NEW MATERIAL:The compound of formula I (R2 is group of formula II or formula III; R2 is H or CH3; R3 is H or C2H5).

EXAMPLE: N-(5-tert-Butyl-3-pyrazolyl)maleamic acid.

USE: An agricultural and horticultural fungicide effective to control the blights of various agricultural and horticultural plants such as rice balst, canker of citrus, fusarium wilt and anthracnose of cucumber, etc., black spot of pear, gray mold of vegetables, etc.

PREPARATION: The maleic acid compound of formula I can be produced by reacting an amine with maleic anhydride in an inert solvent at room temperature. The product is dissolved in an alcohol, left to stand for 1 day in the presence of a small amount of concentrated sulfuric acid, and saturated NaHCO3 solution is added slowly to the product to make the mixture alkaline and obtain the maleic acid ester of formula I . As an alternative method, the fumaric acid compound of formula I is produced by reacting an amine with monoethylfumaric acid chloride in an inert solvent, optionally in the presence of a base at room temperature W 100°C for 1W24hr.