Vol. 54—2000 - NorthEastern Weed Science Society

EARLY POSTEMERGENCE TIMING OF PREMIXES AND GLYPHOSATE: A NICE
MATCH FOR ROUNDUP READY CORN
M.J. VanGessel, Q. Johnson, A. Cooper, and C. Whaley'
ABSTRACT
Growers need effective weed control programs that limit the number of trips across the
field. Recent revisions to herbicide labels allow premixed soil-applied herbicides to be
applied to emerged com (Zea mays). This offers the potential to achieve early
postemergence control followed by residual control.
Labeled rates of the various premixed herbicides were applied to com at the spike to V­
1 stage. These herbicide premixes included airazine in combination w~h s-metolachlor,
alachlor, acetachlor, SAN-582, and FOE-5043 plus metribuzin, as well as Basis Gold.
Atrazine was also tank-mixed w~h pendimethalin and Basis. Fall panicum (Panicum
dichotomiflorum) control at layby was not acceptable for most treatments. Treatments
w~h Basis plus atrazine or Basis Gold did provide 90% control of fall panicum. Poor
control w~h other treatments was due to both poor initial control and lack of effective
residual control for the weed species present.
A second experiment examined most of the same premixed herbicides tankmixed w~h
glyphosate, at 1 Ib aiJA, and applied to 2 to 5-collar Roundup Ready com. Excellent
early-season weed control was achieved w~ all treatments due to addition of
glyphosate. No reduction in glyphosate control was observed with any of the tankmixtures.
Full-season control depended on species present at the various sites, In
particular, momingglory (Ipomoea sp.) control was reduced ~h treatments containing
less than 1.0 Ib aiJAof airazine.
Delaying application of residual herbicides results in effective weed control until the
crop is at a more advanced stage compared to applications made at planting. The use
of Roundup Ready com and addition of glyphosate as a tank-mixture improves
postemergence control. Finally, control of the initial flush of weeds is not dependent on
rainfall or irrigation to move the soil-applied herbicide into the soil.
'Assoc. Prof., Ext.Assoc., Res. Assoc., and Grad. Res. Assoc., Univ. Delaware,
Georgetown.
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