Abbreviations

Standard biochemical nomenclature has been used where appropriate. Trivial names and company numbers have been used to refer to some chemicals. Their structures are given in the chemical glossary, page 261.

1. chlorsulfuron (page 175)

2. sulfometuron methyl

3. imazapyr

4. imazaquin

5. AC 222164

6. N-phthalyl-L-valine anilide

7. 2-nitro-6-methyl sulphonanilide

Introduction

Sulphonylureas (E.I. du Pont de Nemours and Co) and imidazolinones (American Cyanamid Co) are new classes of herbicides characterised by low use rates (as little as 4 g/ha for some sulphonylureas), pre- and post-emergent activity and low toxicity. Variants have been developed to control weeds in a wide range of different crops.

Sulphonylureas, imidazolinones and sulphonanilides (a type of herbicide described in recent patent from Dow Co) kill plants in an identical and distinctive fashion. The symptoms of plant death first appear in the meristematic tissues where growth ceases soon after treatment. Chlorosis and the necrosis of the tissue soon follows with die back to the more mature parts of the plant taking a further 3–4 weeks. In this chapter a review of the current ideas of the mechanism of action of these herbicides will be presented. Some of this work has not been reported elsewhere.

Physiological studies of herbicide mode of action

Studies of the physiological effects of the sulphonylureas on plants provided the first clues to their mode of action. Corn seedlings stopped growing within two hours of a foliar application of chlorsulfuron (Ray, 1982a, b).