96 SOIL AND CROP SCIENCE SOCIE1Y OF FLORIDA Reduction of Fusarium Crown and Root Rot in Tomato by 1,3-Dichloropropene plus Chloropicrin in Southwest Florida R.J. McGovern* and C. S. Vavrina ABSTRACT Two experiments were conducted during 199:,-1994 to evaluate the effectiveness of l,3-dichloropropene plus chloropicrin (l,3-DC) at 200.1 and 327.4 L ha' for reduction of Fusarium crown and root rot (FCRR) caused hy Fusarium oxysporllln Schlechtend.:Fr. f. sp. radicis-ly- copersiciW. RJarvis & Shoemaker in tomato (Lycopersicon esculentum Mill.) in southwest Florida. Efficacy of I,3-DC was compared with me- thyl bromide plus chloropicrin (336 kg ha· l ) in reducing FCRR in fields naturally infested with the causal fungus. Incidence and severity of FCRR in non-treated plots were high (295%) and low to moderate (15-25% crown discoloration), respectively. Application of 1, 3-DC re- sulted in reduction of FCRR incidence and severity in both experi- ments equivalent to those achieved by methyl bromide pIns chloropicrin. Yields did not differ between the treatments and non- treated control. Fresh market tomato, valued at $474 million during 2001-2002, is the vegetable crop ill Florida, and ilS southwest region accounted for 42% of state-wide pro- duction (Florida Agricultural Statistics Service 2001, 2002). Fusarium crown and root rot in tomato, caused by F. oxy.ljiOrurn f.sp. radicis-lycopersici, has consistently been the most prevalent soil-horne disease of the crop 111 southwest Florida during the past 15 n; up to 70% losses in tomato production have occurred in this re- gion (\1cGovern ct aI., 1998). In addition. the disease has been estimated to cause yield losses of 15% and 29% in west-central and southeastern Florida, respectively (Sonoda, 1976;J ones et aI., 1990). First detected in Flor- ida during the 1974-1975 tomato cropping season (Son- mIa, 1976), FCRR also has been reported in Canada, Israel, Japan, Mexic(). many countries in Europe, and 01 her states in the CSA including California. NewJersey, :--.Jew York, New llampshire, Ohio, Pcnnsylvania, and Texas Qanis, 1988). The disease poses a significant threat to tomato transplant production and to both field and greenhouse fruit production wherever it oc- curs Qarvis, 1988; McGoycrn ct aI., 1993h). External symptollls of FCRR in mature plants in- clude brown discoloration and rot at the soil level in the crown and roots. The lower leaves of infected plants turn yellow and the entire plant ma\ wilt around the lime of first harn'st. The tap root of infected plants tell rots entirely. \Vhell diseased plants are sectioned lengthwise, extensive brown discoloration and rot arc evident in the cortex of crowns and roots. R. J McGovern, lniycrsit\' of Florida-IF.\S. Pl;ll1t Pathology Dep. and Plant Yledicine Program. (;ainesville. FL :12(,11 and C. S. Vavrina, (1I1iy. of Florida, Southwest Florida Res. and Fduc Center, Immob- lee. FL 34143. This research was supported by the Florida Agric Exp. Stn. and IS apptoH'd for publication as Journal Series No. R-100R. *Corresponding author (rjm@ifas.ufLedu). Contribution published in Soil Crop Sci . .)oc.Nurida Proc. 63:%-99 (2004). Fumigation with methyl bromide-chloropicrin (Trichloronitromethane) (MBC) formllJations has been the most commonly used preplant practice for control of crown rot alld other soil-borne pests in Florida for lht' past 20 yr. However, methyl bromide has been catego- rized as a Class I, ozone-depleting substance by the Mon- treal Protocol (an international treaty promulgated by the United Nations Environmental Program), and it faces removal by the USEPA under the auspices of the Clean Air Act bv 2005 (Watson et aI., 1992; lTSEPA, 1993). This situatioll necessitates development of other management strategies for FCRR and other soil-bome pests including the use of alternative fumigants. The fumigant 1,3-dichloropropene is one of those un- der consideration as a methyl bromide alternative because of its good nematicidal (Overman and JOlles, 1976; StaplelOll and Devay, 1983). In lhe past, propene was combined with methvl isothiocyanate, I,;.!- dichloropropauc. and related hydrocarbons as 1)D- MENCS and other trade names, and showed efficacy against F oxysporum in a number of vegetable crops (Hop- kins and Elstrom, 1976; Manning and Vardaro, I 977;Jones and Overman, 1978). More recently this fumigant has been formulated with various concentralions of chloropi- crin to add disease control. It was our objective to eyaluate the effectiveness of 1,3-dichloropropene plus chloropicri n (1,3-DC) in managing FCRR in southwest Florida. MATERIALS AND METHODS Experimental Sites Two tomato fields of Pomello fine sand (sand\', hy- perthermic Arenic Alaquods; pH = 7.2 to 7.7, organic matter = 10.5 to 13.1 g kg') naturally infested with F. ox- ysporum f.sp. radicis-lycopersici on a commercial farm in Immokalee, southwest Florida were chosen for experi- mentation during 1993-1994 hased 011 previously hi<rjl crown rot Methyl mulations had been used over the preceding 10 yr as the preplant soil sterilallt. Fumigants . Fields were cultivated and irrigated prior to fumiga- tion to ensure adequate soil moisture and tilth for bed formation. Fumigants were injected in beds at a depth of 20 to 23 cm through tubes attached to three chisels spaced 28 em aparJ by means of a tractor-drawn super bedder. Beds were 20-cm high, I-m wiele and spaced on ;.!- m centers. Fumiganls were applied on I ;.!Jan. 1993 in Ex- periment 1 and I;.! Oct. 1993 in Experiment 2. The min- imum/maximum soil temperatures as measured at 10 cm at Southwest Florida Research and Education Center (SWFREC) were 27/20.8° C and 31.6/26.2°C on 12Jan-