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Western Nebraska seeing corn borers
By Cole Randol
Pioneer Hi-Bred agronomist
Second generation European corn borer moth flight has started at many locations in western Nebraska. Egg laying is expected in the near future. Corn borer egg masses are generally found on the underside of the leaf usually within three leaves above or below the ear leaf. These egg masses appear flat and white with black spots appearing as the eggs mature. Generally, late-planted and late-maturing cornfields are more attractive to egg-laying moths than early-maturing fields. Second-generation flight can last for four weeks. Damage due to second brood in corn may contribute to lodging and eardrop losses. The simple method used to determine economic threshold is based on accumulation of the percentage of plants with egg masses during two consecutive weeks of scouting following the early portion of the egg-laying period. If the first and the second scouting show 25 percent of cumulative plants with egg masses, treatments should be made. This percentage should be raised to at least 50 percent after milk stage. Pollination period and watering tips: Moisture stress during pollen shed and silking can cause more yield loss than any other developmental stage in corn. The following tips are provided to avoid unnecessary moisture stress on your irrigated crop:
--Silk through milk = maximum daily water use (2.3 inches per week). Since this cannot be supplied through irrigation alone, ensuring soil moisture profiles are full prior to this peak demand period is critical.
--Evapo-transpiration (moisture loss through heat + transpiration, or water loss through the plant's leaves) peaks during this same period because the reproductive stage of the crop (highest water use period) coincides with the hottest temperatures of the season. Avoid irrigation "off-time" unless significant rainfall volumes are observed.
--Corn's natural response to heat is to "roll up" as its only defense against burning up. Fields under pivot irrigation must supply adequate volumes of water--even if rolling is observed. Quick passes to relieve visual plant stress from heat will be more harmful overall simply because moisture applied at inadequate volumes will have a higher percentage of evaporation, forcing depletion of soil-stored moisture much more rapidly.
What are the stages of reproductive development? There are six stages of reproductive development in corn. They are as follows:
--Tassel (VT): Bottom-most branch of tassel completely visible and silk has not emerged.
--Silking (R1): Silks visible outside the husks.
--Blister (R2): Kernels white on outside, clear liquid inside.
--Milk (R3): Kernel yellow outside, milky white fluid inside.
--Dough (R4): Kernel fluid thick/pasty, cob pink or red.
--Dent (R5): Most kernels at least partially dented.
--Physiological Maturity (R6): Milk line no longer evident, black layer formed. Maximum dry weight is attained.
Editor's note: Crop Talk is brought to you by agronomists serving your community to keep you informed about current growing conditions and crop management issues affecting the crops in your area. Cole Randol, Alliance, Neb., is an agronomist with Pioneer Hi-Bred.
Date: 8/25/04
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