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Sanjeev K. Bangarwa, Jason K. Norsworthy, Edward E. Gbur, and John D. Mattice

Purple nutsedge (Cyperus rotundus) is a troublesome weed in vegetable crops in the southern United States. Methyl bromide is widely used for effective purple nutsedge control in polyethylene-mulched vegetable crops. With the impending ban on methyl bromide in the United States, an effective alternative is needed. Laboratory and greenhouse experiments were conducted to determine the effect of phenyl isothiocyanate (ITC) concentration and exposure period on purple nutsedge tuber viability and to compare the retention of phenyl ITC in soil under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches. Additionally, field experiments were conducted to evaluate the effectiveness of phenyl ITC under VIF mulch against purple nutsedge. A phenyl ITC concentration of 676 ppm in soil for 3 days in a sealed environment reduced purple nutsedge tuber viability by 97% compared with a nontreated control. Phenyl ITC retention was higher in soil covered with VIF mulch than with LDPE mulch. The predicted half-life of phenyl ITC under LDPE and VIF mulch was 6.1 and 8.9 days, respectively. In field experiments, phenyl ITC at 1500 kg·ha−1 under VIF mulch suppressed purple nutsedge shoots and reduced viable tuber density ≥72%, but control was not as effective as methyl bromide at 390 kg·ha−1 (67% methyl bromide:33% chloropicrin). Therefore, phenyl ITC up to 1500 kg·ha−1 under a VIF mulch is not a viable alternative to methyl bromide for effective purple nutsedge control.

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Shengrui Yao, Ian A. Merwin, and Michael G. Brown

This research was supported in part by USDA-IREE Methyl Bromide Alternatives projects NYC-145560 and 145-530 and by CSREES project NYC 145409. We thank Drs. Lailiang Cheng and Alan Lakso for critical reviews of the manuscript. Journal

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W.R. Miller and R.E. McDonald

`Marsh' grapefruit (Citrus paradisi Macf.) produced in Florida must be certified for security against unwanted pests before entry into some domestic and export markets. Application of heat by hot water (HW) has been shown to cause severe injury to grapefruit; however, direct comparisons between forced vapor heat (VH) and HW have been lacking. Grapefruit preharvest-treated with gibberellic acid (GA) or not treated, were postharvest-treated with VH or HW such that the surfaces of fruit were exposed to the same rate of temperature increases and treatment durations. Condition and quality attributes were then compared with ambient air (AA) and ambient water (AW) controls after storage. After 4 weeks' storage at 10 °C plus 1 week at 20 °C, scald affected 5% of HW and 20% of VH-treated fruit. No scald developed on control fruit. At the end of storage, mass loss for HW and VH fruit was ≈5%. HW-treated fruit had a 5-fold higher incidence of aging than VH fruit; however, control fruit showed significantly more aging than all heat-treated fruit. Gibberellic acid (GA) and the heat treatments reduced decay relative to the control. GA-treated fruit remained greener during storage than control fruit. These findings indicate that VH and HW treatments at the temperatures and durations to control the Caribbean fruit fly (Anastrepha suspensa, Loew) will likely cause peel injury to `Marsh' grapefruit produced in Florida, regardless of treatment with GA.

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Bielinski M. Santos and James P. Gilreath

Among the current methyl bromide alternatives under study, propylene oxide (Propozone) has shown potential to control soilborne diseases, nematodes, and weeds in polyethylene-mulched tomato. However, further research is needed to determine the appropriate application rates to control nutsedge in the crop. Also, the effect of this fumigant on tomato nutrient absorption has not been determined yet. Therefore, field trials were conducted for this purpose in Bradenton, Fla. Tested rates of Propozone were 0, 190, 380, 570, 760, and 950 L·ha–1 and were shank-applied in raised planting beds three weeks before `Florida 47' tomato transplanting. Examined data indicated that there was a rapid decrease in nutsedge density with 570 L·ha–1. For phosphorus (P) and potassium (K) foliar content, there was a linear increase of P concentrations as rate increase, whereas K content increased rapidly after 190 L·ha–1. The highest tomato yields were obtained with 760 and 950 L·ha–1 of Propozone.

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Theodore Webster and A. Culpepper

Halosulfuron is an alternative to methyl bromide for managing nutsedges (Cyperus spp.) in several vegetable crops. Field studies were conducted to evaluate eggplant growth and yield when halosulfuron was applied through drip-irrigation before transplant at four rates (0, 26, 39, or 52 g·ha–1 a.i.) or following transplant (26 g·ha–1 applied 1, 2, or 3 weeks after transplant) in spring and fall crops in 2002 and 2003. Inverse linear relationships were observed between rate of halosulfuron and eggplant growth and rate of halosulfuron and eggplant yield. Halosulfuron at 52 g·ha–1 reduced eggplant growth (crop height and canopy width) 19% to 22%. Eggplant fruit biomass at the first harvest was reduced 37% to 63% by halosulfuron applied before transplant. Eggplant was capable of recovering from the initial injury and there was no effect of halosulfuron rate on fruit biomass at the final harvest. Total season fruit biomass was reduced ≤4% from halosulfuron at 39 g·ha–1, while halosulfuron at 52 g·ha–1 reduced fruit biomass 33%. Delay in application of halosulfuron to 3 weeks after transplant (WAT) resulted in ≤7% reduction in fruit biomass and number for the entire season. When halosulfuron was applied 1 WAT, fruit biomass at the first two harvests was reduced >33%, however total season harvest from this treatment was >99% of the yield from the nontreated control. This preliminary study indicates that halosulfuron injected through drip tape may have the potential to assist in the replacement of methyl bromide for nutsedge management in eggplant. However, there are many issues that must be addressed and studied before adopting this practice in eggplant.

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Carlene A. Chase, William M. Stall, Eric H. Simonne, Robert C. Hochmuth, Michael D. Dukes, and Anthony W. Weiss

An evaluation of the effect of bed width (24, 28, 32, and 36 inches) on the control of a mixed population of nutsedge [yellow nutsedge (Cyperus esculentus) and purple nutsedge (C. rotundus)] was conducted with an emulsifiable concentrate formulation of a 1,3-dichloropropene (1,3-D) and chloropicrin (CP) mixture (1,3-DCP) for application through drip irrigation systems. Beds were mulched with either 1.4-mil-thick virtually impermeable film (VIF) or 0.75-mil-thick high-density polyethylene (HDPE) and 1,3-DCP was applied at 35 gal/acre by surface chemigation or via subsurface chemigation 6 inches deep within the bed. HDPE was more permeable to gaseous 1,3-D than VIF so that 1 day after treatment (DAT), 1,3-D gas concentration at the bed centers under VIF was significantly higher than under HDPE. Dissipation of 1,3-D gas with HDPE occurred within 7 DAT, but dissipation with VIF took ∼10 days. In bed centers, 1,3-D concentrations 1 DAT were in the range of 2.3 to 2.9 mg·L–1 whereas in bed shoulders concentrations ranged from 0.1 to 0.55 mg·L–1. In 2002 and 2003, 1,3-D concentration in shoulders of narrower beds was significantly higher than in the wider beds, but dissipated more rapidly than in wider beds. Lower initial 1,3-D concentrations were observed with HDPE film in shoulders than with VIF and the rate of dissipation was lower with VIF. At 14 DAT, nutsedge plants were densely distributed along bed shoulders (19 to 27 plants/m2) with little or no emergence in the centers of beds (fewer than 5 plants/m2), but with no response to bed width. Nutsedge density increased with time, but the nature of the increase differed with bed width. The most effective nutsedge suppression was achieved with 36-inch beds, which had densities of 11–13 plants/m2 on bed centers and 53 plants/m2 on bed shoulders by 90 DAT. Nutsedge suppression was initially more effective with VIF than with HDPE film, so that no nutsedge emerged in the centers of beds mulched with VIF compared with 2–7 plants/ m2 with HDPE by 14 DAT. On bed shoulders there were 2–7 plants/m2 with VIF and 32–57 plants/m2 with HDPE. Increase in nutsedge density with time was greater with VIF so that by 90 DAT nutsedge densities on bed centers and shoulders were greater than with HDPE in 2002 and the same as with HDPE in 2003. Subsurface chemigation did not consistently improve suppression of nutsedge when compared with surface chemigation. Concentrations of 1,3-D in bed shoulders irrespective of bed width were nonlethal. Initial superior nutsedge suppression with VIF did not persist. Nutsedge control in a sandy soil with 1,3-DCP chemigation is unsatisfactory with one drip-tape per bed.

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Gladis M. Zinati

The discovery of disease suppression in certain bark composts increased the interest in using compost as growing substrate to control root rot diseases caused by Phytophthora cinnamomi. Disease suppression mechanisms include antibiosis, competition, hyperparasitism, and induced systemic resistance. Although abiotic factors may influence disease suppression, the latter is often based on microbial interactions—the two common mechanisms being general for pythium (Pythium spp.) and phytophthora root rot (Phytophthora spp.) and specific for rhizoctonia (Rhizoctonia solani). The discovery of disease suppression agents in compost led to the development of biocontrol agent-fortified compost during the last decade of the 20th century. The suggested recommendations for future research and extension outreach may include 1) development of methods to manage bacterial and viral diseases through the use of compost; 2) exploration of the potential effects of fortified compost on insect pests suppression; 3) improvement of inoculation methods of composts with biocontrol agents to produce consistent levels of disease suppression at the commercial scale; 4) development of effective fortified compost teas for suppressing foliar diseases; 5) education of compost producers on methods of production of fortified compost that suppress specific diseases; and 6) education of end-users on uses of fortified compost and its by-products.

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Warren Roberts, Wayne Fish, Benny Bruton, Tom Popham, and Merritt Taylor

Grafted cucurbits are commonly grown in various Asian and European countries, but only rarely in North America. Disease control in fields where crop rotation cannot be practiced is a common justification for grafting cucurbits. In the present study, grafting is being examined as a methyl bromide alternative, which may allow cucurbits to be grown in fields where heavy disease pressure would make production of nongrafted cultivars impractical. A study with watermelons (Citrullus lanatus) grafted onto rootstocks of squash and gourd was conducted at Lane, Oklahoma in 2004. Treatments consisted of watermelon cultivars SF 800, SS 5244, SS 7167, SS 7177, and SS 7187 from Abbot & Cobb Seed Co., grown on their own roots, or grafted onto rootstocks of RS1330, RS1332, RS1420, or RS 1421. Controls consisted of nongrafted cultivars Sangria, Royal Sweet, Jubilee, and Jamboree. Two fields were planted, with three replications per field. Plants were grown on 1 m centers, with rows 3 m apart. Yields of grafted plants were generally equal to or greater than the nongrafted plants. Sugar content, measured as soluble solids, was affected minimally, if any, by grafting. Lycopene content of fruit from grafted plants was equal to, or marginally better than, fruit from nongrafted plants. Fruit firmness, as measured by a penetrometer, was significantly greater in the grafted fruit than in the nongrafted fruit. The firmest fruit occurred with SS 7167 scions, grafted onto RS 1420 rootstock, which had a value of about 2.0 × 105 Pascals. The nongrafted plants had values of about 1.0 × 105 Pascals, or less. Matching of scions with appropriate rootstocks was important, as interactions did occur. Certain combinations were significantly superior to other combinations. We estimate that the cost to purchase a grafted seedling plant from a seedling supplier would be $0.75 to $1.00, which would include the cost of the seed and the grafting operation. This cost would compare favorably with the cost of applying methyl bromide to the soil and then planting nongrafted seeds or transplants. Higher plant survival due to disease resistance along with planting fewer plants per hectare is anticipated with grafted plants. The high values in fruit firmness in grafted fruit should be of particular interest to the fresh-cut industry.

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Bielinski M. Santos and James P. Gilreath

. Conf. Methyl Bromide Alternatives Emissions Reductions. San Diego, 3–6 Nov. 2003. Methyl Bromide Alternatives Outreach, Fresno, Calif. p. 39-1-2. Ajwa, H.A. Trout, T. Mueller, J. Wilhelm, S. Nelson, S.D. Soppe, R. Shatley, D. 2002 Application of

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Theodore P. McAvoy and Joshua H. Freeman

films Phytoparasitica 34 491 501 Chow, E. 2009 An update on the development of TIF mulching films. Proc. 2009 Annu. Intl. Res. Conf. on Methyl Bromide Alternatives and Emissions Reductions Methyl Bromide Alternatives Outreach. 20 Jan. 2012. < http