Winter rape (Brassica napus L.) green manures have shown potential for erosion control and suppression of weeds and other pests in potato cropping systems. However, little information on residue cover, biomass production, glucosinolate concentration, and glucosinolate production with winter rape grown as a green manure is available. In field trials in southern Idaho, ‘Aspen,’ ‘Bridger,’ ‘Cascade,’ ‘Dwarf Essex,’ and ‘Humus’ winter rape were planted in mid-August and incorporated the following spring in late April or early May. All five cultivars provided > 80% fall, winter, and early spring residue cover. Winter rape dry weight just before incorporation was 2,880 to 4,462 kg/ha in 1994 and 5,438 to 7,837 kg/ha in 1995. The major glucosinolate in roots of all five cultivars was phenylethyl glucosinolate; the major glucosinolates in shoots were 4-pentenyl, 2-hydroxybutenyl, 3-butenyl, and 2-hydroxypentenyl glucosinolate. Glucosinolate concentrations varied between years, but concentrations were higher in Dwarf Essex and Humus than in Aspen both years. Glucosinolate production per hectare also was highest in Dwarf Essex and Humus and lowest in Aspen. Dwarf Essex and Humus produced higher amounts of isothiocyanate (ITC) and oxazolidinethione (OZT)-producing glucosinolates than Aspen, Bridger, or Cascade, and therefore may be better biofumigants.

Florida has more non-native species of plants established in the state than has any other state in the continental U.S.; the vast majority of these species are harmless. As settlement and population increased and additional exotic species were introduced at increasing rates, some non-native species were able to obtain the edge needed for exponential growth. Among the weeds discussed are those that demonstrate different types of entry, ecological systems, and control. Weeds representing the potential of a small population, a major escaped ornamental, rapid expansion in vegetables, major pests in tree crops, utilization of a biocontrol, distribution in turf, major invaders along roadsides and into open lands and pastures, and exotic aquatic weeds are discussed.

Until recently melaleuca was spreading at a rate faster than it was being controlled throughout the boundaries of the South Florida Water Management District (District). Although melaleuca is a difficult species to eradicate, apparently District efforts, along with those of other governmental agencies and private groups, are containing its spread within the Everglades Water Conservation Areas (WCAs) and the marsh of Lake Okeechobee. Melaleuca has been completely cleared from WCA-2A, -3B, and -3A, south of Alligator Alley. These areas are now under “maintenance control.” Maintenance control means applying management techniques in a continuous basis to keep an invasive plant population at its lowest feasible level. Today, the melaleuca infestation is no longer increasing; in many areas, it is being reduced. Preliminary results from the latest District survey indicate melaleuca infestation has decreased considerably in South Florida, especially in public lands. The intent of this paper is to provide an assessment of progress made by the District's melaleuca control program over the past 7 yr.

Tropical soda apple (SOLVI) is an introduced, perennial broadleaf plant that has invaded Florida agricultural land and natural ecosystems and has spread to other states (Georgia, Alabama, South Carolina, Louisiana, North Carolina, Tennessee, and Pennsylvania). Tropical soda apple was first collected in Florida in 1988. In 1990, SOLVI-infested land was approximately 10,000 ha, in 1993, 162,000 ha, and in 1995, approximately 0.5 million ha were reported infested in Florida. Rapid spread of this invasive plant has occurred from seeds transported in cattle, hay, sod, grass seeds, water, and wildlife (deer, feral hogs, birds). Animals will not eat the foliage but will consume the fruits and spread the seeds in their feces. This exotic weed is an indeterminate plant with seed production averaging 50,000/plant/yr, seed germination of 70–90%, and seed longevity in soil of up to 1 yr. Integrated weed management strategies include prevention (avoidance of contaminated hay or grass seed, control of movement of cattle), control (mechanical, chemical), and monitoring. Seed production must be prevented and landowners should adopt a zero tolerance toward SOLVI. During the time (1990–1995) research (biology, ecology, control) was being conducted to control SOLVI from Florida, this weed had infested the entire state and escaped into other states. Risk assessment criteria for new plant introductions must be developed and implemented to prevent future biological pollution.

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.

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.

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)

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.