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. Sulfo nylurea and imidazolinone herbicides are selective acetolactate synthase-in hibiting herbicides that have been found effective for Orobanche control. I n greenhouse and field experiments, O. aegyptiaca and O. ramosa were contro lled in potato-infested soils by split foliar applications of low rates of the herbicides imazapic and rimsulfuron. Three doses of imazapic at 4.5 g/h a each, sprayed 2 weeks after crop emergence and re-applied at 2-week inter vals, prevented Orobanche infestation. Although imazapic treatments increas ed crop vigor and potato yield, potato tuber quality was severely damaged i n light sandy loam fields, where tubers were deformed pro rata to imazapic applied doses. A single application of 7.5 g/ha triasulfuron sprayed on pot ato foliage, severely damaged the crop. Three repeated applications of rims ulfuron at 12.5 or 25.0 g/ha at identical timing to imazapic, selectively c ontrolled Orobanche and were found safe for potatoes as well as tuber quali ty. Rimsulfuron has approval for use on commercial crops of potato. (C) 200 1 Elsevier Science Ltd. All rights reserved.