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1 224 NATIVEPLANTS|FALL 2007 THE EFFECT OF five PRE-EMERGENCE HERBICIDESON emergence AND ESTABLISHMENT OF Photo by Susan R Winslow225 NATIVEPLANTS | FALL 2007 REFEREED RESEARCHFOUR NATIVE WILDFLOWERS| James S Jacobs, Susan R Winslow, and Monica L PokornyCareful selection of PRE-EMERGENCE herbicide for control ofweeds may improve establishment of native wildflowers grownfor seed production. In a 28-d greenhouse herbicide injuryexperiment, 4 emerging wildflower species were established onsoil treated with one of 6 PRE-EMERGENCE herbicide wildflower seedlings survived the atrazine treatment and fewsurvived the sulfentrazone treatment. Of the 5 herbicides tested,DCPA applied at 1100 g active ingredient (ai) per ha (8 lb ai/ac)and trifluralin applied at 184 g ai/ha (2 pt ai/ac) caused the leastreduction in wildflower seedling density, height, and shoot drymass of all species.

2 The densities, however, of Dalea candidaMichx. ex Willd. (Fabaceae), Gaillardia aristataPursh (Astera-ceae), and Ratibida columnifera(Nutt.) Woot. & Standl. (Astera-ceae) were each reduced in 1 of the 2 experimental runs, whereasthe height of D. candidaand G. aristataand the shoot dry massof R. columniferaseedlings were reduced by trifluralin. LiatrispunctataHook. (Asteraceae) densities were reduced only byatrazine and JS, Winslow SR, Pokorny ML. 2007. The effect of five PRE-EMERGENCE herbi-cides on emergence and establishment of four native wildflowers. Native PlantsJournal 8(3):224 WORDS wildflower seed crop, herbicidal weed control, herbicide injury,Dalea, Gaillardia, Liatris, Ratibida NOMENCLATUREUSDA NRCS (2007) ABSTRACT226 EFFECT OF PRE-EMERGENCE HERBICIDES ON FOUR NATIVE WILDFLOWERSNATIVEPLANTS|FALL 2007ecognizing the role of diversity in plant communityand ecosystem function, prairie restorationists andpeople applying conservation plantings are request-ing more wildflower species in seed mixes.

3 Many ofthese species are difficult to propagate for seed productionplantings. Weed competition during establishment is animportant factor contributing to the failure of native wild-flower plantings. Developing PRE-EMERGENCE herbicide man-agement specific to wildflower species may help reduce weedcompetition in the critical early establishment management of weeds during establishment ofwildflower plantings is one of the most active areas of recentresearch (Aldrich 2002); however, there is little informationavailable about herbicide management for wildflower seedproduction. Some PRE-EMERGENCE herbicides have been testedfor wildflower planting. In a study conducted in Nebraska andOregon, about 35% of the 50 wildflower species planted wereadversely affected by EPTC at kg/ha ( lb/ac) mixed kg/ha ( lb/ac) trifluralin applied and incorporated intothe soil before broadcast seeding (Erusha and others 1991).

4 Johnson (1995) lists napropamide, EPTC, alachlor, pendi-methalin, metolachlor, and trifluralin as herbicides for weedmanagement when planting wildflowers along (1992) listed the herbicides benefin, metcholachlor,EPTC, pronamide, alchlor, and trifuralin as pre-emergenceherbicides for other wildflower controlled-environment herbicide injury study is a firststep in developing herbicide management for wildflower seedproduction plantings because in a controlled environment,death or damage to emerging seedlings is more likely to becaused by herbicide injury than by weed competition or envi-ronmental conditions. Our overall objective was to gain a bet-ter understanding of the effects of PRE-EMERGENCE herbicideson establishing native wildflower species grown for seed pro-duction.

5 Our specific objective was to measure the emergenceand early growth of 4 North American wildflower species onsoil treated by one of 5 PRE-EMERGENCE broadleaf herbicidesand to compare that with a non-treated control in a con-trolled-environment greenhouse AND METHODS Our experimental design was a randomized split-plot with 4replications, and it was conducted twice. The 5 herbicides anda non-treated control (Table 1) were the whole-plot treat-ments,and the 4 wildflower species (Table 2) were the sub-plot treatments. The herbicides were selected and applied attheir known efficacy rate for weeds known to exist at theUSDA NRCS Bridger Plant Material Center and according tothe recommendations of chemical companies and the Mon-tana State University Extension Weed Specialist.

6 The wild-flower species chosen are important in revegetation andrestoration. Seed viabilities (Table 2) were tested using tetra-zolium staining (Moore 1985) prior to seeding to increase thelikelihood of a target seeding density of 25 viable seeds pertreatment trays 80 cm long, 30 cm wide, and 5 cm deep (31 in x12 in x 2 in) were filled to a depth of 4 cm ( in) with a pas-teurized mixture of 50% Farland silt loam (fine-silty mixedTypic Argiboroll) and 50% sand (v:v), and the soil waswatered to capacity. Each tray was assigned at random to oneof 4 replications and one of 6 herbicide treatments. All 4 wild-flower species were seeded in rows by species widthwise ineach tray at a rate of 25 pure live seeds (PLS) per row.

7 Theplacement of each species row within the tray was random-ized for each tray. After seeding, trays were loosely coveredwith plastic wrap and placed in a dark room at 4 C (39 F) fora 10-d stratification stratification, herbicide treatments were applied on22 March 2005 for run 1 and 6 June 2005 for run 2 using aspray table fitted with a TeeJet Flat Fan 8002E nozzle (TeeJetTechnologies, Wheaton, Illinois). Prior to application, thespray table was calibrated based on a 35 l/ha ( gal/ac) vol-ume applied at 5 kmph (3 mph) with kg/cm (40-psi) pres-sure. The nozzle height was 30 cm (12 in) above the soil hours after herbicides were applied, each tray wasmisted using a fog nozzle with enough water to incorporatethe herbicide into the soil.

8 Each tray of each run receivedapproximately the same amount of mist herbicide application, the trays were placed at ran-dom on a bench in a greenhouse with supplemental lightingto provide 12 h photoperiod and 25 C (77 F) daytime tem-perature and 16 C (61 F) nighttime temperature. To accountfor environmental variation along the greenhouse bench, alltrays were re-randomized weekly. Soils in the trays were keptmoist by fog watering 3 times per 2 experimental runs were sampled beginning 7 d afterherbicide application (Days After Treatment [DAT]) and at 7-dintervals for 28 d (4 sample times). At each sampling date, liv-ing seedlings per row were counted; and at the final samplingtime (28 DAT), all living seedlings were measured for heightfrom the soil surface, severed at the soil surface, and oven-driedat 45 C (113 F) for 96 h to determine dry AnalysisThe data were analyzed by species.

9 The numbers of plantsper row (density data) were analyzed using a repeated meas-ures, randomized-block analysis of variance model with run,herbicide treatments, and their interaction as main plots, andR227 JAMES S JACOBS, SUSAN R WINSLOW, AND MONICA L POKORNYNATIVEPLANTS | FALL 2007 TTrraaddee nnaammee CChheemmiiccaall nnaammeeMMeecchhaanniissmm ooff aaccttiioonnAApppplliiccaattiioonn rraattee gg aaii//hhaa ((oozz aaii//aacc))Dacthal WPDCPAM itosis inhibitor1100 ( )SpartanSulfentrazonePhotosynthesis inhibitor32 ( )AatrexAtrazinePhotosynthesis inhibitor367 ( )SurflanOryzalinMicrotubule assembly inhibitor370 ( )TreflanTrifluralinMicrotubule assembly inhibitor184 ( )TABLE 1 The trade names, chemical names, modes of action, and application rates (grams active ingredient per hectare) of the 5 herbicides used as the whole-plot treatments in the controlled-environment greenhouse 2 The 4 wildflower species, their seed length, weight, and viability as determined by tetrazolium testing, seeded within each herbicide treatment in the con-trolled-environment greenhouse study.

10 SScciieennttiiffiicc nnaammeeCCoommmmoonn nnaammeeSSeeeedd lleennggtthh ((mmmm))SSeeeedd wweeiigghhtt ((mmgg))VViiaabbiilliittyy ((%%))Dalea candidaMichx. ex Willd. (Fabaceae)white to aristataPursh (Asteraceae)blanketflower2 to 441155 Liatris punctataHook. (Asteraceae)dotted gayfeather 6 to 813987 Ratibida columnifera (Nutt.) prairie coneflower to 3162596 Woot. & Standl. (Asteraceae)228 EFFECT OF PRE-EMERGENCE HERBICIDES ON FOUR NATIVE WILDFLOWERSNATIVEPLANTS|FALL 2007sampling time and all interactions with run and herbicidetreatments as the sub-subplots (Proc GLM, SAS Institute1990). Seedling height and per-plant seedling dry mass at thefinal harvest time of surviving seedlings were analyzed using arandomized block analysis of variance model.