The time for PGR application may correspond, in some areas where cotton is grown, to periods susceptible to rainfall occurrence. Thus, there is the possibility of the product to be washed without being absorbed by the plants. The use of an adjuvant may improve uptake efficiency and persistence of the product on the leaves in case of occurrence of rainfall after PGR application. This work had the objective to evaluate the effect of an adjuvant on the uptake efficiency of Chlormequat Chloride, as well as, the effect of the time for a 30 mm of rainfall occurrence on the necessity of re-application of the product. Rainfall occurrence just after the application of the PGR or even 24 hours later can wash the product from the cotton leaves, being necessary another application of the product to it to be able to express its function of controlling plant growth. The use of adjuvant can help the absorption of the PGR, revealing plants with lower final height, compared with the treatments that didn't have the adjuvant applied with the PGR. Calculating the cotton growth rate, it's possible to determinate the percentage of absorption of the product by the plants and then, quantify in percentage, the necessity of product that must be applied again.