Pre- and post-emergence applications of herbicides for control of resistant fineleaf sheep fescue

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Charlene Holmes
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1 Pre- nd post-emergence pplictions of herbicides for control of resistnt finelef sheep fescue in wild blueberry fields in Mine. Yrborough, D.E. nd Cote, J., School of Food nd griculture, The University of Mine, Orono, ME. SUJECT CTEGORY: lueberry Culture INDEX WORDS: Festuc filiformis, Vccinium ngustifolium, phytotoxicity, herbicide, resistnce, hexzinone, terbcil, diuron, rimsulfuron, linuron, clethodim, formsulfuron, pronmide, weeds, STRCT Finelef sheep fescue (Festuc filiformis) is n introduced perennil grss in Mine wild blueberry (Vccinium ngustifolium) fields, nd growers in the Jonesport, ME re reported tht n herbicide-resistnt popultion hd begun tking over locl fields. In study initited in November 211, herbicides registered for use on wild blueberry s well s unregistered herbicides were evluted for control of finelef sheep fescue nd other weeds, nd injury to blueberry. Kerb (pronmide) (2 lb/; ll rtes in product per cre) ws pplied post-pruning in fll 211 nd pre-emergence in spring 212. Sinbr (terbcil) (2 lb/)/direx (diuron) (2 lb/)/velpr (hexzinone) (1 lb/) = Trimix, Mtrix (rimsulfuron) (4 oz/), nd Lorox (linuron) (2 lb/) were lso pplied pre-emergence, nd rrow (clethodim) (8 oz/) nd Option (formsulfuron) (1.5 oz/) were pplied twice post-emergence. Fll pronmide ppliction resulted in the highest blueberry cover. Linuron nd formsulfuron hd significntly higher initil phytotoxicity but overll levels were not uncceptbly high, nd the plnts grew out of it with the exception of minor phytotoxicity in ugust in the linuron tretment. The Trimix ws most effective on brodlef weeds, while formsulfuron ws the lest effective. Fll pronmide ws lso significntly nd consistently most effective in controlling finelef sheep fescue over

2 time, followed closely by rimsulfuron, while clethodim nd linuron were consistently ineffective. In conclusion, fll ppliction of pronmide nd pre-emergence ppliction of rimsulfuron controlled finelef sheep fescue, nd Trimix could be effective with low finelef sheep fescue pressure. Clethodim, linuron, formsulfuron nd spring ppliction of pronmide were not effective control options under sheep fescue nd/or brodlef weed pressure. Since hexzinone nd terbcil re Group 5 herbicides, pronmide is in Group 3 nd rimsulfuron is in Group 2, the use of these herbicides will prevent the development of resistnt grsses. INTRODUCTION: When single herbicide is used for decdes, such s the herbicide hexzinone, resistnce nd weed shifts will occur (Yrborough nd howmik, 1988, LPointe nd Richefort, 21). Hexzinone hs been the primry pre-emergence herbicide used in wild blueberries since its registrtion in Jensen nd Yrborough (24) reported evidence of resistnce to hexzinone of ntive perennil grsses including poverty ot grss (Dnthoni spict) nd severl Festuc nd grostis species in wild blueberry fields in Nov Scoti. There is n ongoing effort to evlute lterntive herbicides with different modes of ction to lternte with or use in combintion with herbicides now used, in order to prevent resistnt weeds from developing (Yrborough nd Cote, 214). METHODS: The experimentl site ws estblished on commercil blueberry field on Msons y Rod in Jonesport, Mine tht hd n extensive cover of finelef sheep fescue which ws not controlled by either pre-emergent pplictions of Velpr or post-emergent pplictions of Post. Plots were 6 x 4 feet in Rndomized Complete lock Design with six replictions. Kerb 5W

3 t 2 lb/ ws pplied on November 211 when the soil temperture ws below 5 F nd rin ws nticipted within the next dy. Pre-emergence tretments pplied on 2 pril 212 were: Kerb 5W t 2lb/, Sinbr WDG 2 lb/ +Direx 4L 2 lb/ +Velpr L 1 lb/ = Trimix, Mtrix SG 4 oz/, nd Lorox DF 2 lb/. Post-emergence tretments pplied twice on 24 My nd 8 June 212 were: rrow 8 oz/ + NIS.25% v/v, nd Option 1.5 oz/ + MSO 1.5 pt/ + MS 1 qt/ gl. lueberry phytotoxicity (%), blueberry cover, fescue grss cover, other grss/sedge cover nd brodlef weed cover were ssessed in ll smple plots fter the lst post-emergence ppliction on 28 June, nd then on 12 July nd 14 ugust. lueberry nd weed covers were ssessed using the Dubenmire Cover Clss scle, which were converted to percent; nd weed species were lso identified. Dt were nlyzed using Duncn s Multiple Rnge Test with for differences mong tretments t ech evlution dte. RESULTS: Initilly, the Mtrix tretment hd the highest blueberry cover nd ws significntly higher thn ll other tretments except for the Fll Kerb tretment (Figure 1). The Fll Kerb tretment hd incresed blueberry cover nd ws the highest in July nd ugust, but ws not significntly higher thn ny tretment except for Lorox, nd rrow in July only. lueberry phytotoxicity ws not uncceptbly high in most tretments, but the Lorox nd Option tretments did hve significntly more phytotoxicity thn the others in June (Figure 2). oth tretments hd significntly higher phytotoxicity in July, nd Lorox continued to hve phytotoxicity into ugust but ws only t 5%, n cceptble level. When brodlef weed cover ws ssessed, the Kerb tretments were consistently lower thn the check but were not significnt (Figure 3). Option ws the lest effective on brodlef

4 weeds, but there were no significnt differences found until the ugust ssessment when Option becme significntly higher thn the Trimix tretment. Trimix resulted in the lest brodlef weed cover overll. Fll Kerb nd Mtrix gve the best finelef sheep fescue control (Figure 4). Spring Kerb reduced finelef sheep fescue cover but did not hve long-term control, while rrow nd Lorox were not effective. Option nd Trimix gve limited control; they were significntly lower thn the check but significntly less effective thn Fll Kerb or Mtrix. In July nd ugust, it ws noted tht lthough the Lorox nd Option tretments did not eliminte finelef sheep fescue, the inflorescences were stunted. Pressure from other grsses ws very low (<%) nd there were no significnt differences in control (Figure 5). DISCUSSION nd CONCLUSIONS: Kerb fll tretment ws most effective in controlling finelef sheep fescue. Spring tretment hd mediocre control of fescue nd did not lst long-term. oth tretments were fir in controlling brodlef weeds. rrow did not control brodlef weeds or fescue. Lorox hd good control of brodlef weeds, nd reduced the height of fescue inflorescences but did not control it. Mtrix showed miniml control of brodlef weeds but hd excellent control of fescue, while Option hd higher levels of brodlef weeds thn the check, but gve good control of fescue. Trimix ws the most effective in controlling both brodlef weeds while lso exhibiting good control of fescue. fll Kerb ppliction or pre-emergence Mtrix ppliction re the best mterils to control herbicide-resistnt finelef sheep fescue. rrow, spring-pplied Kerb nd Lorox re not effective on fields with resistnt fescue popultions. Option should not be used if there re lso brodlef weeds, but if tnk mixed with n effective brodlef herbicide such s Velpr, could be

5 possible solution. Finlly, Trimix tretment could be sufficient on fields with low resistnt fescue grss pressure. Since Velpr nd Sinbr re Group 5 herbicides, Kerb is in Group 3 nd Mtrix is in Group 2, the use of the ltter two herbicides will prevent the development of resistnt grsses. FIGURES: Figure 1. Percent wild blueberry cover following ppliction of pre- nd post-emergence herbicides for the control of finelef sheep fescue. % blueberry cover C C C C C C b b b b b b b Jun 12-Jul 14-ug Check rrow Kerb F'11 Kerb S'12 Lorox Mtrix Option Sinbr+Direx+Velpr

6 Figure 2. Wild blueberry phytotoxicity following ppliction of pre- nd post-emergence herbicides for the control of finelef sheep fescue. % phytotoxicity b b b b b b 28-Jun 12-Jul 14-ug Check rrow Kerb F'11 Kerb S'12 Lorox Mtrix Option Sinbr+Direx+Velpr Figure 3. Percent brodlef weed cover following ppliction of pre- nd post-emergence herbicides for the control of finelef sheep fescue % cover Jun 12-Jul 14-ug Check rrow Kerb F'11 Kerb S'12 Lorox Mtrix Option Sinbr+Direx+Velpr

7 Figure 4. Percent finelef sheep fescue cover following ppliction of pre- nd post-emergence herbicides for the control of finelef sheep fescue % fescue cover b bc b bc 3 c 2 C d C C d C 28-Jun 12-Jul 14-ug Check rrow Kerb F'11 Kerb S'12 Lorox Mtrix Option Sinbr+Direx+Velpr Figure 5. Percent cover of other grsses following ppliction of pre- nd post-emergence herbicides for the control of finelef sheep fescue % grss cover Jun 12-Jul 14-ug Check rrow Kerb F'11 Kerb S'12 Lorox Mtrix Option Sinbr+Direx+Velpr

8 cknowledgements This mnuscript is publiction number 3387 of the Mine griculturl nd Forest Experiment Sttion. REFERENCES: Jensen, K.I.N. nd Yrborough, D.E. 24. n overview of weed mngement in the wild blueberry industry Pst nd present. Sm. Fr. Rev. 3(3/4): LPointe, L. nd Richefort, L. 21. Weed survey of the lowbush blueberry fields in Sgueny- Lc-Sint-Jen, Quebec following eight yers of herbicide ppliction. Cn. J. Plnt Sci. 81: Yrborough, D.E. nd howmik, P.C Effect of hexzinone on weed popultions nd on lowbush blueberries in Mine. ct Hort. 241: Yrborough, D.E. nd Cote, J Evlution of pre-emergence herbicide combintions to prevent weed resistnce in wild blueberry fields in Mine. Proc. Northest Weed Sci. Soc. 68:71.

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