1. Field of the Invention
The present invention relates to novel N-(2-substituted-4-pyridyl)ureas and thioureas, agricultural composition comprising such active ingredients and methods of treating plants therewith.
2. Brief Description of the Prior Art
In the agricultural and horticultural fields, attention has been directed to plant growth regulators which accelerate or suppress the growth of plants when used in trace amounts and which can regulate plants in desired conditions.
In particular, recently techniques for controlling plant growth utilizing the hormone activity of chemicals such as cytokinin or gibberellin have been heavily investigated. Plant growth regulators echibiting cytokinin-like hormonal activity (hereafter referred to as cytokinin hormone activity) can accelerate plant growth when used in very small amounts. On the other hand, plant growth can sometimes be suppressed when such chemicals are employed in excess amounts, i.e., in amounts over that effective to accelerate plant growth (sometimes referred to as overdose use).
Accordingly, while the terms "plant growth regulation" and "plant growth regulator" used herein refer primarily to acceleration, they sometimes refer to suppression of plant growth (in overdose use) in a broad sense. Such seemingly contrary activities by the plant growth regulator are characteristic of cytokinin activity. In this regard, herbicides for which cytokinin activity has clearly been established are not known, though some herbicides have been established to have auxin activity (The term "auxin" is a general or collective name for a kind of plant growth regulators).
Typical plant growth regulators known as having cytokinin hormone activity are 6-benzyladenine, kinetin and 4-pyridylphenylurea. Further, 2-chloro4-pyridylphenylurea and -thiourea have been proposed by the present inventors in Ser. No. 947,468 filed Oct. 2, 1978. However, development of plant growth regulators having more improved effect is still desired.