Evaluation of a warning system for controlling primary infections of grapevine downy mildew

A warning system based on (i) a model that simulates the development of all cohorts of Plasmopara\r\nviticola oospores, from oospore germination to infection; (ii) short-term weather forecasts;\r\nand (iii) a mobile phone short message system was tested in Northern Italy, from 2006 to 2008.\r\nAn unsprayed control was compared with a “Warning A” treatment (WA, fungicides were applied\r\nwhenever the warning system predicted an infection period), a “Warning B” treatment\r\n(WB, fungicides were applied as in the WA treatment but only when the relative dimension of\r\nany oospore cohort predicted by the model exceeded a threshold), and a “grower” treatment\r\n(fungicides were applied according to a conventional schedule). Average disease incidence on\r\nleaves was reduced by up to 90% in sprayed plots compared with unsprayed plots. On bunches,\r\nefficacy was always >90% at fruit set; when most berries were touching, efficacy was higher for\r\nthe WA (96%) than for grower (89%) and WB (85%) treatments. On average, 6.8 fungicide\r\nsprays were applied following the grower’s schedule; use of the warning system reduced applications\r\nby about one-half (WA treatment) or two-thirds (WB treatment). The grower’s schedule\r\nhad an average cost of 337 €/ha; the average saving with the WA and the WB treatments was 174 and 224 €/ha, respectively.