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Fungicide and Clay Treatments for Control of Powdery Mildew

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Fungicide and Clay Treatments for Control of Powdery Mildew HORTSCIENCE 41(1):176–182. 2006. disrupted by fungicides which in turn could affect wine quality. An important fungal plant pathogen of Fungicide and Clay Treatments for grapes is Erysiphe necator Schwein. var. necator (formerly Uncinula necator) which Control of Powdery Mildew Infl uence causes powdery mildew (Pearson, 1988) reducing yield and quality of juice and wine Wine Grape Microfl ora from infected grapes (Calonnec et al., 2004; Gadoury et al., 2001). Powdery mildew is Peter Sholberg, Colleen Harlton, Julie Boulé, Paula Haag controlled by several fungicides belonging Pacifi c Agri-Food Research Centre, Agriculture and Agri-Food Canada, 4200 to the demethylation-inhibiting, strobilurin, Highway 97, Summerland, B.C. V0H 1Z0, Canada and quinoxyfen classes (Sholberg, 2004). It is also controlled by a number of organically Additional index words. bacteria, ‘Chancellor’, fungi, ‘Pinot noir’, pseudomonads, produced materials in which sulphur is the ‘Riesling’, Uncinula necator, Vitis vinifera, yeast most important member. Some other organics are mineral and vegetable oils (Northover and Abstract. There is very little information on the interaction of wine grape microfl ora with Schneider, 1996), potassium silicate (Reynolds fungicides used to control grape diseases. The objective of this study was to determine et al., 1996), and clay (Ehret et al., 2001; Shol- how fungicides used in a standard grape pest management program and an experimental berg and Boulé, 2001). In addition to powdery clay being developed for control of powdery mildew affect grape microfl ora. Grape leaves mildew, bunch rot and phomopsis cane and leaf and fruit were surveyed for bacteria, fungi and yeast six times over the growing season spot are important in grape pest management. in 2000 after treatment with clay or fungicides. In 2001 only clay was studied for control Thus, in commercial vineyards fungicides are of powdery mildew in ‘Chancellor’ grapes. The total number of propagules present on applied several times in a season according to untreated leaf and fruit tissue were 76% bacteria, 14% yeast, and 9% fungi. Fungicides a specifi c pest management program which used for grape disease control signifi cantly reduced epiphytic fungi (P < 0.0001), bacteria attempts to control powdery mildew, bunch (P = 0.03), and yeast (P = 0.0001) on grape berries and epiphytic fungi (P < 0.0001), and rot, and sometimes phomopsis cane and leaf yeast (P = 0.03) on leaves. The clay treatment had no detectable effect on grape micro- spot while striving to prevent fungicide resis- fl ora because no signifi cant differences were recorded between clay or untreated grape tance. Because several different fungicides berries or leaves on any of the sampling dates. Over the growing season the fungicide are repeatedly used throughout the season the spray program reduced incidence and severity of powdery mildew better than clay. Clay natural microfl ora could be disrupted and this controlled powdery mildew on ‘Chancellor’ fruit in 2000 and 2001. could have consequences for wine quality and disease control. The effect of fungicides on epiphytic 2002). Bacteria also occur within grape vines The objectives of this study were to 1) grape microfl ora composed of bacteria, yeast, as was fi rst documented by Bell et al. (1995) compare the microfl ora from one hybrid and fungi has not been seriously taken into from vines found in Nova Scotia. Fungicides (‘Chancellor) and two vinifera (‘Pinot noir’ consideration in grape pest management. The applied externally for control of plant patho- and ‘Riesling’) grape cultivars; 2) monitor primary concern with pesticide use that has gens could infl uence bacterial populations by microfl ora on grape berries and leaves after been addressed is the possibility of pesticide killing sensitive bacteria. each treatment (fungicide, clay, untreated) resistance. Strategies that have been developed Leaf surfaces are colonized by several application to determine the effect on grape to prevent fungicide resistance are the use genera of saprophytic yeasts generally catego- microfl ora; and 3) compare the conventional of reduced number of applications, alterna- rized collectively as red yeasts (predominantly fungicide treatment with an organic clay treat- tion, or mixtures of fungicides with different Sporobolomyces and Rhodotorula spp.), white ment for control of powdery mildew. cross-resistance groups, and directing the yeasts (mainly Cryptococcus spp.), and the fungicide against the most vulnerable stage yeast-like fungus Aureobasidium pullulans Materials and Methods of the pathogen in its life cycle (Jutsum et al., (Andrews and Buck, 2002). This community 1998). Little attention has been paid to the of yeasts is thought to provide a natural buf- Plot details. The trials were conducted at effect these materials might have on epiphytic fer against plant pathogens (Fokkema et al., the Pacifi c Agri-Food Research Centre, Sum- bacteria, yeast, and fungi that could infl uence 1979) and individual yeast species have shown merland, British Columbia, Canada (PARC) disease control and wine quality. biological control potential against plant (lat. 49°34'N, 119°39W; elevation 454 m) on Bacteria colonize actively growing plant diseases (Andrews, 1992). A comparison of ‘Chancellor’, ‘Pinot noir’, and ‘Riesling’ own- tissue fi rst, while fungi, and yeast become yeast counts shows that some plant surfaces rooted wine grape cultivars. The vines were prominent as tissue maturity approaches, and as have greater yeast populations than others 16-years old in 2000 with ‘Chancellor’ spaced the plant part becomes necrotic and dies (Leben, (Davenport, 1976). Buds of ‘Cascade’ grapes at 2.5 × 3.6 m in linear groups of adjacent vines 1965). For this reason, epiphytic bacteria as- had higher counts than leaves, and mature fruit consisting of three vines, ‘Pinot noir’ spaced sume a central position, with importance in had much higher counts than immature fruit. at 1.4 × 3.6 m in panels of fi ve vines, and inciting frost damage to plants, altering plant Yeast populations are infl uenced by climate ‘Riesling’ spaced at 2.0 × 2.9 m in panels of development via exogenous phytohormone and spray program. Rain reduces the yeast fi ve vines. All the vines were cordon trained, production and as agents of plant disease population (Longo et al., 1991) and grape spur pruned (about 20 nodes/m) on vertical (Kinkel et al., 2000). Knowing whether epi- temperature can determine which species trained canopies that were hedged around lag phytic bacterial populations are immigration are present. Hanseniaspora spp. is found in phase of berry development. The experimental or growth limited has important implications warm climates and Kloeckera is associated design was a randomized complete block with on management of these populations (Lindow, with cold temperatures (Villa and Longo, four replicate panels for ‘Chancellor’ and fi ve 1996). On plants that harbour large numbers of 1996). Commercial fungicides tend to inhibit replicate panels for ‘Pinot noir’ and ‘Riesling’. bacteria (e.g., 107 CFU/leaf), growth appears fermentative yeast species favouring prolifera- ‘Chancellor’ three vine replicates with half of to be the dominant process that determines tion of oxidative or apiculate species (Villa vines of 1 and 3 as guards for disease evalu- bacterial population sizes (Upper and Hirano, and Longo, 1996). Sachromyces cerevisiae ation, thus treatments were separated by two is quite sensitive to antifungal compounds half vines. ‘Pinot noir’ and ‘Riesling’ fi ve vine Received for publication 12 Aug. 2005. Accepted whereas species belonging to Rhodotorula, replications had vines one and fi ve as guards for publication 7 Nov. 2005. Cryptotoccus, and Sporobolomyces show for disease evaluation, thus treatments were 1To whom reprint requests should be addressed; polyresistance to such agents (Villa and Longo, separated by two buffer vines. e-mail [email protected]. 1996). Therefore, yeast populations could be Microfl oral assessment. Leaves and berries 176 HORTSCIENCE VOL. 41(1) FEBRUARY 2006 FFebruaryBookebruaryBook 1 117676 112/14/052/14/05 110:56:230:56:23 AAMM Table 1. Fungicide and clay application dates and rates for ‘Chancellor’, ‘Pinot noir’, and ‘Riesling’ Canada Corp., Edmonton, Alta.) located about grapes. 1 km from the vineyard. Chancellor/Pinot noir/Rieslingz Chancellor Data analysis. Microbial counts found on Applications in 2000 Applications in 2001 the various media types was determined for Application Fungicidey Clay Fungicide Clay each fruit or leaf sample of ‘Chancellor’, ‘Pinot date (g/100 L) (kg/100 L) (g/100 L) (kg/100 L) noir’, and ‘Riesling’ grapes on each sampling 16 May M(350) Not applied Not applied Not applied date. These numbers were combined to obtain 23 May M(350) + K(300) Not applied N(20) 2 the total sum of fungi, bacteria, pseudomonads, 30 May D(450) + K(300) Not applied Not applied Not applied and yeast found on the different hosts over the 6 June M(350) + N(20) 4 N(20) 2 2000 growing season for each treatment. A two 27 June M(350) + N(20) 4 N(20) 2 way analysis of variance was conducted using 18 July M(350) + K(300) 4 R(150) + N(20) 2 the three grape cultivars as blocks against six 8 Aug. R(150) + N(20) 4 R(150) + N(20) 2 application dates followed by Bonferroni post 29 Aug. R(150) + K(300) 4 Not applied Not applied tests (GraphPad Software Inc., San Diego, 6 Sept. Not applied Not applied R(150) + N(20) 2 12 Sept. M(350) + K(300) 4 Not applied Not applied Calif.). Mean fungal, bacterial, pseudomonad, 21 Sept. Not applied Not applied R(150) + N(20) 2 and yeast microfora (log CFU/g tissue weight) 28 Sept. M(350) + K(300) 4 Not applied Not applied were plotted at each application date and for zThe fi rst fungicide and clay applications were not made to ‘Riesling’ grapes until 6 June 2000. each treatment standard error of the mean was yFungicides are abbreviated as follows: M = Maestro 75 DF (captan); K = Kumulus 80 (sulphur); D = shown with error bars (GraphPad Software Dithane M 45 (mancozeb); N = Nova 40W (myclobutanil); 6R = Rovral 50W (iprodione).
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