"长出穗状雄花" can be translated as "develop/produce spicate male flowers" or "form spicate male inflorescences" in English.
Here, "spicate" refers to something arranged in a spike (a long, slender, unbranched inflorescence with sessile flowers), and "male flowers" or "male inflorescences" clearly indicate the gender and structure of the flowers. You can choose the phrase that best fits the context of your sentence.