Pumpkin and Corn Rust - Knowledgebase Question

Sierra Vista, AZ
Question by tomcook
October 19, 1999
I was reading the question by Johanna Roy about the fungus in her pumpkins. You said that it could be a frass. I had the same problem. There was an orange/yellow fungus growing in my vines. Some of the vines had come open. I had very long vines and I seemed to have a good crop growing. My problem seemed to start with the Monsoons. The water does fall off the house into the bed. I thought this was a good thing. Some of my plants died off. This fungus or frass also attacked my corn that I had growing in the same bed. The year before I had planted peppers in that raised bed. We have also had an ant problem and the ants did seem to use this bed the most. The raised bed across the walk did not have a problem. I grew watermelon and pole beans in that one.

I took out all the plants from the infected bed and let the soil warm up to hopefully kill the fungus. My plans are to plant garlic in that bed. I plan to overwinter them and will mulch with pine needles from my pine tree.

Are any of these problems a clue to what happened to my plants and should I do anything else to help this bed?

Answer from NGA
October 19, 1999


Let's start with some terminology! Frass is a polite word for debris or "poop" left behind by insects. It's not the same as a fungus. I looked up the earlier question you were referring to, and frass was given as a possibility.

Orange/yellow spots are often some type of rust, a fungal disease that can live to pop up when conditions are right--often warm weather and high humidity--which is exactly what happens during the monsoons. It's a great idea to harvest water from the rains, but if it is just splashing down uncontrolled into your garden, it may splash fungus from the soil up onto plant leaves, which is how many fungi spread. Rust is not a real common problem on vegetables, but corn rust can occur.

You were correct to destroy the infected plants and rotate crops every season. To kill pathogens in the soil, you need to solarize the soil--really heat it up for 2 months or so, by incorporating fresh manure, watering, and covering with plastic. It works best during the summer. If you have any of the infected plant material left, I suggest that you take it or mail it to the Cochise County Cooperative Extension so they can identify exactly what it is. 450 South Haskell, Willcox, 85643, 520-384-3594. Good luck!

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