can be carried by water and irrigation systems to other plants.


Aphanomyces, Pythium, Fusarium and Rhizoctonia can all result in the yellowing of the leaves of the sweet pea plant. As this disease infects the root system of the sweet pea plant, you may notice that the plant develops roots and stems that have decayed and turned yellow or pink. As they continue to decay, they turn a brownish-black colour. The leaves of infected plant starts showing signs of disease by turning yellow, and as the disease progresses, the leaves start to shrivel and fall to the ground.


The best method of root rot control is prevention. Promote healthy growth by planting sweet pea plants in fertile, well-drained soils that have been treated with a fungicide. Monitor the soil regularly to maintain a pH of 6.5 to 7.0, and avoid over-watering the soil. Unfortunately, no sweet pea varieties are resistant to this disease, so close monitoring in the spring and summer is essential.