Experiments on setting fruit with growth-regulating substances on field-grown tomatoes in California

does not appear. First page follows. Introduction The failure of tomatoes to set fruit on the early flower clusters is a common complaint of California growers who produce for the spring and summer market. Poor fruit-set is usually ascribed to low temperatures. (Went (1944)) has suggested that night temperatures in particular have an important influence on fruit-set. In each spring-market area, after the danger of winter frost, there follows a period of 6 weeks to 3 months when day temperatures are conducive to good vegetative growth, but night temperatures may drop too low for proper setting. The cool period in the Imperial and Coachella valleys occurs in late February and early March, but by late March night temperatures usually are satisfactory. In the Tulare district, night temperatures may run too low during early and mid-April, but normally no trouble in setting is experienced after May first. In the coastal districts, which are influenced by cool breezes from the ocean, low night temperatures may occur well into June; in the San Francisco Bay district they occur even into July. In each district the earliest fruit generally brings the best market price. Failure of the early clusters to set fruit may mean a delayed harvest period; even, perhaps, a short one because of competition from districts which produce for a later market. Fruit-set for the canning crop is satisfactory in most years. Early production is less important. Only in the San Francisco Bay district do growers frequently complain of poor fruit-set of this crop. In the northern United States, where fruit-set on greenhouse tomatoes is poor during the short overcast days of winter, growth-regulating substances have proved effective for increasing yields. In California, where no commercial field tests had been reported, experiments were begun in 1945 to determine if growth substances would increase fruit-set under field conditions.