EXALTATA ON PLANT NEMATODE POPULATIONS AND

Transcription

1 RHOADES: CROTALARIA-SESBANIA-NEMATODES-BEANS-CABBAGE EFFECT OF CROTALARIA SPECTABILIS AND SESBANIA EXALTATA ON PLANT NEMATODE POPULATIONS AND SUBSEQUENT YIELD OF SNAP BEANS AND CABBAGE H. L. RHOADES Central Florida, Experiment Station Sanford Rotations that include nematode resistant plants can be effective in reducing the damage caused by many nematodes and, under certain conditions, this method may be used profitably. In Florida, the kinds of nematode-resistant plants that can be grown successfully in vege table culture are limited because of climatic con ditions, and because s frequently are injured by several different kinds of nematodes including such important parasites as. root-knot, sting, stubby-root, and awl nematodes. One, spectabilis Roth., a poisonous plant that has been grown widely as a summer cover has been shown to be either resistant to or a non-host of a number of nema todes including Meloidogyne spp. (1,, 4, 5, 11), Tylenchorhynchus claytoni (8), Radopholus similis (, 6), and Trichodorus christiei (1). Wat son and Goff (1) recommended growing C. spec tabilis in rows and keeping it free of weeds by cultivation for control of root knot in Florida. This paper reports the results of greenhouse and field experiments conducted to determine the effect of C, spectabilis and exaltata (Raf.) Rydb., on nematode populations and sub sequent yields. S. exaltata serves as a host to many plant nematodes but is frequently grown as a summer cover in commercial vegetable fields. Materials and Methods Greenhouse Experiment. C. spectabilis seed was planted in 6-inch pots of steamed sand. When the plants were approximately inches high, duplicate pots were infested with 5 hand picked specimens of each of the following: sting (Belonolaimus longicaudatus Rau, 1958), awl (Dolichodorus heterocephalus Cobb, 1914), lance (Hoplolaimus galeatus (Cobb, 191) Thorne, 195), Florida Agricultural Experiment Stations Journal Series No and stubby-root (Trichodorus christiei Allen, 1957) nematodes. Root-knot larvae (Meloidogyne incognita (Kofoid and White, 1919) Chitwood, 1949) were added at the rate of 5 per pot. In addition, duplicate pots of a known host of each species (cucumber for M. incognita and sweet for the others) were infested with the same number of nematodes to compare the reproductive rate on the two plants. Duplicate pots containing a mixed planting of C. spectabilis and sweet and C. specta bilis and cucumbers were infested with 5 T. christiei and 5 M. incognita larvae respec tively to determine if a nematocidal substance might possibly be given off by the roots of the crotalaria and prevent the buildup of nematode populations in the surrounding soil. After 9 days, the ectoparasitic nematode populations were determined by removing soil samples from the pots with a soil probe and pro cessing by the centrifugal-flotation technique (7). Root-knot population was determined by planting cucumbers following the crotalaria, then ex amining the roots after 4-6 weeks for galling. Field Experiments. Two randomized block experiments with five replicates were conducted in the field on Leon fine sand; one for a period of years in an area infested with B. longicaudatus, D. heterocephalus, and T. christiei and the other for one year in an area infested with M. incog nita. The crotalaria was grown in -inch wide rows the first year and inches the second. The majority of the weeds were kept out by cul tivation and some hand weeding. The sesbania was grown in -inch wide rows and kept culti vated the first year but the second year it was broadcast seeded since it is a vigorous grower and keeps weeds down. The s were planted early in June and plowed under in late August. Two types of checks were used: one, a natural growth of weeds; and the other, weeds followed by soil fumigation with 5 gallons per acre of l,-dichloropropane-l, dichloropropene (D-D). Approximately weeks after fumigation Con tender snap beans were planted, and when these had been harvested, Marion Market cabbage was transplanted without further soil treatment.

2 4 FLORIDA STATE HORTICULTURAL SOCIETY, 1964 Table 1. Effect of spectabilis on nematode populations as compared to a known host and a mixed planting of Co spectabilis and the known host. Nematode Plant Nematode populations8" Meloidogyne incognita Cucumbers following crotalaria No galling Cucumbers alone Roots heavily galled & cucumbers mixed Roots heavily galled Trichodorus christiei & sweet mixed 8,75 6, Belonolaimus longicaudatus, Dolichodorus heterocephalus 1,15 Hoplolaimus galeatus 8 75 a Approximate number of nematodes in a 6-inch pot after 9 days; 5 nematodes were used as inoculum for all species except M. incognita for which 5 larvae were used. Table. Ectoparasitic nematode populations following spectabilis. exaltata, and weeds Nematode populations8- s I a Nematodes extracted from 1 cc of

3 RHOADES: CROTALARIA-SESBANIA-NEMATODES-BEANS-CABBAGE 5 Table * Yield of snap beans subsequent to spectabilis, exalta, weeds, and soil fumigation, and ectoparasitic nematode populations at end of bean. Yield 195 IBu/A) 19^ Nemaiode populations8* i k followed by 5 gal. D-D k LSD k 51 7 a Nematodes extracted from 1 cc of soil at end of bean. Table 4. Yield of second (cabbage) subsequent to spectabiliss exaltata, weeds, and soil fumigation, and < ectoparasitic nematode populations at end L of cabbage. (5 lb Yield bags/a) Nematode populations8* k followed by 5 gal. D-D too 41 LSD.5.1 NS a Number of nematodes extracted from 1 cc of soil at end of the cabbage.

4 6 FLORIDA STATE HORTICULTURAL SOCIETY, 1964 Table 5. Effect of spectabilis, exaltata, weeds, and soil fumigation on root knot and subsequent yield. Bean yield (Wa) Boot knot galling index? Cabbage yield (5 lb bags/a Ik followed by 5 gal LSD.5.1 5* N.S. a Root-knot filing of bean roots based on an index of 1, no galling, to 5, severe galling. "b Cabbage followed immediately after beans with no further soil treatment. Soil samples were taken at the end of each and processed as described before for nematode population determination. Results and Discussion In the greenhouse experiment, C. spectabilis did not serve as a host for any of the nematodes except H. galeatus (Table 1). However, when growing in the same pot with a host of T. christiei and M. incognita, it did not prevent the re production and buildup of these two nematodes, indicating that there are no nematocidal sub stances extruded by the roots. Results of the field experiments conducted in the area infested with the ectoparasitic sting, stubby-root, and awl nematodes showed that the nematodes built up on S. exaltata, declined on C. spectabilis, and were maintained at a moderate level on the weeds which consisted primarily of crabgrass (Digitaria sanguinalis (L.) Scop.) and signal grass (Brachiaria piligero) (Table ). Yield of both snap beans and cabbage was much higher following C. spectabilis and soil fumiga tion than following S. exaltata or weeds (Tables and 4). The population of stubby-root nema todes returned most rapidly on the s fol lowing soil fumigation than for other treatments. This phenomena was observed and reported by Perry (9) as early as 195. Root knot also built up on S. exaltata, declined on C. spectabilis, and was maintained at a mod erate level on the weeds (Table 5). Snap bean yield was much higher following the crotalaria and soil fumigation than following sesbania and somewhat higher than after weeds. Cabbage, which is seldom damaged by root knot during the cooler season, yielded about the same for all treatments. Information gained from these experiments indicates that C. spectabilis grown in rows and kept free of weeds may be a valuable summer cover for reducing T. christiei, B. longicaudatus, and D. heterocephalus as well as M. incognita populations prior to fall and winter vegetable production in Florida. S. exaltata, on the other hand, builds up populations of these nematodes and aggravates the problem of nematode control. Since C. spectabilis is a toxic plant and dan gerous to livestock and poultry it should be handled with responsibility and seeded only in

5 STALL, HORTENSTINE, ILEY: BOTRYTIS-TOMATOES-LIMING 7 areas where it can be controlled. Fields utilized for vegetable production only, appear to be a suitable location. Summary Populations of the plant nematodes Belonolaimus longicaudatus, Dolichodorus heterocepha- Iu8, Meloidogyne incognita, and Trichodorus christiei failed to survive on spectabilis in the greenhouse. Field populations of the nematodes declined greatly during the summer months in plots planted to C. spectabilis but per sisted in plots of exaltata and those al lowed to grow up in weeds. Subsequent yields of snap beans and cabbage were higher on the plots planted to C. spectabilis than to S. exaltata or those allowed to grow up in weeds. LITERATURE CITED 1. Barrons, K. C Studies on the nature of rootknot resistance, Jour. Agr. Res. 58: Bates, G., and D. Fairchild Protecting papaya plants from nematodes by the planting of specta bilis. Proc. Fla. State Hort. Soc. 57: Birchfield, W., and F. Bistline s in relationship to the burrowing nematode, Radopholus similis. Plant Disease Reptr. 4: Christie, J. R Host-parasite relationships of the root-knot nematode, Heterodera marioni. II. Some effects of the host on the parasite. Phytopathology 6: Edwards, E. E Studies on resistance to the root-knot nematode of the genus Meloidogyne Goeldi, Proc. Helminth. Soc. Wash. : Feder, W. A., and J. Feldmesser Additions to the host list of Radopholus similis, the burrowing nema tode. Plant Disease Reptr. 41:. 7. Jenkins, W. R A rapid centrifugal-flotation technique for separating nematodes from soil. Plant Disease Reptr. 48: Krusberg, L. R Studies on the tesselate stylet nematode. Phytopathology 46: Perry, V. G Return of nematodes following fumigation of Florida soils. Proc. Fla. State Hort. Soc. 66: Rohde, R. A., and W. R. Jenkins Host range of a species of Trichodorus and its host parasite relationship on tomato. Phytopathology 47: Steiner, G Plant nematodes the grower should know. Part I. Proc. Soil Sci. Soc. of Fla. 4: Watson, J. R., and C. C. Goff 197 Control of root-knot in Florida. Fla. Agr. Expt. Sta. Bull. 11, pp. FACTORS IN REDUCTION OF BOTRYTIS CINEREA PERS. EX FR. INCIDENCE ON TOMATO BY LIMING PRACTICES R. E. Stall1 C. C. HORTENSTINE J. R. ILEY Botrytis gray mold of tomato caused by Botrytis cinerea Pers. ex Fr., is one of the three most prevalent fungus diseases of tomato in Florida. Several fungicides have been effective in pre venting the disease, but none has controlled all other foliage diseases of tomato. Since other fungicides must be combined with effective ma terials to control the spectrum of foliage diseases (1), the fungicide program is very expensive. Cox and Hayslip () pointed out that gray mold has been economically important on tomato plants in Florida during the period nabam-zinc sulfate, zineb and maneb have been in general use. However, very little damage from gray mold has occurred in areas of naturally alkaline, cal careous soils, even though maneb and zineb have Florida Agricultural Experiment Stations Journal Series No lformerly Associate Plant Pathologist, Indian River Field Laboratory, Ft. Pierce, (Now Associate Plant Path ologist, Department of Plant Pathology, University of Flor ida, Gainesville). Formerly Assistant Soils Chemist, Everglades Experi ment Station, Belle Glade, (now Assistant Soils Chemist, Department of Soils, University of Florida, Gainesville). Assistant Soils Chemist, Everglades Experiment Station, Belle Glade). been used extensively. Also gray mold has become progressively less severe upon repeated farming of the same land, which usually increases in alka linity and calcium content as the result of re peated liming. This paper reports on effects of lime on de velopment of the disease. Factors involved help explain the distribution of the disease in Florida and are important as a new approach to control of the tomato gray mold disease. Materials and Methods. Plots were outlined on Immokalee fine sand which is naturally low in ph and calcium content. Both randomized block and split-plot experimental designs with 4 repli cations were utilized. Weighed amounts of treat ment materials were spread by hand on a mea sured area. The materials were incorporated into the soil by disking. Manapal or Indian River variety tomato plants were set in the plots. Planting was usually in late October or early November. Standard fertilization and cultivation practices for ground culture of tomatoes in the Indian River area were employed. Soil of each plot was randomly sampled and analyzed for P, Ca, and ph after the last harvest. Determination of ph was in 1:1: :soil:ho with glass electrode ph meter; P was extracted with