Abstract: Disclosed is a boom sprayer assembly for applying herbicides, or the like, in a controlled pattern about a row of trees, bushes, etc. A boom arm of changing length and angular position carries a bell-shaped sprayer hood which is free to rotate independently of the spray nozzle it encloses. The hood acts as a position sensing element to guide the boom so that the desired spray pattern is put down around the row of trees or bushes without permitting the spray to reach the foliage of the bushes or tree trunks.