Control of Orobanche aegyptiaca and O. ramosa in potato

Potato (Solanum tuberosum) is a susceptible host of the root holoparasites Orobanche aegyptiaca and Orobanche ramosa in the Mediterranean region, and suffers severe yield losses due to high levels of field infestations. Sulfonylurea and imidazolinone herbicides are selective acetolactate synthase-inhibiting herbicides that have been found effective for Orobanche control. In greenhouse and field experiments, O. aegyptiaca and O. ramosa were controlled in potato-infested soils by split foliar applications of low rates of the herbicides imazapic and rimsulfuron. Three doses of imazapic at 4.5g/ha each, sprayed 2 weeks after crop emergence and re-applied at 2-week intervals, prevented Orobanche infestation. Although imazapic treatments increased crop vigor and potato yield, potato tuber quality was severely damaged in light sandy loam fields, where tubers were deformed pro rata to imazapic applied doses. A single application of 7.5g/ha triasulfuron sprayed on potato foliage, severely damaged the crop. Three repeated applications of rimsulfuron at 12.5 or 25.0g/ha at identical timing to imazapic, selectively controlled Orobanche and were found safe for potatoes as well as tuber quality. Rimsulfuron has approval for use on commercial crops of potato.