Time responses, particularly daily oscillations, of seven species of plants were studied. Five of the species were weeds: Ambrosia artemisiifolia L., common ragweed; Ambrosia trifida L., giant ragweed; Cirsium arvense (L.) Scop., Canada thistle; Euphorbia esula L., leafy spurge; and Taraxacum officinale Weber, common dandelion. Two were desirable as roadside ground cover: Medicago sativa L., alfalfa, and Trifolium pretense L., red clover.
Methods were developed for germinating weed seeds, a process which is often difficult to accomplish in a laboratory. A chlorophyll assay that was selected and modified for the study should be valuable in monitoring the status of injury to a variety of roadside plants.
Variations in plant populations and the lack of good statistical evidence were important factors in not being able to designate any one time of day to be consistently better for controlling weeds by 2, 4-dichlorophenoxyacetic acid (2, 4-D) under controlled environmental conditions.
It is possible that changes which take place throughout the day in leaf orientation could be an important factor when considering procedures for controlling roadside weeds, such as sicklepod in southern states or velvetleaf in Minnesota.
Minnesota Local Road Research Board and the Minnesota Department of Transportation
Koukkari, Willard L..
Time Responses and Susceptibility of Roadside Plants to Growth Regulation.
Minnesota Agricultural Experiment Station.
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