Field studies were conducted to compare the short- and long-term control of hemp dogbane by POST applications of Dowco 433, clopyralid, and 2,4-D amine. Dowco 433 at 140 g ae ha–1controlled 81 to 93% of weeds at 8 wk after treatment. Good control (79 to 89%) was also achieved with 560 g ae ha–12,4-D amine at 8 wk after treatment. Twelve months after treatment, control of hemp dogbane averaged 65 to 75% where Dowco 433 was applied at rates of 140 g ha–1or higher. Similar results were obtained with 2,4-D amine at 560 g ha–1. Control with clopyralid was minimal. Weed height and dry weight were reduced with all treatments except clopyralid. The effect of early versus late application was also evaluated in two studies. In certain situations, control 8 wk after treatment was greater when application was made during the early reproductive growth stage as opposed to the vegetative growth stage.
Hemp dogbane is sensitive to fluroxypyr and tolerant to clopyralid. Absorption, translocation, and metabolism of clopyralid and fluroxypyr were studied in hemp dogbane to determine if differences in these processes could be responsible for differential sensitivity. In addition, the effect of growth stage on herbicide absorption and translocation was evaluated. The14C-herbicides were applied to the adaxial side of a single leaf located near the midpoint of hydroponically cultured plants. Uptake of fluroxypyr was more rapid than clopyralid. At 72 h after treatment (HAT), fluroxypyr and clopyralid absorption was 62 and 38%, respectively. Clopyralid was much more mobile than fluroxypyr, with 75% of the absorbed14C from14C-clopyralid recovered outside the treated leaf compared to only 45% for fluroxypyr 72 HAT. Relative to fluroxypyr, a higher percentage of14C-clopyralid recovered outside the treated leaf translocated acropetally, especially when plants were treated during the vegetative stage. Treatment during the early reproductive stage increased basipetal and reduced acropetal translocation relative to the vegetative stage. Neither herbicide was metabolized rapidly. Approximately 60 and 90% of the recovered14C was attributable to unaltered fluroxypyr and clopyralid, respectively, 72 HAT. Some differences in absorption, translocation, and metabolism between clopyralid and fluroxypyr exist, but they cannot fully account for differential sensitivity of hemp dogbane to these two herbicides. Differences in activity at the target site may be responsible for differential activity of these herbicides on hemp dogbane.
Yellow cards coated with adhesive were used to survey for the presence, relative abundance and seasonal patterns of lady beetles in research and commercial fields of processing sweet corn in central and western New York in 1992 and 1993. The lady beetles species recorded, in order of abundance were: Coleomegilla maculata lengi Timberlake, Coccinella septempunctata L., Psyllobora vigintimaculata (Say), Hippodamia parenthesis (Say), Propylea quatuordecimpunctata (L.), Cycloneda munda (Say), Hippodamia glacialis glacialis (F.), Adalia bipunctata (L.), Coccinella trifasciata perplexa Mulsant, and Coccinella transversoguttata richardsoni Brown. Coleomegilla maculata lengi was in sufficient number to reflect seasonal patterns. Coleomegilla maculata lengi populations rapidly increased in early July, peaked in late July or early August and then rapidly declined. The timing of C. maculata lengi peak abundance was more closely related to day-of-year than to stage of crop development based on accumulated degree days from planting. The pattern of capture of C. maculata lengi at incremental distances into the field did not indicate colonization from the field edge.
Experiments were conducted to examine morphological variation among hemp dogbane populations. Rootstocks collected from 16 sites throughout Michigan and Illinois were used to establish nurseries in East Lansing, MI, and Champaign, IL. Growth, stem characteristics, and leaf characteristics were measured for each ecotype at both nurseries. Differences among ecotypes were observed for all measurements except emergence date and growing degree days to emergence. The number of shoots per plot produced by the ecotypes ranged from 5 to 54 and shoot height ranged from 69 to 126 cm. Ecotypes spread laterally at different rates, with the most aggressive covering 19 times more ground area than the least aggressive. Total shoot dry weight accumulation varied greatly among ecotypes. Some ecotypes could be identified from others by their unique leaf shape. Shoot number, shoot height, and ground area covered were greater for plants grown in Michigan than in Illinois. Differences in growth and morphological characteristics among ecotypes were not correlated with the geographical region where they were collected. Differences in measurements between the two nurseries illustrate the role of environment and genetics in the growth and morphology of this plant species.
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