Efficacy of 1,3-dichloropropene Formulations for Control of Plant-parasitic Nematodes on Tomato

Several formulations of 1,3-dichloropropene and chloropicrin were compared with a methyl bromide/chloropicrin formulation for nematode control on tomatoes (Lycopersicon esculentum Mill.) grown on a sandy soil in Immokalee, Collier Florida Agricultural Experiment Station Journal Series No. N-01294. This work was supported by funding from the United States Department of Agri culture Specific Cooperative Agreement #58-6617-5-015. No endorsements or registrations implied herein. County, Florida, during 1995-96. Numbers of the root-knot nematode (Meloidogyne incognita [Kofoid and White] Chitwood) and root galling were lower in 1,3-dichloropropenetreated plots than in nonfumigated control plots, but root-knot nematodes and root galling were absent from plots fumigated with methyl bromide. At harvest, population levels of the stub by-root nematode (Paratrichodorus minor [Colbran] Siddiqi) had increased in all plots, regardless of treatment. Numbers of sheath nematodes (Hemicyciiophora spp.) were low and unaf fected by treatment. Formulations of 1,3-dichloropropene were effective in reducing the most serious nematode pest of toma toes (M. incognita), but not below detectable levels. Additional data from future tests are needed to reliably assess the conse quences of this level of nematode management. Soil fumigation with methyl bromide/chloropicrin for mulations is the most commonly-used pre-plant practice for control of soil-borne pests in tomato (Lycopersicon eculentum Mill.) production in Florida (Jones et al., 1995). However, the classification of methyl bromide as an ozone-depleting sub stance and its impending removal by the U.S. Environmental Protection Agency necessitates the development of alterna tive management strategies, including the use of alternative 184 Proc. Fla. State Hort. Soc. 109: 1996. fumigants, for soil-borne pests such as nematodes (Noling and Becker, 1994). A number of alternative fumigant nematicides are currently available, among the oldest of which are the chlorinated C3 hydrocarbons, 1,3-dichloropropene and 1,2-dichloropropane (Hague and Gowen, 1987). These chlorinated hydrocarbons have been used for many years for control of nematodes in vegetable crops in Florida (McSorley et al., 1985; Overman and Jones, 1984). In the early 1980s, a formulation of 80% chlorinated C, hydro carbons and 20% methyl isothiocyanate (MS/DD = Vorlex) was as effective as methyl bromide/chloropicrin formulations in reducing galling from root-knot nematodes (Meloidogyne spp.) and population levels of several nematode species in soil, in several tests conducted on tomatoes in west central Florida (Overman and Jones, 1984) and southeast Florida (McSorley et al., 1985; 1986). In one test, the methyl bro mide/chloropicrin formulation was more effective than MS/ DD in reducing soil population levels of the reniform nema tode, Rotylenchulus reniformis Linford and Oliveira (McSorley et al., 1985). In 1985, Overman (1985) established that 1,3dichloropropene alone or in combination with 16.5% chloropicrin (C-17) provided levels of control of root-knot nema tode juveniles in soil which were similar to that achieved with the older mixture, MS/DD. Subsequently, 1,3-dichloropro pene has been used in potato (Solarium tuberosum L). produc tion in Florida for control of Meloidogyne incognita (Kofoid and White) Chitwood and other nematode pests, but has not been successful against stubby-root nematodes (Paratrichodorz^spp., Trichodorus spp.) (Weingartner et al., 1993; Weingartner and Shumaker, 1990). More recently, C-17 provided root-knot nematode control similar to that achieved with methyl bromide/chloropicrin formulations (Gilreath et al., 1994; 1996), although methyl bromide/chloropicrin was somewhat better in one case (Jones et al., 1995). The objective of the current experiment was to compare the efficacy of several different formulations of 1,3-dichloropropene and chloropicrin with a methyl bro mide/chloropicrin formulation for control of plant-parasitic nematodes in a staked fresh-market tomato crop. black polyethylene mulch immediately following fumigation. Six-week-old transplants of the tomato cultivar Sunny were planted in the beds on 2 Nov. 1995 using a 46 cm in-row spac ing. Conventional cultural and pest management practices for staked tomato production in southwest Florida were used, including drip irrigation and fertigation. A freeze on 7 Feb. 1996 severely damaged all experimen tal plants and allowed only one premature harvest on 8 Feb. All fruit from 15 plants per plot were harvested regardless of size to obtain an approximation of the potential fruit number which would have resulted from two harvests. On the same date, plants were rated for Fusarium crown rot, although methods and results (McGovern, unpublished) are not re ported here. Soil samples for nematode analysis were collected from each plot on 2 Nov. 1995 (post fumigation, at planting) and 21 Feb. 1996 (end of experiment). Each soil sample consisted of six soil cores (2.5-cm-diameter x 20 cm deep) collected in a systematic pattern from an individual plot using a soil sam pling cone (Esser el al., 1965). The cores comprising a sample were mixed and stored in a plastic bag at 10 C for two to three days prior to extraction. Nematodes were then extracted from a 100-cm* soil subsample using a modified sieving and centrifugation procedure (Jenkins, 1964). All individual specimens extracted were then identified and counted using an inverted microscope. On the final sampling date (21 Feb.), five plants were removed from each plot, and root systems were rated for galling from root-knot nematodes (Meloidogyne spp.) using a 0 to 5 scale, such that 0=0 galls, 1=1-2 galls, 2=3-10 galls, 3=1130 galls, 4=31-100 galls, and 5=>100 galls per root system (Tay lor and Sasser, 1978). All nematode data (soil counts and root ratings) were an alyzed using single degree of freedom orthogonal contrasts (Sokal and Rohlf, 1969) performed using MSTAT-C software (Freed et al., 1988). Three contrasts were examined: 1) meth yl bromide/chlorpicrin treatment vs. control; 2) methyl bro mide/chloropicrin treatment vs. 1,3-dichloropropene/ chloropicrin treatments; and 3) 1,3-dichloropropene/chloropicrin treatments vs. control. Materials and Methods A commercial tomato field on Pomello fine sand (95.5% sand, 3.0% silt, 1.5% clay) in Immokalee, Collier County, Florida, was used in this study. The site was chosen based on previously high incidences of Fusarium crown rot and rootknot nematodes. The field was cultivated and wetted prior to bed formation and fumigation. Beds were 81 cm wide with a spacing between beds of 1.8 m. Six different experimental preplant soil treatments were applied: an unfumigated con trol, methyl bromide/chloropicrin (formulated as Terr-OGas 67 = 67% methyl bromide, 33% chloropicrin) at 448 kg ha1, and four treatments with 1,3-dichloropropene (Telone) formulated by weight with different percentages of chloropi crin. These 1,3-dichloropropene/chloropicrin treatments were: C-17 (17% chloropicrin) at 200 liters ha', C-17 at 327 li ters ha1, C-25 at 224 liters ha1, and C-35 at 259 liters ha. Each soil treatment was replicated four times using single-bed plots 15.2 m long separated by 7.6-m-long buffers between plots, and arranged in a randomized complete block design. Fumi gants were applied to the beds by means of a tractor-drawn super-bedder at a depth of 23 cm using three chisels spaced 28 cm apart on 12 Oct. 1995. Beds were mulched with 31-|Llm Results No visible phytotoxicity (plant height reduction, foliar distortion, or chlorosis) resulted from any of the treatments. No significant yield differences among treatments were de tected in the premature harvest. Initial nematode population densities present in this site were very low, and root-knot nematodes (Meloidogyne) were Table 1. Effect of soil fumigation on initial plant-parasitic nematode levels in a site at Immokalee, 2 Nov. 1995 (post fumigation, at planting).