Corn smut anyone?

When your sweet corn has tasseled and those ears are starting to swell and grow, it's a constant battle to keep it free from bugs and animals. Raccoons and squirrels can decimate those ears just before you get to them, and somehow they manage to make it look like the corn is still there. If you manage to avoid them, then there is always the chance that under those husks lurks a corn earworm. However, there is another insidious organism waiting to hijack your corn. It's called corn smut, and it's been written about by scientists for over 100 years. This particular disease looks like some sort of alien growth bursting out of your corn (either the ears or the tassels).

Silvery gray galls of the corn smut on an ear of corn

What causes it?

It's caused by the fungal pathogen Ustilago maydis. This pathogen can infect the ears, tassels, stalks and the leaves of corn. They infect the host (in this case corn) tissue and they cause tumors to start to form. These are light gray/silver to a medium grayish-purple depending on the age of the tumor. The deeper color is the spores that are getting ready to be released.  

Hot dry weather followed by a nice wet period seems to be great for disease formation. However, some sources say that cool conditions and dry weather followed by a rain event can promote disease. Regardless, last year we saw a lot of smut, and, after my last garden harvest, this year seems to be another great year for the disease.

Close up of a smut gall, you can see the dark spores just under the silvery surface

How to manage it

Proper fertilization is important for minimizing disease severity, with higher amounts of disease being seen in over or under-fertilized corn (Aydogdu 2011). If you do get the disease the bet thing you can do is remove the infected tissues BEFORE the dark spores are being released. If the ears are infected you can eat them (see the next paragraph) or you can bag them up and throw them in the trash (not your compost). If some of the galls have black spores being released, go ahead and bag those up and throw them away. You'll need to rotate with a different crop for at least 2 years to manage the disease properly. The Virginia Tech Cooperative Extension office has a good list of sweet corn varieties with some level of resistance/tolerance in one of their bulletins as does an Oregon State University Extension bulletin:

Argent

Brilliance

Fantasia

Pristine

Seneca (Sensation, Snow Prince, Sugar Prince)

Silver (King, Prince)

Summer Flavor 72W

I have never grown any of these varieties, but what I can say is that the variety (I'll let you know what it is as soon as I find the package) I planted this year was quite susceptible. If you want to produce smut however, this might be a great variety to grow.

Fun tidbits

Believe it or not the disease (if you catch it early) is considered a delicacy and is served in many restaurants under the name huitlacoche or cuitlacoche. For those of you wanting to try it, you'll need to harvest it when the galls are still a silvery gray color. Huitlacoche can be used in soups, appetizers, tacos or served plain - here are some recommendations from the University of Illinois. Now before you go grimacing at the thought of eating it, think about it. This is a fungus, mushrooms are fungi. If you'd eat a mushroom, you should be willing to try huitlacoche.

 So if you can avoid getting this disease, that's great! But if you can't, go ahead and be adventurous and make the best of it.

Aydogdu M. and Boyraz N. 2011. Effects of nitrogen and organic fertilization on corn smut (Ustilago maydis DC Corda.). African Journal of Agricultural Research 6: 4539-4543

Skibbe DS., Doehlemann G., Fernandes J., and Walbot V. 2010. Maize tumors caused by Ustilago maydis require organ-specific genes in host and pathogen. Science. 328:89-92