Fusarium ear rot on maize (Photo credit: CIMMYT)
It”s sweet corn season, and farm stands are popping up all over the country to feed the need. So where do you go for your sweet corn? Organic or conventional? Do you grow your own corn?
This time of year brings back memories of my days working on an organic farm and roadside stand where customers could pull in and yell out the window ” got any corn?”, and I would run out into the field and snap off a ripe ear, opening the husk and cracking off the top inch or so of cob to get rid of the earworm and damaged kernels at the top of nearly every ear that I picked. We told customers that ‘if they were handy with a knife’, a little pest damage was easy to remedy and that organic produce was bound to have some pest damage. In particular, we believed that a damaged organic ear of corn was safer to eat than a conventional ear harboring pesticide residue.
I took this experience to my next job interview, another seasonal farm labor job in Wisconsin at a ‘you-pick’ vegetable operation, where the owner scoffed at my experience on an organic farm, saying that pesticides were far less toxic than naturally occurring fungal toxins, and that production in organic systems would never be enough to ensure food security due to high losses from pest damage. Needless to say, I did not work for this farmer, and I paid no attention to his words because he had lectured me, a complete stranger, for several hours in a manic monologue and I thought he was a fanatic. That summer I worked as a cashier instead and forgot all about him until I took a field plant pathology class this year. Incredibly, this ‘fanatic’ who did not hire me was right, at least in the case of sweet corn.
Truths about natural fungal toxins on sweet corn that can kill you:
1. Since the 70’s, we have known that a fungus called Fusarium ear rot produces a toxin called Fumonisin that is directly linked to pancreatic cancer in humans and various other cancers in livestock. This is a fact that is poorly publicized and is more of a problem in humid environments that favor fungal growth, and the toxin is found in apparently healthy kernels as well as obviously infected kernels (Wild and Gong, 2010)
2. The fungus produces more of this potent carcinogen as the season goes on, with the highest concentrations near the end of the season (Picot-et-al. 2011)
3. Controlling caterpillar pests such as corn earworm or army worm provide some measure of control against Fusarium ear rot because the fungus is a secondary invader whose spores gain access to the ear by means of the bore hole made by the caterpillar. There are many ways to control caterpillars, and one of the most controversial is genetically modified (GMO) Bacillis Thurnigensis (BT) corn, which makes a bacterial toxin that kills caterpillars, turning them from healthy hungry larvae to stretchy black lines of tar(Wu, 2007). The main objection to this corn is that it contains bacterial genes. Organic corn growers can also utilize this wonderful chemical which is nontoxic to humans by spraying the actual bacterium on non-genetically modified corn varieties. Other options include spooning oil onto the silks of each unripe corn ear, a practice common before world war II, and spraying organophosphate, a chemical that is more toxic than either BT or oil and which is being phased out here in California due to its toxicity to aquatic insects. Of these options, oil and BT spray are options available to both organic and conventional growers. Whether produced by bacteria or by genetically modified corn, BT is much less toxic than Fumonisin toxin produced by ‘all natural’ Fusarium ear rot, and very likely stops Fusarium from entering the ear by killing the borer caterpillars before they can make the ear vulnerable to Fusarium attack.
Pesticide residues are higher in conventionally grown produce than in organically grown produce (Spangler et al 2012), but ignoring pests and pest damage entirely in an organic or a conventional system has the potential to invite natural toxins in which could pose a greater health threat.
Take home message: Organic pest damage isn’t always safe. Nature has had chemical warfare much longer than humans have been breeding crops and cultivating the land! An organic or conventional grower should stay on top of insect pests in corn in particular because Fusarium head rot is much more frightening for human health than the pesticides used to kill the worms.
References
Wild and Gong 2010 Mycotoxins and Human Disease-a largely ignored human health concern
Wu, F. 2007 BT corn shows less fungal infection
Related articles
- [One to watch] Sweetcorn crop at risk in the US (newstalk.ie)
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