Pink Root

Onions, chives, and garlic plants with pink roots are not happy.

This disease rarely causes significant problems in garlic but can shrink your onion and chive harvests by quite a bit.

Onion infected with pink root (Gardener.Wikia) CC BY-SA 3.0

The pink root pathogen

Pink root is a fungal disease caused by Phoma terrestris. Phoma terrestris is nearly always present in the soil and is relatively eternal. It causes no serious problems most of the time. But, if your onion plants are experiencing drought, insufficient or excessive fertilizer, water stress, insect feeding, compacted soil, or any other less-than-ideal circumstances, they may become susceptible. This pathogen thrives in temperatures between 75°F and 85°F. It can move around the garden by splashing rain and irrigation water, on tools and shoes.

Symptoms of pink root

Aside from the pink roots, plants infected with this fungal disease also exhibit roots that darken to red, purple, and, eventually, black. These roots shrivel up and die. These discolorations may move up into the bulb. This infection leads to stunting, but it rarely kills the plant. This disease looks a lot like fusarium wilt.

Preventing and controlling pink root

Keeping plants healthy and employing crop rotation are the two best ways to prevent pink root from causing too many problems. A note on crop rotation: do not follow a cereal crop with onions, as it creates conditions that promote this particular pathogen. Soil solarization is the only option in severe cases, but that’s a pretty drastic measure for the home gardener.

If you see pink, purple, or black shriveled roots on your onions, try growing them in a different area, in fresh soil.