The classification of herbicides by site of action, published in 1997, has been revised. The classification system uses a numbering system for a herbicide's site of action, chemical family, and common name. Regulatory agencies in the United States and Canada have published labeling guidelines based on the classification to aid in herbicide resistance management.

A classification of herbicides according to their sites of action was developed to help maintain the usefulness of herbicides as a tool in crop production to delay the selection of herbicide-resistant weeds. The classification includes a numbering system for the site of action, the chemical family, and the common name of the herbicide. The United States of America trade name and package mixes also are included.

The performance of BAS 9052 {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexen-1-one} was evaluated when applied postemergence to rhizome and seedling johnsongrass [Sorghum halepense(L.) Pers. # SORHA] in soybeans [Glycine max(L.) Merr. ‘Bragg’ and ‘Centennial’] when the soybeans had four or five trifoliate leaves (V3 to V4 stages) or when they had six to eight trifoliate leaves (V5 to V7 growth stages). The degree of weed control was more strongly associated with rainfall conditions than with the size of the johnsongrass. An exponential equation was used to describe the relationship of soybean seed yield to BAS 9052 rate. BAS 9052 applications of 0.28 kg ai/ha provided an estimated 98% of the potential soybean yield increase when rainfall was adequate but, 0.41 kg ai/ha was required when the plants were grown under moisture stress. Soybean yields were increased by 260 kg/ha when BAS 9052 was applied at the V3 to V4 compared to the V5 to V7 growth stage.

Sicklepod (Cassia obtusifoliaL. ♯3CASOB) seed were obtained from 10 locations in nine southern states, and plants were grown in a nursery for 3 yr. In field experiments, plant height, seed per pod, number of seed per plant, and number of pods per plant varied among seed sources and years. The vegetative growth phase, as measured from emergence to the initiation of the first floral buds, was approximately 30 days shorter for plants grown from the Tennessee source than for those grown from seed collected in Alachua, FL, in all 3 yr. Hand-harvested seed from plants grown from the 10 seed sources that were planted in 1982 were planted beside the original source sicklepod seed in 1983, and both flowered at approximately the same time, indicating self-fertilization. Percent germination of hand-harvested sicklepod seed from the 10 sources ranged from 2 to 11% for 1981 and 3 to 23% for 1982.

: SAMOA (Second Active Mode of Action) is a program that was developed by American Cyanamid as a way to prevent/delay selection of resistance to the imidazolinones and to manage resistant weed populations if they are selected. The program consisted of three major components, all of which had to be implemented for the program to be successful. These components comprised educating sales persons, distributors and farmers on resistance management, developing efficacious and cost-e †ective tank mixtures or sequential programs and providing incentives for using this program.