RESULTS OF TREATING FRESHLY CUT SEED POTATOES WITH FUNGICIDES AND ANTIBIOTICS

Transcription

1 WEINGARTNER & SHUMAKER: TREATING SEED POTATOES 201 RESULTS OF TREATING FRESHLY CUT SEED POTATOES WITH FUNGICIDES AND ANTIBIOTICS D. P. WEINGARTNER and J. R. Shumaker IF AS, Agricultural Research Center Hastings Abstract Fungicides used both alone and in combination with antibiotics were evaluated dur ing for control of potato seed piece de cay caused by a bacterial-fungal complex. Fungi cide treated seed pieces emerged faster than nontreated seed pieces in 1970, 1971, and, but not in Statistically significant differences in yield which were observed in general efficacy tests performed during 1970, 1971, and 1972 were as sociated with phytotoxicity of some chemicals (potassium azide, Demosan, Mertect, and Busan 72) rather than with disease control. In when weather conditions were favorable for seed piece decay, treating of cut seed with fungicides re sulted in both improved stands and increased yields. Results were comparable when seed was dusted with, Manzate 200, Dithane M-45, or ; or when these materials were applied in-furrow at time of planting. In separate experiments performed during 1972 and and seed treatments significantly increased yields in 1972, but not in. Emergence and final stands of potatoes are often reduced in Florida due to seed piece decay and infection of young plants by fungi such as Rhizoctonia solani Kuehn, Fusarium spp., and Sclerotium rolfsii Sacc. (1), and bacteria such as Erwinia carotovora (L. R. Jones) Holland and E. atroseptica (Van Hall) Jennison (2, 3). The rela tive importance of bacteria and fungi and of tuber and soil-borne sources of inoculum in reducing potato stands in Florida is not known and prob ably varies with the source of seed potatoes, geo graphic location within the state, soil type, and weather conditions following planting. We previously reported that relative effective ness of treating freshly cut seed tubers with Poly ram 7D varied according to geographic sources of seed potatoes (2, 3). The purpose of this paper is to summarize data obtained from six experiments performed during which evaluated efficacy of fungicides, antibiotics and fungicide-antibiotic combinations against seed piece decay. Methods and Materials Certified seed potatoes of the Sebago cultivar were used in all experiments. Seed was cut by hand into seed pieces weighing approximately oz. ( g). Fungicides were applied to seed tubers at approximately 1.0 lb. (0.45 kg) formula tion per 100 lb. (45.5 kg) cut seed by shaking fungicides and cut seed potatoes in paper bags. Streptomycin sulfate formulations were applied by dipping freshly cut seed potatoes for 30 minutes in a water solution containing 100 ppm of the antibiotic. When fungicide-antibiotic combinations were used, fungicides were applied following the antibiotic treatment. In-furrow applications of fungicides were made at 6.8 lb. ai per acre in-therow (7.6 kg/ha) immediately before planting. During each year seed was planted 12 inches (30.5 cm) apart in randomized block designs with six replications. Each plot consisted of 13 hill units in single rows. Controls generally were freshly cut nontreated seed, 2-3 week old cut nontreated seed, nontreated noncut B-sized seed, and freshly cut seed treated with the talcum (mag nesium silicate) used to dilute some fungicides. The chemicals tested are listed in Table 1. Only those chemicals which are registered for use on potato or which were phytotoxic in one or more experiments are discussed. Additional details from each experiment were presented in previous reports (4, 5, 6, 7). During 1972 and and were evaluated as seed treatments as part of two experiments designed to test effect on stands and yields of nematicides, herbicides and seed treat ments when used in various combinations. Only the effect of fungicide seed treatments is reported in this paper. Methods were similar to those de scribed above except that split-split plot designs were used. Seed treatments were evaluated in the sub-sub plots. Results In the general efficacy experiments performed during 1970, 1971, and 1972, significant differences in stands and yields of potatoes which were ob-

2 202 FLORIDA STATE HORTICULTURAL SOCIETY, 1974 Table 1, List of trade, chemical and common names of fungicides and antibiotics used in tests reported in this paper, Trade name Common name Chemical name Agri-strep streptomycin streptomycin sulfate sulfate Busan 72 Mertect 2-(thiocyanomethylthio)benzothiazole thiabendazole 2-(4-thiazolyl) benzimidazole Thynon dithianon 5,10-dihydro-5,10-dioxonaphtho[2,3-b]- p-dithiin-2,3-dicarbonitrile Azide potassium azide Manzate 200 Dithane M-45J mancozeb zinc ion and manganese ethylenebisdithiocarbamate 80, a coordination product of manganese 16, zinc 2, ^ethylenebisdithiocarbamate 62 chlorothalonil tetrachloroisophthalonitrile captan N-trichloromethylthio-4-cyclohexene-l, 2-dicarboximide NIA 25,050 unavailable Terraclor PCNB pentachloronitrobenzene Demosan Tersan SP chloroneb chloroneb l,4-dichloro-2,5-dimethoxybenzene l,4-dichloro-2,5-dimethoxybenzene Semes an Bel 12.5 hydroxymercurinitrophenol hydroxymercurichlorophenol Benlate benonjyl methyl l-(butylcarbamoyl)-2-benzimidazolecarbamate metiram mixture of 5.2 parts by weight (.9) of ammoniates of [ethylenebis-(dithiocarbamato)]zinc with 1 part by weight (16.1) ethylenebis-[dithiocarbarc±c acid], bimolecular and trimolecular cyclic anhydrosulfides and disulfides

3 WEINGARTNER & SHUMAKER: TREATING SEED POTATOES 203 Table 2. Effect of fungicide treatments on the number of days from planting for potatoes to attain maximum stands in 1970, 1971 and. Number of days from planting 5 to < ittain maximum stand Fungicide2 Seed treatments Seed treatment in-furrow Dithane M means treatments 40 Manzate Freshly cut (nontreated) LSD.05 5 NS NS NS Seed treatment = Fungicides ( 7D, Manzate 200 8D, Dithane M-45 8D, 7.5D and 7.5D) applied to freshly cut seed at 1.0 lb (0.45 kg) formulation per 100 lb (45.5 kg) cut seed. In-furrow application «= Fungicides applied in seed furrows at the following rates per acre in-the-row: 80W, Manzate W, and Dithane l*-45 80W each at 8.5 lb (9.5 kg/ha), 6F at 1.1 gallons (10.2 1/ha), and 50W at 13.6 lb (15.2 kg/ha); Fungicide + Agrimycin 17» Fungicides used as with seed treatments, following a 30 minute dip in 100 ppm. served among treatments and the nontreated con trols were due to phytotoxicity of some chemicals at the rates tested rather than due to disease con trol. Chemicals which were associated with reduced stands and/or yields during both 1970 and 1971 were Demosan 5D, Mertect 10D and Busan 72 10D applied to freshly cut seed. In 1972 potassium azide (0.1, 0.2, 0.4, 0.8, and 2.0) applied to freshly cut seed, 80W and Tersan SP 65W applied in-furrow at 13.5 lb. formulation per acre in-the-row (15.1 kg/ha) reduced yields or emergence and NIA 25,050 5D applied to freshly cut seed delayed emergence. Seed treated with effective fungicides emerged earlier than nontreated freshly cut seed in 1970, 1971, and, however, when expressed as the number of days to attain maximum stand, differ ences were statistically significant only in 1970 (Table 2). During statistically significant reductions in stands and yields were associated with a severe Rhizoctonia sp. infestation in the test area. Maxi mum attained stands were significantly increased over those of nontreated freshly cut seed by Poly ram 80W and Dithane M-45 80W applied in-fur row, and Manzate 200 8D applied to seed (Table 3). Statistically significant increases in yield were observed when 80W and Dithane M-45 80W were applied in-furrow, and when 8D +, Manzate 200 8D, Manzate 200 8D +, and 7.5D were applied to cut seed Table 4). Increases in stand and yield associated with several other treatments closely approached significance at 5 (Tables 3 and 4). In the split plot tests performed in 1972 and application of 7D or 7.5D to freshly cut seed significantly increased yields, but not stands in 1972 (Table 5). Yield increases were also observed in, however, differences were not statistically significant. Discussion We previously reported that treating cut seed with 7D significantly improved final

4 204 FLORIDA STATE HORTICULTURAL SOCIETY, 1974 Table 3, Effect of fungicides,, and fungicide + Agrimycin 17 combinations on maximum attained stands of potatoes in. Fungicide Maximum attained stand Seed2 in-furrow2 Fungicide +z Manzate 200? Dithane M-45? Controls Freshly cut nontreated B-size Talcum dust nontreated treatment application LSD zseed treatment = Fungicides ( 7D, Manzate 200 8D, Dithane M-45 8D, 7.5D and 7.5D) applied to freshly cut seed at 1.0 lb (0.45 kg) formulation per 100 lb (45.5 kg) cut seed. In-furrow application = Fungicides applied in seed furrows at the following rates per acre in-the-row: 80W, Manzate W, and Dithane M-45 80W each at 8.5 lb (9.5 kg/ha), 6F at 1.1 gallons (10.2 1/ha), and 50W at 13.6 lb (15.2 kg/ha); Fungicides + Agrimycin 17 = Fungicides used as with seed treatments, following a 30 minute dip in 100 ppm, yfungicides diluted with talcum (magnesium silicate) used in control stands and yields of less vigorous seed stocks (2, 3). Data presented in this paper suggest that al though stands and yields are not improved by seed treatment every year, treating seed with recom mended fungicides or application of fungicides to soil can effectively improve stands of certified Sebago seed potatoes when conditions favor pathogenesis of soil-borne fungi such as Rhizoctonia spp. Although the economics of treating soil with fungicides in north Florida at the rates used in these studies is questionable, returns from use of registered fungicides as seed treaters outweigh dis advantages of this practice. We believe that more rapid emergence as sociated with some fungicide treatments when com pared to nontreated controls is due to control of root-infecting fungi in the rhizosphere of emerg ing plants. Literature Cited 1. Eddins, A. H., G. D. Ruehle, and G. R. Townsend Potato diseases in Florida. Florida Agr. Exp. Sta. Bull p. 2. Shumaker, J. R. and D. P. Weingartner Response of grower-available Sebago potato seed stocks to different seed piece treatments. Proc. Florida State Hort. Soc. : and.. Certified Sebago seed stocks and seed piece treatments. Amer. Potato J. 50: Weingartner, D. P Seed piece decay. P. 86. In Fungicide Nematicide Tests, Results of VTGJ. Amer. Phytopath. Soc. Vol Seed piece decay. P In Fungicide and Nematicide Tests. Results of Amer. Phytopath. Soc. Vol Seed piece decay complex. P In Fungicide and Nematicide Tests. Results of Amer. Phytopath. Soc. Vol Seed piece decay complex. P. 1. In Fungicide and Nematicide Tests. Results of. Amer. Phytopath. Soc. Vol. 29.

5 WEINGARTNER & SHUMAKER: TREATING SEED POTATOES 205 Table 4. Effect of fungicides,, and fungicide + Agritnycin 17 combinations on yields of potatoes in, Fungicide Yield (cwt/acre) Seedz in-furrow2 Fungicide +z treatment application Manzate 200y Dithane 1^45y Controls Freshly cut nontreated 104 B-size nontreated Talcum dust LSD zseed treatment = Fungicides (P olvram 7D. Manzate 200 8D.. Dithane M-45 8D, 7.5D and 7.5D) applied to freshly cut seed at 1.0 lb (0,45 kg) formulation per 100 lb (45.5 kg) cut seed. In-furrow application = Fungicides applied in seed furrows at the following rates per acre in-the-row: 80W, Manzate W, and Dithane M-45 80W each at 8.5 lb (9.5 kg/ha), 6F at 1.1 gallons (10.2 1/ha), and 50W at 13.6 lb (15.2 kg/ha) ; Fungicides + Agrimycin 17 = Fungicides used as with seed treatments, following a 30 minute dip in 100 ppm. yfungicides diluted with talcum (magnesium silicate) used in control. Table 5. Effect of 7D and 7.5D seed treaters on maximum attained of potatoes in experiments performed during stands and yields 1972 and.z Treatment 7D 7.5D Control 1972 maximum Yield attained (cwt/acre) stand() 152* 154* maximum Yield attained (cwt/acre) stand() Fungicides applied at 1.0 lb (0.45 kg) per 100 lb (45.5 kg) cut seed. Asterisks indicate treatments within each column which differ signi ficantly from the nontreated control (P =.05). Lack of an asterisk denotes nonsigxiificance.