About the Author
Willie Kirk received his Ph.D. in 1987 from the University of Dundee while working at the Scottish Crop Research Institute, Invergowrie, Dundee. He has worked as a potato seed inspector, research associate, and research officer with Ciba in the UK. He also worked as a crop consultant, and presently as Associate Professor and Extension Plant Pathologist in the Department of Botany and Plant Pathology at Michigan State University, East Lansing. While with Ciba Agriculture in the UK, Kirk was the potato specialist responsible for development and "survival" of Ridomil in the UK during the late blight and mxl-sensitivity debates of the early 1990's. He worked on the early development of phenylpyrolles for seedborne disease management (Maxim). Kirk presently has a 50/50 research and extension assignment focused primarily on chemical control, with fungicide evaluations, novel active ingredients, application timing, containment strategies, and variety evaluations for resistance. He is also focusing some of his effort on survival of the late blight fungus at low temperatures within host tissue. Kirk also manages a potato late blight clinic and laboratory.
Current and Future Developments for Chemical Control of Potato Late Blight
Willie Kirk
Michigan State University
Department of Botany and Plant Pathology
East Lansing, MI
(with Duane Preston and Ed Plissey)
After recent severe potato late blight epidemics in North America, chemical control of late blight is accepted by growers and advisors as the most appropriate and effective means of crop protection. Products for crop protection are subject to scrutiny by a wide variety of interested parties such as EPA, environmental groups and of course the users of such products. Metalaxyl-based products (Ridomil prepacks) were for several years consistently used to control metalaxyl-sensitive genotypes predominant in North America. The displacement of genotypes sensitive to metalaxyl by metalaxyl-insensitive genotypes has renewed interest in alternative fungicides for late blight control as well as other cultural methods for disease control.
During 1995 and 1996 most of the potato growing states in the US requested and were granted Section 18 registrations for three novel fungicides. The fungicides were Tattoo C (propamocarb + chlorothalonil) from Agrevo, Acrobat MZ (dimethomorph + mancozeb) from American Cyanamid and Curzate M8 and Manex C8 (cymoxanil + mancozeb) from DuPont and Griffin respectively.
Currently available protectant fungicides applied as recommended by manufacturers and university extension services have given excellent control of late blight during recent years. Data gathered from several locations in North America has clearly shown that there is no advantage in applying systemic or semi-systemic materials over contact protectant sprays applied as recommended at regular intervals. The advantage offered by the systemic fungicides is clearly seen when application schedules are delayed or when disease has been introduced into the growing crop.
The efficacy of several novel fungicides either registered in Europe or currently within research and development programs also gave excellent disease control when applied within protectant schedules. The results of trials carried out at several locations established the efficacy of the strobilurin group of fungicides e.g. ICI 5504 (azoxystrobin) and other novel fungicides such as IB 17022 and fluazinam for control of late blight. Results from studies comparing application timings, frequencies and dose rates were presented at the conference and early results indicated that these three novel compounds still require considerable research. The problems associated with incorporating appropriate fungicides into disease protection programs according to individual modes of action were discussed.
Trials in 1996 throughout North America have shown that under severe disease pressure there are still no currently available fungicides or products in development that have the capacity to eradicate metalaxyl-insensitive late blight. The implications of incomplete control by chemical means on the permanence of the epidemic, on tuber blight, on transmission of the disease by seed and survival of the fungus within stems, foliage and tubers (especially at low temperatures) is a topic for stimulating discussion.
Presente y Futuro Del Desarollo de Control Quimico De Tizon Tardio
Willie Kirk
Despues de recientes severas epidemias de tizon tardio en Norte America, control quimico de tizon tardio es aceptado por los agricultores y consejeros como la mas apropiada y efectiva de proteccion del cultivo. Los productos para la proteccion del cultivo estan sujetos a un escrutinio a traves de una gama amplia de intereses tales como EPA, grupos medio ambientalistas y por cierto los consumidores de estos productos. Fungicidas basados en Metalaxil (Ridomil Prepacks) fueron usados en forma consitente por muchos anos para controlar genotipos sensitivos a metalaxil en Norte America. El desplazamiento de genotipos sensitivos a metalaxil por genotipos insensitivos a metalaxilha renovado interes en un fungicida alternativo para control tizon tardio, tanto como las practicas culturales como metodos de control de esta emfermedad.
Durante 1995 y 1996 la mayor parte de los estados productores de papa de los EEUU solicitaron registros de nuevos fungicidas y fueron consedidos por la seccion 18 tres nuevos fungicidas. Los fungicidas registrados fueron Tattoo C (propamocarb + chlorothalonil) de Agrevo, Acrobat MZ (dimethomorph + mancozeb) de American Cyanamid y Curzate M8 y Manex C8 (cymoxail + mancozeb) de DuPont y Griffin respectivamente. Para conducir ensayos de control de tizon tardio con fungicidas registrados o completamente provados en los EEUU y Canada deben ser presentados a la seccion 18. En adicion, muchos nuevos fungicidas registrados en Europa o los que estan en programas de investigacion y desarrollo van a ser discutidos. Los resultados de eficacia de los ensayos del grupo de strobilurin por ejemplo de ICI5504 (azoxystrobin) y otros fungicidas nuevos como IB 17022 y fluazinam para control tizon tardio tambien seran presentados. Resultados de estudios de comparacion de epocas de aplicacion, frecuencias y dosis de los fungicidas actualmente disponibles y de fungicidas que todavia estan en proceso de investigacion para control tizon tardio en papas tambien seran presentados. Los problemas asociados con la incorporacion de fungicidas dentro de los programas de proteccion de enfermedades de acuerdo a su modo de accion van ha ser discutidos en forma individual.
Ensayos en 1996 a traves de Norte Amarica ha demostrado que bajo una severa presion de la enfermedad no existe actualmente fungicidas o productos disponibles que tienen la capacidad de erradicar la insensibilidad de metalaxil a tizon tardio. Las implicaciones de un control incompleto con quimicos da lugar a la permanencia de la epidemia, en tuberculos con tizon, en transmision de la enfermedad por semilla y sobrevivencia del hongo dentro de los tallos, hojas y tuberculos (especialmente a bajas temperaturas) van a ser estimulados en una activa discusion.
