Importance of early season insect protection
While working on sugarcane beetles in corn, one of our graduate students (Mr. Kevin Lanford) was artificially simulating sugarcane beetle damage to V3 stage corn by removing ½ – ¾ inch of soil and manually damaging the underground portion of the stem (damage was slight stem penetration with a drill bit, simulates sugarcane beetle perfectly). We then replaced the soil and monitored the above ground symptomology that occurred. We developed an above ground rating scale to separate levels of visual above ground damage into categories, hand yielded each plant, and analyzed according to its ranking. We did this in 2 locations for 2 years.
ABOVE GROUND RATING SCALE
0 = no apparent damage, plants look the same as undamaged plants
1 = slight stunting or mild leaf streaking
2 = moderate to severe stunting or severe leaf streaking
3 = dead heart
Plants that showed zero above ground symptomology had 9% shorter ears than plants that were undamaged and yielded 18% less than undamaged plants. Think about this: even slight damage below the soil that does not manifest itself above ground in any way at all may still be enough to cause significant yield reduction in field corn.
This is possibly why we see consistent results in yield protection with at-planting insecticides in field corn in Mississippi even when there appears to be no damage. It is also why we often see even more of a response when we increase the rate or add a granular or in-furrow spray on top of seed treatments. Under significant soil insect pressure it further minimizes below ground insect damage, which results in more yield protection.
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