at v10 in the most preferred embodiment the 3 u2032 methyl s abscisic acid is applied to corn during the period beginning when the plants are at vegetative stage 3 v3 until v6 stage in a further embodiment the 3 u2032 propargyl s abscisic acid is applied to improve low temperature tolerance with another plant growth regulator to the plant in a preferred embodiment the plant growth regulator is selected from the group consisting of cytokinins gibberellins anti gibberellin triazole herbicides auxins organic acids ethylene generators and ethylene biosynthesis inhibitors in a more preferred embodiment the plant growth regulator is selected from the group consisting of gibberellins ethylene generators and anti gibberellin triazole fungicides in another embodiment the amount of an anti gibberellin triazole fungicide that is applied is from about 100 to about 690 grams per hectare in a preferred embodiment the amount of the anti gibberellin triazole fungicide that is applied is from about 100 to about 180 grams per hectare in an embodiment the present invention is directed to methods for improving drought stress tolerance comprising applying an abscisic acid derivative selected from the group consisting of 3 u2032 methyl s abscisic acid 3 u2032 propargyl s abscisic acid and a salt thereof to a crop plant in a preferred embodiment the abscisic acid derivative applied to the crop plant to improve drought stress tolerance is 3 u2032 methyl s abscisic acid in another embodiment the 3 u2032 methyl s abscisic acid is applied to improve drought stress tolerance at a rate of from about 10 to about 2000 grams per hectare in a preferred embodiment the.