Vol. 51—1997 - NorthEastern Weed Science Society

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49
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PFMERGENCE
CONTROL OF PROSTRATE KNOTWEED
, J. C. Neall
ABSTRACT
Prostrate kno eed (Polygonum aviculare L. NPOLAV) is a common weed in turfgrass thinned
due to compactio , traffic, athletic use or pest damage. It is difficult to control postemergently with
available herbici and is best controlled preemergently. Although, commonly associated with hot,
drought-pronesi , prostrate knotweed germinates very early in the spring - typically before
preemergent herb cides are applied. In my previous research, many preemergent herbicides labeled
for prostrate kno eed control failed to provide adequate control in golf course fairway turf when
applied in early s ring. In this study, we investigated the effectiveness of late fan applications of
labeled herbicide as compared to spring treatments for preemergence control of prostrate knotweed.
Herbicides w re applied on November 30, 1995 or April 12, 1996 to a predominantly Poaonnua
and perennial rye rass (Lolium perenne) golf course fairway mowed at th inch. November
applications were about 7 weeks after the last mowing for theseason. April treatments were only 2
days after snow c er had melted from the plots but prostrate knotweed seedhad already germinated;
most of thegermi ated seed were on thesoil surface and the primary roots had not yet penetrated the
soil surface. The soil surface and 2 inch depth temperatures at the time of thespring treatments were
53 F and 45 F, pectively. The herbicides applied included prodiamine (Barricade) at 0.75 and 1.1
Ib ail A, isoxaben (Gallery) at 0.75 and 1.0 Ib ailA, and pendimethalin (pre-M) at 1.5 Ib ailA.
Late fall appl cations of each herbicide controlled prostrate knotweed better than spring
treatments. Late all-applied prodiamine controlled 50 and 83 % of the prostrate knotweed at 0.75
and 1.1 IblA, res tively; spring applications provided only 33% and 43 % control. Similarly, late
faU application 0 pendimethalin controlled prostrate knotweed 98% but only S5% with spring
treatment. Iso n provided complete control at 0.75 IblA with fall applications but no control
with the spring tments.
In a separate tudy, the effects of late fan preemergent herbicide applications on spring
overseeding was valuated. In that test, prodiamine and isoxaben were applied on November 30,
1995 at the same tes as in theprostrate knotweed study. The area was treated with Roundup on
May 1 and slit s ed with perennial ryegrass on May 9, 1996. Plots were rated once a month.
Prodiamine redu turfgrass cover ~~ by 70% in July ratings. By theend of August turfgrass had
partially recover with only 20 to 33 % reduction in cover from 0.75 and 1.1 lb ailA, respectively.
In contrast, isoxa n caused no stand reduction in June or August ratings. In July ratings, a slight
(18%) reduction as observed with 1.0 Ib/A isoxaben. In August 1996 ratings, other weeds from
seed controlled b
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November applications of isoxaben at 0.7S IblA included creeping woodsorrel,
(Oxalis comicu ll), broadleaf plantain (Plantago major) and white clover (Trifolium repens) from
seed. These data s wed that several herbicides were effectively controlled prostrate knotweed when
applied in late fal , including prodiamine, pendimethalin and isoxaben. But only isoxaben did so
without iDlederir with springoverseeding,
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'Assoc. Prof.1Dept. of Horticultural Sci., N.C. State Univ., Raleigh, NC 27695