Department of Plant Pathology, Punjab Agricultural University, Ludhiana-141004
National Symposium on “Plant Pathology in the Changing Global Scenario” held at National Bureau of Plant Genetic Resources, New Delhi on February 27–28, 2009
The efficacy of fungicides with different modes of action i.e. Curzate M-8 (cymoxanil 8% + mancozeb 64% 72 WP), Amistar 25% SC (azoxystrobin) and Acrobat 50% WP (dimethomorph) along with Ridomil MZ 72 WP (metalaxyl 8% + mancozeb 64%) and Indofil M-45 (mancozeb 75%) was determined against metalaxyl resistant population of Psuedoperonospora cubensis in a cucumber field in village Jand (Amritsar) during 2007–08 crop season. The cucumber fields in this village have been facing the problem of inferior efficacy of Ridomil MZ in controlling downy mildew because of development of metalaxyl resistance in P. cubensis due to repeated application of Ridomil MZ in the past several years. Cultivar Poinsette was used for conducting the experiment and standard agronomic practices were followed to raise the crop planted in December 2007–08 under low plastic tunnel. Three replications were used per treatment and each replication had a plot size of 2.0 m x 15.0 m. Fungicide applications were started with the initial appearance of downy mildew symptoms in the field towards end February followed by three more applications at 10 days interval. The data on disease severity on cucumber leaves were recorded after 10 days of the last spray following a 0–5 rating scale. Data revealed that Ridomil MZ applications badly failed to control the disease effectively and the disease scenario in the plots treated with this fungicide appeared like that in untreated plots with disease severity of 55.0%. Curzate M-8 72 WP was able to control the disease to the maximum level with an average disease severity of 2.6%. Similarly, Amistar 25% SC, a strobilurin compound and Acrobat 50% WP (dimethomorph) also appeared quite effective against resistant population of P. cubensis and showed average disease severity of 6.0 and 5.0%, respectively. The performance of Indofil M-45 also appeared satisfactory and showed disease severity of 10.5% as compared to 70.0% in untreated control. The results revealed that where metalaxyl resistance has developed in P. cubensis, fungicides like Curzate M-8, Amistar and Acrobat can be used for effective disease control.
