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Experiments were conducted to determine the effects of dry heat, direct flame, and straw burning on germination of several weed species from lowbush blueberry fields. Dry heat experiments were designed as factorial arrangements of temperature (100, 200, and 300 C in experiment 1 and room temperature, 100, 200, and 300 C in experiment 2) and exposure time (0, 5, 10, 20, 40, and 80 s in experiment 1 and 2, 5, 10, and 20 s in experiment 2) to determine the exposure time required to reduce germination for each temperature. Susceptibility to dry heat varied across species tested, but germination of spreading dogbane, meadow salsify, fireweed, and hair fescue seeds collected from lowbush blueberry fields in Nova Scotia, Canada generally declined exponentially as a function of duration of heat exposure at the temperatures tested. Germination decreased more rapidly at higher temperatures in all species, although the duration of heat exposure required to reduce germination by 50 and 90% varied across temperatures and species. Exposure of seeds to direct flame rapidly reduced germination, with less than 1 s of exposure required to reduce seed germination of witchgrass, spreading dogbane, and meadow salsify by > 90%. Straw burning did not consistently reduce germination of hair fescue or winter bentgrass, indicating that a surface burn occurring above weed seeds may not be consistently effective at reducing seed viability. These results provide important estimates of the temperature and exposure times required to reduce viability of weed seeds in lowbush blueberry fields and suggest that thermal technologies that expose weed seeds to direct flame will be the most consistent in reducing seed viability.

Spreading dogbane is a common perennial weed in wild blueberry fields. It is highly competitive and spreads rapidly once established. Herbicides can provide effective control of spreading dogbane, but application timing is important. The emergence pattern, ramet height, and flowering time of spreading dogbane were observed in 2008 and 2009, and thermal-based emergence, growth, and development models were developed and used to estimate optimum herbicide application timing. Spreading dogbane emergence and height were described with a three-parameter, sigmoid, nonlinear regression model, whereas flowering was described with a four-parameter, Weibull, nonlinear regression model. Spreading dogbane ramets initiated emergence soon after the biofix date of April 1. Peak emergence tended to occur at 420 growing degree days (GDD). Spreading dogbane reached its peak height by about 558 GDD. The maximum number of flowers per plant was reached at approximately 750 GDD. This study suggested that POST herbicides should be applied between 486 and 535 GDD to maximize efficacy. This time frame occurs after peak emergence and during early floral bud development.

Spreading dogbane is a troublesome weed of wild blueberry fields. Field studies were conducted in 2008 and 2009 to evaluate efficacy of different herbicides and application techniques on spreading dogbane as well as blueberry tolerance. Results indicated that summer-broadcast nicosulfuron at 25 g ai ha−1with 0.5% v/v blend of surfactant with petroleum hydrocarbons suppressed (> 60%) spreading dogbane at three of four sites. Spot sprays with dicamba at 1 kg ae ha−1effectively controlled (> 80%) spreading dogbane with minimal (19 to 23%) blueberry damage at three of four sites. Glyphosate spot sprays at 5 g ae L−1water provided more effective and longer control than hand pulling. Wiping with glyphosate at 154 g ae L−1water or wiping triclopyr at 29 g ae L−1water onto the shoots is also an effective control method for localized patches of spreading dogbane. Although low to moderate crop damage may accompany these techniques, it may still be tolerable for growers to apply these options to limit long-term yield loss caused by spreading dogbane.

Spreading dogbane is an important weed of wild blueberry fields that decreases yields and hinders harvest operations. A range of experiments was conducted to evaluate the impact of abiotic factors on dogbane seed germination. Freshly harvested seeds were largely nondormant with viability ranging between 67 and 84%. Prolonged exposure to light neither promoted nor inhibited germination. Germination rates and total seed germination varied with temperature and osmotic potential. Significantly fewer seeds germinated at 5 C compared with 10, 15, and 20 C. There was a significant quadratic relationship between dogbane germination and osmotic potential, with significant numbers of seeds germinating at levels as low as −0.5 MPa. Emergence rates declined exponentially with depth in the soil and as many as 9% of seeds germinated but were unable to reach the soil surface. Results indicate that substantial seed germination in blueberry fields is possible and primary dispersal without wind occurs over a very short distance.

Absorption and translocation of nicosulfuron and dicamba applied alone and combined was studied in 25-cm-high hemp dogbane originating from lateral roots that had overwintered. Absorption of 14C-nicosulfuron by hemp dogbane was not affected by applications of 70 g ai/ha unlabeled dicamba. Upward translocation of 14C-nicosulfuron in hemp dogbane was 86% greater 6 d after treatment (DAT) when dicamba was tank mixed with nicosulfuron, compared to nicosulfuron applied alone. Combinations of nicosulfuron plus dicamba increased translocation of nicosulfuron to hemp dogbane crown and roots 237 and 130%, 1 and 6 DAT, respectively, compared to nicosulfuron applied alone. Absorption of 14C-dicamba by hemp dogbane was not affected by the addition of 31 g ai/ha nicosulfuron. Upward translocation of dicamba in hemp dogbane was 42% greater 6 DAT for nicosulfuron plus dicamba compared to dicamba applied alone. Increased hemp dogbane control with nicosulfuron plus dicamba compared to either herbicide applied al...

Field studies were conducted from 1994 to 1996 in Michigan to evaluate postemergence (POST) herbicides for hemp dogbane control in corn. Studies were initiated at no-tillage and chisel-plowed sites each of the three years. Nicosulfuron and primisulfuron were evaluated alone and in combination with 2,4-D amine or dicamba. In 1995 and 1996, CGA-152005 plus primisulfuron was also applied alone and in combination with 2,4-D or dicamba. Control varied among years and sites. Nicosulfuron, primisulfuron, and CGA-152005 plus primisulfuron applied alone controlled 30% of the hemp dogbane, and dicamba or 2,4-D alone controlled 42 and 66%, respectively. Tank mixtures of nicosulfuron, primisulfuron, or CGA-152005 plus primisulfuron with dicamba were more effective and more consistent than dicamba alone. Combinations of nicosulfuron, primisulfuron, or CGA-152005 plus primisulfuron with 2,4-D gave the most effective and consistent control across sites, with an average of 93% control. In general, treatments controlled only shoots that had emerged at the time of application. New shoots emerged following herbicide application at the chisel-tillage sites in 1994 and 1995 but not at the no-tillage sites. However, in 1996, shoot emergence following treatment occurred in both no-tillage and chisel-tillage sites.

Clonal individuals from 16 hemp dogbane populations with phenotypic variation were analyzed using isozyme and randomly amplified polymorphic DNA (RAPD) analysis. Plants originated from populations in Michigan and Illinois. Three knownApocynumspecies, spreading dogbane, hemp dogbane, and prairie dogbane, were evaluated. Genetic distance among populations was more pronounced with isozyme analysis compared to RAPD analysis. The combined isozyme and RAPD analysis data separated spreading dogbane from all other plants analyzed. Genetic variation was present among the 16 hemp dogbane populations, but was less than expected based on the phenotypic variation present among the collections. The short genetic distance between the 16 hemp dogbane collections and the threeApocynumspecies suggests that variation among populations of hemp dogbane may be from outcrossing with other closely relatedApocynumspecies. Isozyme and RAPD analyses were also conducted on plants from two populations in Michigan to determine the level of genetic variation among plants within the same population. Genetic analysis revealed that one population was entirely clonal, while the other population was a mixture of clonal and segregating plants.

Field research was conducted to characterize hemp dogbane crown root carbohydrates, to quantify crown root lipids, and to determine seasonal fluctuation of each. The effect of day length on the release of hemp dogbane crown bud dormancy was studied in growth chambers. Total nonstructural carbohydrate (TNC) levels fluctuated with seasonal lows occurring during bud to mid-flowering and seasonal highs in fall predormancy periods. Starch was the primary storage carbohydrate, comprising up to 39.6% of crown root dry weight at the highest seasonal level. Ethanol soluble reducing sugar levels were negatively correlated with seasonal starch levels, and appeared to be maltose and glucose accumulated before conversion to sucrose for translocation. Most lipids were in ethanol soluble fractions and were inversely correlated with seasonal TNC patterns. The maximum level of total lipids in crown roots was 6%. Lipids appeared to be by-products of metabolism in nonarticulated lacticifers and not a significant carbon energy source. An 18-h day length resulted in a 10-fold increase in intact, 2-yr-old crown root dormancy release compared with 10- or 14-h day lengths in growth chamber studies. Seasonal carbohydrate fluctuations in hemp dogbane suggest the most effective control with mowing or tillage would occur when applied at mid- to full flower before root carbohydrates begin to recover. The most effective translocation of phloem mobile herbicides to crown roots would occur after mid- to late flower through leaf senescence when carbohydrates are being stored in the roots.

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.

Control and regrowth of hemp dogbane, wild blackberry, and triazine-resistant common lambsquarters (TR-CHEAL) were studied in no-till corn from 1992 to 1994. Hemp dogbane, wild blackberry, and TR-CHEAL population increased 10, 123, and 177%, respectively, between 1992 and 1994 in plots treated with PRE applications of paraquat, atrazine, and metolachlor (weedy checks). POST applications of tank mixtures of 35 g ai/ha nicosulfuron or 20 g/ha primisulfuron with 280 g/ha 2,4-D or 140 g/ha dicamba, and 560 g/ha dicamba applied alone controlled hemp dogbane, wild blackberry, and TR-CHEAL 67 to 98%. These treatments reduced the population or prevented expansion of these weeds the year following treatment. In 1992, corn yield response to weed control was inconsistent. In 1993 and 1994, all plots treated with POST herbicides yielded higher than the weedy check. Corn yield of plots treated with combinations of nicosulfuron or primisulfuron with 2,4-D or dicamba and 560 g/ha dicamba applied alone were 102 to 149% and 124 to 153% higher than the weedy check in 1993 and 1994, respectively. Nomenclature: Atrazine, 6-chloro-N-ethyl-N'-(1-methylethyl) -1,3,5-triazine-2, 4-diamine; dicamba, 3,6-dichloro-2-methoxybenzoic acid; metolachlor, (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-meth- oxy- 1-methylethyl) acetamide); nicosulfuron, 2-(((((4,6-dimethoxy-2-pyrimidinyl)amino)- carbonyl) amino)sulfo nyl)-N,N-dimethyl-3-pyridinecarboxamide; paraquat, 1,1 '-dimethyl-4,4'-bipyr- idiniumion; primisulfuron, methyl 2-(((((4,6-bis (difluoromethoxy)-2-pyrimidinyl) ami

Management of perennial weeds is a major concern in reduced-tillage cropping systems. Field research was conducted at Nashua, IA, from 1977 through 1990 to evaluate the long-term impacts of tillage and cropping patterns on perennial weed populations in corn and soybean production. Continuous corn and a corn/soybean rotation were conducted utilizing moldboard plow, chisel plow, ridge tillage, and no-tillage systems. The research area was free of established perennial weed species at the initiation of the experiment in 1977. Hemp dogbane was observed by 1980, with the greatest densities in no-tillage. By 1990, continuous corn had greater hemp dogbane densities with no-tillage than other tillage system by crop rotation treatments. American germander densities were not affected by tillage systems in 1980 and 1981, but by 1990, corn/soybean rotations had greater densities in moldboard plow than other tillage systems. Field bindweed developed primarily in the corn/soybean rotations with the greatest densities occurring in no-tillage. Greater and more diverse populations of perennial weeds developed in reduced-tillage systems than in the moldboard plow system. However, practices used to control annual weeds and environmental factors interacted with tillage to regulate perennial weed populations.

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. The 14C-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 absorbed 14C from 14C-clopyralid recovered outside the treated leaf compared to only 45% for fluroxypyr 72 HAT. Relative to fluroxypyr, a higher percentage of 14C-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. Approxi- mately 60 and 90% of the recovered 14C 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. Nomenclature: Clopyralid, 3,6-dichloro-2-pyridinecarbox- ylic acid; fluroxypyr, ((4-amino-3,5-dichloro-6(fluoro-2- pyridinyl)oxy)acetic acid; hemp dogbane, Apocynum can- nabinum L. #3 APCCA. Additional index words: Uptake, translocation, metabolism, selectivity, APCCA.

Hemp dogbane and wild blackberry have become significant weed problems in no-tillage corn production in Maryland. Nicosulfuron (31 to 62 g ha−1) plus crop oil concentrate (COC) gave 67% or more hemp dogbane and wild blackberry control. There was no difference in hemp dogbane or wild blackberry control between 31 and 94 g ai ha−1nicosulfuron. Tank mixtures of 2,4-D or dicamba with nicosulfuron gave 72 to 100% hemp dogbane and wild blackberry control. Hemp dogbane control following applications of 560 g ha−12,4-D was 97% in 1989 and 63% in 1990. Wild blackberry control with 2,4-D was 40% both years. Dicamba at 280 g ha−1gave 70 and 55% control of hemp dogbane and 75 and 65% control of wild blackberry in 1989 and 1990, respectively. Triclopyr plus 2,4-D provided 72 to 98% hemp dogbane control and 92 to 98% wild blackberry control. However, triclopyr plus 2,4-D applied at 280 plus 560 g ha−1injured corn, and corn yields were reduced compared with weedy controls in 1990.

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.

Detached leaves of hemp dogbane (Apocynum cannabinumL.) were treated with14C-glyphosate [N-(phosphonomethyl)glycine] with and without adjuvants in the treatment solution. In the absence of adjuvants,14C absorption was not significant after the first 30 min harvest. Adjuvants increased the amount of glyphosate initially absorbed but did not extend the period of absorption. The pattern of glyphosate absorption in isolated leaf cells was similar to the pattern found in detached leaves. Significant absorption was obtained at the first 15-min sampling with no additional absorption occurring during the remainder of the 2-h incubation period. The quantity of14C absorbed by cells was proportional to the external concentration, but the pattern of cellular absorption was unaffected by the glyphosate concentration. After 2 h of incubation, an average of 0.1% of the glyphosate had been absorbed by the leaf cells. In similar studies using14C-leucine, 1.0% of the14C was absorbed after 2 h with absorption still increasing in a linear fashion. A uniform distribution of14C was obtained in detached leaves that had absorbed14C-glyphosate through the stem. In vitro and in vivo binding studies indicated this absorbed14C was not tightly bound to cellular components and was probably free to be absorbed by and translocated out of the cells. Since the absorption pattern in detached leaves was similar to the pattern obtained in isolated cells, cellular absorption appears to represent the major barrier in the foliar absorption of glyphosate by hemp dogbane.

Field and greenhouse studies of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and glyphosate [N-(phosphonomethyl) glycine] absorption, translocation, and metabolism were initiated to explain field observations which indicated susceptibility of common milkweed (Asclepias syriacaL.) but not hemp dogbane (Apocynum cannabinumL.) to glyphosate and the reverse response to 2,4-D. Glyphosate was absorbed less than 2,4-D in both species with absorption of both herbicides being greater in common milkweed. Greater herbicide absorption by common milkweed was attributed to less epicuticular wax, less cuticle, lower contact angle of the herbicide spray, and the presence of stomata and trichomes on the adaxial leaf surface. No major translocation differences of the herbicides were noted between species. Translocation of glyphosate was more rapid than that of 2,4-D. More glyphosate than 2,4-D accumulated in areas of high meristematic and metabolic activity. Rapid 2,4-D metabolism occurred in common milkweed leaves above treated leaves. There was no detectable 2,4-D metabolism in hemp dogbane roots after 20 days, while 60% of the 2,4-D in common milkweed roots was metabolized. Limited absorption of glyphosate but not 2,4-D by hemp dogbane and metabolism of 2,4-D but not glyphosate by common milkweed were considered the primary factors involved in explaining observed susceptibility differences.

All land uses in eastern and southeastern Nebraska were infested to some extent with hemp dogbane (Apocynum cannabinumL.). The highest infestations were observed in oats (Avena sativaL.) and soybeans [Glycine max(L.) Merr.] and the lowest infestations were in alfalfa (Medicago sativaL.), pastures, and winter wheat (Triticum aestivumL.). Yield reductions from hemp dogbane infestations ranged from 0 to 10% in corn (Zea maysL.), 28 to 41% in soybeans, and 37 to 45% in sorghum [Sorghum bicolor(L.) Moench]. Emergence of hemp dogbane from crown roots occurred when the soil temperature was 17 to 19 C, during April in 1977 and 1978. Plants attained the bud stage within 4 to 7 weeks after emergence. Early flower, full bloom, and pod initiation occurred subsequently at about 1 week intervals. Seeds produced were first viable 10 weeks after full bloom. Root activity or regenerative capacity as measured by length and number of new shoots and roots produced at monthly intervals in the germinator showed a cyclic pattern. The highest activity occurred in the spring and late fall and lowest activity in summer and early fall. Protein levels in the roots ranged from 7 to 9% in the fall and spring to 4 to 5% during the summer. Percentage total nonstructural carbohydrates (TNC) ranged from 20 to 31% in lateral roots and 32 to 53% in crown roots, but there was not a consistent cyclic pattern of percentage TNC during the growing season.

Hemp dogbane (Apocynum cannabinum L.) was investigated relative to seed germination, depth of seedling emergence, response to clipping, influence of soil type and fertility on vegetative growth, and herbicidal control. Seed germination in this study was influenced by light and scarification. Seedling emergence was influenced by the amount of soil cover. Soil type and fertility affected vegetative growth. In a greenhouse clipping study, hemp dogbane became perennial 41 days after emergence and by 65 days was producing more than one shoot per plant following clipping. Hemp dogbane was more completely controlled following September application of herbicide than from application made in June.