PHYTOTOXIC RESPONSES of fruit trees to soil-persistent herbicides have been observed to vary considerably from orchard to orchard, and both sprinkler and flood irrigation have been associated with more injury in sandy soils than has furrow irrigation. The series of orchard irrigation-herbicide studies reported here were conducted from 1963 to 1968 to obtain further information on these problems. Five field experiments comparing furrow with flood irrigation and different levels of sprinkler irrigation were conducted at four different locations—three in Fresno County and one at Riverside. Trees ranged from one year to 20 years in age. All but two trials were conducted on first- or second-year peaches, plums, and almonds. The soils varied in content of organic matter from 0.6 to 2.1 per cent. The sand ranged from 40 to 67 per cent, silt from 24 to 39 per cent, and the clay from 9 to 20 per cent. The herbicides tested included simazine (Princep), diuron (Karmex), terbacil (Sinbar), dichlobenil (Casoron), and fluometuron (Cotoran).

Assistance was received from the Geigy Chemical Company, Kurt Richardson of Geigy's Research Farm, Fresno; and by the staffs of the Kearney and Riverside Field Stations. The soil analyses were conducted by Jim Quick, Soil Laboratory, U.C., Davis, and by John Rible, Agricultural Extension Service Diagnostic Laboratory, U.C., Riverside.