Effect of postinfection application of phosphorous (phosphonic) acid on the incidence and sporulation of Plasmopara viticola on grapevine

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1 University of Wollongong Reserch Online Fculty of Engineering nd Informtion Sciences - Ppers: Prt A Fculty of Engineering nd Informtion Sciences 1991 Effect of postinfection ppliction of phosphorous (phosphonic) cid on the incidence nd sporultion of Plsmopr viticol on grpevine T J. Wicks South Austrlin Deprtment of Agriculture P A. Mgrey South Austrlin Deprtment of Agriculture M F. Wchtel South Austrlin Deprtment of Agriculture A B. Frenshm South Austrlin Deprtment of Agriculture, lismith@uow.edu.u Publiction Detils Wicks, T., Mgrey, P., Wchtel, M. & Smith, A. B. (1991). Effect of postinfection ppliction of phosphorous (phosphonic) cid on the incidence nd sporultion of Plsmopr viticol on grpevine. Plnt Disese, Reserch Online is the open ccess institutionl repository for the University of Wollongong. For further informtion contct the UOW Librry: reserch-pubs@uow.edu.u

2 Effect of postinfection ppliction of phosphorous (phosphonic) cid on the incidence nd sporultion of Plsmopr viticol on grpevine Abstrct Phosphorous cid (H3P03) pplied t 1.2 gil up to 12 dys fter infection reduced the incidence nd severity of Plsmopr vitieol. When pplied up to 13 dys fter infection, H3P03 reduced sporultion. In some experiments, the postinfection ctivity of H3P03 ws better thn metlxyl, while in other experiments it ws less effective. Both fungicides pplied fter infection reduced the incidence nd severity of disese on leves nd flower clusters, indicting tht postinfection pplictions should reduce the production of inoculum nd the consequent spred of disese within vineyrd. In most cses, the ddition of copper oxychloride did not ffect the efficcy of H3P03 Keywords viticol, cid, incidence, sporultion, effect, grpevine, postinfection, plsmopr, ppliction, phosphorous, phosphonic Disciplines Engineering Science nd Technology Studies Publiction Detils Wicks, T., Mgrey, P., Wchtel, M. & Smith, A. B. (1991). Effect of postinfection ppliction of phosphorous (phosphonic) cid on the incidence nd sporultion of Plsmopr viticol on grpevine. Plnt Disese, This journl rticle is vilble t Reserch Online:

3 Effect of Postinfection Appliction of Phosphorous (Phosphonic) Acid on the Incidence nd Sporultion of Plsmopr viticol on Grpevine T. J. WICKS, P. A. MAGAREY, M. F. WACHTEL, nd A. B. FRENSHAM, South Austrlin Deprtment of Agriculture, GPO, Adelide, South Austrli, 5001 ABSTRACT Wicks, T. J., Mgrey, P. A., Wchtel, M. F., nd Frenshm, A. B Effect of postinfection ppliction of phosphorous (phosphonic) cid on the incidence nd sporultion of Plsmopr vitieol on grpevine. Plnt Dis. 75: Phosphorous cid (H 3P0 3) pplied t 1.2 gil up to 12 dys fter infection reduced the incidence nd severity of Plsmopr vitieol. When pplied up to 13 dys fter infection, H 3P0 3 reduced sporultion. In some experiments, the postinfection ctivity of H 3P0 3 ws better thn metlxyl, while in other experiments it ws less effective. Both fungicides pplied fter infection reduced the incidence nd severity of disese on leves nd flower clusters, indicting tht postinfection pplictions should reduce the production of inoculum nd the consequent spred of disese within vineyrd. In most cses, the ddition of copper oxychloride did not ffect the efficcy of H 3P0 3 Downy mildew, cused by Plsmopr viticol (Berk. & Curtis) Berlese & de Toni, is mjor disese of grpes in mny viticulturl res of the world (2). In most grpe-growing districts of Austrli, downy mildew cuses some crop loss ech yer, nd in wet yers, complete crop loss my occur in some vineyrds. The disese is controlled with well-timed pplictions of copper or mncozeb fungicides. Since the mid- 1970s, mixtures of metlxyl formulted with either copper oxychloride or mncozeb hve lso controlled downy mildew when pplied before nd fter infection. Fungicides with modes of ction differing from tht of metlxyl nd relted mterils re needed in Austrli for use in ntiresistnt strtegies. Resistnce to metlxyl hs been detected in popultions of P. viticol in Europe, where in some res, it is no longer effective ginst tht pthogen (1). Phosphorous (phosphonic) cid (H 3P0 3) ws first evluted s downy mildew fungicide in Austrli during (3,6), nd its potentil s suitble lterntive to metlxyl ws demonstrted. This work showed H 3P0 3 ctivity ginst P. viticol nd indicted need for more extensive investigtion, prticulrly into its efficcy when pplied either before or fter infection. As result of these nd relted studies (P. A. Mgrey nd T. 1. Wicks, unpublished), formultion of H 3P0 3 ws developed nd is currently registered in Austrli for the control of grpevine downy mildew. Accepted for publiction 18 June 1990 (submitted for electronic 1991 The Americn Phytoptholog icl Society The objectives of this study were to further evlute the efficcy of H 3P0 3 or n H 3POr copper oxychloride mixture when pplied t vrious times fter infection. MATERIALS AND METHODS Generl methods. Experiments were conducted in 1988 nd 1989 t the reserch centers of the South Austrlin Deprtment of Agriculture t Loxton, Nuriootp, nd Northfield, which re pproximtely 300 km northest, 100 km north, nd 8 km north of Adelide, respectively. At these loctions, vineyrds of the Vitis vinifer L. cvs. Shirz, Grenche, White Grenche, nd Mtro, which re commonly grown in Austrli, were used s test sites. Ech site comprised mture vines drip-irrigted nd trined on vriety of trellis systems nd, prt from the fungicide tretments, stndrd culturl prctices were mintined. Shoots were inoculted by sprying 2-3 hr before dusk freshly prepred suspension of I X 10 4 P. viticol sporngi per millileter. The shoots were then seled in moistened plstic bgs to mintin lef wetness overnight. Fungicides were pplied t Loxton with knpsck spryer nd t Nuriootp nd Northfield with pressurized hnd-wnd. Vines were spryed to run off, nd from 0.75 to 1.5 L of spry liquid ws pplied per vine depending on the mount of vine folige. H 3P0 3 s Foli-R-Fos 200, n queous solution contining 20%.i. H 3P0 3 neutrlized to ph with equl mounts of KOH (U.I.M. Agrochemicls, Queenslnd, Austrli), ws used in ll experiments. Copper oxychloride (50%.i. CuOCl) nd metlxyl (25WP) or formulted mixture of metlxyl (4%) nd mncozeb (64%) s Ridomil MZ-WP, (Cib Geigy, Aust. Ltd., New South Wles, Austrli) were used in vrious experiments s stndrd tretments. In some experiments, H 3P0 3 ws tnk-mixed with copper oxychloride immeditely before ppliction. The surfctnt Citowet (100% lkylryl polyglycol ether; BASF, Aust. Ltd., North Melbourne, Austrli) t the recommended rte of 6 ml/ 100 L ws used in ll tretments. Rndomized block designs were used in ll experiments. Dt were nlyzed using the sttisticl pckges GLIM (Numericl Algorithms Group, Oxford, UK) nd STATISTIX (NH Anlyticl Softwre, Roseville, MN). Weighted regression techniques were used to exmine differences in tretment responses over time. Ech prmeter (for exmple, the intercept, liner, nd qudrtic coefficients) of set of regression curves ws tested for equlity with n F test. If this ws significnt, pirwise tretment comprisons of prmeters (using Wller Duncn's k-rtio t test) followed. In some trils it ws not relevnt to consider reltionships over time but rther to compre tretments t prticulr times. Dt of this type were nlyzed by first performing n overll test for equlity using chi-squre or F test s pproprite. If these were significnt, then pirwise tretment comprisons were crried out with Z or t tests. Experiment 1-Loxton. On II N 0- vember 1988, the youngest five fully expnded leves (>4 em in dimeter) nd two bunches on ech of four shoots per vine (cv. Shirz) were inoculted. Singlevine replictes, seprted by brrier vines, were ech spryed to run-off once with either 1.2 g/ L of H 3P0 3, 1.2 g/ L of H 3P0 3 mixed with 1.25 g/ L of copper oxychloride or the formulted mixture of 112 mg of metlxyl nd 1.8 g of mncozeb per liter. Fungicide tretments were replicted three times nd pplied t 7, 10, 12, or 14 dys fter inocultion. Three replictes ech of six inoculted vines were left unspryed s controls. Twenty-four dys fter inocultion, leves nd bunches were removed from the vine, seled in moistened plstic bgs, nd incubted overnight t 23 C ± I C to induce sporultion of disesed tissue. The following morning, the incidence of leves with oilspots ws recorded nd the extent of sporultion of oils pots s proportion of oilspot re ws rted on 40 Plnt DiseselVol. 75 No.1

4 scle of 0-3 where I = sporultion on <1% of the re of oil spot, 2 = 1-25% sporultion, nd 3 = % sporultion. The production of sporngi in ctegories 2 nd 3 ws quntified by selecting 10 sporulting oils pots from ech ctegory, mesuring the re of ech sporulting lesion, nd wshing the lesions in wter. A hemcytometer ws used to determine concentrtions of sporngi. Experiment 2-Nuriootp. This experiment ws conducted on cv. Grenche vines in April 1988.H 3P0 3 t either I or 2 g/ L ws pplied to vines t either 1,3, or 7 dys fter inocultion. A men of 16 leves per shoot on t lest five shoots per vine were inoculted on singlevine plots which were replicted four times. Metlxyl t 250 mg/ L ws pplied to inoculted shoots for comprison. Seven dys fter the finl spry, inoculted shoots were removed nd sporultion ws induced s previously described. Sporultion ws ssessed by recording the number of sporulting leves per shoot. Experiment 3-Nuriootp. This experiment ws lso conducted on cv. Grenche to which either 1.2 g/ L of H3P03, 1.2 gil of H 3P0 3 mixed with 1.25 g/ L of copper oxychloride, or 112 mg of metlxyl plus 1.8 g of mncozeb per liter ws pplied t either 5, 8, 13, 16, 19, or 22 dys fter inocultion. A men of 10 leves per shoot on five shoots per vine on ech of three replicte vines per tretment were inoculted on 9 N 0- vember Inoculted shoots were removed 7 dys fter the lst spry nd plced in moistened plstic bgs to induce sporultion. The extent of necrosis nd sporultion ws rted on both leves nd flower clusters of inoculted shoots. Experiment 4-Nuriootp. This experiment ws crried out on cv. White Grenche to which the sme fungicide tretments s experiment 3 were pplied to similr number of vines. A men of 13 leves per shoot on five shoots per vine were inoculted on 22 November 1988 nd fungicides were pplied t either 6, 9, or 13 dys fter inocultion. Sporultion ws induced s previously described nd the extent of sporultion ws ssessed s percentge of the totl inoculted lef re. Experiment 5-Northfield. Shoots of cv. Mtro vines were inoculted with P. viticol on 10 November 1988 nd spryed 4, 7, nd 12 dys lter with the sme fungicides s used in the Loxton experiment. Tretments were pplied to single-vine plots replicted six times. A men of three leves per shoot on four shoots per vine were inoculted. Treted vines were seprted by n unspryed brrier vine. Shoots were removed from the vines 20 dys fter inocultion nd sporultion ws induced nd ssessed. The incidence of necrotic flower clusters nd the production of sporngi on the clusters ws lso ssessed. RESULTS Experiment I-Loxton. Oilspots were first seen 14 dys fter inocultion, but their incidence ws low nd vrible. For exmple, on unspryed vines, oil spots developed on between 7.3% nd 35% of the inoculted leves. Anlyses of dt indicted tht metlxyl-mncozeb nd H3P0 3 with copper tretments pplied before oilspot ppernce (7 dys fter inocultion) significntly (P < 0.05) reduced the number ofleves with oil spots. H3P03 lone ws effective only on vines spryed 10 dys fter inocultion while vrying response ws observed with regrd to the level of sporultion (Tble I). No tretment reduced the number of oil spots per lef when pplied lter thn 10 dys, nor sporultion lter thn 12 dys fter inocultion. The level of infection on bunches ws low nd vrible nd not suitble for sttisticl nlysis. Oilspots with sporultion rted ctegory 3 hd n verge of 630 sporngi/ mm 2, nd ctegory 2 oilspots hd 460 sporngi/ mm 2 ; these differences were not significnt. Sporngi from ctegory rting I were too few to mesure. Experiment 2-Nuriootp. Sprys were pplied in lte April when lef senescence ws beginning nd leves were less susceptible to infection. As result, sporultion on infected leves ws sprse nd only the incidence of sporulting leves ws recorded. Nevertheless, lrge numbers of leves on unspryed vines were infected, resulting in men of lmost six infected leves sporulting per shoot. H 3P0 3 t I or 2 g/ Lnd metlxyl lmost completely inhibited sporultion when pplied 3 dys fter inocultion (Tble 2). Seven dys fter inocultion, metlxyl ws more inhibitory to sporultion thn H 3P0 3, lthough ech fungicide significntly reduced the incidence of sporulting leves compred to the control. Experiment 3-Nuriootp. High levels of infection were chieved on unspryed vines where sporngi developed on over third of the lef re on most leves on inoculted shoots. In contrst, the metlxyl-mncozeb formultion pplied 5 dys fter inocultion ws the most effective tretment s sporultion on leves ws completely inhibited (Fig. I). H 3P0 3 with or without copper oxychloride ws less inhibitory t this time. Sporngi developed on men of four leves per H 3POr treted shoot with pproximtely 12% of the lef re covered with spores. The efficcy of ll fungicides decresed with time s shown by the regression of incidence of sporulting leves expressed s percentge of the control (Fig. I). Fitted vlues from the regression equtions (r2 = 0.96) re s follows: Metlxyl-mncozeb, y = x; H 3P0 3 + copper, y = x; nd H3P0 3, y = x, where y = disese incidence (s percentge of control) nd x = number of dys fter inocultion. Tble 1. The effect of fungicides pplied fter inocultion on the incidence nd sporultion of Plsmopr viticol on grpe cv. Shirz t Loxton, December 1988 Spry timing (dys fter inocultion), Tretment rte Disese incidence,. Sporultion' (g.l/l) Metlxyl-mncozeb ( ) b H]PO] + Cu ( ) b b H]PO] (1.2) 23.7 b b 0.10 b 0.54 bc Unspryed 19.8 b 19.8 b b c Y Within columns, different letters denote significnt differences (P < 0.05). Z sttistics were used in pir-wide comprisons of incidence nd t sttistics for weighted men sporultion scores. 'Assessments of percentge inoculted leves disesed nd men sporultion rting per lef were men scores from 60 leves from ech spryed tretment nd 360 leves from untreted vines. Tble 2. The effect of H 3P0 3 nd metlxyl pplied I, 3, or 7 dys fter inocultion on the incidence of sporultion of Plsmopr viticol on grpe cv. Grenche t Nuriootp, April 1988 Tretment rte Spry timing (dys fter inocultion) (g.l/l) Metlxyl (0.25) 0.05' H 3P0 3 (I) H]PO] (2) Unspryed LSD: P< 'Vlues re men number of sporulting leves per shoot from mximum of 17 leves per shoot. Plnt Disese/Jnury

5 Overll, the efficcy of H 3P0 3 with or without copper ws less thn tht of the metlxyl-mncozeb formultion. Necrosis nd! or sporngi were evident on 56% of inoculted clusters on unspryed shoots. All fungicides pplied 5 dys fter inocultion prevented necrosis of flower clusters nd when pplied up to 13 dys fter inocultion restricted flower infection to 3%. Fungicides pplied from 16 to 22 dys fter inocultion L +-' C u 4- ~ '-../ 125 Metoloxyl + MZ H3P H3P03 + Cu C 50 :.;:; 0 ::J L Q. (J) 25 gve some control but were less effective with 20-30% of clusters disesed. Experiment 4-Nuriootp. Sporultion covering slightly more thn third of the lef re developed on men of 12.5 leves on unspryed vines (Tble 3). When pplied 6 dys fter inocultion, ll tretments significntly reduced both the number of sporulting leves nd the re of sporultion, however, the metlxyl-mncozeb formultion ws. ~ /" /" O~ ~ , ~ o Dys fter inocultion Fig. 1. The effects of single sprys of fungicides pplied between 5 nd 22 dys fter inocultion on the incidence of sporultion of Plsmopr viticol on leves of cv. Grenche t Nuriootp, November Tble 3. The effect of fungicides pplied 6, 9, nd 13 dys fter inocultion on sporultion of Plsmopr viticol on grpe cv. White Grenche t Nuriootp, December 1988 /" Spry timing (dys fter inocultion) Sporulting leves Are of lef Tretment rte per shoot sporulting" (g.i./l) Metlxyl-mncozeb ( ) O.l 5.1 HJPOJ (1.2) HJP0 3 + Cu ( ) Unspryed LSD: P= Percent of lef re with sporulting oilspots. Tble 4. The effect of fungicides pplied 4, 7, nd 12 dys fter inocultion on the incidence of sporultion of Plsmopr viticol on grpe cv. Mtro t Northfield, November 1988 Tretment rte Spry timing (dys fter inocultion) (g.i./l) Metlxyl-mncozeb ( ) 0.04" H)PO) (1.2) HJPOJ + Cu ( ) Unspryed LSD: P= Vlues re numbers of sporulting leves per shoot. 42 Plnt Disese/Vol. 75 No.1,/ o the most effective tretment. Sprse sporultion developed on men of 2.5 leves per shoot in the metlxylmncozeb tretment compred to sporultion on more thn six leves per shoot on the H 3P0 3 tretments. When pplied 9 dys fter inocultion, metlxylmncozeb nd H 3P0 3 without copper reduced the numbers of sporulting leves, nd ll tretments significntly inhibited the re of sporultion when compred to the unspryed control. Fungicides pplied 13 dys fter inocultion did not reduce the number of sporulting leves but ll significntly inhibited the re of lef sporulting compred to the control. The ddition of copper oxychloride did not ffect the ctivity of H 3 P0 3 except for the ppliction 9 dys fter inocultion where n increse in the number of sporulting leves nd the re of lef sporulting occurred. Experiment 5-Northfield. In this experiment, 68% of inoculted shoots on unspryed vines developed sporulting oilspots with men of 2.3 sporulting leves per shoot (Tble 4). The metlxyl-mncozeb tretment nd H 3 P0 3 with or without copper oxychloride lmost completely inhibited sporultion when pplied t either 4 or 7 dys fter inocultion. Fewer thn two leves with sporultion were detected on ll shoots of the 4- or 7-dy tretments. At 12 dys fter inocultion, H 3P0 3 with or without copper oxychloride severely inhibited sporultion. By contrst, the formultion of metlxyl-mncozeb pplied t this time ws less effective s sporultion developed on men of IAleves per shoot (Tble 4). Neither necrosis nor sporultion developed on most clusters spryed with the H 3P0 3 or H 3P0 3 plus copper tretments up to 12 dys fter inocultion. Similr effects were found on clusters spryed with the metlxyl-mncozeb formultion 4 nd 7 dys fter inocultion, but t 12 dys, necrosis nd! or sporultion developed on 65% of the clusters. On unspryed vines, sporngi developed on 75% of the flower clusters, most of which developed extensive necrosis. DISCUSSION These results show tht H 3P0 3 pplied fter infection significntly inhibits the development of P. viticol on both leves nd flower clusters. In some experiments, the effect of H 3P0 3 pplied 7 to 12 dys fter infection ws equivlent to or better thn tht chieved with metlxyl or metlxyl- mncozeb mixture pplied t similr time. In other experiments, however, the effect of H 3P0 3 pplied 7 dys or less from inocultion ws less effective thn metlxyl. The postinfection ctivity of H 3P0 3 ws demonstrted on four cultivrs of V. vinifer; whether similr ctivity occurs on Americn

6 vrieties nd hybrids of Vitis needs to be evluted. All experiments showed tht either metlxyl or H)PO) pplied fter infection reduced the incidence of disese nd the level of sporultion, indicting thi postinfection pplictions of either of these fungicides should effectively reduce the production of inoculum nd the consequent spred of disese. Currently, HJPO) is registered fo r postinfection use on vines in Austrli nd is pproximtely two-thirds the cost of metlxyl. Therefore, it offers reltively inexpensive lterntive to metlxyl nd relted fungicides. The mode of ction of H)PO) is lso likely to differ from tht ofmetlxyl nd other phenylmide fungicides. Alternting these fungicides in spry progrms should reduce the likelihood of popultions of P. viticol developing resistnce to either fungicide. H1P01<copper oxychloride mixtures were evluted in these experiments becuse previous work (4) hd shown tht the protectnt ctivity of H)PO) ws limited to less thn 7 dys fter ppliction, probbly becuse of the rpid trnsloction of H)P01 from spryed leves. The use of H)PO)<copper oxychloride mixture should provide l lest 7-dy postinfection nd 14-dy protective ctivity for ech ppliction. The present experiments showed tht the postinfection ctivity of H)PO) ws in most cses unffected by the ddition of copper oxychloride. Tllis ws not unexpected becuse previous studies (5) hd shown copper oxychloride to hve no postinfection ctivity. These studies hve shown tht the use of either H)PO) or metlxyl cn control P. vilieol when pplied fter infection. Efficient use of either of these mterils will rely on the development of disese forecsting systems tht monitor climtic conditions nd ccurtely predict the occurrence of disese. The ppliction of H1P01 lone could be effective if pplictions were mde within few dys from the strt of n infection period. In mny viticulturl res, ccurte disese forecsting systems re not yet vilble, nd the mosi pproprite use of H)PO) would be in mixture with copper oxychloride or nother protectnt fungicide such s mncozeb. ACKNOWLEDGMENTS We thnk the Au~utin Grpe nd Wine Re5erch Council nd U. I.M. Chemicls for funding the proje<:l. We lso thnk Mrs. B. Hll, Mrs. G. Ellis. R. Schuisis. A. Welk, R. Allen, R. Cirmi. D. Short. nd M. A. Skewes for their nistn" with this work. We thnk U.I.M. Chemicls for the donlion of 1M H)J'O) nd Cib Geigy for the dontion of the mellxyl. LITERATURE CITED I. Cohtn. Y. nd Coffey. M. D Sys(emic fungicide. nd tm control of oomyccle. Annu. Rev. Phytopthol. 24: Lfon, R., nd Suli!. J Downy mildew of the vine. Pges in: The Downy Mildews. D. M. Spencer, ed. Acdemic PrtS&, New York. 3. Mgrey. P. A. WChICI. M. F., nd NeWlon, M. R Evlu(ion of phosphorous cid, phosc:thyl.ai nd.evul phenylmide funsicide5 for post-infection control of grpevine downy mildew cus«! by PI"smOJ1'1ro. vi/icof". AUSlrllS. Plnt Plho!. [n press. 4. Mglrey, P. A.. Wicks. T. J.. nd Wchlel. M. F Fitld evlution of phosphorous cid for the control of grpevine downy mildew. (AbSlr.) AUSlrls. Plnt Plh. Soc. 8th Conf. 1: Wicks. T., nd lee, T. C Evlution of fungicides pplied fler infection on the control of PI"smopo,o vi/kol on grpevine. Plnt Dis. 66: Wich, T. lee, T. C., nd OVerlOn, J Sens;(iv;(y of AUSlrlin isolte. of Plo.smopr vi/icol" to cylnline fungicides. Au.t. J. Exp. Agric.27: Plnt Disese/ Jnury