Vol. 54—2000 - NorthEastern Weed Science Society

LONGEVITY OF PREEMERGENCE CRABGRASS HERBICIDES
Jeffrey F. Derr'
ABSTRACT
Studies were conducted to determine the length of residual control for commonly-used
turf preemergence herbicides. In the first study, flats were buried in a field location aod filled
with native soil. The pH was 5.3 with 1.5% organic matter. Six flats were used per plot.
Herbicides applied as sprays aod their application rates were: prodiamine, 0.75 Ib ai/A;
pendirnethalin, 3.0 IblA; dithiopyr, 0.5 IbfA; bensulide, 10.0 IbfA; siduron, 10.0 IblA; aod
oryzaIin, 3.0 IbiA. The following herbicides were applied in granular form at 3.0 IbfA: benefin,
benefin plus trifluralin aod oxadiazon. Plots were treated on April 3, 1998. A rain totaling 1.75"
fell 1 day after treatment. Flats were removed at 0, I, 2, 3, 4, aod 5 months after treatment
(MAn aod seeded with large crabgrass [Digitaria sangutnolis (L.) Scop.] aod yellow foxtail
[Setaria glauca (L.) Beauv.]. Flats were maintained in the greenhouse. Shoot fresh weight was
recordedapproximately1monthafterseeding.
At 0 MAT, all treatments controlled both weed species greaterthao 95%. At 1 MAT, all
chemicalsexceptbenefinplustrifluralinreducedlargecrabgrassshootweight by over 95%. All
treatmentsexcept bensulide, benefin, and benefinplus trifluralinreducedyellow foxtail shoot
weight by over 90%. At 2 MAT, only prodiamine,pendimethalin,andoxadiazonreducedshoot
weight of both species by over90%. By 3 MAT, only prodiamineprovidedover 90%reduction
in large crabgrass shoot weight, while oxadiazon reduced shoot weight by 89%. At 3 MAT,
numerical reduction in large crabgrass shoot weight was in the order, from greatest to least:
prodiarnine, oxadiezon, oryzalin, pendirnethaIin, bensulide, dithiopyr, siduron, benefin, aod
benefin plus trifluraIin. Only prodiarnine aod oxadiazon reduced yellow foxtail shoot weight
over 90% at 3 MAT. BY 4 MAT, no treatmentreduced large crabgrass shoot weight by 90% or
more. Prodiamine reduced large crabgrass shoot weight by approximately 80% while all other
treatments gave less than a 50% reduction. Oxadiazon reduced yellow foxtail shoot weight by
approximately 85% at 4 MAT. All other treatments provided less than70% reduction. At 5
MAT, all treated flats had a similar large crabgrass shoot weight as the untreated flats. At 5
MAT, prodiamine aod oxadiazon reduced yellow foxtail shoot fresh weight by approximately 55
and 75%, respectively. Shoot weights in the other treatments were similar to that in untreated
flats.
A second study was conducted in an established turf site. At 3 MAT, prodiamine,
pendimethalin, dithiopyr, bensulide, benefin plus trifluralin, oxadiazon, andbenefin all provided
over 800/0control of a mixtureof large and smooth crabgrass. At 5 MAT, prodiarnine, benefln
plus trifluralin, and oxadiazon controlled large and smooth crabgrass 70% or greater.
Pendimethalin, dithiopyr, bensulide, and benefin controlled large and smooth crabgrass less than
60% at 5 MAT. Herbicide longevity is dependent upon the herbicide usedand weed species.
'Professor,
23455.
Virginia Tech, Hampton Roads Ag. Res. and Ext. Center, Virginia Beach, VA
120