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Clyde L. Elmore, Lawrence R. Costello, and W. Douglas Hamilton

Cider gum (Eucalyptus gunnii Hook. F.), Monterey pine (Pinus radiata D. Don), and camphor tree [Cinnamonium camphora (L.) J. Presl] were evaluated in a field study comparing the effects of herbicides on tree growth. Trees were planted on 13 May 1983 and treated on 20 May 1983, 10 Apr. 1984, and 4 Oct. 1984 with simazine, oryzalin, napropamide, and oxyfluorfen. Glyphosate was applied as a postemergence treatment in all basins on 20 Mar. 1984. None of the herbicides injured the trees. Trunk circumferencesin treated plots increased as much as 553% over untreated plots. All species showed a positive response to increasing weed control. Chemical names used: 6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine (simazine); 3,5-dinitro-N4,N4-dipropylsulfanilamide (oryzalin); N,N-diethyl-2-(1-naphthalenyloxy)-propanamide (napropamide); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene (oxyfluorfen); N-(phosphonomethyl)glycine (glyphosate).

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K.V. Sharman

Four granular formulations of preemergence herbicides-oxadiazon, oxadiazon in combination with simazine, dichlobenil, and oxyfluorfen + oryzalin-were evaluated for weed control and phytotoxic effects on 10 species of container-grown Australian rain forest plants. Herbicides were applied at half and at one and two times the manufacturer's recommended rate. Oxyfluorfen + oryzalin, oxadiazon, and oxadiazon + simazine controlled all weed species at half the recommended rates (1.0 + 0.5, 2.0, and 2.0 + 0.5 kg·ha-1, respectively) with no phytotoxic effects after 10 weeks to nine of the 10 rain forest species tested: broad-leafed lilly-pilly [Acmena hemilampra (F. Muell. ex Bailey) Merr. and Perry], red ash [Alphitonia excelsa (Cunn. ex Fenzl) Reisseck ex Benth.], rusty bean [Dysoxylum rufum (A. Rich.) Benth.], macaranga [Macaranga tanarius (L.) Muell. Arg.], fibrous satinash [Syzygium fibrosum (Bailey) T. Hartley and Perry], Queensland golden myrtle [Metrosideros queenslandica L.S. Smith], cluster fig [Ficus racemosa L.], corduroy tamarind [Arytera lautereriana (Bailey) Radlk.], and celerywood [Polyscias elegans (F. Muell and C. Moore) Harms]. Dichlobenil depressed plant growth of red ash and failed to control bittercress (Cardamine hirsuta L.) and green amaranth (Amaranthus viridus L.), even at twice the recommended rate (4.0 kg·ha-1). All herbicides applied at half the recommended rates produced minor to moderate plant injury within 5 weeks of the first application to corduroy tamarind and northern silky oak [Cardwellia sublimis F. Muell.]. A second application 10 weeks after the first caused no significant plant injury to corduroy tamarind but resulted in severe plant injury to northern silky oak. This finding validates the previously reported sensitivity of Proteaceous spp. to preemergence herbicides. Chemical names used: (2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4 oxadiazoline-5-one) (oxadiazon); (2-chloro-4,6-bisethylamino-1,3,5-triazine) (simazine); 2,6-dichlorobenzonitrile (dichlobenil); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene (oxyfluorfen); and 3,5-dinitro-N4,N4 -dipropylsulfanilamide (oryzalin).

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Joanna Hubbard and Ted Whitwell

Twelve ornamental grasses from the genera Calamagrostis, Cortaderia, Eragrostis, Erianthus, Miscanthus, Sorghastrum, Spartina, Panicum, and Pennisetum were evaluated for tolerance to the postemergence herbicides fenoxaprop-ethyl, fluazifop-P, and sethoxydim at 0.4 kg a.i./ha. Calamagrostis was uninjured by fenoxaprop-ethyl as measured by visual injury ratings, height, and foliage dry weight. Greenhouse studies evaluated the tolerance of three Calamagrostis cultivars to fenoxaprop-ethyl rates of 0.4 to 3.2 kg a.i./ha with no observed visual injury from any treatment. However, the expansion rate of the youngest Calamagrostis leaf was reduced linearly with increasing herbicide rates each day after application. The highest rate (3.2 kg a.i./ha) reduced the leaf expansion rate by 1 day and all other rates by 3 days after treatment. Leaf expansion rate differed between Calamagrostis cultivars at different times after herbicide treatment. Dry weight of Calamagrostis arundinacea `Karl Foerster' was reduced at 4 weeks after treatment but not at 10 weeks after treatment. Chemical names used: (±)-ethyl 2-[4-[(6-chloro-2-benzoxazolyl)oxy)phenoxy]propanoate (fenoxaprop-ethyl); (R)-2-[4-[[5-trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid (fluazifop-P); 2[1-(ethoxy imino)butyl]-5[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one (sethoxydim).

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Jeffrey F. Derr

Assessing herbicide impacts are difficult due to the indirect effects of weeds on apple (Malus domestica Borkh) growth and development. Herbicide loss will increase potential for development of herbicide-resistant weeds. A limited number of alternatives exist for herbicides currently used in apple production. Switching to certain herbicides increases potential for crop injury. Certain alternatives have higher acute toxicity or are more expensive. No alternatives exist to 2,4-D for broadleaf control in grass alleyways. Nonselective herbicides are alternatives to 2,4-D within the row but pose a greater risk of crop injury. It is difficult to assess long-term impact of 2,4-D loss due to impact on pollination and pest management. Loss of glyphosate will result in yield losses in apple production. Most alternatives to glyphosate are less effective on perennial weed species. Paraquat, one alternative to glyphosate, poses greater hazard to the applicator due to its higher acute toxicity. Diuron is important for rotation with simazine to prevent the development of herbicide-resistance weeds. Norflurazon has an important use in recently planted orchards, where few alternatives exist for yellow nutsedge (Cyperus esculentus L.) control. Oryzalin is commonly used for newly planted orchards and certain alternatives can only be used on nonbearing trees. Alternatives to paraquat pose greater risk of tree injury, although there would be increased worker safety with alternative products. Glyphosate would be the predominate alternative if paraquat was no longer available. Simazine would be the predominate replacement if diuron were no longer available and diuron would be the predominant alternative if simazine was no longer registered for use. Resistance management would be negatively impacted if growers relied on simazine or diuron as their primary preemergence herbicide.

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C.A. Weber

A partial diallel design was used to investigate the inheritance of tolerance to terbacil herbicide in cultivated strawberry, Fragaria ×ananassa Duch. Two tolerant cultivars, `Honeoye' and `Earliglow', two moderately tolerant cultivars, `Lester' and `Allstar', and two susceptible cultivars, `Red Chief' and `Guardian' were used as parents to create populations that segregated for tolerance to the herbicide. Tolerance rankings of the populations closely coincided with expected rankings based on the published tolerance levels of parental cultivars. `Honeoye' and `Earliglow' derived populations had the highest average tolerance ratings, while `Guardian' derived populations had the lowest tolerance ratings. Heritability was estimated at h2 = 0.50, indicating that significant progress in increasing the tolerance of new cultivars to terbacil can be achieved through traditional recurrent selection procedures. General and specific combining abilities suggest that the tolerant cultivars in this study may be fixed in their tolerance and that increased mean tolerance will be most apparent in progenies combining tolerant and susceptible cultivars. As such, a broader pool of germplasm may be needed to develop cultivars that are more tolerant than those in this study. Chemical names: terbacil (3-tert-butyl-5-chloro-6-methyluracil)

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Daniel D. Beran, Roch E. Gaussoin, and Robert A. Masters

Native wildflowers are important components of grassland communities and low-maintenance wildflower seed mixtures. Weed interference limits successful establishment of native wildflowers from seed. Experiments were conducted to determine the influence of the imidazolinone herbicides imazethapyr, imazapic, and imazaquin on the establishment of blackeyed susan (Rudbeckia hirta L.), upright prairieconeflower [Ratibida columnifera (Nutt) Woot. and Standl.], spiked liatris [Liatris spicata (L.) Willd.], blanket flower (Gaillardia aristata Pursh.), purple coneflower [Echinacea purpurea (L.) Moench.], and spotted beebalm (Monarda punctata L.). Wildflower response to the herbicide treatments was variable and appeared to be influenced by the level of weed interference. Establishment of the native wildflowers after application of imazethapyr or imazapic at 70 g·ha-1 a.i. was generally improved at sites with greater weed interference. Emergence and density of wildflowers was often reduced by imazapic in sites with low weed interference. Flower density during the second growing season was usually either improved or not reduced by either imazethapyr or imazapic. Based on these findings, imazethapyr and imazapic can reduce weed interference and improve the establishment of some native wildflowers in areas with high weed infestations. Chemical names used: (±) -2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid (imazapic); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid (imazaquin); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid (imazethapyr).

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Jack D. Fry and Ward S. Upham

In 1992 and 1993, 12 postemergence herbicide treatments were applied to field-grown buffalograss [Buchloe dactyloides (Nutt.) Engelm.] seedlings having 1 to 3 leaves and 2 to 4 tillers, respectively. The only herbicide treatments that did not cause plant injury at 1 or 2 weeks after treatment (WAT) or reduce turf coverage 4 or 6 WAT compared to nontreated plots (in 1992 or 1993) were (in kg·ha–1) 0.6 dithiopyr, 0.8 quinclorac, 2.2 MSMA, and 0.8 clorpyralid. Evaluated only in 1993, metsulfuron methyl (0.04 kg·ha–1) also caused no plant injury or reduction in coverage. Fenoxaprop-ethyl (0.2 kg·ha–1) caused severe plant injury and reduced coverage by >95% at 6 WAT. Dicamba reduced coverage by 11% at 6 WAT in 1992 but not 1993. The chemicals (in kg·ha–1) triclopyr (0.6), 2,4-D (0.8), triclopyr (1.1) + 2,4-D (2.8), 2,4-D (3.1) + triclopyr (0.3) + clorpyralid (0.2), and 2,4-D (2.0) + mecoprop (1.1) + dicamba (0.2) caused plant injury at 1 or 2 WAT in 1992 or 1993, but coverage was similar to that of nontreated turf by 6 WAT. Chemical names used: 3,6-dichloro-2-pyridinecarboxylic acid (clorpyralid); 3,6-dichloro-o-anisic acid (dicamba); (+/–)-2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid (diclofop); 3,5-pyridinedicarbothioic acid, 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-S,S-dimethyl ester (dithiopyr); 2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy] propanoate (fenoxaprop-ethyl); 2-(2,4-dichlorophenoxy)propionic acid (mecoprop); methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-amino]carbonyl]amino]sulfonyl]benzoate (metsulfuron methyl); monosodium salt of methylarsonic acid (MSMA); 3,7-dichloro-8-quinolinecarboxylic acid (quinclorac); [(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid (triclopyr); (2,4-dichlorophenoxy) acetic acid (2,4-D).

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Jack E. Staub, Larry D. Knerr, and Herbert J. Hopen

The growth and yield of three cucumber (Cucumis sativus L.) genotypes were evaluated in 1987 and 1988 using three planting arrangements and four weed control treatments. A monoecious, indeterminate, normal leaf cultivar, Calypso, a gynoecious, normal leaf size determinate × monoecious determinate F1 hybrid (UW 11234), and a gynoecious, determinate little leaf inbred line (WI 50476) were evaluated for fruit yield at a 30-cm equidistant (109,000 plants/ha), a 20-cm equidistant (242,000 plants/ha), and a 43-cm row (272,000 plants/ha) spacing. Weed control treatments consisted of an unweeded control, naptalam benzoic acid at 6.7 kg ae/ha, chloramben at 4.5 kg ae/ha, and the herbicides in combination. Although number and weight of fruit per hectare increased with increasing plant density, fruit weight per plant decreased with increasing density. Fruit harvested from plants in unweeded control plots were significantly smaller than those in herbicide-treated plots, and fruit yield of unweeded control plots was lower than in nonweedy plots in 1987. In 1987, plants in plots treated with naptalam produced smaller fruit than plants in plots treated with chloramben or chloramben plus naptalam. Although fruit yield per plant in 1987 was similar in chloramben plots with or without naptalam and generally higher than that of plots treated only with naptalam, fruit yields from naptalam-treated plants were highest in 1988. `Calypso' usually produced more and larger fruit than the determinate genotypes. Based on comparisons of fruit per plant under comparable spacings, productivity of WI 5047G was often lower and its fruit were smaller than those of normal leaf genotypes. Plants of WI 5047G may not attain the source capacity needed for adequate fruit growth before the onset of anthesis, thus producing smaller fruit. Chemical names used: (2-[(1-naphtalenylamino)carbonyl)benzoic acid (naptalam); 3-amino-2,5dichlorobenzoic acid (chloramben).

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Edgar L. Vinson III, Kaitlyn J. Price, J. Raymond Kessler, Elina D. Coneva, Masuzyo Mwanza, and Matthew D. Price

. Figueroa et al. (2005) stated that only 39% of the strawberry acreage in the United States received herbicides, which was primarily accommodated through the applications of only two chemistries with different modes of action, napropamide and terbacil

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Scott B. Lukas, Joseph DeFrank, Orville C. Baldos, and Glenn S. Sakamoto

protective top layer. In Hawaii, seashore dropseed is slow to establish (>3 months) from cuttings and provide a weed-suppressing canopy. Preemergence herbicides can greatly increase the success of native plant establishment ( Tjelmeland et al., 2008