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S.A. Fennimore, M.J. Haar, and H.A. Ajwa

The loss of methyl bromide (MB) as a soil fumigant has created the need for new weed management systems for crops such as strawberry (Fragaria ×ananassa Duchesne). Potential alternative chemicals to replace methyl bromide fumigation include 1,3-D, chloropicrin (CP), and metam sodium. Application of emulsified formulations of these fumigants through the drip irrigation system is being tested as an alternative to the standard shank injection method of fumigant application in strawberry production. The goal of this research was to evaluate the weed control efficacy of alternative fumigants applied through the drip irrigation system and by shank injection. The fumigant 1,3-D in a mixture with CP was drip-applied as InLine (60% 1,3-D plus 32% CP) at 236 and 393 L·ha-1 or shank injected as Telone C35 (62% 1,3-D plus 35% CP) at 374 L·ha-1. Chloropicrin (CP EC, 95%) was drip-applied singly at 130 and 200 L·ha-1 or shank injected (CP, 99%) at 317 kg·ha-1. Vapam HL (metam sodium 42%) was drip-applied singly at 420 and 700 L·ha-1. InLine was drip-applied at 236 and 393 L·ha-1, and then 6 d later followed by (fb) drip-applied Vapam HL at 420 and 700 L·ha-1, respectively. CP EC was drip-applied simultaneously with Vapam HL at 130 plus 420 L·ha-1 and as a sequential application at 200 fb 420 L·ha-1, respectively. Results were compared to the commercial standard, MB : CP mixture (67:33) shank-applied at 425 kg·ha-1 and the untreated control. Chloropicrin EC at 200 L·ha-1 and InLine at 236 to 393 L·ha-1 each applied singly controlled weeds as well as MB : CP at 425 kg·ha-1. Application of these fumigants through the drip irrigation systems provided equal or better weed control than equivalent rates applied by shank injection. InLine and CP EC efficacy on little mallow (Malva parviflora L.) or prostrate knotweed (Polygonum aviculare L.) seed buried at the center of the bed did not differ from MB : CP. However, the percentage of weed seed survival at the edge of the bed was often higher in the drip-applied treatments than in the shank-applied treatments, possibly due to the close proximity of the shank-injected fumigant to the edge of the bed. Vapam HL was generally less effective than MB : CP on the native weed population or on weed seed. The use of Vapam HL in combination with InLine or CP EC did not provide additional weed control benefit. Chemical names used: 1,3-dichloropropene (1,3-D); sodium N-methyldithiocarbamate (metam sodium); methyl bromide; trichloro-nitromethane (chloropicrin).

Free access

Jayesh B. Samtani, Husein A. Ajwa, Rachael E. Goodhue, Oleg Daugovish, Zahanghir Kabir, and Steven A. Fennimore

Fumigants are used to control soilborne pests before planting high-value crops such as strawberry. The use of specialized tarps during fumigation can reduce fumigant emissions and mitigate the need for large buffer zone requirements mandated by regulators. Increased fumigant retention by use of barrier films during fumigant application may increase fumigant retention and allow use of lower fumigant rates to control soil pests than would be needed with permeable film. The objective of this study was to determine the minimum effective rates of the alternative fumigants, 1,3-dichloropropene (1,3-D) + chloropicrin (Pic), and Pic required under virtually impermeable film (VIF) and a high-density polyethylene (HDPE) tarp to provide weed control equivalent to methyl bromide:chloropicrin (67/33% v/v MBPic) standard soil fumigation at 392 kg·ha−1 under HDPE. A second objective was to determine fumigant rates under VIF and HDPE tarps needed to provide weed control and the economic costs of using VIF and reduced rates of the alternative fumigants. In 2002–2003 and 2003–2004 growing seasons, the fumigants 1,3-D + Pic and Pic were tested at 0, 56, 112, 224, 336, and 448 kg·ha−1 under HDPE and VIF tarps at Oxnard and Watsonville, CA. An untreated control and a MBPic standard at 392 kg·ha−1 were also included in the study. Weed control was assessed using weed propagule viability bioassays for four common weeds, time required for hand weeding, and weed fresh biomass. The fumigant rate that would be needed for a 90% reduction in viability (GR90) for all weeds was 21% to 84% less for 1,3-D + Pic under VIF compared with the HDPE tarp. For Pic, the GR90 values were 5% to 64% less under VIF compared with the HDPE tarp. Hand weeding times and weed biomass decreased with increasing fumigant rates. With the exception of Pic in 2002–2003 at Oxnard, VIF reduced the rate required for weed control compared with the HDPE tarp for both fumigants and at both locations. Economic benefits of VIF relative to the HDPE tarp were not consistent and additional work is needed to quantify these relationships and the production conditions under which VIF will be beneficial.

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Johan Desaeger and Alex Csinos

The effects of drip-applied 1,3-dichloropropene (1,3-D) and chloropicrin on fumigant soil gas levels and growth of vegetable seedlings were investigated in three separate tests in Tifton, Ga. Tests were conducted in Spring 2002, Fall 2002, and Spring 2003. Phytotoxicity of 1,3-D + chloropicrin was induced in the 2002 tests by applying progressively higher rates (0 to 374 L·ha–1) of drip-irrigated InLine (an emulsifiable formulation (EC) containing 60.8% 1,3-D and 33.3% chloropicrin) and planting vegetable seedlings within four days after application. Vegetables evaluated were tomato, pepper and cucumber (Spring 2002), and tomato and squash (Fall 2002). In Spring 2003, the effects of 1,3-D formulation (InLine versus Telone EC, an EC containing 94% 1,3-D), plastic mulch type [low density polyethylene (LDPE) versus virtually impermeable film (VIF)] and drip tape configuration (one versus two drip tapes) on fumigant soil gas levels and growth of tomato were investigated. Tomato was planted after the recommended 3-week waiting period. Fumigant concentrations in soil were measured using Gastec detection tubes at 1 to 4 days after drip fumigation in all three tests. Measured fumigant soil gas concentrations were correlated with fumigant application rates in Spring 2002, but not in Fall 2002. Vegetables were visibly affected by residual fumigant levels in the soil and showed symptoms such as leaf chlorosis (cucumber, squash and pepper), leaf bronzing (tomato) and stem browning and stunting (all crops). Fumigant soil air levels were negatively and linearly correlated with different plant growth parameters, in particular plant vigor. The cucurbit crops showed an immediate response and high mortality within 1 week after planting. Surviving plants recovered well in fall. The solanaceous crops showed a more delayed response and lower mortality rates. However, phytotoxic effects with tomato and pepper were more persistent and plants did not seem to recover with time. Overall, fumigant residue levels and potential phytotoxicity were greater in spring than in fall. Greater fumigant soil concentrations were measured under VIF as compared to LDPE plastic mulch. The effect of drip-tape configuration varied with the type of plastic mulch that was used. The double-tape treatment resulted in lower fumigant levels at the bed center under LDPE mulch, and higher fumigant levels at the bed shoulder under VIF mulch. The formulation containing 94% 1,3-D resulted in higher soil fumigant levels as compared to the formulation containing 61% 1,3-D and 33% chloropicrin, especially with VIF mulch. Early plant vigor of tomato was negatively correlated with fumigant soil gas levels, and was especially poor following drip fumigation with 94% 1,3-D under VIF mulch.

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Yan Xu, Rachael E. Goodhue, James A. Chalfant, Thomas Miller, and Steven A. Fennimore

by treatment (US$/ha): Spence, in 2011–12 production season, in annual strawberry plasticulture production system in Central Coast region of California. CP + 1,3-D = chloropicrin + 1,3-dichloropropene 59.6:39. Fig. 3. Box plots of returns net of

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James P. Gilreath, Bielinski M. Santos, and Timothy N. Motis

Montreal Protocol, because it is an ozone-depleting molecule ( Watson et al., 1992 ). One of the leading MBr alternatives is 1,3-dichloropropene (1,3-D) + chloropicrin (Pic), which merges the nematicidal activity of 1,3-D with the fungicide Pic and has

Open access

Dong Sub Kim, Mark Hoffmann, Steven Kim, Bertha A. Scholler, and Steven A. Fennimore

The majority of U.S. field-grown specialty crop production depends on a few fumigants to control soilborne pests in the post-methyl bromide era: 1,3-dicloropropene (1,3-D), chloropicrin, methyl isothiocyanate and dimethyl disulfide ( Porter and

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Rachel E. Rudolph, Thomas W. Walters, Lisa W. DeVetter, and Inga A. Zasada

plant roots and has a broad host range of more than 400 plant species ( Castillo and Vovlas, 2007 ). A common strategy to manage RLN in red raspberry is through preplant soil fumigation, primarily with fumigants containing 1,3-dichloropropene (1,3-D

Open access

Mark Hoffmann, Husein A. Ajwa, Becky B. Westerdahl, Steven T. Koike, Mike Stanghellini, Cheryl Wilen, and Steven A. Fennimore

restricted to use in strawberry nurseries. As of May 2019, 1,3-dichloropicrin (1,3-D), chloropicrin (Pic), dimethyl disulfide (DMDS), dazomet, and methyl isothiocyanate (MITC) have been the prevalent fumigants used for cropping systems in the United States