Droughty Seasons and Aflatoxins
News Release Courtesy of University of Illinois Extension
The droughty 2011 season has created some very real aflatoxin concerns and the presence of some "green" ears in area fields has really brought that concern home. What predisposes a crop to problems with aflatoxins?
Aflatoxin is considered to be a "type" of a much larger group of toxic carcinogens generally termed "mycotoxins." By far the most prominent of the mycotoxins, aflatoxin is known to cause liver cancer and the amount of aflatoxin deemed acceptable in grain is therefore regulated.
Aflatoxins are produced by one of two fungi belonging to the genus "Aspergillus." The more common of the two fungi, typically responsible for the appearance of aflatoxins in corn, is termed "Aspergillus flavus" (thus the reason chemicals produced by the fungus are termed "A-fla"-toxins/ "A – Aspergillus" and 'fla – flavus"). "A. flavus" can develop on many types of organic material. The fungus produces hardy survival structures that can rest in the soil and/or on residues for years minus fungi-favoring conditions. During hot, humid periods spores are produced and moved via wind to various parts of the plant. Those spores landing and germinating on silks send fungal material down individual silk channels somewhat like the germ tube originating from a pollen grain. Silk infections become more likely with high daytime and nighttime temperatures. Once beneath the husk, the fungus may colonize both damaged and undamaged kernels. The signs of "Aspergillus" infection resemble a yellow-green mold, growing between and on the kernels. Specific conditions favoring this disease include 80 to 110 degree temperatures during the period of grain fill, nitrogen deficiency, high plant populations and poor root development, etc. Fungi and toxin development are most favored in kernels when "Aspergillus-prone" conditions synchronize with corn testing 17-18 percent moisture. The potential for infection by "Aspergillus" does not end once corn is in storage and thus will require vigilance on the part of the producer to ward off toxin development until the crop is delivered.
What can be done to keep aflatoxins from "gaining a foothold" in the field? Most resources recommend that one harvest those fields most prone to "Aspergillus" (i.e. those fields under intense moisture stress and/or subject to intense insect pressure) when corn percent moisture readings reach the low 20s. If such corn can be picked and dried to 13 to 15 percent (the former for corn to be stored longer than 6-9 months) within 24 hours, "Aspergillus" development should be tapered if not eliminated thus decreasing alfatoxin production.
Source: Matt Montgomery, Extension Educator, Local Food Systems and Small Farms, mpmontgo@illinois.edu