Field and greenhouse studies were conducted in 2002 and 2003 to evaluate mechanically stimulated compensatory growth response of ivyleaf morningglory, common waterhemp, and giant ragweed. Compensatory growth was initiated by the physical removal of the apical shoot to break apical dominance. The amount of apical shoot removed had an effect on mechanically stimulated compensatory growth of common waterhemp and giant ragweed. With these species, the more of the apical shoot removed from the plant, the less compensatory growth occurred. Removal of the shoot from above the cotyledons resulted in giant ragweed that were 48% shorter and weighed 41% less than control plants at 6 wk after shoot removal. However, the amount of apical shoot removed had no effect on the growth of ivyleaf morningglory compared with control plants at the completion of the study. The influence of plant height at the time of shoot removal on compensatory growth was specific to each weed species. Ivyleaf morningglory exhibited less compensatory growth when the plants were 10 cm at the time of shoot removal compared with 20-, 30-, and 40-cm-tall plants. Removal of the shoot when common waterhemp plants were 30 or 40 cm in height reduced plant weight by 23 and 21%, respectively, compared with control plants. However, no reductions in plant weight were observed when common waterhemp were 10 or 20 cm tall at the time of shoot removal. Giant ragweed subjected to shoot removal was smaller in most growth parameters than control plants, regardless of plant height at the time of shoot removal.

Nomenclature: Common waterhemp, Amaranthus rudis Sauer AMATA; giant ragweed, Ambrosia trifida L. AMBTR; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE.