The use of certain herbicides for weed control is often restricted because of their persistence in the soil and the detrimental effect on subsequent crops. This is particularly true of short-season vegetables where a second crop may follow in from three to four months. In southern California tests two of the urea herbicides, neburon and monuron, were found to disappear relatively slowly. From 4 to 5 months were required for monuron and 8 to 9 months for neburon to fall to the 50 per cent disappearance levels.

The above progress report is based on Research Project No. 1175-D-R.