Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)


1. Total leaf removal (stripping) at weekly intervals. from four-leaf to first tassel stages, caused reduction in yield in almost direct proportion to the percentage of the leaves unrolled at the time the injury was inflicted. The yield reduction ranged from 9 percent during early June to 100 percent about July 20, at the pre-tassel stage, decreasing gradually after the completion of fertilization and ending with a 5 percent reduction in yield on Sept. 7 when the corn was nearly mature.

2. Severe shredding at weekly intervals, which removed about 50 percent of the unrolled leaves, caused a reduction in yield of 2 percent for the first 2 weeks in June. Yields dropped gradually at each weekly period until the low point, with a 50 percent reduction, was reached at the pre-tassel stage, and then gradually rose, ending with a 7 percent reduction on Sept. 7.

3. Removal of one-third and two-thirds of the leaves followed the same trends as shredding and stripping. There was very slight reduction for the first 2 weeks, then a drop in yields to a low point of 30 percent and 70 percent reduction, respectively, at the critical tasseling-silking stage, and a gradual increase to 8 and 12 percent reduction on Sept. 7.

4. Removal of half of each leaf at the pre-tassel stage, the full tassel stage and the milk stage reduced yields 27 percent, 33 percent and 13 percent, respectively.

5. Minor leaf injuries which were designed to upset the elaboration and translocation of synthesized plant food did not result in significant decreases in yield.

6. Severe bruising of stalks and ears a week before the tasseling stage reduced the yield 20 percent which increased to a 35 percent reduction at the full tassel stage. Yields gradually rose to a 6 percent reduction on Sept. 7.

7. Severe bruising of stalks and ears and severe shredding of leaves reduced yields 64 percent a week before tasseling and 77 percent at the tasseling stage. Yields gradually rose to a 9 percent reduction on Sept. 7.

8. A comparison of shredding only, bruising only, and shredding and bruising for 1931 and 1932 shows that while shredding reduced yields 64 percent and bruising 35 percent at the critical tasseling period a combination of the two reduced yields only 13 percent more than shredding only.

9. Severe shredding of six different strains of corn at two critical periods did not result in significant differences in yield reduction for the different strains.

10. Severe drouth in 1930 caused moisture to become the limiting factor so that leaf and stalk injuries did not result in as great a decrease in yield as in normal seasons. In June, reduction in leaf area reduced transpiration and resulted in somewhat larger yields from the injured plots than from the checks.

11. Leaf and stalk injury at all stages of development resulted in little reduction in kernel development, as measured by bushel test weight, except where a very large proportion of the leaf area was removed either just preceding, during, or following the tasseling-silking period. Earlier in the season the size of the ears was reduced by leaf removal but the weight per bushel was nearly normal.

12. Bruising of the ears resulted in 2 to 3 percent of damaged kernels, which would cause the corn to grade No.2. This is not important since corn seldom, if ever, grades better than No.2 under farm conditions.

13. Injury during the rapidly developing period preceding the tasseling stage resulted in some increase in percentage of smutted plants, the number varying directly with the amount of smut occurring each year in uninjured corn. There was no relation between the type of injury and smut infection except in 1929 when bruising the ears just as silking began resulted in a decided increase in ear smut. This did not occur in any of the other seasons. No noticeable increase in other corn diseases resulted from any type of injury.



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