Bur Ragweed

 
(Ambrosia grayii)

Also known as Wollyleaf bursage

Deep-rooted, perennial forb

Habitat:
            *Prefers consistent moisture, but can withstand extended drought 
            *Cropland
            *Fallow

Flowers:
            *Inconspicuous, greenish-gray
            *July-August
            *Male flowers on upper leaf axils, females lower on stem
            *"Bur" is a cluster of female flowers, light tan with barbs

Seeds:
            *12-24" tall
            *Can produce a single flower stalk from each stem
            *New shoots arise from root-borne vegetative buds

Roots:
            *Tap root can extend 15 feet deep
            *Lateral roots can penetrate to 6 feet however, most are in top 3-10" of soil

Growth and reproduction:
            *Four year old plant" roots 6 ft. deep, 1/4" diameter
            *12 plants per sq. ft. can produce 380-460 burs per sq. ft. 
            *Reproduces primarily from root-borne buds, also seed

Management:
            *1) Tillage: 3-4" deep every 14-21 days, for 2-3 years
            *2) Herbicides: dicamba, glyphosate, imazapic, picloram, 2,4-D LVE
            *Picloram+2,4-D or banvel provide best control
            *Apply herbicide when flowering (July-August)
            *Monitor for 12-24 months after eradication

Threats:
            *Aggressively competes for light, moisture and nutrients
            *Infestation during "bad" year can result in total crop loss
            *Infestation during an "average" year can reduce yields by 40-75%