This erect summer annual flowers from August through October, spreading allergy-causing pollen in the air. This plant can be identified by the purple color found on the undersides of its cotyledons. It is similar to giant ragweed, just smaller. This plant prefers full sun, and slightly dry conditions. It can be found growing in disturbed areas such as fields, pastures, and roadsides.
Control with night tillage reduces emergence by around 45%. Small grains in rotation will also suppress common ragweed if they are overseeded with clover. Otherwise, the ragweed will grow and mature and produce seed in the small grain stubble.
Source: Virginia Polytechnic Institute & State University