Field Validation Of Four Decision Support Systems For The Control Of Late Blight In Potatoes

Abstract

Field experiments were carried out between 2001 and 2003 to determine the efficacy of the NegFry, Simphyt, ProPhy and Plant Plus decision support systems (DSS) in controlling late blight of potatoes compared with routine fungicide treatments. The experiments were also used to determine the potential of the systems to reduce fungicide inputs. Over the three year period of the experiment the 7-day routine programme received an average of 13.7 fungicide applications while the DSS programmes varied between 5.7 and 12.3 applications. All decision support systems resulted in a reduction in the number of fungicide application (Fig. 2). Compared with the routine control, the NegFry and SimPhyt programmes resulted in a 58-44% reduction in application frequency. The ProPhy and Plant Plus programmes resulted in more modest savings of between 10 and 25% (Tables 1 & 2). All fungicide treatments significantly delayed the date of disease onset compared with the untreated control. Compared with the routine control treatment, the NegFry and Plant Plus significantly delayed disease onset in King Edward in 2001 as did NegFry and ProPhy in Rooster. In 2002 there were no differences between treatments in terms of delaying disease onset, while in 2003, disease developed significantly earlier the Plant Plus programme compared with the routine control. In general, the date of disease onset was not significantly different between routine programmes and DSS programmes irrespective of the cultivar. In each of the three years, all fungicide treatments significantly reduced the incidence of foliage blight at the end of the season compared with the untreated control. When compared with the routine control, no decision support system resulted in significantly more foliage blight at the end of the season, irrespective of the cultivar or year. Similar results were achieved when the treatments were compared using the area under the disease progress curve (AUDPC). These results would confirm that none of the DSS’s resulted in inferior disease control when compared with the 7-day routine application of fluazinam. All fungicide treatments resulted in significantly higher marketable yields compared with the untreated control in all years, irrespective of the variety. Within the fungicide treatments the DSS programmes generally out-yielded the routine fungicide treatment. However, these differences were only significant for Plant-Plus in King Edward in 2001. Within the DSS treatments there were no significant differences in marketable yield in any of the years or either of the varieties. Within the fungicide treatments there were no significant differences between treatments in terms of tuber blight control for the resistant variety Rooster. In the case of the more susceptible variety, King Edward, all the DSS programmes resulted in significantly lower levels of tuber blight than the routine Shirlan control in 2001 except for Simphyt. More importantly, the routine Shilan did not result in significantly better tuber blight control in any of the years when compared with any of the DSS programmes. This confirms that all DSS programmes give equivalent tuber blight control to the routine Shirlan application at 7-day intervals even with a very tuber blight susceptible variety.