Vol.12_No.2 - Pesticide Alternatives Lab - Michigan State University

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Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2The results support the excellent local larvicideactivity of the virus-based products, spinosad andthiacloprid, whose efficacy was superior, even if not ina statistically significant way, to azinphos-methyl.Instead, the average damage recorded in the plotstreated by indoxacarb was greater than with thecompared insecticides, thus not ensuring sufficientprotection (10.7% damage) (Fig. 6).In Trentino the field experiments were carried outin different years and with different CM populationdensities. The insecticides evaluated were spinosad,methoxyfenozide, thiacloprid, and indoxacarb ascompared with chlorpyriphos. Each experimentalregime comprised a treatment with an IGR at the startof egg-laying. Different insecticides were appliedaccording to the intensity of egg-laying recorded byscouting in the orchard. Only chlorpirifos was appliedcuratively, 3 times in high-pressure years and 2 timesin low-pressure years. In this context, spinosad andthiacloprid resulted to be as effective asmethoxyfenozide and indoxacarb (Fig. 7).insecticide resistance was first detected. The firstobjective to be achieved in the farms with high fruitdamages was to reduce such damage within acceptablelevels. Hence, plant protection strategies weredeveloped that provided for integration betweenbiological and chemical products. As regards the IGRs,diflubenzuron was substituted by flufenoxuron, whichshowed it could maintain a good degree of efficacy inpopulations resistant to this class of product. The use offlufenoxuron on pear orchards, however, is notadvisable because of its secondary effects on psillapopulations.Chlorpyriphos, because of its demonstrated lack ofcross-resistance with the azinphos-resistant strain, wascritical in managing resistance in both regions. The useof chlorpyriphos has to be limited due to its hightoxicity for humans and its negative side effects onbeneficial organisms. The reduction of organophosphatesuse has for the moment been made possibleby the use of the granulosis virus that demonstrates anefficacy equal to or superior to chemical products.Hence, it is now being widely employed in Emilia-Romagna. Moreover, in this region CM-GV and theapplication of mating disruption are the main strategiessuggested for orchards with low CM population levelsfor the resistance management.In Trentino, on the other hand, as the levels of theCM population are generally quite low, the wideapplication of mating disruption allowed pesticideresistance to be successfully managed. Furthermore,according to the results of the field trials carried out inthese two fruit-growing areas, it has been shown thatnew pesticides, such as spinosad and thiacloprid, couldbe introduced into the IRM programs. Nevertheless,attention should be paid to their possible negative sideeffectsagainst the beneficial organisms controlling thepear-psilla populations.REFERENCESBoselli M., Vergnani S.(2001). Attività di alcuni insetticidi nei confrontidella prima generazione di Cydia pomonella L. Informatorefitopatologico. 6: 40-46.Ioriatti C., Bouvier J.C. (2000). La resistenza agli insetticidi; il caso dellacarpocapsa (Cydia pomonella L.). Informatore Fitopatologico 9: 5-10.Ioriatti C., Bouvier J.C., Butturini A., Cornale R., Tiso R. (2003).Carpocapsa: la situazione della resistenza ad azinphos methyl ediflubenzuron in Trentino ed Emilia-Romagna. InformatoreFitopatologico. 1: 53-60.Sauphanor B., Brosse V., Monier C., Bouvier J.C. (1998). Differentialovicidal and larvicidal resistance to benzoylureas in the codlingmoth, Cydia pomonella. Entomol. exp. appl., 88: 247-253.C.IoriattiISMAAS.Michele a/A TrentoItalyCONCLUSIONS Technical recommendation IRMstrategies were applied in both regions after someM.BoselliServizio FitosanitarioRegione Emilia-Romagna, BolognaItaly68
Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2A.ButturiniServizio FitosanitarioRegione Emilia-Romagna, BolognaItalyR.CornaleCentro Agricoltura AmbienteCrevalcore (Bologna)ItalyS.VergnaniCentro Ricerche Produzioni VegetaliCesenaItalyFungicide ResistanceResistance to QoI Fungicides in Podosphaera xanthii Associated with Reduced Control of Cucurbit PowderyMildew in Research Fields in the Eastern United StatesINTRODUCTION Application of fungicides continues tobe the principal practice for managing powderymildew, the most common disease of cucurbit cropsthroughout the world. Powdery mildew, which iscaused by Podosphaera xanthii, needs to be controlledon both leaf surfaces to avoid premature death ofleaves. It is especially important to control powderymildew on the underside of leaves where conditions aremore favorable for disease development than on uppersurfaces. Using systemic or translaminar fungicides isthe best approach. Unfortunately, most of thesefungicides are at risk for resistance developmentbecause they have single-site modes of action. Thecucurbit powdery mildew fungus has demonstrated ahigh potential for developing resistance. Each chemicalclass active for powdery mildew that is at risk forresistance somewhere in the world following repeateduse has developed resistance. Presence of resistantstrains has been associated with control failure. Thusmanaging fungicide resistance is an important aspect ofeffectively managing powdery mildew (McGrath2001).The fungicide program that has beenrecommended recently in the United States is astrobilurin fungicide (azoxystrobin formulated asQuadris® or trifloxystrobin formulated as Flint®)applied in alternation with the DMI fungicidemyclobutanil (formulated as Nova® or Rally®) tankmixedwith a protectant fungicide. This program usestwo strategies for managing resistance:1. alternation among systemic fungicides in at leasttwo chemical classes, and2. inclusion of protectant fungicides which are not atrisk for resistance development because they havemulti-site modes of action.Strobilurins are in fungicide group 11, the quinoneoutside inhibitor (QoI) activity group. Myclobutanil isa triazole fungicide in the DMI activity group, which isfungicide group 3. Quadris and Nova have beenavailable for commercial use for powdery mildew oncucurbits in the US beginning in 1998 when theyreceived Section 18 registration in some states. USfederal (Section 3) registration was granted for Quadrisin March 1999 and Nova in May 2000. Flint wasregistered in September 1999.Resistance is a major concern with QoI fungicidesused for cucurbit powdery mildew due to past historywith this pathogen developing resistance. Therefore itis important to monitor fungicide efficacy and, if poorperformance occurs, to determine if it is due toresistance. These were the goals of this study. Efficacywas monitored in NY. Pathogen isolates were alsoassayed for resistance from other areas where poorcontrol was reported.MATERIALS and METHODS Quadris applied in alternationwith Nova tank-mixed with chlorothalonil (formulatedas Bravo Ultrex®) was included in fungicide efficacyexperiments conducted with pumpkin from 1998 to2002 in Riverhead, NY. Quadris was used alone on aweekly schedule for another treatment in 2002 becauseother fungicides used with Quadris in a programdesigned for managing resistance, as recommended forproduction fields, might provide enough control ofpowdery mildew to mask the presence of strobilurinresistant strains, especially if they were at a lowfrequency. Fungicides were applied weekly with atractor-mounted boom sprayer. Applications wereinitiated after the IPM threshold of one leaf withsymptoms of 50 old leaves examined was reached in all(or almost all) plots (McGrath, 1996b). A randomizedcomplete block design with four replications was used.Upper and lower surfaces of 5 to 50 leaves, dependingon incidence, in each plot were examined weekly forpowdery mildew. Average severity for the entirecanopy was calculated from the individual leafassessments. Area under disease progress curve(AUDPC) values were calculated as a summationmeasurement of powdery mildew severity over thetreatment period. Cultural practices used and otherfungicide treatments tested are described in previousreports (McGrath 2000, 2002b; McGrath and Shishkoff1999, 2001, 2003). One other treatment was Flintapplied alone weekly in 1998 to obtain manufacturerrequestedefficacy data.An additional opportunity to evaluate Quadrisapplied alone or with Nova plus Bravo was provided69
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Vol.12_No.2 - Pesticide Alternatives Lab - Michigan State University

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