Study On The Timing Of Chemical Control Of Potato Late Blight

Potato late blight is a devastating disease in potato production which causes leafdeath and tuber rot with high epidemic rate and wide distribution. At present, potatogrowers mainly use chemical control to manage late blight because the most of thecultivars used are not resistant to the disease. However, fungicide application is eitherabuse or not in time, which result in increasing of input and environment pollution ordisease epidemic causes severe loss, due to potato growers could not grasp spray timingaccurately. Hence, it is the key issue to be solved in potato production that how todetermine the rational spray timing specially the first spray. In this study, four strategiesto determine the first spray were designed based on the production practice and a Chinesepotato late blight warning system (Chinablight). They are1) first spray conducted whenthe plant height of potato reach20cm,2) first spray conducted according to the lateblight outbreak forecasting of “Chinablihgt”,3) first spray conducted when the firstsymptom of late blight appeared in the field and,4) first spray conducted two weeks afterthe first symptom of late blight appeared in the field, with the aim to make clear theoptimum timing of first spray and to provide theoretical basis and technical support forthe effective management of the disese. The main results are as follows:1. The field tests of2012and2013indicate that the date of first symptomappearance of late blight forecasted by “Chinablight” was consistent with the actual dateobserved in the field.2. All the strategies of “first spray conducted when the plant height of potato reach20cm”,“first spray conducted according to the late blight outbreak forecasting of‘Chinablihgt’” and “first spray conducted when the first symptom of late blight appearedin the field” could give effective control on potato late blight, and without difference inefficacy between each other. However, the last two strategies could save17～25%and33～38%sprays respectively compared to the first strategy.3. The single normal protective fungicide80%Mancozeb WP could control lateblight effectively according to the spray time determined by “Chinablight”. However,even if the excellent protective and curative fungicide687.5g/Lpropamocarb-HCl·fluopicolide SC sprayed with the strategy of “first spray conductedtwo weeks after the first symptom of late blight appeared in the field” could not control the disease effectively.