Vol. 51—1997 - NorthEastern Weed Science Society

111
SUPPRESSI N OF A CROWNVETCHIBIRDSFOOT TREFOIL LIVING MULCH FOR
NO-TILLAGE CORN PRODUCTION
N. L. Hartwig and W. S. Curran!
ABSTRACT
Most of herbicides presently labeled for use on field com were applied preplant (PP)
andlor post to a 0 e year old stand of crownvetch (Coronilla varia L.) and birdsfoot trefoil CL2tY.s
comiculatus L.) t at was seeded in com in 1995. Preplant treatments were applied on May 17,
1996 when the cr wnvetch was 4 to 8" and birdsfoot trefoil 8 to 10" in height. On May 31 the
whole trial area treated with metolachlor (Dual II) +pendimethalin (Prowl) @ 1 + 0.825#aiIA
to control most ual weeds without affecting crownvetch or birdsfoot trefoil growth. Since
imazethapyr (Pur uit) was one of the treatments, an imidazolinone resistant com (~~L)
variety was plant . Post treatments were applied June 17, 1996 when crownvetch was 8 to 10
inches and birdsf t trefoil 8 to 12 inches tall and com in the 4 to 5 leaf stage.
The soil as a Hublersburg Silt Loam (Typic Hapludult) with a pH of 6.8. All treatments
were applied wi a tractor mounted small plot sprayer with 800 15 extended range flat fan nozzles
at 28 psi in 20 g A of water. 'Asgrow RX623T' com was planted in 10 by 25 ft. plots with a
four row no-till panter in 30 in. rows on May 22, 1996 with 100 Ib/A of 10-30-10 fertilizer in the
row. Liquid nitr en @ 120 Ib N/A was applied as a sidedress treatment on May 31. Annual
broadleaf weed c ntrol was virtually 100% for all treatments and annual grass control was 95% or
better. There wa some horsenettle (Solanum carolinense L.), hemp dogbane (Apocynum
cannabinum L.) d goldenrod (Solidago spp.) scattered through the trial area.
a solid stand of birdsfoot trefoil by mid May with a sparse stand of crownveteh
mixed with it. e highest com yield was 135 but A where birdsfoot trefoil suppression was 95%
and the crown vet h was completely killed. Previous research would suggest that crownvetch
suppressed 95% r more for the first 6 weeks after com planting will seldom compete with com
and the stunted c wnvetch canopy may indeed save more moisture that it uses.
Twenty 0 the 36 herbicide treatments were glyphosate or growth hormone type herbicides
applied preplant t the com after the crownvetch had 4 to 8 inches and birdsfoot trefoil 8 to 10
inches of new gr . This herbicides almost totally killed the one year old crownvetch but did
suppress the bird foot trefoil about 95% which is probably the right amount. Recovery growth of
the birdsfoot tref il was between 250 and 800 lblA of biomass by September and generally
anything less th 500 Ib/A of biomass will not cause a significant loss in com yield. Glyphosate
was used at 0.75 b/A preplant as a bumdown treatment followed by various growth hormone and
sulfonylureas w ch provided some additional birdsfoot trefoil suppression. Well established
crownvetch will so tolerate these treatments but a one year old stand is too sensitive.
The best over crop suppression was obtained with contact herbicides such as paraquat,
glufosinate or cy azine for bumdown in combination with or followed by other herbicides such
as atrazine, alae or, metolachlor, acetochlor, dimethanamid, pendimethalin, flumetsulam or
flumiclorac for idual weed control and to slow the rate of cover crop recovery. Atrazine at rates
0.5 to 0.751b/A i necessary to slow the rate of birds foot trefoil recovery. Without atrazine in the
mixture the birds oot trefoil recovers so fast that it suppresses com yields excessively.
Crownvetch is n t suppressed quite as much as birdsfoot trefoil by these treatments but the
ultimate goal is t have the crownvetch take over and then manage just the crownvetch as a
perennial living ulch.
1 Prof. and Asso . Prof. of Weed Sci., Dept. of Agronomy, Pennsylvania State University,
University Park, PA. 16802.