Studies were initiated in Wyoming to determine the potential of grass competition as an alternative to repetitive herbicide treatment or other cultural practices for control of Russian knapweed. An experiment was established to evaluate the effects of five grass species, including Russian wildrye cv. ‘Bozoisky.’ Picloram, applied to Russian knapweed during the first frost, reduced Russian knapweed from an average of 80.1% live canopy cover which equates to 0% control. Untreated, unseeded checks resulted in 83.9 and 81.1% control in tilled and nontilled treated plots, respectively. Grass cover increased in untreated seeded plots from an average of 11.3 and 8.2% in tilled and nontilled plots, respectively, to 65% in tilled and 66% in nontilled plots treated with clopyralid plus 2,4-D. Grass cover also increased 69.7% in tilled and 66% in nontilled plots treated with picloram. There was no significant difference between grass varieties when compared to percent Russian knapweed cover. Reductions to zero live canopy cover of Russian knapweed were obtained with a single application of picloram. Economic feasibility thresholds were obtained from four out of five varieties, including a significant difference provided by nontilled Russian wildrye treated with picloram.

Field experiments were conducted in 1994 and 1995 to evaluate weed control in imidazolinone-resistant corn with postemergence applications of imidazolinone and sulfonylurea herbicides. Imazethapyr controlled 100% of redroot pigweed, jimsonweed, and eastern black nightshade. Control of fall panicum with imazethapyr was inconsistent, with control ranging from 42 to 85%. Imazethapyr provided less than 55% control of common lambsquarters and 43% of large crabgrass. Imazethapyr plus either atrazine, 2,4-D, or dicamba increased control of common lambsquarters compared to imazethapyr alone. Fall panicum control was > 95% with nicosufluron. CGA-152005 and MON 12000 did not control eastern black nightshade. In 1995, corn yield was greater with the hand-weeded check compared to all herbicide treatments. The greatest return over herbicide cost with imazethapyr was obtained with imazethapyr plus atrazine. Nicosulfuron plus CGA-152005 provided the greatest return over herbicide cost when averaged across years.

Cogongrass is a weed throughout the tropics and subtropics. Introductions early this century have spread into forests, rangelands, reclaimed mined areas, roadsides, and natural ecosystems in the southeastern United States. Vegetative reproduction is the primary mechanism for survival and local spread, and sexually produced seeds of this obligate outcrossing species provide natural long-distance dispersal. Highly germinable (≥ 90%) seeds have no dormancy, though spikelet fill may be low (≤ 40%) in natural populations. Early seedling establishment, prior to rhizome development, is low (< 20%), occurring in areas with little competition; ≥ 75% bahiagrass sod cover is required to prevent cogongrass seedling establishment. Imazapyr and glyphosate are the most effective herbicides for cogongrass control. Younger cogongrass shoots are very susceptible to these herbicides; however, longer term control of adult plants requires translocation and thereby control of the rhizomes. Autumn applications of glyphosate and imazapyr provided greatest suppression of rhizome regrowth. Effective cogongrass management options exist and depend on integrating several control strategies. Mechanical control alone provides short-term control, whereas multiple discings plus herbicide application provide longer term control. Some combinations of herbicide, discing, and revegetation with desirable plant species provide excellent control. Because of the large geographic area infested with cogongrass and the often economically and environmentally unacceptable management techniques, biological control organisms also should be researched.

Leafy spurge, a long-lived perennial, grows in many habitats, from floodplains to grasslands and mountain slopes. The plant emerges in early spring and produces showy, yellow bracts that appear in late May. The true flowers emerge in mid-June. The plant spreads by both seeds and roots and contains a white sticky latex that deters grazing by many animals. Dicamba, 2,4-D, glyphosate, and picloram have commonly been used to control leafy spurge. Picloram plus 2,4-D is frequently used for leafy spurge control in North Dakota. Ten insect species for leafy spurge biocontrol have been released in North Dakota; the most successful have been the flea beetles, Aphthona nigriscutis, A. czwalinae, and A. lacertosa. The leafy spurge gall midge (Spurgia esulae) has been most successful near wooded areas. Herbicides combined with either the leafy spurge flea beetles or gall midge have controlled leafy spurge better than either method used alone. Grazing with sheep or goats is a cost-effective method for controlling leafy spurge top growth in large infestations. Grazing combined with fall-applied picloram plus 2,4-D reduced leafy spurge density more rapidly and maintained control longer than either method used alone. Several grass species are competitive with leafy spurge including ‘Rebound’ smooth brome, ‘Rodan’ western wheatgrass, ‘Pryor’ slender wheatgrass, and ‘Manska’ pubescent wheatgrass. Cultivating twice each fall after harvest for 3 yr in cropland completely controlled leafy spurge. A successful long-term management program should be designed for specific situations and should include combinations of herbicides, insects, grazing, and/or seeding competitive species.

Field experiments were conducted at three locations in Mississippi in 1995 and 1996 to evaluate labeled and alternative herbicides and herbicide combinations for weed desiccation prior to soybean harvest. Weeds evaluated included pitted morningglory, hemp sesbania, spotted spurge, common cocklebur, and sicklepod. Soybean yield and harvestable soybean losses were not affected by preharvest herbicide treatments, spray volume, or surfactant concentration. Soybean moisture was most consistently reduced by glufosinate compared to the untreated and other herbicides and herbicide combinations evaluated. Most desiccation treatments at Stoneville and Brooksville resulted in foreign material similar to the weed-free check. Glufosinate at 0.84, 1.1, and 1.4 kg ai/ha desiccated all weeds evaluated 90% or more with no differences among rates. The addition of 3.4 or 6.7 kg ai/ha sodium chlorate to 0.28 kg ai/ha paraquat, 1.1 and 2.2 kg ai/ha glyphosate, or 0.28 and 0.56 kg ai/ha oxyfluorfen increased desiccation of most weeds evaluated, with no difference between sodium chlorate rates. In some instances, reducing application volume from 281 to 94 L/ha improved pitted morningglory desiccation when 0.28 g/ha paraquat was applied alone. There were no differences between 0.25 and 0.50% (v/v) surfactant for most parameters evaluated.

Exotic species invasions in natural areas are one of the most significant threats to biological diversity globally. Pest plants pose a significant problem because they often go undetected until widespread ecological damage has already occurred. Effective control is both uncertain and expensive. However, not all introduced species become invasive, leading to the hope that we can develop risk assessment criteria for new plant introductions. Two recently proposed assessment programs are reviewed, one based on North American woody plants and the other based on Australian pest species, and the challenges in their application are discussed. Among the significant issues are spatial and temporal variation in plant performance that affect the documentation of invasive behavior and the tendency for horticulturists to value traits that produce invasive behavior (rapid growth, early and consistent flowering, lack of pests and diseases, and vegetative persistence). Two policy alternatives are suggested for botanical gardens as examples of models for plant introduction policies that could be adapted to other institutions: the Conservation Aware Garden and the Strict Conservation Garden. The former is based on risk assessment, whereas the latter prohibits movement of species across barriers to their dispersal. Information needs, the importance of international communication, and adaptive management are discussed as elements of a program to reduce the spread of pest invaders.

About 15 years ago, I heard several speakers saying that our crop yields were “leveling off.” This stimulated me to assemble data on the subject. The result is shown in Table 1, which gives the U.S. average yields for 10-yr periods during this century for nine crops. The increases are spectacular, varying from two- to sevenfold. Factors contributing to these increases differ from crop to crop. To obtain information on this subject, several experts on each crop were consulted, and their conclusions are summarized in the following text. Only those factors contributing to increased yields are covered. However, great improvements in efficiency of production, product quality, and reduction in soil erosion also have occurred as cultivars and production practices have changed. For most of the crops, increases in yields started in the 1940s and have increased dramatically during the rest of the century. We have not attempted to predict the future at this time, but the rate at which yields are increasing does not appear to be slowing.

With the shift to earlier maturing soybean cultivars, harvest interference data are needed at low weed densities that will not reduce yield, but may affect soybean quality or harvesting efficiency. Field experiments were conducted in 1995 and 1996 to determine the density of five weeds necessary to warrant desiccation treatments. There were no consistent differences in losses of harvestable soybean due to weed density. Common cocklebur increased foreign material and soybean moisture at a greater rate than did hemp sesbania, ivyleaf morningglory, or redroot pigweed, with sicklepod intermediate among these species. Soybean test weight was reduced by 17, 13, and 59 g/L for each plant/meter of row with redroot pigweed, sicklepod, and common cocklebur, respectively, whereas hemp sesbania and ivyleaf morningglory did not affect test weight. However, all species evaluated increased damaged soybean seeds by 8.2 to 11.1% for each plant/meter of row. Combine speed was not affected substantially by the weed densities evaluated.

Studies were established near Devil's Tower in Crook County, WY, to determine the potential of 11 grass species to compete with leafy spurge as an alternative to repetitive herbicide treatments. Of the 11 species, ‘Bozoisky’ Russian wildrye and ‘Luna’ pubescent wheatgrass showed the most promise for successful competition with leafy spurge and were selected for further study. Pubescent wheatgrass limited percent canopy cover of leafy spurge to 10 and 15% or less in tilled and no-till plots, respectively, 7 and 10 yr after seeding. Russian wildrye limited percent canopy cover of leafy spurge to 21% or less in tilled and 7 and 27% in the no-till plots, respectively, 7 or 10 yr after seeding. The control plots not seeded to a forage grass averaged 55% leafy spurge canopy cover.

Degradation of Great Plains rangelands can be linked to past management practices that reduced native species diversity and accelerated establishment and expansion of exotic weeds and less desirable native species. Leafy spurge is an exotic perennial weed that infests more than 1 million ha in the northern Great Plains and reduces rangeland carrying capacity by competing with desirable forages and causing infested areas to be undesirable to cattle and wildlife. Research was conducted to determine the feasibility of using herbicides to suppress leafy spurge and other resident vegetation, which facilitated planting and establishment of native tallgrasses. Four experiments were conducted where 0.28, 0.56, and 0.84 kg ai/ha imazapyr and 0.1 kg ai/ha sulfometuron were applied alone and in combination and 0.84 kg ai/ha glyphosate was applied to leafy spurge-infested range sites in fall 1991 near Ainsworth, NE, and in fall 1991, 1992, and 1993 near Ansley, NE. Research areas were burned about 200 d after herbicide application to reduce plant residue. Monoculture stands of big bluestem and switchgrass were then no-till planted in each experiment and indiangrass was no-till planted in experiments initiated at Ansley in 1992 and 1993. Yields of the planted grasses, leafy spurge, and other vegetation were measured in August at each location starting the year after planting. Imazapyr was an essential component of treatments applied before planting to facilitate establishment of highly productive stands of the tallgrasses. Generally, yields were maximized by fall treatments of 0.28 kg/ha imazapyr + 0.1 kg/ha sulfometuron for big bluestem, 0.84 kg/ha imazapyr for indiangrass, and 0.84 kg/ha imazapyr + 0.1 kg/ha sulfometuron for switchgrass. Yields of the planted grasses were frequently four times greater where these herbicides were applied compared to where glyphosate or no herbicide were applied. Leafy spurge yields were usually reduced in areas where tallgrass yields were greatest. The sequential combination of suppressing vegetation with fall-applied herbicides, burning standing dead plant residue, then no-till planting desirable native tallgrasses in the spring increased productivity of these leafy spurge-infested range sites.

The rough burn-thistle spreading wide

Amang the bearded ear—

I turned the weeding heuk aside

An’ spared the emblem dear!

(Robert Burns [1759–1796], Scottish poet)

Various chemical and mechanical weed control treatments for kidney bean production were evaluated on irrigated, sandy loam sites from 1993 to 1995 near Staples, MN. Weed biomass can be controlled either mechanically or chemically, but a combination of the two gave the most effective and dependable weed control over years. Good weed control by either mechanical or chemical means reduced white mold infection of dry bean because of better aeration of dry bean plants and thus less favorable conditions for infection. Dry bean seed yields were inversely related to weed yields, and weed competition was similar from indigenous stands of either grass or broadleaf weeds. Row cultivation was more effective than rotary hoeing for controlling weeds, reducing white mold infection of dry bean, and increasing dry bean seed yields.

Dr. Calvin G. Messersmith is Professor of Plant Sciences at North Dakota State University (NDSU), where he has been involved in teaching and research since 1966. He developed the undergraduate weed science option, the introductory weed science course, and the internship program for crop and weed science majors at NDSU. Dr. Messersmith introduced many teaching innovations into his undergraduate courses, including development of autotutorial laboratories, lecture and laboratory manuals, permanent plant mounts embedded in plastic resin, and educational films. Dr. Messersmith serves as coordinator of the departmental undergraduate teaching program, advisor for about 20 undergraduate students annually and assists in career placement. Dr. Messersmith has served as major professor for seven Ph.D. and eight M.S. graduates.

Dr. Messersmith has specialized in perennial weed control, especially leafy spurge. He is coordinator of a multidisciplinary leafy spurge control project at NDSU that includes biological, chemical, cultural, and physical control. The project includes cooperating scientists from the Departments of Agricultural Economics, Animal and Range Sciences, Botany, Plant Sciences, Entomology, and Plant Pathology.

Dr. Messersmith served the North Central Weed Science Society (NCWSS) as Editor of the Research Reports for 8 yr and was on the board of directors for about 16 yr, including 1 yr as President in 1985. Prior to becoming the WSSA Vice President in 1995, he served on the WSSA board of directors for 3 yr and was the first Editor who designed and launched Weed Technology from 1985 to 1990. Dr. Messersmith has been honored as an NCWSS Honorary Member and WSSA Fellow.

Dr. Messersmith received his B.S. and M.S. degrees from the University of Nebraska and his Ph.D. degree from NDSU. He has received several awards for contributions to education, including the American Society of Agronomy CIBA-Geigy Award, the first NDSU-wide Odney Award for Excellence in Teaching, the FarmHouse Fraternity Master Builder of Men Award, the WSSA Outstanding Teacher Award, the Burlington Northern Foundation Faculty Achievement Award at NDSU, and the NACTA (National Association of Colleges and Teachers of Agriculture) Teaching Award of Merit.

Field studies were conducted in 1995 and 1996 at three locations in Illinois to determine soybean response to combinations of thifensulfuron and bentazon. Thifensulfuron was applied at 2.2 to 8.8 g ai/ha alone or in combination with 280 to 560 g/ha of bentazon. Soybean injury 30 d after treatment ranged from 0 to 22% when thifensulfuron was applied alone at 2.2 g/ha. Increasing thifensulfuron rate to 8.8 g/ha increased soybean injury to a range of 12 to 44%. Soybean grain yield was significantly reduced compared to the yield of untreated soybean when thifensulfuron was applied at 4.4 and 8.8 g/ha in two of five and four of five experiments, respectively. The addition of bentazon to thifensulfuron consistently reduced soybean injury and stunting. In many cases, increasing the bentazon rate to 420 g/ha decreased soybean injury from thifensulfuron to a greater extent than 280 g/ha. In cases where thifensulfuron decreased soybean yield, the addition of 420 or 560 g/ha of bentazon restored yields to levels that were not lower than untreated soybeans. These studies demonstrate that thifensulfuron at 2.2 to 8.8 g/ha in combination with bentazon at 420 g/ha may be safely applied to soybean for broadleaf weed control.

Long-term control of downy brome with an integrated approach is needed in order to sustain range productivity. Studies were conducted to study the effectiveness of a combination of downy brome control practices. In two studies, glyphosate and paraquat were evaluated at various rates for up to three successive years for control of downy brome in rangeland. A third study evaluated the competitiveness of perennial cool-season grasses against downy brome in the absence of herbicides. Glyphosate, at 0.55 kg/ha, and 0.6 kg/ha paraquat provided selective downy brome control on rangeland when applications were combined with intensive grazing. Downy brome control was greater than 90% following two sequential years of 0.6 kg/ha paraquat at either the two- to eight-leaf stage or bloom stage at both study locations. At one study location, 0.55 kg/ha glyphosate provided 97% control after the first application at both growth stages. In the second study, control averaged greater than 92% following three sequential applications of glyphosate. When perennial cool-season grasses were seeded in the spring following fall tillage (no herbicides) and allowed to establish for three growing seasons, three of the five species were effective in reducing the reestablishment of downy brome. ‘Luna’ pubescent wheatgrass, ‘Hycrest’ crested wheatgrass, ‘Sodar’ streambank wheatgrass, ‘Bozoisky’ Russian wildrye, and ‘Critana’ thickspike wheatgrass controlled 100, 91, 85, 45, and 32% of the downy brome, respectively. Yields of perennial grass dry matter were 1,714, 1,596, 1,135, 900, and 792 kg/ha. Replacing noncompetitive annual grasses with competitive cool-season perennials will provide a longer term solution to a downy brome problem than the use of herbicides alone or with intensive grazing.