Stalk Breakage of Dent Corn Infested with the August Generation ofthe European Corn Borer12

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Abstract
The damage caused by Pyrausta nubilalis was studied in 1944 in a field of dent corn hybrids infested by hand with different numbers of egg masses. An avg. increase of 10.1 borers per plant in 16 hybrids caused an increase of 15.3% in the number of plants that broke below the ear, an increase of 38.9% in the number of plants that broke above the ear, and a decrease of 18.9% of the total yield of those plants. Of every 100 plants broken below the ear, 7 had ears touching the ground, and of 100 plants not broken below the ear, the ear of 1 plant had fallen to the ground. The hybrids differed in the amt. of breakage. When the breakage below the ear in the presence of 0.5 borer per plant in the stalks below the ear averaged 2.2, 4.4, 6.8, 13 and 25% in the different hybrids, each additional borer was associated with 1.9, 3.3, 5.8, 7.0, and 9.7% additional breaks, respectively, an indication that each additional borer caused progressively more increase in breakage. A group of hybrids involving a line known to be resistant to diplodia stalk rot broke less than a group involving a line known to be susceptible. Some inbred lines in hybrid combination were apparently more resistant to shank infestation than other lines. Locations outside the stalks in the ears and behind leaf sheaths and locations inside the stalks above the ears lost a total of 5.3 borers per plant between Sept. 9 and Oct. 5 and locations inside the stalks below the ears gained 1.3 borers per plant. The difference of 4.0 borers, or 40.4% of the total borers on Sept. 9, disappeared from the plants and most of these apparently disappeared without entering the stalks, but before they did so it is believed that they materially reduced the yield of grain by feeding on the leaf tissues.

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