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S. Alan Walters and Bryan G. Young

Petersen, 2016 ; Rapp et al., 2004 ). Weeds often become the primary problem in NT production systems because tillage is often used in CT systems to reduce weed populations that preemergence (PRE) herbicides fail to control. Although early-season weed

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C. Hamel, F. Morin, A. Fortin, R.L. Granger, and D.L. Smith

Herbicides are increasingly used in orchards. Since apple trees strongly depend on mycorrhizae, the effects of three commonly used herbicides on the host plant and endophyte were examined. Symbiosis between tissue-cultured P16 apple rootstocks and Glomus versiforme (Karsten) Berch was established under greenhouse conditions. Simazine (1, 2, 10, and 20 μg a.i./g), dichlobenil (1, 5, 10, and 25 μg a.i./g), paraquat (0.5, 1, 10, and 100 μg a.i./g), or water was applied to mycorrhizal and nonmycorrhizal plants as a soil drench. The response of mycorrhizal plants to herbicide was greater, and the relative elongation rate was more sharply reduced in mycorrhizal (76%) than in nonmycorrhizal plants (33%). Six weeks after herbicide application, dry mass reduction due to herbicides was similar (39% and 36%) for mycorrhizal and nonmycorrhizal plant shoots, respectively, while root dry mass reduction was larger for mycorrhizal (63%) than nonmycorrhizal plants (46%). None of the herbicide treatments affected root colonization. However, an in vitro hyphal elongation test with G. intraradices Schenck & Smith and herbicide-amended (0, 1, 10, 100, and 1000 μg a.i./g) gellan gum solidified water showed that either dichlobenil or paraquat, even at the lowest concentrations, could significantly reduce hyphal elongation. Simazine did not affect hyphal elongation in vitro, a result suggesting that improved absorption capacity of mycorrhizae explains, at least in part, the increased phytotoxicity of some herbicides. It was found that plant mortality was higher among mycorrhizal than nonmycorrhizal apple trees for all herbicide treatments. The increased CO2 assimilation rates of dichlobenil-treated mycorrhizal plants contrasted with the decreased rates of control plants measured 1 week after dichlobenil treatment. This indicates a physiological interaction between mycorrhizal colonization and dichlobenil in the toxic response of apple plants. Chemical names used: 2-chloro-4,6-bis-ethylamino-s-triazine (simazine), 2,6-dichlorobenzonitrile (dichlobenil), 1,1'-dimethyl-4,4'bipyridinium (paraquat).

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Peter H. Dernoeden

Abstract

Fenoxaprop is an effective postemergence herbicide for summer annual grass weed control in cool-season turfgrasses. Following emergence of smooth crabgrass [Digitarla ischaemum (Schreb.) Muhl.] and goosegrass [Eleusine indica (L.) Gaertn.], fenoxaprop was applied alone or in combination with one of several preemergence herbicides. The objective of these field studies was to determine whether these herbicide combinations would provide both effective postemergence control of smooth crabgrass and goosegrass, as well as subsequent preemergence control of annual grass weed seed germinating thereafter. When fenoxaprop was applied alone in June or July to smooth crabgrass, the level of control ranged from poor (40%) to excellent (99%), depending on herbicide rate and timing of application. Smooth crabgrass control was erratic where plants had more than four tillers, particularly on a droughty site. When fenoxaprop (0.17, 0.20, or 0.39 kg·ha–1) was applied in combination with bensulide, benefin, DCPA, oxadiazon, pendimethalin, or prodiamine, excellent (90% to 100%) season-long smooth crabgrass control was achieved. Fenoxaprop + preemergence herbicide combinations exhibited complementary action, particularly in tank mixes applied to tillered smooth crabgrass. Fenoxaprop applied alone controlled goosegrass (two-leaf to three-tiller stage), but goosegrass reinfested treated plots from seed germinating after the herbicide application. When fenoxaprop (0.20 kg·ha–1) was applied with oxadiazon (2.2 kg·ha–1) to nontillered goosegrass, exceptional (99%) season-long goose-grass control was achieved. Chemical names used: (±)-ethyl 2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy] propanoate (fenoxaprop); N-butyl-N-ethyl-2,6-dinitro-4-trifluoromethyl)benzenamine (benefin); O,O-bis(l-methylethyl)-S-[2-[(phenylsulfonyl)amino]ethyl]phosphorodithioate (bensulide); dimethyl 2,3,5,6-tetrachloro-1,4-benzenedicarboxylate (DCPA); 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-l,3,4-oxadiazol-2-(3H)-one (oxadiazon); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin); 2,6-dinitro-N 1,N 1,-dipropyl-6-(trifluoromethyl)-1,3-benzenediamine (prodiamine).

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Patrick E. McCullough, Ted Whitwell, Lambert B. McCarty, and Haibo Liu

poor shade tolerances, heavy thatch/mat accumulation, and disease susceptibility ( Bunnell et al., 2005 ; White, 1998 ; White et al., 2004 ). These cultivars are also sensitive to herbicides and plant growth regulators used for managing higher

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Christopher A. Proctor and Zachary J. Reicher

along sidewalks and drives, herbicide control of purslane may be necessary. Labels of many turfgrass herbicides list purslane as a weed species controlled, but limited published research is available on herbicide control of purslane in turf. Several

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Shital Poudyal and Bert M. Cregg

). In a study by Gilliam et al. (1992) , 80% of applied granular herbicide landed off-target when empty 2.8-L containers were spaced 30 cm apart. Typically, only a small fraction of pesticides leach out of containers because of high pesticide retention

Open access

O. F. Curtis Jr. and J. N. Cummins

Abstract

Simazine applied to Malling-Merton (MM) 106 (Malus sp) stoolbeds at 1 kg/ha in early June + 1 kg/ha in late July had no effect on either rooting or grade of stoolshoots subsequently harvested. Application of simazine at 3 kg/ha in late July in 2 successive years reduced grades of stoolshoots, especially as percent of non-rooted shoots. The split application appeared to be suitable for commercial weed control without damage to the crop.

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Michele R. Warmund, David H. Trinklein, Mark R. Ellersieck, and Reid J. Smeda

Auxin herbicides have been registered for postemergence control of broadleaf weeds in agricultural crops for more than 50 years ( Peterson et al., 2016 ). Since their initial development, different formulations of auxin herbicides, such as 2,4-D

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Megh Singh, Mayank Malik, Analiza H.M. Ramirez, and Amit J. Jhala

, herbicides are an important choice commonly used by citrus growers either as strip applications within the crop row or as broadcast applications to the grove floor ( Sharma et al., 2008 ). Nonbearing young citrus trees (<4 years old) require greater attention

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S. Christopher Marble, Andrew K. Koeser, and Gitta Hasing

Since 2,4-D was discovered in the 1940s, development and use of herbicides has continually increased ( Timmons, 2005 ). Use of herbicides in residential landscapes is also increasing. From 1994 to 2007, there has been a 60% increase in sales of