Vol. 54â2000 - NorthEastern Weed Science Society
Vol. 54â2000 - NorthEastern Weed Science Society
Vol. 54â2000 - NorthEastern Weed Science Society
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MANAGING QUACKGRASSINFESTATIONSAS COVERCROPSIN HERBICIDE-REsiSTANTCORN<br />
N. Gift, RR Hahn,and J. Mt. Pleasant'<br />
ABSTRACT<br />
Quackgrass (Elytrigia repens (L.) Nevski) is an invasive weed - not normally considered<br />
to bea desirablecover crop. However.its highnutritionalvaluemakesthis weed moretolerable<br />
in alfalfa (Medicaga sativa L.) than in com (Zea mays L.). Growers typically attempt to<br />
eradicate quackgrass from com fields, but manage this weed less aggressively in alfalfa, where it<br />
contributes to bay quality and yield. The objective of this study was to evaluate herbicides for<br />
use in herbicide-resistantcom whichcould:1)suppressquackgrassto minimize its effect on com<br />
silage yield, 2) leave adequatequackgrassresidueto controlerosion(actas a good covercrop).<br />
and 3) leave quackgrass as a grass companion crop for alfalfa. Results of the first objective are<br />
reported here.<br />
This studywas establishedattwo sites.bothwithheavyexistingquackgrassinfestations.<br />
In Dryden, NY, com hybrids 'DK493GR' (glufosinate-resistant) and 'DK493RR' (glyphosate<br />
resistant) were planted on May 20,1999 in a split plot arrangement, with com hybrid as the main<br />
plot, and herbicide as the subplot. Late post-emergence treatments were applied to both hybrids<br />
on June 30, 1999. Treatments included an untreated check (both hybrids), glufosinate (0.37 and<br />
0.441b ai/A) (GR only), glyphosate (1.0 Ib ailA) (RR only), primisulfuron (0.57 oz ai/A) (RR<br />
only), and nicosulfuron (0.50 oz ailA) (both hybrids). In Valatie, NY, 'DK493SR' was also<br />
included, as well as the additional treatments ofsethoxydim (0.19 and 0.281b ai/A) (SR only).<br />
Untreatedcheckandnicosulfurontreatmentswerealso appliedto SR com. Com in Valatiewas<br />
planted on May 28,1999, and herbicides were applied on June 24, 1999.<br />
Responsevariablesincludequackgrassratings,com ratings(includingyellowing andleaf<br />
rolling.due to droughtconditions).com silageyields,andgroundcovermeasurements.Yields<br />
werelow dueto droughtconditionsacrossNew York. Glyphosatetreatmentsresultedin the<br />
highest yields at both locations (14.9 tonslA in Dryden; 14.8tonslA in Valatie). Yields of<br />
glufosinate treatments did not differ from glyphosate treatments in Dryden, but were lower than<br />
glyphosatetreatmentsin Valatie. Primisulfuronandnicosulfurontreatments'yields werenot<br />
different from those of glyphosate treatments at Valatie, but were lower than glyphosate<br />
treatmentsin Dryden. Sethoxydim(Valatieonly)yieldswereequivalentto theweedy check.<br />
<strong>Weed</strong>y check treatments had the lowest yields in Dryden (9.5 tonslA), and were statisically<br />
equivalentto theworsttreatmentsin Valatie(12.0tons/A). In-seasonquackgrassinjuryratings<br />
for both locations indicate that yields were highly correlated with the degree of quackgrass<br />
suppression.Inextremelydryseasonssuchas 1999,thepotentialformaintaininga healthy<br />
quackgrasscover,withoutreducingcom yields, seemslow. Fallevaluationsof quackgrasscover<br />
will revealwhetherthe suppressedquackgrassin thehigh-yieldingtreatmentswill provide<br />
adequategroundcover.<br />
, Ph.D. StudentlExtension Assoc., Assoc. Prof., and Assoc. Prof., Dept. of Crop and Soil Sci.,<br />
Cornell Univ., Ithaca. NY 14853-1901<br />
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