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  • Author or Editor: Milton J. Haar x
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Field studies were conducted to determine the potential economic impact of the loss of pronamide herbicide to artichoke (Cynara scolymus L.) growers, and to evaluate pendimethalin as an alternative herbicide during establishment of artichoke. Two rates of pronamide and one rate of pendimethalin were applied to perennial and annual artichokes. With the exception of wild oat (Avena fatua L.), pendimethalin controlled weeds as well as or better than pronamide. Financial analysis of treatment effects was based on weed management expenses and value of yield. The financial effect of using pronamide in perennial artichoke ranged from a loss of $247 to a gain of $326 per ha, whereas its use in annual artichoke increased revenue $542 to $5499 per ha. The effects on revenue of using pendimethalin varied with weed species composition and density. For three sites, revenue increased from $267 to $5056 per ha, while a loss of $1034 per ha occurred at a site with a heavy infestation of wild oat. We conclude that pendimethalin has potential as a pronamide replacement, or as a complement to pronamide. Chemical names used: 3,5-dichloro (N-1,1-dimethyl-2-propynyl)benzamide (pronamide); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).

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Methyl bromide alternative fumigants were evaluated for weed control efficacy in low- and high-elevation strawberry (Fragaria ×ananassa L.) runner plant nurseries. Preplant soil fumigation treatments of methyl bromide plus chloropicrin (MBPic), iodomethane plus chloropicrin (IMPic), 1,3-dichloropropene plus chloropicrin mixture followed by (fb) dazomet, chloropicrin fb dazomet, and a nonfumigated control were evaluated at three California strawberry runner plant nurseries through two production cycles. Fumigant efficacy was measured by weed seed viability bioassays, weed density counts, and time of handweeding. Generally, all alternative fumigant treatments controlled weeds at levels comparable to MBPic. All fumigant treatments, including MBPic, killed more than 95% of common knotweed, common purslane, common chickweed, and strawberry seed. Iodomethane, chloropicrin fb dazomet, and 1,3-dichloropropene plus chloropicrin mixture fb dazomet controlled carpetweed, common lambsquarters, hairy nightshade, palmer amaranth, and prostrate spurge. Handweeding inputs for all fumigants were similar to MBPic at three of four locations. The exception was at the low-elevation nursery in 2000 where handweeding times with MBPic were lower than for IMPic. Treatment and handweeding costs were calculated. The handweeding costs for all treatments were approximately the same. However, the higher iodomethane material cost resulted in a substantially higher treatment cost.

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For years, strawberry (Fragaria ×ananassa L.) runner plant nurseries have relied on methyl bromide (MB) fumigation of soil to produce healthy transplants. Methyl bromide, however, has been phased out due to its environmental risks. The potential for alternative fumigants to replace MB was evaluated at low and high elevation strawberry nurseries in California. The alternative fumigant iodomethane plus chloropicrin (IMPic) and a nonfumigated control (NF) were compared to methyl bromide plus chloropicrin (MBPic) at a low elevation nursery (LEN) and at a high elevation nursery (HEN) near Susanville, Calif. At a HEN near Macdoel, Calif., MBPic was compared to alternative fumigants IMPic, 1,3-dichloropropene plus chloropicrin mixture (Telone C35) followed by dazomet, chloropicrin (Pic) followed by dazomet and NF. Plants produced at the LEN were transplanted at the Macdoel HEN to measure the effects of soil fumigant history on plant health and runner plant production. Plants produced at both high elevation nurseries were evaluated for fruit yield and quality at two commercial fruit production sites in soils previously fumigated with MBPic or Pic. Runner plant production at the nurseries was similar in plots fumigated with either MBPic or alternative fumigants. All fumigation treatments had higher runner plant production than plants produced for two production cycles on NF soils. Generally, fruit yields from nursery plants produced on soils fumigated with IMPic, Pic followed by dazomet, or Telone C35 followed by dazomet, were similar to fruit yields from plants produced on MBPic fumigated soils. Overall, our results indicate that preplant soil treatments with IMPic, Pic followed by dazomet, and Telone C35 followed by dazomet, are potential alternatives to MBPic fumigation for strawberry runner plant nurseries. Fruit yields by plants in MBPic and Pic fumigated soils were comparable; however, they were more variable in Pic fumigated soils. Chemical names used: 1,3-dichloropropene (1,3-D), methyl bromide, methyl iodide (iodomethane), trichloronitromethane (chloropicrin), tetrahydro-3, 5-dimethyl-2 H-1,3,5-thiadiazine-2-thione (dazomet).

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