The Effects of Weed Pressure and Row Spacing On Pollination, Ear Development and Yield in Corn.

THE IMPACT OF WEED DENSITY ON POLLINATION OF CORN, M.K. Williams, R.W. Heiniger, D.L. Jordan, and W.J. Everman,  North Carolina State University, Raleigh, NC.

ABSTRACT

Weeds and their management continue to be important in optimizing corn yield. Cultural practices such as planting date, cultivar selection, and row pattern/plant population can affect weed interference with corn. Twin row plantings (rows spaced 8 inches apart on 36-inch centers) could reduce weed interference by closing the canopy more quickly than single rows. The interaction of row pattern has not been thoroughly evaluated in LibertyLink® and Roundup Ready® systems.  The role of weed population, as influenced by herbicide program, on silking and quality characteristics associated with corn ears also has not been evaluated.  Therefore, research was conducted to determine weed control and corn response to interactions of herbicide resistant trait (HRT) and the appropriate herbicide used in these hybrids when grown in single and twin row planting patterns on the coastal plain of North Carolina.

The experiment was conducted at Peanut Belt Research Station during 2011 on a Norfolk fine sandy loam soil typical of the Coastal Plain of North Carolina under sprinkler irrigation. Corn was planted in conventionally-prepared raised beds spaced 36 inches apart. Glufosinate-resistant (LibertyLink®) and glyphosate-resistant (Roundup Ready®) hybrids were planted in single rows or twin rows (8-inch spacing on 36-inch centers) in mid April. Within each HRT and planting pattern combination, Dual Magnum was applied preemergence (PRE), followed by postemergence (POST) herbicide programs including:1) no POST; 2) dicamba POST; 3) glufosinate or glyphosate POST in the appropriate hybrid; 4) atrazine POST; 5) atrazine plus dicamba POST; and 6) atrazine plus dicamba plus glufosinate or glyphosate POST.  Corn was 10 to 14 inches in height when herbicides were applied.  Visible estimates of percent common ragweed control were determined 3 wks after POST application.  Density of common ragweed was also determined 3 and 6 weeks after POST herbicides were applied. In addition to corn yield per unit area, yield components and number of days from planting to silk emergence were determined.  Data for common ragweed density and visible control, corn grain yield, corn height, corn ear type, and days from planting to silk emergence were subjected to ANOVA appropriate for the factorial treatment structure and means were separated using Fisher’s Protected LSD test at p ≤ 0.05.  Pearson Correlation Coefficients were determined for weed population and visible control vs. corn parameters at p ≤.05.

The interaction of HRT, herbicide program, and planting pattern was not significant for common ragweed population, visible control, or any of the measurements associated with corn. The interaction of HRT and herbicide program also was not significant for weed population or control and corn growth. These data suggest that under conditions of this experiment and with common ragweed, twin row planting patterns offer no advantage to single row patterns when the total corn population per unit area is the same.  Also, lack of an interaction of HRT and herbicide program suggests that both glufosinate and glyphosate are equally effective when applied in their appropriate herbicide-resistant hybrid for this weed.  Although the main effect of HRT was significant for several parameters, HRT did not react with other treatment factors in most instances. Factors associated with these hybrids other than HRT could have contributed to these differences.  All herbicide programs that included a POST herbicide were more effective in controlling common ragweed than S-metolachlor alone.  Corn yield was improved in all but one instance when POST herbicides were applied, but few differences in ear characteristics were noted when comparing among herbicide programs.  Correlations among common ragweed density or visible control and corn grain yield and nubbin ears were noted.  A higher density of common ragweed decreased yield, increased the number of nubbin ears, and the number of days to silk emergence.  This response was not unexpected as interference from weeds often decreases grain yield, and establishment of shorter ears with fewer grains would be a possible mechanism of yield reduction.  Also, delayed development of ears as reflected in delayed emergence of silks is consistent with weed interference with corn. In the future, herbicide programs will be designed to provide a broader range of common ragweed densities to better establish correlations.