Issue 25, September 17, 2015 • USDA-NIFA Extension IPM Grant
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Kernel red streak (KRS) is commonly observed, but not well understood. KRS is triggered by the wheat curl mite, Aceria tosichella, feeding on the kernel’s pericarp or seed coat. These mites are known to be blown in on winds from maturing wheat in the summer and use corn as an alternative host until small grains are available in the fall. In the Great Plains states, wheat curl mite can occasionally vector economically damaging viruses, including the wheat streak mosaic virus. Fortunately this viral disease is seldom a problem in Indiana’s small grains (due to planting dates and less favorable climate).
What little literature exists on KRS often describes the reddish discoloration as being caused by a “toxin” being injected into the kernel’s pericarp by the feeding mite. Unfortunately, when phyto-chemical processes were not understood years ago, they were given catch-all terms, such as “toxin.” Obviously, the word “toxin” carries many negative connotations, especially in today’s society. The “toxin” is in fact the plant’s version of an immune response to a foreign substance entering the disrupted cell, not a by-product that would compromise the nutritional value of the grain.
There are two suspected mechanisms causing the red streaking. One is the triggering of anthocyanin, a red pigment, in the pericarp as a response to mite feeding. Hybrids vary greatly in how much and where anthocyanin accumulates (e.g., purple seedling corn under cool, wet conditions). The other is the elicitation of another red pigment, phlobaphene, that determines cob (white vs. red), pericarp (great variability as shown with Indian corn), and silk (yellow vs. pink) coloration. Both pathways are genetically controlled. In other words, the mite feeding and injecting saliva is disrupting the normal plant chemical and genetic processes causing plant responses, one of which results in abnormal pigment coloration. This does not affect plant nutrition, and certainly does NOT create a poison or “toxin” that would be harmful to end products of the grain (e.g., animal/human feed, starch, oil, etc.). These kernels look different, but are as tasty as any others!
Frequent and excessive rainfall throughout much of northern Indiana early in the 2015 growing season resulted in ponded fields, saturated soils, root damage / death, and severe stunting of corn plants. The amounts and duration of the rains was almost unprecedented, certainly beyond the experiences of many farmers and agronomists. This video discusses the end-of-season consequences to plant size, ear size, relative ear placement, and kernel maturity. More information that addresses crop damage by excessive rain, ponding, and floods is available online at https://www.agry.purdue.edu/ext/corn/cafe/flood.
Click on the following video:
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