Insect-proof net tunnels can help reduce virus infection of clean virus-tested sweetpotato seed produced by decentralized seed producers. However, optimal management is required to maintain both quality and quantity of seed produced. This study investigated the effect of the ratoon cropping technique on vine production in net tunnels and open fields. Virus-tested planting material of two varieties, Kabode and Mataya, were grown in net tunnels and open fields. Each variety had 80 plants per plot, with 40 following the ratooning technique and 40 a replanting technique. The ratooned crop was harvested six times, comprising the initial harvest and five regrowths. This covered 14 months representing six generations of vine production. The number of vines, number of nodes per vine, and vine length were recorded. The number of plants showing virus symptoms was also recorded. The ratoon cropping technique produced more vines compared with the replanting technique in both net tunnels and open fields. Cv. Kabode produced more vines in open fields compared with net tunnels regardless of cropping technique. On the other hand, cv. Mataya produced relatively equal numbers of vines in net tunnels and open fields. Despite ratooning leading to more vine production compared with replanting, the technique led to higher virus incidences on plants grown in the open. This also varied with variety with the highest virus disease incidences being recorded on cv. Mataya. We recommend the ratoon cropping technique for sweetpotato vine production in net tunnels. Replanting technique should be adopted for vine production in the open fields because it acts as a key control strategy for virus infections even for susceptible varieties.

The potential for yellow nutsedge (Cyperus esculentus L. var. leptostachyus Boeck. # CYPES) regrowth was reduced by increasing plant age and by glyphosate [N-(phosphonomethyl)glycine] and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene]. Of the amount of glyphosate transported to underground parts, most was found in the tubers, with immature rhizomes, roots, and tubers having 2 to 3 times higher concentrations than comparable mature tissues. Addition of unlabeled oxyfluorfen as a tank mixture with glyphosate increased absorption and translocation, mainly into leaves and new tubers, of radioactivity from 14C-glyphosate in 30-day-old plants. In contrast to the younger plants, the addition of oxyfluorfen decreased 14C-glyphosate detected in 60-day-old plants. The greater effectiveness of glyphosate when applied with oxyfluorfen on yellow nutsedge at the early growth stage has important implications in the field because the tuberization process must be stopped early in the development of the plant for successful control.

Tall ironweed (Vernonia altissima Nutt.) is a perennial with underground, axillary vegetative buds from which new shoots are produced. In a 2-yr study, tall ironweed plants averaged 6115 seeds/plant. Germination of buried seeds increased with increased time of burial. Foliar herbicide applications were evaluated for control of tall ironweed plants in the pre- to early-bud stages of growth. The triethylamine salt or ethylene glycol butyl ether ester of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} was the most effective, providing 93 to 90% control of top growth and regrowth of tall ironweed. The butoxyethanol and propylene glycol butyl ether esters of 2,4-D [(2,4-dichlorophenoxy) acetic acid] alone and in combination with the amine salt of triclopyr also provided excellent control.

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.

Bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was evaluated for Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] control and birdsfoot trefoil (Lotus corniculatus L. ‘Norcen’) tolerance. Bentazon applied in split applications controlled more Canada thistle than a single application of equal rate in both greenhouse and field studies. Bentazon applied four times reduced the level of total nonstructural carbohydrates (TNC) in the roots of both greenhouse- and field-grown Canada thistle and increased birdsfoot trefoil injury more than bentazon applied in a single application of equal rate. All bentazon treatments caused unacceptable injury when birdsfoot trefoil was grown for seed.

The effect of reduced water availability on glyphosate efficacy and adventitious shoot growth in male and female clones of Canada thistle was studied. Water availability was regulated with polyethylene glycol (PEG) in hydroponically grown plants or by withholding water from soil-grown plants. In hydroponic media, there was 50% more adventitious shoot growth from male plants than from female plants. Both PEG and foliarly applied glyphosate reduced the number of adventitious shoots, regardless of gender. In soil, the same number of adventitious shoots formed on untreated male and female plants. However, when glyphosate was applied to plants growing under dry conditions, there was 75% more adventitious shoot growth from males than females. Distribution of glyphosate was similar in male and female plants. Approximately 23% of applied 14C-glyphosate was transported throughout Canada thistle plants within 10 d of treatment regardless of gender or moisture condition. Gender differences in capacity for vegetative reproduction may alter the sex ratio of Canada thistle populations in the field following glyphosate application.

Greenhouse and field studies were conducted to characterize wild poinsettia growth response to imazaquin (140 g ai ha−1), fomesafen and acifluorfen (420 g ai ha−1), and chlorimuron (9 g ai ha−1) applied at 5 to 7 cm (POST1), 8 to 10 cm (POST2), and 15 to 20 cm (POST3). Based on reductions in weed height and lateral branch number 28 DAT, wild poinsettia was controlled more effectively in both greenhouse and field studies for all herbicides applied at POST1 than at POST3. In the greenhouse studies, reduction in wild poinsettia biomass with the herbicides 28 DAT was similar when applied at POST1 and POST2 and, with the exception of chlorimuron, was higher at POST2 than at POST3. In the field study, weed biomass reduction measured approximately 4 mo after herbicide application was higher for imazaquin, acifluorfen, and chlorimuron applied at POST2 than at POST1. Wild poinsettia biomass was reduced more with imazaquin applied at POST3 than at POST1. Increased lateral branch production, indicative of decreased weed control, was often manifested in higher seed production per plant. With application of all herbicides at POST3 seed production was equal to the untreated check.

Experiments were conducted under controlled environment and field conditions to evaluate the influence of growth stage and fluroxypyr dosage on control of field bindweed. In controlled environment studies fluroxypyr effectively controlled 8- to 12-leaf field bindweed. Shoot number, length, and dry weight, and root dry weight decreased as herbicide dose increased. The estimated ED50 (effective dose for 50% reduction) values for shoot and root dry weight were 50 and 33 g ai/ha, respectively. The ED50 for shoot length was 98 g ai/ha. Fluroxypyr was applied at rates from 0.2 to 0.4 kg/ha under field conditions to field bindweed at selected stages of growth. Regardless of herbicide dosage, fluroxypyr applied at the late flowering stage of growth controlled field bindweed better than when applied at the bud or early flower stage. Corn grain yield increased as a function of fluroxypyr dose in 1988 but not in 1987. Dry weight of roots and shoots of field bindweed harvested one year after treatment decreased with increasing rates of fluroxypyr. These studies demonstrate the potential of fluroxypyr for the control of field bindweed.

Acid-scarified hogpotato (Hoffmanseggia densiflora Benth. ex. Gray # HOFDE) seed incubated in distilled water germinated at least 94% when incubated at constant 15, 20, 30 C, and at alternate 20/30 C (20 C for 16 h and 30 C for 8 h) temperatures. Highest germination in buffered solutions occurred at pH 5.0 and 6.0 with reduced germination at lower and higher pH levels. Sodium chloride concentrations of 50 mM and greater reduced the germination rate. Percent germination after 9 days was reduced at NaCl concentrations of 100 mM and greater. Radicle lengths measured after 3 days were significantly reduced with increasing NaCl concentration. Twenty-day-old hogpotato seedlings having three true leaves were able to resprout after topgrowth removal. Regrowth occurred on 15% of the seedlings approximately 15 days after top removal.

Copper content and growth of excised hydrilla [Dioecious Hydrilla verticillata (L.f.) Royle # HYLLI] apical shoot segments were determined following exposure to copper sulfate (CuSO4), copper-triethanolamine (Cu-TEA), and copper-ethylenediamine (Cu-EDA). For all copper formulations, inhibition of growth was related to the amount of copper associated with the excised shoots. At equal copper exposure, the Cu-EDA formulation produced the greatest inhibition of growth and generally the highest copper levels in the plants. The Cu-EDA formulation inhibited dry weight gain by more than 80% 3 weeks after a 2-h exposure to 2.0 or 4.0 ppmw copper. Under similar conditions, CuSO4 or Cu-TEA produced 60% inhibition. The presence or absence of light during a 2-h exposure had no effect on the efficacy of uptake of copper from any of the formulations. Formulation-dependent differences in the mechanism of copper uptake is suggested because rinsing of exposed shoots with dilute acid (0.01N HNO3) removed copper from shoots treated with CuSO4 or Cu-TEA but not from those treated with Cu-EDA.

In field studies effective dogfennel control was obtained with glyphosate, dicamba + 2,4-D, triclopyr + 2,4-D, and fluroxypyr at rates of 1.68, 0.44 + 1.25, 0.56 + 1.12, and 0.28 kg ai/ha, respectively, applied after dogfennel was 75 cm tall. Mowing alone reduced dogfennel regrowth by 81% and when combined with dicamba + 2,4-D or triclopyr + 2,4-D regrowth was reduced over 94%. Triclopyr, dichlorprop, and sulfometuron also controlled dogfennel greater than 90% but metsulfuron did not.

Annual bluegrass is a pervasive weed on golf courses in the Transition Zone of the United States and is difficult to selectively remove. For years, superintendents have applied glyphosate on dormant zoysiagrass to remove cool-season weeds. In 2007, a population of annual bluegrass in Columbia, MO, was not controlled with glyphosate after more than 10 yr of continuous applications. Greenhouse studies were established to compare the response of suspect glyphosate-resistant (CCMO1) and -susceptible annual bluegrass to glyphosate. Seedling plants were treated with glyphosate from 0 to 6.27 kg ae ha−1. At 21 d after treatment, reductions in biomass for susceptible annual bluegrass reached a maximum at glyphosate rates of 0.78 kg ha−1 or higher. Comparatively, the biomass of CCMO1 plants was only reduced by 50% at 0.78 kg ha−1, and reductions did not exceed 60% at rates up to 6.27 kg ha−1, which is eight times the labeled rate. At rates necessary to reduce plant dry weights by 50%, the resistance factor (RF) for CCMO1 was 5.2. Twenty-one days following biomass assessment, regrowth of plants was non-existent on susceptible plants at 0.78 kg ha−1 glyphosate or above, but CCMO1 plants reached 1.7 cm regrowth at the 6.27 kg ha−1 rate. Based on the regrowth, the RF for CCMO1 was 5.2. Results indicate a new species has been identified with resistance to glyphosate, and this represents the first report of glyphosate resistance in turfgrass.

Greenhouse and growth chamber experiments were conducted to investigate the sprouting potential of rootstock; the effect of temperature, burial depth, and length of rootstock on sprouting; and the effect of shoot removal on resprouting ability of rootstock in redvine and trumpetcreeper. Glyphosate translocation along the rootstock of redvine was also measured. Higher sprouting was observed at 20 to 40 C in trumpetcreeper (60 to 73%) and at 30 to 40 C in redvine (45 to 47%) compared with other temperatures. Redvine sprouting was totally inhibited at 15 C, whereas trumpetcreeper had a sprouting of 12%. Emergence of shoot from a 28-cm planting depth was completely inhibited in redvine, whereas trumpetcreeper had 23% sprout emergence. After shoot removal treatments applied every 3 wk, redvine rootstock segments ≤2 cm long were totally depleted after fifth shoot removal treatment (15 wk after planting [WAP]). In trumpetcreeper, total depletion was not reached by 15 WAP, regardless of rootstock length. 14C-glyphosate was translocated from the treated shoot attached to the apical end of a 35-cm rootstock to the untreated end with slightly less 14C-glyphosate recovered at the untreated end compared with 5 to 10 cm from the treated shoot. These results indicated that vegetative reproduction in redvine is more sensitive to cool temperatures, deep burial depth, and short rootstock segment than trumpetcreeper. Variable control of redvine with glyphosate could be due to inadequate herbicide translocation within the rootstock.

During the past century, common ragweed has spread from its native eastern North America to Europe, where it has become an increasing problem from both an agricultural and a human health perspective. Two field experiments were performed over a 2-yr period in a naturally infested fallow field in northern Italy to evaluate the effects of common ragweed plant density on its growth dynamics and to study its response to clipping. In the first experiment, three plant densities were tested (4, 12.5, and 25 plants m−2) and plant height, aboveground biomass, and leaf area were assessed. Intraspecific competition had a substantial negative effect on leaf area and aboveground biomass on a per plant basis in both years, but did not affect plant height. However, the high-density (25 plants m−2) treatment resulted in the highest total aboveground biomass (1,428 and 4,377 g m−2) and leaf area index (5.6 and 12.6 m2 m−2) in 2006 and 2007, respectively. In the second experiment, common ragweed plants were clipped at reaching 20 cm (four clippings during the season), 50 cm (three clippings), or 80 cm (two clippings) plant height. Number of surviving plants, flowering plants, and aboveground biomass were assessed before each clipping. Clipping resulted in a partial reduction in the surviving plants and did not prevent flowering. Under the most stressing condition (clipping at 20 cm height), more than 67% of plants survived to the last clipping and, among these, more than 97% flowered, whereas before the last clipping at reaching 80 cm height from 50 to 100% of plants survived and 100% of them flowered. These findings in northern Italy confirm that common ragweed is a fast-growing annual species, capable of producing considerable aboveground biomass at various pure stand densities and that plants can still flower from plants clipped at various frequencies.

Greenhouse and growth chamber experiments were conducted to study glyphosate efficacy, rainfastness, absorption, and translocation in redvine. Glyphosate at 0, 0.56, 1.12, 2.24, and 4.48 kg ai/ha was applied to redvine plants raised from rootstocks at the five- to seven-leaf stage (about 25 cm tall). Redvine control ranged from 55% at 0.56 kg/ha glyphosate to 98% at 4.48 kg/ha. Glyphosate at rates above 1.12 kg/ha, greatly reduced regrowth from rootstocks of treated plants. A simulated rainfall of 2.5 cm (7.5 cm/h intensity) within 24 h of glyphosate application reduced efficacy by 23% compared with no simulated rainfall. Absorption of 14C-glyphosate in redvine increased from 1.8 to 21.9%, and translocation increased from 0.1 to 8.1% from 6 to 192 h after application, respectively. Translocation was both acropetal and basipetal, and by 96 h of exposure, the 14C radioactivity was widely distributed throughout the plant. Absorption and translocation was greatly affected by posttreatment temperature. Absorption and translocation were highest (34.9 and 10.6%, respectively) in plants maintained at 35/30 C (14/10 h, day/night), followed by 15/10 C (21.2 and 4.9%, respectively), and was lowest (7.8 and 1.6%, respectively) in plants maintained at 25/20 C. Results suggest that longer periods of leaf exposure to the herbicide and high temperatures could increase glyphosate absorption, translocation to redvine rootstocks, and subsequent control. These data also suggest that effective control of redvine in the field will require glyphosate rates higher than those recommended for use in glyphosate-resistant crops.

Death of the apical shoot and subsequent compensatory growth from previously inhibited axillary buds is a possible result of POST weed control practices. The objective of this research was to determine the efficacy of glyphosate and lactofen on ivyleaf morningglory, common waterhemp, and giant ragweed during mechanically stimulated compensatory growth. Plants were grown in the greenhouse to a height (or lateral growth) of 15 cm; at which time, the apical shoots were removed by cutting just above the cotyledonary node. Plants were allowed to regrow to 15 cm and treated with lactofen or glyphosate. Herbicide treatments were also applied to intact plants that were 15 cm in height for comparison. Weed response to herbicides during mechanically stimulated compensatory growth varied by weed species and herbicide. Giant ragweed under compensatory growth was less sensitive to both glyphosate and lactofen compared with intact plants. Comparison of GR50 (the herbicide dose that reduced dry weight by 50%) values indicated that ivyleaf morningglory under compensatory growth was 1.5 times more sensitive to glyphosate than intact plants. Conversely, previously injured ivyleaf morningglory plants were less sensitive to lactofen than intact plants. The GR50 for glyphosate applied to intact common waterhemp plants and plants under compensatory growth was similar. However, common waterhemp plants under compensatory growth were more sensitive to lactofen at the three lowest rates evaluated compared with intact plants. In summary, the efficacy of foliar herbicides applied to weeds that exhibit compensatory growth may be different from weeds under a normal growth state.

The effects of pelargonic acid and rainfall on glyphosate activity, absorption, and translocation in trumpetcreeper were investigated. Four- to six-leaf–stage plants raised from rootstocks were treated with glyphosate at 0, 0.42, 0.84, 1.68, and 3.36 kg ae/ha. Glyphosate at 1.68 kg/ha and higher controlled trumpetcreeper >98% and completely inhibited regrowth from rootstocks of treated plants. A simulated rainfall of 2.5 cm water applied at 6 h after glyphosate application (HAA) reduced efficacy by one-fifth compared with no rainfall. Absorption of 14C-glyphosate in trumpetcreeper increased from 2.3 to 20.2%, whereas translocation increased from 0.4 to 10.5% from 6 to 192 HAA. At 192 HAA, 9.7% of the recovered 14C-label remained in the treated leaf, 0.6% moved above the treated leaf, and 9.0% moved to fibrous roots and rootstock. The addition of pelargonic acid to glyphosate did not improve glyphosate absorption or translocation or synergize activity in trumpetcreeper compared with glyphosate alone. These results suggest that a 24-h rain-free period and 4 d without disturbance from tillage could maximize glyphosate absorption and translocation in trumpetcreeper.

There are differences in grass-clover proportions and chemical composition between herbage from primary growth (PG) and regrowth (RG) in grass-clover leys. Mixing silages made from PG and RG may provide a more optimal diet to dairy cows than when fed separately. We tested the hypotheses that increasing dietary proportions of grass-clover silage made from RG compared with PG would increase digestion rate of potentially degradable NDF (pdNDF), and increase ruminal accumulation of indigestible NDF (iNDF). Eight rumen cannulated Norwegian Red cows were used in two replicated 4×4 Latin squares with 21-day periods. Silages were prepared from PG and RG of an organically cultivated ley, where PG and RG silages were fed ad libitum in treatments with RG replacing PG in ratios of 0, 0.33, 0.67 and 1 on dry matter basis in addition to 8 kg concentrate. We evaluated the effect of the four diets with emphasis on rumen- and total tract fiber digestibility. Increasing RG proportions decreased silage intake by 7%. Omasal flow of pdNDF decreased, whereas iNDF flow increased with increasing RG proportions. Increasing RG proportions decreased rumen pool sizes of NDF and pdNDF, whereas pool sizes of iNDF and CP increased. Increasing RG proportions increased digestion rate of NDF, which resulted in greater total tract digestion of NDF. Pure PG diet had the highest calculated energy intake, but the improved rumen digestion of NDF by cows offered 0.33 and 0.67 of RG leveled out milk fat and protein yields among the three PG containing diets.

This study aimed at developing allometric models from destructive sample field data for estimating both aboveground and belowground tree biomass and assessing changes in root biomass after old-growth Brachystegia-Julbernardia (miombo) woodland clearing in central Zambia. Logarithmic linear models were selected for estimating tree biomass because they gave the most accurate (low mean error) predictions. On average aboveground and belowground biomass in regrowth woodland represented 29% and 41%, respectively, of the biomass in old-growth woodland. The root:shoot ratios were 0.54 and 0.77 in old-growth and regrowth woodland, respectively. Ten years after clear-cutting old-growth woodland, root biomass loss was about 60% of the original biomass. The main cause of post clearing root biomass loss was fire which at the study sites occurred annually or biannually. Control of fire in cleared sites should be encouraged in forest management for carbon storage and sequestration in miombo woodland of southern Africa.

Flood depth has been frequently used to explain the distribution of plant species in seasonally flooded grasslands, but its relation with vegetation production has remained ambiguous. The relationship between flooding and above-ground biomass at the end of the flooding season and during the dry season was studied to assess the impact of reflooding on the Logone floodplain, Cameroon. Above-ground biomass of a combination of all species and of the individual perennial grasses Oryza longistaminata and Echinochloa pyramidalis showed a positive linear relationship with maximum flood depth up to 1 m. The gradient of these relationships became steeper and their fit better during the 2 y following the installation of the flooding, showing the response lag to floodplain rehabilitation. Flood duration only explained the above-ground biomass of the combination of all species and not of the individual species. Above-ground biomass data from other floodplains in the three main African geographic regions showed a similar relationship with maximum flood depth less than 1 m. Dry-season regrowth, important because of its high nutrient quality during forage scarcity, was not directly related to maximum flood depth, possibly because of its dependency on the period of burning and soil moisture. Presented data indicate that a rise of water level of 1 cm corresponds to an increase in above-ground biomass of c. 150 kg DM ha−1.