To exploit the potential of ecological intensification during sunflower cropping, it is crucial to understand the potential synergies between crop management and ecosystem services. We therefore examined the effect of pollination intensification on sunflower yield and productivity under various levels of soil fertilization over two seasons in the eastern Free State, South Africa. We manipulated soil fertility with fertilizer applications and pollination with exclusion bags. We found a synergetic effect between pollination and soil fertilization whereby increasing pollination intensity led to a far higher impact on sunflower yield when the soil had been fertilized. Specifically, the intensification of insect pollination increased seed yield by approximately 0.4 ton/ha on nutrient poor soil and by approximately 1.7 ton/ha on moderately fertilized soil. Our findings suggest that sunflower crops on adequate balanced soil fertility will receive abundant insect pollination and may gain more from both synergies than crops grown in areas with degraded soil fertility.

Safflower (Carthamus tinctorius L. ‘Hartman’) in the rosette growth stage or early bolting stage tolerated thiameturon {3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] amino] sulfonyl]-2-thiophenecarboxylic acid} at 5, 10, and 15 g ai/ha. Safflower also tolerated chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} at 18 g/ha if safflower was taller than 15 cm at time of application. The fresh weight of above-ground biomass of common sunflower (Helianthus annuus L. #3 HELAN), treated at two plant sizes with thiameturon, was reduced more than 88%. Soil activity of thiameturon also reduced the seedling vigor of common sunflower, but thiameturon in soil was not as lethal to common sunflower as were foliar applications.

Long term weed management programs for annual weeds should take into account seed production as well as yield losses from weeds. In this research economic optimum thresholds, determined with a simulation model, were compared to the economic thresholds derived from field studies with common sunflower and velvetleaf in soybean. An economic optimum threshold model, including a biological submodel and a submodel evaluating the financial benefit from controlling each weed species in soybean, was constructed to estimate the biological events and processes and economic costs of each weed. Long-term weed management programs were simulated in continuous soybean over a 15-yr period. The model optimized a POST treatment of bentazon by computing costs associated with weed interference and changes in estimated seedbank size. The economic optimum threshold populations were estimated to be 0.3 to 0.4 velvetleaf plants per 10 m2 and 0.4 common sunflower plants per 10 m2. The economic thresholds calculated to be 2.6 velvetleaf plants per 10 m2 and 1.5 common sunflower plants per 10 m2. The economic optimum threshold was calculated to be 7.5-fold and 3.6-fold lower than the economic thresholds for velvetleaf and common sunflower, respectively. The larger ratio for velvetleaf reflected the large quantity and longevity of seeds produced. The smaller ratio for common sunflower reflected the shorter persistence of the seeds and higher seed predation rates.

Scanning electron micrographs of spray droplet residual on wheat, sunflower, and kochia indicated that salts and various adjuvants applied with glyphosate affected deposit crystal content, thickness, and contact with the leaf surface. Spray deposits of glyphosate applied with diammonium sulfate contained distinct crystals, which related to enhanced toxicity of glyphosate applied alone, or to overcoming antagonism of glyphosate toxicity by calcium chloride, when applied to wheat. In general, glyphosate applied with antagonistic calcium chloride salt formed spray deposits that were amorphous, thick, and without crystals. Glyphosate sprayed with nonantagonistic diammonium sulfate and ammonium chloride salts had deposits with crystals and an evenly spread residue beneath the crystals. The various micrographs indicate that the antagonism of glyphosate phytotoxicity by salts may be in part from physical entrapment of glyphosate in the spray deposit. Glyphosate spray droplet residue contact with wheat, sunflower, and kochia surfaces related to observed differences in glyphosate toxicity to these species.

Barnyardgrass and many broadleaf weeds were severely stunted by POST applications of isoxaben. Most grasses were only moderately affected by isoxaben at rates up to 1 kg/ha. POST activity was enhanced by soil interception, but evident with foliar interception alone. Cell swelling in stems and in interveinal leaf lamina was observed after foliar application. A radiotracer study in redroot pigweed showed that only a small amount (3.3% of applied) of isoxaben entered the leaf following foliar application, and that little (0.08% of applied) isoxaben migrated beyond the point of application. The potential of isoxaben as a POST herbicide may be limited, in part, by poor absorption and translocation.

The effect of rainfall on the performance of a tank mixture of desmedipham [ethyl m-hydroxycarbanilate carbanilate(ester)] and phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) applied postemergence to redroot pigweed (Amaranthus retroflexus L. ♯ AMARE), wild mustard (Sinapsis arvensis L. ♯ SINAR) and sunflower (Helianthus annuus L.) was evaluated in field studies. The occurrence of 1 mm of rain immediately after herbicide application significantly decreased the control of redroot pigweed and wild mustard. A rainfall quantity of 1 mm also reduced injury symptoms on sunflower. Simulating a 12.7-mm rain less than 18 h after desmedipham and phenmedipham application effectively reduced toxicity to redroot pigweed and sunflower. Toxicity to these two species increased at a lesser rate than for wild mustard as the time interval prior to rain was increased. A rain-free period of 6 h was predicted for near-maximum control of wild mustard with these herbicides.

Field research was conducted during the summers of 1981 and 1982 in order to determine relative infection and population increase of lesion nematodes (Pratylenchus spp.) on seven weed species that commonly occur in field-bean (Phaseolus vulgaris L.) fields in western Nebraska. Weeds were grown at three densities with and without fieldbeans. A representative sample of the root systems from plants in each plot was removed in August and the nematodes were extracted and counted. No difference in nematode infection rate was found among weed population levels. Nematodes per gram of dry root were not different in weeds grown with or without fieldbeans. Weeds grown with fieldbeans had smaller root systems, and consequently total nematodes per root system were less than in weeds grown in the absence of fieldbeans. There was a significant difference among most weed species when nematodes per gram of dry root were estimated. Hairy nightshade (Solanum sarachoides Sendt. ♯3 SOLSA) and barnyardgrass [Echinochloa crus-galli (L.) ♯ ECHCG] supported the highest numbers of nematodes per g oven-dry roots, redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE) had least numbers of nematodes/g oven-dry roots, and infestation levels on other weed species were variable but generally intermediate.

Spring-applied herbicides were evaluated in the field in 1982 through 1984 in western Nebraska for selective weed control in irrigated seedling alfalfa (Medicago sativa L. ‘Appollo’). Weed densities were least in plots treated preplant with benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] in combination with postemergence applications of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. Combinations of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and fluazifop-butyl {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} with bromoxynil provided less grass control than sethoxydim or fluazifop-butyl applied alone. Annual weeds did not reduce alfalfa stand density.

Growth and morphological characteristics of four weed and two crop species were analyzed to determine how small-seeded weeds can compete with large-seeded crops despite the initial size disadvantage. Small-seeded weeds had higher relative growth rates because of increased percentages of biomass devoted to leaves. This morphological scheme was achieved primarily through a reduction in the percentage of biomass devoted to roots. Yet, small-seeded weeds were able to develop larger mean plant root lengths as a result of having both roots of smaller diameter and higher rates of root length increase.

Management systems for direct-seeded and transplanted sugarbeets (Beta vulgaris L. ‘Mono Hy D2′) were compared for weed control and sugarbeet selectivity from 1983 through 1985 in western Nebraska. Broadleaf weed density was similar, but yellow foxtail [Setaria glauca (L.) Beauv. # SETLU] density was lower in transplanted compared to direct-seeded sugarbeets. Preplant soil-incorporated applications of cycloate (S-ethyl cyclohexylethylcarbamothioate) plus trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] at 3.3 plus 0.6 kg ai/ha or ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] plus trifluralin at 2.2 plus 0.6 kg/ha was noninjurious to transplanted sugarbeets but caused severe injury to direct-seeded sugarbeets. The combination of cycloate or ethofumesate with trifluralin improved weed control over that obtained when cycloate or ethofumesate was used alone. By combining the improved weed control obtained from cycloate plus trifluralin or ethofumesate plus trifluralin with the transplanting crop establishment technique, a superior sugarbeet weed control program was developed.

The response of corn (Zea mays L. ‘Sokota TS 46’), flax (Linum usitatissimum L. ‘Culbert 79’), grain sorghum [Sorghum bicolor (L.) Merr. ‘Sokota 466’), soybeans [Glycine max (L.) Merr. ‘Corsoy 79’], and sunflowers (Helianthus annuus L. ‘Sokata 4000’) to soil residues 12 and 24 months after application of 17, 34, and 68 g ai/ha chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino] carbonyl] benzenesulfonamide} was determined at two locations, Redfield and Watertown, in eastern South Dakota. All crops at Redfield were injured significantly at 17 g/ha, 12 months after application as determined by plant dry weight and visual evaluations. Corn and sorghum were the most susceptible while flax was the least susceptible. Injury at Watertown was significantly less than at Redfield. Differences in carryover were related to a lower soil pH at Watertown.

Applications of glyphosate [N-(phosphonomethyl)glycine] to the leaves of pea (Pisum sativum L. ‘Burpee's Blue Bantam’), sunflower (Helianthus annuus L. ‘Mammoth’), and bean (Phaseolus vulgaris L. ‘Red Kidney’) reduced transpiration in all three species. The reduction varied with species and concentration applied. Eight-day-old bean leaves responded earlier than leaves on older plants. However, after 29 h, there was no difference in transpiration rates with seedling age, since treated leaves on both ages investigated were transpiring at about one-half the rate of control leaves. Addition of surfactant to the solution shortened the time interval between treatment and transpirational response but did not affect the final transpiration rate as compared to glyphosate without surfactant. The effect of glyphosate on transpiration was not due to changes in water availability or to the surface of the leaf that was treated. It is suggested that these results can give some insight into uptake, translocation, and mode of action of glyphosate.

An experiment was initiated in 1970 and continued through 1979 by exhuming and germinating seed of 12 economic weed species buried beneath 23 cm of soil in eastern and western Nebraska. Loss in germination of exhumed seeds over years is mathematically characterized by the formula for the rectangular hyperbola, which represents many shapes of curves that have zero as their lower limit. Of the 12 weed species, only fall panicum (Panicum dichotomiflorum Michx.) and redroot pigweed (Amaranthus retroflexus L.) seed germination did not drop significantly over the 10-yr burial period. Germination of redroot pigweed seed was higher when buried in eastern Nebraska, but was higher for smooth groundcherry (Physalis subglabrata Mack&Bush.) and velvetleaf (Abutilon theophrasti Medic.) when buried in western Nebraska. Germination of the other nine species were not affected by burial location. The 12 weed species can be ranked as those showing most to least rapid loss of germination during burial for 10 yr as follows: honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.], hemp dogbane (Apocynum cannabinum L.), kochia [Kochia scoparia (L.) Schrad.], sunflower (Helianthus annum L.), large crabgrass [Digitaria sanguinalis (L.) Scop.], common milkweed (Asclepias syriaca L.), musk thistle (Carduus nutans L.), velvetleaf, fall panicum, redroot pigweed, green foxtail [Setaria viridis (L.) Beauv.], and smooth groundcherry.

From 1976 to 1981, emergence date, height, and dry weight per plant were taken for eight weed species grown at Bushland, TX, at two stand densities. Height and dry weight per plant were related to precipitation and degree-days for air and soil temperatures using base temperatures of 10, 15.5, or 21 C. Kochia [Kochia scoparia (L.) Schrad. ♯ KCHSC] emerged early in March and was followed by poison suckleya [Suckleya suckleyana (Torr.) Rydb. ♯ SUKSU], sunflower (Helianthus annuus L. ♯ HELAN), and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE) in early April. Buffalobu(Solanum rostratum Dunal. ♯ SOLCU), puncturevine (Tribulus terrestris L. ♯ TRBTE), lanceleaf sage (Salvia reflexa Hornem. ♯SALRE), and barnyardgrass (Echinochloa crus-galli L. Beauv. ♯ECHCG) emerged in late April. The weeds began to increase in height during May but plants did not start increasing in weight until June. Kochia, common cocklebur, and sunflower grew tallest, produced most dry matter, made most efficient use of water, and weighed most per plant. Heat unit accumulations were strongly correlated with plant height.

In the field, eight barley (Hordeum vulgare L.) cultivars tolerated postemergence applications of AC 222,293 [a mixture of methyl 6 and 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) m- and p-toluate] at 0.4 to 1.4 kg/ha. AC 222,293 at 0.4 kg ai/ha applied at the 1.5- to 2-leaf stage controlled wild oats (Avena fatua L. # AVEFA) 96%, whereas 0.7 kg/ha applied at the 3.5- to 4-leaf stage controlled wild oats only 93%. Sugarbeets (Beta vulgaris L.) but not alfalfa (Medicago sativa L.), corn (Zea mays L.), pinto beans (Phaseolus vulgaris L.), or sunflower (Helianthus annus L.), were injured when planted 6 to 8 months after fall applications of AC 222,293 at 0.4 to 1.1 kg/ha.

Field experiments were conducted to study the feasibility of applying glyphosate [N-(phosphonomethyl) glycine] postemergence with a recirculating sprayer and a vertical roller for the control of common lambsquarters (Chenopodium album L.), common sunflower (Helianthus annuus L.), kochia [Kochia scoparia (L.) Schrad.], redroot pigweed (Amaranthus retroflexus L.), and velvetleaf (Abutilon theophrasti Medic.) in sugarbeets (Beta vulgaris L.). Glyphosate was applied twice each year at 1.7 kg/ha with a recirculating sprayer in 1977 and 1978, or twice as a 20% (v/v) solution with a vertical-roller applicator in 1979. By harvest, 70 to 74% of the total population of treated common sunflower, kochia, and redroot pigweed, 61% of the common lambsquarters, and 30% of the velvetleaf was dead. Root yields in glyphosate-treated plots, when averaged over 3 yr, were increased 5800, 8500, 12 500, and 13400 kg/ha at densities of 6, 12, 18, and 24 broadleaf weeds (equal densities of common lambsquarters, kochia, and redroot pigweed)/30m of row, respectively. Where equal densities of common sunflower and velvetleaf competed with sugarbeets, root yields in glyphosate-treated plots, when averaged over 2 yr, were increased 4400, 11900, 11700, and 10700 kg/ha, respectively, at these same densities.

Eight field studies were conducted in soybeans at seven locations in Kansas over a 3-yr period to examine the efficacy of using reduced rates of the herbicides acifluorfen, bentazon, chlorimuron, and tank mixes of acifluorfen and bentazon. POST applications of these herbicides at 1/2X rates at 2 wk after planting (WAP) resulted in broadleaf weed control similar to that obtained from standard treatments of 1X rates applied at 4 WAP at six of seven studies with acifluorfen, bentazon, and acifluorfen plus bentazon and at five of seven studies with chlorimuron. One-quarter rates applied 2 WAP were equivalent to standard treatments for broadleaf weed control in four of seven studies with acifluorfen and chlorimuron, five of seven studies with bentazon, and six of seven studies with acifluorfen plus bentazon. One cultivation at 4 WAP, increased the broadleaf weed control with all herbicide treatments.

Experiments were conducted to determine whether differences in sensitivity of sunflower (Helianthus annuus L.), and rapeseed (Brassica napus L.) to 14C-picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) and 14C-clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) can be attributed to differences in absorption, translocation, or metabolism of the herbicides. Within 24 h, more than 97% of the radioactivity from picloram or clopyralid was absorbed by the foliage of both plant species. Acropetal transport of both herbicides was similar in the two plant species, with approximately 60% or more of the recovered radioactivity from picloram and clopyralid treatments moving acropetally out of the treated leaf 144 h after application. Less than 6% of the 14C-label from either herbicide treatment moved basipetally in both species. Therefore, differences in absorption and translocation did not account for intra- or inter-species sensitivity differences to the two herbicides. Significantly more 14C-picloram and 14C-clopyralid was converted to water-soluble metabolites in rapeseed than in sunflower plants. However, in rapeseed plants, the pattern of metabolism of both herbicides was similar, indicating that the difference between the metabolism of picloram and clopyralid did not account for the sensitivity difference within this species. It appears that only one picloram and clopyralid metabolite was formed in both plant species as determined by TLC. The metabolite of picloram or clopyralid was a water-soluble conjugate that yielded the carboxylic acid amide of the respective herbicide upon ammonolysis.

A four-year experiment was conducted near Scottsbluff, NE to evaluate the effect of different methods of preplant tillage, post-plant cultivation, and herbicides on weed density and grain yield. Ridge-till enhanced the development of kochia and reduced the density of wild proso millet and common lambsquarters. Tandem disking increased longspine sandbur and redroot pigweed density whereas moldboard plowing increased common sunflower density. Cultivation reduced weed density 86% but weeds that remained after cultivation reduced corn grain yield by 40% as compared with a hand-weeded control. Weed control treatments that integrated cultivation and herbicides controlled a broader spectrum of weed species than cultivation or herbicide treatments alone.

2,4-D diethanolamine control of kochia was influenced by the source of water used as the spray carrier. Sodium bicarbonate in one water source related to the reduced kochia control. Sodium bicarbonate in a water spray carrier antagonized 2,4-D control of all plant species evaluated. Antagonism increased with the tolerance of a species to 2,4-D, concentration of sodium bicarbonate, and spray volume. Sodium bicarbonate antagonism of 2,4-D phytotoxicity was greatest with low temperature and relative humidity.