EVALUATION OF FUMIGANTS FOR THE CONTROL OF FUSARIUM WILT AND ROOT-KNOT NEMATODE OF WATERMELON, 2000: On 20 May, watermelon seedlings were transplanted into field plots. Plots consisted of 150-ft rows spaced 6 ft apart. Watermelon plants were spaced 5 ft apart for 30 plants per row. Plots were fumigated on 2 May with 3 knives on 7-inch spacings. Standard triploid 'seedless' watermelon production requires the interplanting of triploid hybrids with diploid hybrids for pollination purposes. Therefore, triploid hybrid Millionaire and diploid hybrid Jade Star were interplanted with the latter occurring every third plant within a row. Each row was mulched with 2 ft wide x 2 mil black plastic (Visqueen 4020). BioYield LS 213 (Gustafson LLC), a combination of Paenobacillus macerans and Bacillus amyloliquefaciens, was mixed at the rate of 1:40 v:v with a soilless transplant mix before seeding. The experimental design was a randomized complete block with four replications. The plots were rated approximately every 7 days for Fusarium wilt symptoms from 14 Jun to 5 Jul using a 1 to 5 scale. The rating system was as follows: 1= a plant with wilt of individual leaves; 2= a plant with individual leaves with necrotic symptoms; 3= a plant with one vine of the plant with wilt symptoms; 4= an entire plant with wilt symptoms; and 5= a dead plant. An attempt was made to isolate the pathogen from the crown portion of all plants with a severity rating of 5. Disease severity for each rating period was calculated by multiplying the number of plants at each severity level by the severity rating. These numbers were added together for all rating periods to obtain the cumulative disease severity. Root knot nematode severity was estimated on 10 Aug by evaluating the root systems of three Millionaire plants chosen at random within each replication. The percentage of each root system affected by root knots was estimated using the Horsfall-Barratt scale. Yield data were recorded on 18 Jul and 10 Aug. No disease severity or yield data were taken from any plant within 15 ft from either end of plot. Disease severity ratings and yield data were separated using Fisher's LSD at the 5% level except where indicated.

All plants with a severity rating of 5 tested positive for F. oxysporum f. sp. niveum . No fumigation treatment significantly reduced wilt symptoms compared to the nonfumigated control. Both treatments with LS 213 as well as the 6 GPA Telone C35 treatment had milder symptoms than the methyl bromide/chloropicrin treatment. All fumigation treatments eliminated root knot nematode symptoms. LS 213 without Telone C35 did not completely control root knot nematode symptoms. The relatively low root knot nematode rating of the nonfumigated treatment indicates low disease pressure in the experimental plot. The nonfumigated treatment had lower yields than any other treatment. LS 213 + C35 improved yield of Millionaire and total yield compared to LS 213 alone. None of the Telone treatments had significantly different yields from the methyl bromide/chloropicrin treatment. The vigor ratings, in general, coincided with the yield data. The lack of correlation between wilt rating and yield data may be due to activity of soil borne fungi other than F. oxysporum f. sp. niveum.