Anderson, John : J. Anderson is Consultant, Hedgerow Farms, Winters

Lanini, W. Thomas : W.T. Lanini is Extension Weed Ecologist, Department of Vegetable Crops, UC Davis

Long, Rachael

Preemergence herbicides have little effect on vigor of perennial grasses W . Thomas Lanini o Rachael F . Long o John Anderson ing , drilling and transplanting . Com - Perennial grass stands offen face petition from annual weeds has stiff competition from weeds , par - caused many new plantings to fail , ticularly during the first few years discouraging some people and agen - affer grass establishment.Field cies from using native perennial studies were conducted to evalu - grasses in revegetation programs . Al - One - sidedbluegrassWinters plots show ate the tolerance of several estab - dense common chickweed growth except though many factors affect stand per - to pre - lished perennial grasses where chlorsulfuron plus orazylin was sistence , such as adaptability of the used . emergence herbicides in order to species to the site , competition from selectively suppress weeds . invasive annual grass and broadleaf Grass vigor was reduced by some weeds remains the most troublesome herbicides , but most had minimal and difficult to manage . effects . The herbicides that con - Weed management during early de - trolled weeds best also caused the velopment of the perennial grass stand greatest reduction in grass vigor . is critical to successfulestablishment . Once native grass stands achieve full coverage of a site and are properly Before the sweeping alteration of managed , they are able to compete for Californiaâ??s landscape by European in - light , nutrients and water and to re - troduction of livestock , agricultural tard weed invasion . Some weed con - crops and invasive weeds , perennial trol measures may be necessary in es - bunchgrasses dominated much of tablished perennial grasses where California and other western states . large weed seed banks exist or where The introduction of livestock , com - grass stands are sparse . Management bined with drought , led to overgraz - tools available to control weeds in pe - ing of many areas . The massive influx rennial grass stands include tillage , of settlers in the 1800sincreased the Chlorsulfuronprovided good control of weeds in 2 - year - old Idaho fescue , without hoeing , mowing , grazing and use of land under cultivation and also led to affecting grass vigor . fire and herbicides . The cultural meth - the introduction of many alien species . ods by themselves suppress weeds in The result is that the native flora has most cases , but tend to be costly and been almost entirely replaced by intro - time consuming , and may not be fea - duced annual and perennial weedy sible or appropriate in some situations , plant species ; California grasslands such as on hilly land or near urban ar - today are mostly composed of intro - eas . Chemical weed management is of - duced annual species.This shift in the ten a faster and cheaper means of native grass community has resulted in a degradation of rangelands , in - weed control . Severalpostemergence broadleaf creased problems with soil erosion herbicides can controlbroadleaf weeds and weed control , enhanced fire dan - in perennial grasses . Preemergence ger and loss of wildlife habitat . herbicides , including picloram and To address these concernsthere atrazine , control annual weeds with have been attempts to propagate na - low phytotoxicity to perennial grasses . tive perennial grasses in California Picloram is not labeled for use in Cali - landscapes , including parks and recre - fornia , and atrazine use has been re - ation areas , agricultural and urban ar - stricted due to its detection in wells . eas , and along right - of - ways.Current Older grasses , such as this 2 - year - old Information on tolerance of Califor - methods of establishing perennial California melic , were often not affected nia native perennial grass speciesto grass stands include broadcast seed - by herbicidetreatment . CALIFORNIA AGRICULTURE , VOLUME 50 , NUMBER 5 38 ings on untreated plots was often less preemergence herbicides and the ap - We arranged the experiments in a ran - than 5 due to the competition from propriate use rates for California con - domized complete block with three weeds reducing growth . ditions is limited . Therefore work on replications , with each plot measuring Idaho fescue . At both study sites , nonnative perennial grasses was ex - 10 feet by 20 feet . 1 - year - old Idaho fescue was less vigor - amined for possible leads on candidate At both locations and in both years , ous when oryzalin or the combination herbicides . Two perennial grasses , seasonal native grass growth had just of chlorsulfuron and oryzalin was Kentucky bluegrass ( Poa pratensis ) and started at the time of herbicide appli - used ( table2 ) . The Idaho fescue vigor tall fescue ( Festuca arundinacea ) , were cation . The herbicides evaluated in on oryzalin - treated plots at Winters found to be relatively tolerant of these studies were all preemergence was reduced in spite of less rainfall chlorsulfuronat rates less than 0.70 herbicides , requiring rainfall or irriga - and a reduction in the rate of the her - ounces per acre ( oz / ac ) , but at rates tion for activation ( table 1 ) . We ob - bicide . Additionally , at Winters , up to 4 oz / ac tall fescue growth was served excessivenative grass injury in chlorsulfuron treatment reduced the reduced by 30 % . Six species of con - the 1992 studies when chlorsulfuron or vigor of Idaho fescue . The reduction in tainer - grownornamental grasses were oryzalin was used and therefore re - vigor from chlorsulfuron treatment found to be tolerant of oxidiazon at 2 duced application rates for these in the corresponded closely with observa - pounds per acre ( lb / ac ) , and four of 1993studies . Herbicides were applied tions made in other studies . In 2 - year - the six specieswere tolerant to ory - using a C02 - poweredbackpack old Idaho fescue plantings , no differ - zalin at 2 lb / ac . Several preemergence sprayer , using 8002 nozzles at 30 PSI ; ence in vigor was observed among herbicides were identified in prelimi - spray volume was 25 gallons per acre . treatments . Height measurements of nary studies as having potential to At the Rio Vista site , plots were 1 - year - oldIdaho fescue indicated that control annual weeds without signifi - sprinkler - irrigated with 0.75 inches of treatment with either chlorsulfuron or cant injury to established perennial water following treatment to incorpo - oryzalin caused significantheight re - grasses . rate the herbicides . The Winters site ductions ( table 3 ) . Height of 2 - year - old The objective of this study was to lacked irrigation so we timed applica - Idaho fescue was not affected by her - evaluate weed control in and tolerance tions to coincide with the start of sea - bicide treatment . of six California native perennial grass sonal rainfall . Rainfall from the time of At Rio Vista , weed control was im - species to selected preemergence her - herbicide application to the time of proved by the herbicide treatments bicides . vigor evaluation was 17.45inches at with the exception of the simazine Rio Vista and 6.68 inches at Winters . Trials at Rio Vista and Winters treatment ( table4 ) . Simazine at the Weed control and grass vigor were 1lb / ac rate was not effective in con - We set up field trials on Sept . 23 , evaluated on March 15,1993and trolling broadleaf weeds . At Winters , 1992 and Nov . 17,1993on established March 31,1994 . The principal weeds at in 1 - year - oldIdaho fescue , the major California native grasses : meadow both sites were winter annuals . Weed weeds were chickweed ( Stellaria media ) barley ( Hordeum brachyan therum species were combined , and percent and annual sowthistle ( Sonchus oler - Nevski ) ; blue wildrye ( Elymus glaucus weed control was visually assessed , aceus ) . Treating with chlorsulfuron or Buckley ) ; Californiamelic ( Melica noting the weed species that were not the combination of chlorsulfuron and californica Scribner ) ; Idaho fescue controlled . Grass vigor - a visual oryzalin resulted in complete weed ( Festuca idahoensis Elmer ) ; nodding ranking of grass height , tillering and control for the duration of the winter needlegrass [ Nassellacernua ( Stebb . & color - was evaluated in each plot . A growing season , while other treat - Love ) Barkworth ] ; and one - sided blue - vigor ranking of 5 represented ments were less effective . In 2 - year - old grass ( Poa secunda spp . secunda J.S . healthy , robust grass with excellent Idaho fescue , chlorsulfuron , the com - Presl . ) . The 1992 trials were located color . A value of 1represented grass bination of chlorsulfuron and oryzalin , near Rio Vista ( 25miles south of Sacra - with no new growth or tilleringbut simazine and oxadiazon all provided mento ) in a soil with 3.3 % organic still alive . A value of 0 represented good weed control . Oryzalin at the matter , 11 % sand , 43 % silt and 46 % dead grass . Values less than 5 were es - 0.75 lb / ac rate and diuron both failed clay . The 1993trials were located near timates of percent growth and color to control the common groundsel Winters ( 30miles west of Sacramento ) reduction . Grass height was measured ( Seneciovulgaris ) and little mallow in a soil with 1.2 % organic matter , 17 % at the Winters location.Height mea - sand , 45 % silt and 38 % clay . Grasses surements were made on four random had been planted as monocultures one individuals in each plot and averaged or more years prior to the initiation of to give mean grass height for each this study ; thus each grass species rep - treatment . resented a separate trial . In 1992 one Weed control and grass vigor locationwas used for each species ; in 1993two locationswere used for As shown in table 2 , grass vigor Idaho fescue , California melic , varied by species , age of stand at treat - meadow barley and one - sided blue - ment time , herbicide and weed pres - grass , and one for the other species . sure on the study site . Grass vigor rat - CALIFORNIA AGRICULTURE , SEPTEMBER - OCTOBER 1996 39 CALIFORNIA AGRICULTURE , VOLUME 50 , NUMBER 5 40 ( Malvaparviflora ) that were common at needlegrass was field bindweed ( Con - sulfuron provided almost complete this location . volvulus arvensis ) , with only chlor - control of the principal weeds at Win - California melic . One - year - old sulfuron , oryzalin and oxadiazon pro - ters , common chickweed and little grass vigor was reduced more in Win - viding weed control greater than mallow . ters than in Rio Vista ( table2 ) . observed on untreated plots . Meadow barley . Vigor of meadow Chlorsulfuronplus oryzalin in Rio Blue wildrye . Both chlorsulfuron barley did not differ among treatments Vista was the only treatment with a and chlorsulfuron plus oryzalin re - for any of the age groups evaluated vigor rating significantlylower than duced vigor of 4 - year - old blue wildrye ( table2 ) . Poor common chickweed untreated grass . In 2 - year - old Califor - plants ( table 2 ) , while l - year - old blue controlwas observed at Winters on all nia melic , vigor was not significantly wildrye was not significantlyaffected plots not using chlorsulfuron or different among treatments . Two - year - by treatment . One - year - oldblue chlorsulfuron plus oryzalin ( table4 ) . old California melic had higher vigor wildrye treated with oryzalin had the Two - year - old meadow barley plants ratings than l - year - old grasses at Win - lowest vigor ratings . Weed control generally were less vigorous than 1 - ters . The larger 2 - year - old grasses may was significantlyimproved by all her - year - old plants at Winters . Weed pres - have been more competitive with the bicide treatments in l - year - old blue sure was much greater in the 2 - year - weeds that were present , improving wildrye ( table 4 ) . No differencein old grass plots than in the l - year - old weed control ( table4 ) . Also , a deeper weed control was seen in the 4 - year - plots . The decreased weed control on root system in the older grass may old blue wildrye , as weed pressure the 2 - year - old plots resulted in more have reduced the exposure to the was very low on this site . This site had competition and less grass vigor . preemergence herbicides . Weed con - been burned approximately 1month Three - year - oldmeadow barley gen - trol on the l - year - old Californiamelic prior to establishing the trial , and very erally displayed increased vigor com - did not vary among treatments at Rio few annual weeds survived the fire or pared to younger grasses , particularly Vista , but was generally higher for the emerged after the burn . This may also when oxadiazon , diuron or simazine treatments that included chlorsulfuron have predisposed blue wildrye to her - was used ( table 2 ) . In 1992 higher rates at Winters ( table4 ) . All herbicide bicide injury . of chlorsulfuron and oryzalin were treatments were significantlybetter at One - sided bluegrass.One - sided used , which may have caused the in - increasingweed control in contrast bluegrass vigor was significantlyre - creased injury seen on these plots . with the untreated in 2 - year - old Cali - duced by oryzalin and by oryzalin Conclusion fornia melic . Although the principal plus chlorsulfuron treatments ( table 2 ) . weeds at Winters in California melic Reducing the rate of oryzalin or Vigor of established perennial plots were similar to those in the chlorsulfuron in 1993did not improve bunchgrasses was affected by herbi - Idaho fescue plots , weed control was the vigor rating in one - sided blue - cide treatment . Vigor was also gener - greater on the Californiamelic sites grass . The Winters site had a dense ally reduced by dense weed cover . The and is probably related to the greater common chickweed population , which treatments that consistently controlled height and vigor of California melic reduced vigor in all plots compared to the winter annual weeds in these trials ( tables2 and 3 ) . Rio Vista . were chlorsulfuron and the combina - Nodding needlegrass.Vigor of 3 - Simazinereduced the vigor of 2 - tion of chlorsulfuron and oryzalin . year - old nodding needlegrass was re - year - old one - sided bluegrass , which However , these treatments generally duced by oryzalin at 2 lb / ac rate and was unexpected since previous work caused some reduction in grass vigor . by chlorsulfuron ( table2 ) . Neither has shown reduced vigor of several Rates of chlorsulfuron and oryzalin vigor nor height of 2 - year - old nodding native perennial grass specieswhen si - were both reduced after the first year needlegrass was significantlyaffected mazine was used at 2 lb / ac , but little of study in an attempt to reduce grass by treatment , although some trend or no injury at the 1lb / ac rate . The 2 - injury , with only limited improvement toward less vigor was noted in the year - old one - sided bluegrass was lo - observed after rates were reduced . oryzalin - treatedgrass . The higher cated a short distance from the other Since weed control is still very good at treatment rates for chlorsulfuron and grass species and had different soil the reduced rates , particularly with oryzalin used in 1992 on the 3 - year - old characteristics.The soil had less or - chlorsulfuron , further rate reduction grass may have accounted for the ob - ganic matter ( 0.85 % ) and more sand may be possible without reducing served reduction in vigor . All herbi - ( 36 % ) than at the other locations . weed control and could reduce grass cide treatments significantlyimproved Treatments that reduced vigor of one - injury . weed control in 3 - year - old nodding sided bluegrass also reduced height needlegrass ( table4 ) . Herbicide treat - ( table 3 ) . The most dramatic effects W.T . Lanini is Extension Weed Ecologist , ments were generally less effective at were from chlorsulfuron , where height Department of Vegetable Crops , UC increasing weed control in 2 - year - old growth was reduced by 50 % . Improve - Davis ; R.F . Long is UC Cooperative Ex - nodding needlegrass compared to 3 - ments in weed control were greatest in tension Farm Advisor , Solano and Yo10 year - old grass . The principal escape plots where grass vigor reduction was counties ; and J . Anderson is Consultant , weed in the 2 - year - old nodding also greatest ( tables2 and 4 ) . Chlor - Hedgerow Farms , Winters . CALIFORNIA AGRICULTURE , SEPTEMBER - OCTOBER 1996 41