Problems with Pythium

Growers often call Extension when they are experiencing a problem with their plants that they need help addressing. Sometimes they know what the issue is, whether it be a disease or pest problem. Other times they don't know what is causing the damage, so Extension must also help with identifying the problem first, then working with the grower to help address it.

In this instance, we visited a grower who happens to live in North Carolina. This grower is growing broccoli transplants and having several problems, one being worms eating the leaves. When we arrived at his greenhouse, one of the first things we noticed was the holes all over many of his transplants. We also noticed another problem- Pythium.

Holden, the volunteer entomologist from NC State, identified some parasitic wasps present in the greenhouse and on and around the broccoli transplants. These wasps are actually beneficial, since they eat the worms that are causing the damage.

Damping off is a disease where pathogens kill or weaken seedlings before or after germination. Damp conditions and over-watering make this worse. The soil organism Pythium is the main culprit when it comes to damping off. All Pythium species favor wet conditions and high soluble salts in the potting medium. Poor sanitation of tools and containers can also infect sterilized soil mixes, so spread can occur easily. Pythium can remain anywhere, including plant material and potting media.

Pythium Root Rot on a broccoli plant

Once we saw how big a problem the grower was having with damping off, we had to provide him with some control measures.  There are numerous fungicides labeled for Pythium control. Care must be taken to prevent resistance. There are also certain pesticide restrictions if a grower does not have his or her private pesticide applicator license.

To try to prevent Pythium problems in the future, there are actions that can be taken. Sanitize everything- bench surfaces, tools, trays, containers, and equipment that will come into contact with the potting mix. Take into consideration media used and its components. High water holding capacity can be good, but too much water with poor drainage can lead to disease problems. Overwatering is bad and makes your plants more susceptible.

Simply being proactive is the key. Root rot is very difficult to control once it has begun, so prevention is the best method of control. Contact your local Extension office for more information.

Beckerman, J. (2010, November 24). Pythium Root Rot of Herbaceous Plants. In Disease
          Management Strategies. Retrieved August 3, 2015, from
          https://www.extension.purdue.edu/extmedia/bp/bp-181-w.pdf