How to spot it

Swollen, silvery-gray galls on ears, tassels, or stalks that later burst open into black powder.

What it does

It ruins the ears it grows on; the rest of the plant is fine. Young, firm galls are a delicacy in Mexico, called huitlacoche.

What to do now

• Cut off galls before they break open and throw them away (or cook them while young).

Keep it away next time

• Grow corn in a new spot each year.
• Avoid damaging plants while weeding.
• Grow resistant varieties, and don't overdo nitrogen.

Plants it affects