THE ENEMY: Common sunflower (Helianthus annuus L.)
Strategy: This is an annual plant grows up to 10 feet tall. It very much resembles the normal sunflower, yet seed head is only a few inches across. We find this weed growing along our disturbed roadsides and abandon fields. It has wide arrow shaped leaves, yellow ray flowers and brown internal disk flowers (as the seed head is actually a combination of many smaller flowers). It only produces one stalk, but can have many flower clusters protrude from the top of the plant.
Attack: As mentioned this plant loves to invade disturbed sites such as roadsides. In the summer months it grows tall enough that is shades desirable vegetation and with its deeper roots in robs the plants of nutrients and water. We even see this plant causing line of site and traffic impediment issues, thus the importance of roadside weed control programs. The weed blooms later in the summers when the others have practically died off. In large clusters it adds to the problem of snow drifting in the winter.
Defense: As this is an annual weed mechanical control is very effective when just a few plants are found. Mowing is not generally useful as it will only suppresses the plant, which will grow back at a later date. In open fields, replanting of desirable species will keep the plant from returning in following years. Herbicides are very effective. 2,4-D (3pts/ac) in early summer works well. Once the plants develop vegetative growth shoots you will need to go to stronger herbicides such as Opensight (2oz/acre), Milestone (6oz/ac), Escort XP (1oz/ac), or a new product Method (10oz/ac). Good surfactants are a must when spraying later in the summer as the plants develop a tough outer coating of wax.