the following materials: zineb and Dithane M-45

Transcription

1 162 FLORIDA STATE HORTICULTURAL SOCIETY, 1967 EFFICACY OF NEW FUNGICIDES FOR CONTROL OF GRAY LEAF SPOT OF TOMATOES Robert A. Conover University of Florid Sub-Tropil Experiment Sttion Homested Mneb hs been the most widely used fungi ide for ontrol of fungl diseses of tomtoes for nerly fifteen yers. Its only fult s fungiide for Florid tomtoes is its ompr tive ineffetiveness ginst Botrytis gry mold (Botrytis inere Pers. ex Fr.) (3). Stll (4) found tht Dyrene ws effetive s ontrol for Botrytis gry mold, but ws less effetive thn mneb s ontrol for lte blight (Phytophthor infestns (Mont.) d By.). Dyrene ws reported by Coe nd Conover (2) to be more effetive thn mneb for ontrol of gry lef spot (Stemphylium solni Weber). Conover nd Stll (3) proposed ombintion of one pound eh of mneb nd Dyrene whih provided pro tetion ginst ll the fungl diseses of tomto throughout the tomto-growing seson in Flor id. In ddition to these fungiides the Florid Agriulturl Extension Servie (1) reommends the following mterils: zineb nd Dithne M-45 for ll fungl diseses exept Botrytis gry mold; dihlone for Botrytis gry mold nd lte blight; nd thirm nd ferbm for Botrytis gry mold. No single fungiide hs been found whih provides good ontrol of ll the fungl diseses of Florid tomtoes. Three new fungiides, Donil 2787, Polyrm nd Difoltn, hve shown onsiderble promise s tomto fungiides in experiments dur ing the pst four yers. These were developed, respetively, by the Dimond Alkli Compny, Nigr Chemil Division of the FMC Corpo rtion, nd the Chevron Chemil Compny. The performne of these mterils in experiments on the ontrol of gry lef spot is desribed in this report. Methods Donil 2787, Polyrm nd Difoltn were ompred with mneb, mneb + Dyrene nd n Florid Agriulturl Experiment Sttions Journl Series No unspryed hek in field experiments t the Sub-Tropil Experiment Sttion. The sme proedure ws followed eh yer. Plots on sisted of one row of tomtoes trnsplnted 18 inhes prt in-the-row. The Homested 24 vri ety ws used in ll experiments exept in when gry lef spot suseptible, Vertiillium resistnt breeding stok ws used. A rndom ized blok design with four replites ws used in ll experiments. Fungiides were pplied weekly with power spryer operted t forwrd speed of bout 3 mph. Depending on plnt size from three to nine nozzles per row were used nd these were djusted to provide thorough overge of ll lef surfes. Sprys were pplied t pressure between 200 nd 250 psi nd in volume suffi ient to thoroughly wet the folige nd to use some run-off from leves overed by two or more nozzles. The mount rnged from 50 to 150 gl lons per re depending on plnt size. Fungi ides were pplied lone exept in the experiment testing the omptibility of Donil 2787 with ertin other mterils. Inset pests were on trolled by seprte blnket pplitions of re ommended insetiides. Fungiides were evluted by ounting gry lef spot lesions on ten-leflet smples from eh plot. Individul leflets were piked t rn dom but, in given smpling, were tken from the sme generl lotion on the plnts. Anly sis of vrine nd Dunn's Multiple Rnge Test were used to determine sttistil signifi ne of the results. Results 196S-6U Experiment: DAC 2787 (now nmed Donil 2787), Polyrm nd Difoltn were om pred with mneb (with zin dded) nd mneb + Dyrene. This experiment ws termi nted by freeze on Jnury 15 fter ten fungiidl pplitions hd been mde nd before gry lef spot hd beome severe. The tret ments were rted three times before the freeze. Gry lef spot ws uniformly distributed in the plots nd signifint differenes were obtined even though the disese ws not severe (Tble 1). The lesions ounted on Deember 26 re sulted from inoultion with spores of Stem-

2 CONOVER: TOMATO FUNGICIDES 163 phylium solni on Deember 12. Lter rtings reflet nturl spred of the disese. All of the new fungiides provided signint ontrol om pred to the hek, but only DAC 2787 t 4 /100 gllons ompred fvorbly with reom mended fungiides Experiment: Severl formultions of DAC 2787 of differing prtile sizes, om bintion DAC 2787 nd mneb, nd Polyrm were ompred with mneb nd mneb + Dyrene in this experiment. Difoltn ws not inluded in this test. Fungiides were pplied weekly be ginning on Deember 10 nd ending Februry 11. Vertiillium wilt nd potto virus Y were quite severe nd s result vine growth ws restrited nd yields were very poor nd showed no response to fungiidl tretment. Gry lef spot ppered during the week by Jnury 3 nd ws uniformly distributed in the plots. It inresed grdully in severity but it ws not until lte Februry tht it used mrked defolition of hek plots. Tretments were rted three times nd the results re presented in Tble 2. Polyrm nd the DAC 2787 formultion with prtile size of 2.5 mirons were equl to mneb nd mneb + Dyrene in the ontrol of gry lef spot. DAC 2787 formultions of lrger prtile size were less effetive, with the 1 miron formultion showing mrked brek down in ontrol by Februry Experiments: Two experiments were mde in the seson. The first experi ment ws plgued throughout by unfvorble wether nd by potto virus Y. Although gry lef spot ws present throughout the test it did not use signifint defolition of hek plots. Therefore seond test ws strted on Mrh 16. This experiment ws designed so tht Tble 1. Control of gry lef spot in the fungiide experiment. Fungiide nd mount formultion/100 gl of of wter Avg. no. 12/26/63 lesions/leflet 1/13/64 Index k 1/15/64 Mneb + Dyrene Mneb (with zin) b 2.8 b DAC b 3.3 be ii bed 3.5 ti bed 3.8 Polyrm d 3.8 Difoltn d 3.5 Chek (No fungiide) 2 b 30.2 e 5.0 d * Plots rted visully on bsis of 1 (fewest lesions) to 5 (most lesions) ** Differenes between numbers followed by sme letters re not sttistilly signifint (t 5% level) ording to Dunn's Multiple Rnge Test.

3 164 FLORIDA STATE HORTICULTURAL SOCIETY, 1967 Tble 2. Evlution of new fungiides in the experiment. Fungiide nd mount of Avg. no, lesions/leflet Yield formultion/100 gl of wter 2/8/65 2/15/65 2/23/65 s/plot Mneb + Dyrene, Mneb DAC b DAC mneb DAC 2787 (2.5 miron) DAC 2787 (4.2 n ) b 10.3 b 72 DAC 2787 (1 " ) 23.7 b 6.6 b ** d 72 Polyrm b Chek (No fungiide) ** d 63 * Differenes between numbers followed by sme letters re not sttistilly signifint (t 5% level) ording to Dunnfs Multiple Rnge Test. ** Lesions too numerous to ount or plnts defolited. eh tretment plot ws bordered on eh side gurd rows were not spryed. Both tests were by n unspryed row. Even so, gry lef spot spryed 13 times t weekly intervls beginning did not develop suffiiently to provide good November 10 nd ending Februry 1. test of the fungiides (Tble 3). All tretments Gry lef spot lesions were sttered throughwere pproximtely equl in ontrol of gry out the plots in both tests on November 10 when lef spot. fungiides were first pplied, but it ws not until Experiments: Two experiments were erly Jnury tht the disese used suffiient onduted simultneously during the dmge to justify rtings of the tretments, seson, the first ompring Donil 2787, Poly- Gry lef spot beme very severe during Jnurm nd Difoltn with reommended fungiides. ry, nd between Jnury 10 nd 30 it om- The seond experiment tested the ompti- pletely defolited plnts in unspryed rows in bility of Donil 2787 with severl ommonly used both experiments. griulturl hemils. In the first experiment The results of the first experiment (Tble the outside rows nd every third row were left 4) show tht ll fungiidl tretments gve exunspryed to provide inoulum nd, hopefully, ellent ontrol of gry lef spot under the severe severe disese onditions. Thus every tretment disese onditions nd differenes mong them plot ws djent to n unspryed row. In the were negligible, seond experiment only the hek nd outside In the seond experiment, effiy of Donil

4 CONOVER: TOMATO FUNGICIDES 165 Tble 3. Control of gry lef spot in two fungiide experiments during the seson. Fungiide nd mount of formultion/100 gl of wter Avg,» no,» lesions/leflet First Experiment 3/25/66 4/8/66 Seond Experiment 5/18/66 Mneb + Dyrene b* 0.9 b 4.1 Mneb b 1.9 b 5.2 Donil b 1.1 b 2.3 Mneb + Donil Polyrm b 2.6 be 5.1 Difoltn b 1.6 b 5.3 Chek (No fungiide) d 16.2 b * Differenes between numbers followed by sme letters re not sttistilly signifint ording to Dunn's Multiple Rnge Test ws not ffeted by ny of the mterils ombined with it (Tble 5). All tretments, in luding mneb, gve exellent ontrol of gry lef spot. Sine gry lef spot did not beome tive in either experiment until the hrvest period, yields were not signifintly ffeted by disese ontrol exept in the hek plot of the first experiment (Tbles 4 nd 5). In view of the high yields obtined, it is evident tht no fungiidl tret ment in either experiment hd depressing effet on yield. Disussion Donil 2787, Polyrm nd Difoltn were s effetive s mneb or mneb + Dyrene for on trol of gry lef spot in tests over the pst three yers. The improved performne of these fungiides in lter tests, ompred to their per formne in the first yer, ws probbly due to improved formultions. The reltionship be tween prtile size nd performne is strik ingly demonstrted by the results obtined with the three DAC 2787 formultions ompred in the test (Tble 2). The ombintion of mneb nd Donil 2787 ws the highest rnk ing tretment in nerly every rting in eh test where it ws used, but the differenes in fvor of this ombintion were not sttistilly signifint. None of the fungiides showed evidene of phytotoxiity when spryed on trnsplnted to mtoes during the winter. However, Difoltn ws phytotoxi to smll seedlings in two plntbed experiments during hot, humid wether. Growers report tht they re sometimes un ble to obtin stisftory ontrol of gry lef spot with reommended fungiides even when pplitions re mde twie weekly. The nturl tendeny in suh situtions is to suspet tht the fungiide used is indequte or its dosge too low. The results of the experiments, when gry lef spot ws severe enough to om pletely defolite unspryed plots within threeweek period, do not support this view. Exellent

5 166 FLORIDA STATE HORTICULTURAL SOCIETY, 1967 Tble 4. Inidene of gry lef spot nd yields from plots spryed with new fungiides in the experiment. Fungiide nd mount of Avg. no. lesions per leflet Yields formultion/100 gl of wter. 1/10/67 1/17/67 1/24/67 1/30/67 s/plot Mneb + Dyrene 1 + Mb b Mneb (with zin) ** b Donil 2787 ** b 3.8 b Mneb + Donil Polyrm ** 0«8 4.0 be 6.5 b Difoltn ** 0.9 b b 5.6 b 16 Chek (No fungiide) b d *** b * Differenes between numbers followed by sme letters re not sttistilly signifint (t 5% level) ording to Dunn's Multiple Rnge Test. ** Amount inresed to 2 s per 100 gllons on Jn. 13. *** Plnts defolited. ontrol ws obtined with mneb nd mneb + literture ited Dyrene, s well s the new fungiides. In these i. Brogdon, J. E., M. E. Mrvel, nd R. s. Mullin experiments reful ttention ws given to ob- AgT.^x^^e^^rl i?93f &nd disese C ntro1 guide* Fl* tining thorough Coverge but pplitions Were 2. Coe, D. M. nd'r/a. *Conover Use of B-622 s -,,, ii«i i^i.' * ontrol for gry lef spot of tomtoes. Plnt Dis. Reporter mde only t weekly intervls. Observtions of 40: dnrpvind* n-nprsitinnq in nnmrviovnil fi isle i-nain+ 3- Conover, R. A. nd R. E. Stll Use of om- Sprymg Opertions in Commeril ftelos indite bintions of mneb nd Dyrene for ontrol of tomto distht poor overge, rther thn ineffetive m- eses. Pro. Fl. stte Hort. So. 72: ,.,,,.,, 4. Stll, R. E Control of diseses of unstked terils Or low dosges, IS the min reson lor tomtoes grown on the sndy soils of south Florid. Fl. poor ontrol. Chnging fungiides, or inresing Agr- Exp- st- Ann- Report 291~292- the number of pplitions or mount of tive ingredient, will not overome the problems used by poor overge.

6 CONOVER: TOMATO FUNGICIDES 167 Tble 5. Comptibility of Donil 2787 with ertin griulturl hemils s mesured by effet on ontrol of gry lef spot nd yield. Tretments nd mount of Avg. no. lesions per leflet Yields formultion/100 gl wter 1/9/67 1/16/67 1/23/67 1/30/67 s/plot Mneb, * 0.4 ** Donil 2787, Donil 2787, 1 + isneb, Donil 2787, 1 + Dithne M-45, Donil 2787, 2 + Tribsi opper, Donil 2787, 2 + Prthion 8E, 0.5 pt Donil 2787, 2 + Guthion 2E, 1 qt Donil 2787, 2 + Nutri-lef 60, O6 178 Chek (No fungiide) 7.5 b 13.3 b 70.8 b *** 178 * Inresed to 2 /100 gllons on Jnury 13. ** Differenes between numbers followed by the sme letter re not sttisti lly signifint (t 5% level) ording to Dunnfs Multiple Rnge Test. *** Plnts defolited.