Vol. 54—2000 - NorthEastern Weed Science Society

INFLUENCE OF CROWNVETCH WITH AND WITHOUT SECONDARY COVER CROPS
ON ANNUAL WEED CONTROL AT REDUCED HERBICIDE RATES IN CORN
N. L. Hartwig'
ABSTRACT
In previousresearch,crownvetch(CoronillaYIIii) when used as a perennialliving mulch
and suppressed sufficientlyto preventcompetitionwith a companion com CZaI~ L.) crop, did
oot contributeanythingto annualweed control.In this experiment,oats (a-a ~ L.) and a
mixture of Canadianpea and triticale(X Iriticosecale Wittmack)were drilled as 2' cover cropsat
2.5 buiA and 1.00IblA resepectivelyinto establishedcrownvetchon April 3 to see if there wasan
improvementin weed control overthat providedby crownvetchalonewhen treatedwith lowerrates
ofherbicidesthatareat leastsomewhatselective(orbothcrownvetchandthe2° covercrops.
To identifyweedsuppressivepotentialsof the different covers as well as the potential for
reducingberbicideinputs, the followingweed controltreatmentswere randomly assignedto 12
plotswithin each cover crop block.Weeds were controlledwith 1/4 X, II2X, and IX application
rates (levels)of the following earlypost emergencebroadcast appliedherbicidetreatments.The
com was planted 00 April 30, ooe monthbefore herbicide applicationswere made. On May 27,
comwasin thespikestageandcrownvetchwas 3-4"~ oats6_8 11 andpea+ triticale6-8".
I. May 27, '97 - rimsulfuron + thifensu1fiJronmethyl (Basis®) plus atrazine+ metolachlor
(Bicep II®)I @ 0.0125 + 1335 + 1,6 #aj/A*
2. May 27, '97 - rimsulfuron + thifensulfuron methyl (Basis®) plus isoxaflutole (Balance®)+
metolachlor (Dual n®)1 @ 0,0125 + 0.07 + 1,95 #ai1A*
3. May 28, '97 - rimsulfuron + thifensulfiJronmethyl (Basis®) plus atrazine + imazethapyr
(Contour®) + metolachlor (Dual n®)1 @ 0,0125 + 0,5 + 0,0625 + I 95 #aj/A*
4. May 28, '97 - rimsulfuron + thifensulfuronmethyl (Basis®)plus imazethapyr (Pursuit®)
plus metolachlor (Dual n®)1 @ 0.0125 + 0 0625 + I 95* (* = IX rates)
1Cbas.,.4l(NIS @0.25%vlv+ UAN @ 1.5%vlv) includedwith all the above treatments.
The soil was a Hagerstown SiltLoam (Typic Hapludult)with a pH of 6.8. All treatments
wereapplied with a tractor mounted smallplot sprayerwith XR80015flat fan nozzlesat 28 psi in
10,20 and 40 gallA ofwsler. 'Pioneer 3395 IR' (109 day) com was planted io 15by 25 ft. plots
with a six row no-till planter in 30 in. rows on April 30, 1997with 100lb/A of 10-30-10fertilizerin
therow.Imidazolinoneresistantcomwasplantedsinceimazethapyr(Pursuit)wasa componentof
of treatments 3 and 4. Urea @ 160Ib NtA was applied broadcast at com plantingtime.
Therewas an excellentstandof oats, Canadianpea and triticalein the crownvetchby late
May. Annual grass was virtually 100'10controlledby the herbicides at all rates but broad1eafweed
control;triazine resistant pigweed (AmlUllD\husbybridus) and lambsquarters(ChenoDodium
B!lmm)wasgenerally significantlyless at lower herbiciderates without a cover crop fOrthe first two
herbicidemixtures(Table I). Weed controlwas generallysignificantlyimproved (>93%) even at the
lowestherbiciderateswith crownvetchand slightlybetteryet with 2' cover crops.Althoughaverage
com height,populationand yieldwere all significantlyreduced,especiallyat lowerherbiciderates,it
wasnotonlydueto increasedcrownvetchgrowthbutrathercompetitionfroma combinationof
crowovtetchand the secondarycover crops (oats,triticale) and uncontrolledannualbroadleafweeds.
At this point, it would appearthat annualweed control is possiblewith competitionfrom a
partiallycontrolledcovercropbutattheexpenseof growthandyieldofcom, especiallyin a yearof
inadequaterainfall.
I Prof. of Weed Sci., Dept. of Agronomy,PennsylvaniaState University,UniversityPark, PA.
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