Effect of Liming and Nitrogen Source on Fusarium Wilt of Cucumber and Watermelon1

Two field experiments (Spring, 1974 and 1975) were conducted on Myakka fine sand to determine the effect of lime and nitrogen source on the development of Fusarium wilt of cucumber and watermelon. The same site, with the same experimental design, was used for each experiment. In both experiments, gross yields were increased and wilt development decreased by raising the soil pH with hydrated lime. In the first experiment with watermelon and in the sec ond experiment with both crops the beneficial ef fect of liming was reversed by the use of am monia-nitrogen compared to nitrate-nitrogen. For maximum control of wilt, liming had to be aug mented by the use of nitrate-nitrogen. lFlorida Agricultural Experiment Stations Journal Series No. 6091. Everett and Blazquez (2) demonstrated that increasing amounts of lime from zero to 9,000 lbs/A decreased Fusarium wilt, incited by Fusar ium oxysporum f. niveum, development and linear ly increased marketable yields of watermelon from zero to 13.8 T/A. They further demonstrated that wilt control resulted from an increased soil pH, not from an increased calcium supply. Several workers (1, 2, 3, 4, 5, 6, 8) have re ported control or decreased incidence of Fusarium wilt of tomato, incited by F. oxysporum f. lycopersici, by applying lime to the soil. Jones and Woltz (3, 4) demonstrated that this control resulted from an elevated soil pH that created a micronutrient imbalance which decreased the growth, sporulation, and virulence of the soil-borne pathogen. Although control of watermelon and canta loupe wilt (7) by lime amendments has been re ported, similar control has not been demonstrated for cucumber wilt. Because of this and because Crall and Hopkins (personal communication) were unable to duplicate the work of Everett and Blazquez, two field experiments (Spring, 1974 and 1975) were carried out to determine the effect of lime and nitrogen source on development of Fusarium wilt of cucumber and watermelon inJONES ET AL: FUSARIUM WILT OF CUCUMBER & WATERMELON 201 cited Toy F. oxysporum f. cucumerinum and F. oxysporum f. niveum, respectively. Materials and Methods Experiment 1 (Spring 1974). The field plot area was located on Myakka fine sand which several years previously had been limed with dolomitic limestone to pH 6.5 and had been cropped to ornamentals and vegetables. To create plots of high (7.5) and low (4.0) soil pH, hydrated lime (Ca(OH)2) and elemental sulfur, respectively, were applied to the soil March 7 and rototilled to a depth of 6 inches. Additionally, all low pH plots received gypsum (CaS04) to furnish calcium in an amount equiva lent to that of the high pH plots receiving hy drated lime. All plots to be planted to watermelon were infested in the furrow, March 20, 1974, with F. oxysporum f. niveum (grown on a 1,000 ml white sand :681 g corn meal medium) at the rate of 11 quarts of sand-cornmeal-Fusarium per 25 linear feet. All plots to be planted to cucumber were identically infested with F. oxysporum f. cucumerinum on the same date. Nine days later Toinsett' cucumbers (Cucumis sativus L.) and 'Sugar Baby' watermelons (Citrullus vulgaris Schrad.) were planted in hills one foot apart. Two weeks after seeding each hill was thinned to two plants. Two different fertilizers were used: one had an N-P-K-Mg analysis of 11-0-19-1.5 and the second 18-0-25-2. Nitrogen for the former was de rived primarily from NH4SO4 and consisted of 80% NH4-N and 20% N03-N derived from NH4N03. Nitrogen for the latter fertilizer was derived from KNO3 and NH4N03 and consisted of 80% NO3-N and 20% NH4-N. The 11-0-19-1.5 fertilizer was applied once at the rate of 2,700 lbs/A and the 18-0-25-2 fertilizer once at the rate of 2,000 lbs/A. Superphosphate (500 lbs/A) and fritted minor elements (FTE-503 at 20 lbs/A) were broadcast prior to infesting the area and were rototilled to a depth of 6 inches. Both crops were harvested 3 times; water melons from June 14 to 26 and cucumbers from June 3 to 12. Soil samples for pH determinations were taken June 6, 1974. Experiment 2 (Spring 1975). Plots of the second experiment were superimposed onto the plots of the first experiment without further lime, sulfur, gypsum, or superphosphate + FTE 503 amendments. The differential fertilizers, 11-0-191.5 (80% NH4:20% NO3-N) and 18-0-25-2 (80% NO3:20% NH4-N) were applied at the same rates as before but in split applications, one applied the first week after seed germination and the second at layby. All plots were seeded March 20 with the same cultivars as before and thinned where necessary to one plant every one-half foot. Watermelons were harvested once on June 18, and cucumbers 3 times from May 28 to June 6. Soil samples were collected just prior to seed ing and shortly after harvest for pH determina tions. In both tests a split-split plot experimental de sign was used. Whole plots were lime vs. sulfur, subplots cucumber vs. watermelon, and subsubplots ammonia vs. nitrate-nitrogen. Results and Discussion Experiment 1. The original soil pH values for the limed whole plots averaged 7.5 and for the sulfured whole plots (4.0 (Table 1)). By harvest season the 80:20% NH4:N03-N and 20:80% NH4:NO3-N fertilizers applied to the sulfured whole plots changed the initial pH to 3.9 and 4.2, respectively. Where applied to limed whole plots, the 80:20% NH4:NO3-N and 20:80% NH4:N03-N fertilizers altered the soil pH to 7.3 and 7.8, re spectively. An average of 52% and 4% of the water melon plants grown on low pH and high pH plots, respectively, developed Fusarium wilt symptoms (Table 2). An average of 84% of the cucumber plants grown on low pH plots developed wilt symptoms compared to 23% of the plants grown on the high pH plots. Ammonia-nitrogen applied to the sulfured, low pH plots increased watermelon wilt from 31% (80% NO3-N) to 73% (80% NH4-N) (Table 2). On the limed high pH plots, watermelon wilt in cidence increased from 0% (80% N03-N) to 8% with NH4-N. Nitrogen source did not affect wilt development of cucumbers on the low pH sul fured plots but greatly affected wilt development on the limed high pH plots (Table 2). Forty-two percent of the plants receiving 80% NH4-N wilt ed compared to 4% of the plants receiving 80% N03-N. Watermelon yields at the low pH averaged 9.9 T/A and at the high pH 14.8 T/A (Table 3). Cucumber yields were affected even more drastical ly. Yields at the low pH averaged 41 bu/A and at the high pH 264 bu/A. 202 FLORIDA STATE HORTICULTURAL SOCIETY, 1975 Table 1, Soil pH values in two experiments before planting and after