Studies of weed and crop competition can be used to predict yield losses from weed presence and to determine optimum levels or periods of weed control. However, competition is a complex phenomenon that is governed by various biological, environmental, and proximity factors. The factors of proximity include plant density, species proportion, and spatial arrangement among individuals. Several experimental methods have been developed that attach different levels of importance to proximity factors. These methods are described, and the advantages and disadvantages of each are discussed. Density, proportion, and arrangement of plants influence the outcome of competition experiments and should be incorporated into studies of crop-weed interference, since differing estimates for the effects of weeds on crop productivity can be obtained, depending upon the experimental method used.

Predicting crop yield reductions from weeds continues to challenge weed science. Useful methods based upon weed densities and upon area weeds influence have been developed. Results vary greatly from year to year and location to location for several reasons which are reviewed: 1) the shift in crop yield from a weed density-dependent to a weed density-independent relationship; 2) the effect of density on essential growth factor competed for; 3) differences among weed species in relative competitiveness for essential growth factors; 4) the differential effect of environmental conditions on the competitiveness of weed species; and 5) the effect of time of emergence on competition. To reduce the variability in prediction methods will necessitate developing a method based upon the factor(s) responsible for yield reduction.

Research was conducted from 1983 through 1985 in east central Texas to determine the effect of grass-specific herbicides, herbicide rates, and weed height on johnsongrass [Sorghum halepense (L.) Pers. #3 SORHA] control and cotton (Gossypium hirsutum L. 'Stoneville 825’) yield. Seven herbicides were applied to johnsongrass less than 30 cm tall with 2 to 5 leaves approximately 4 weeks after cotton emergence. Good-to-excellent johnsongrass control was observed for each herbicide except cloproxydim {(E,E)-2-[l-[[(3-chloro-2-propenyl)oxy]imino] butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.56 kg ai/ha and sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.28 kg ai/ha. Few significant differences were found in seed cotton yields even though johnsongrass control ranged from 43 to 99% 26 days after treatment (DAT). These data suggest that johnsongrass regrowth and/or reinfestation following initial control of 75% or higher during the first 4 to 6 weeks after cotton emergence has a minimum negative effect on cotton yield. Johnsongrass control was highest when either fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} or haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} was applied to 15 to 30 cm tall johnsongrass.

Several herbicides were evaluated for the control of velvet lupine (Lupinus leucophyllus Dougl. #3 LUPLE), a plant poisonous to sheep on western mountain ranges, and a secondary target species, mountain big sagebrush [Artemisia tridentata Nutt. # ARTTR]. Change in foliar cover of the two target species and associated vegetation was used to evaluate efficacy of the herbicides. Velvet lupine cover was reduced by greater than 50% in the 1983 trial by the butyl ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 and 4.5 kg ae/ha, the butoxyethanol ester of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] at 1.1 and 2.2 kg ae/ha, the dimethylamine salt of dicamba (3,6-dichloro-2-methoxybenzoic acid) at 2.2 kg ae/ha, and 2,4-D plus dicamba at 1.1 plus 0.6 kg/ha. Cover of velvet lupine and other forbs was reduced by drought in the spring of 1985 and obscured the comparison among herbicides in the 1984 trial. Cover of mountain big sagebrush was consistently reduced (>88%) by 2,4-D at 4.5 kg/ha in both trials, and by three rates of the butoxyethyl ester of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} (>67%) in the 1984 trial. Grass cover increased in plots where herbicides effectively reduced velvet lupine, forbs, and mountain big sagebrush.

The upper 30 cm of soil in a field infested with purple nutsedge (Cyperus rotundus L. #3 CYPRO) contained 4900 to 5100 corms and tubers/m2 6 weeks after soil rotovation and irrigation. The upper 4, 8, 12 and 16 cm of soil had 45, 79, 95 and 99%, respectively, of the corms and tubers. Lower depths of soil contained larger tubers with higher percent dry matter than the shallow depths. Of the total number of corms and tubers, 51% were from the parent population. At 6 weeks, only 15% of the total tuber and corm population were not connected to aerial parts. Tubers from the parent population had a higher fresh weight than those from the new population. Parent tubers occurred singly or in chains of up to eight tubers.

Common bermudagrass [Cynodon dactylon (L.) Pers. #3 CYNDA] and johnsongrass [Sorghum halepense (L.) Pers. # SORHA] ecotypes were collected from seven locations in Texas. Ecotype responses to glyphosate [N-(phosphonomethyl)glycine], SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate), sethoxydim {2-[l-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, fluazifop {(+)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, and quizalofop {(+)-2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid} were evaluated in 1982, 1983, and 1984. Johnsongrass ecotype-by-herbicide interactions and ecotype differences were detected in only one of three years. Differences were observed consistently among the herbicide treatments. Numerous bermudagrass ecotype-by-herbicide interactions were detected each year with greater diversity occurring with less-than-optimum herbicide rates. The interactions were herbicide-by-ecotype specific and were not predictable with respect to geographic site of collection.

Experiments were conducted to evaluate varietal susceptibility of azalea [Rhododendron obtusum (Lindl.) Planch] to fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid } and sethoxydim {2-[l-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}. Injury observed on ‘Delaware Valley White’, ‘Hinocrimson’, and ‘Poukhanense’, following broadcast applications of fluazifop-P at 1.12 kg ai/ha, ranged from 5 to 53% foliar damage. Injury symptoms observed were leaf burn, spotting, and distortion, especially in younger leaves. Sethoxydim at 2.24 kg ai/ha caused either slight or no foliar injury to the cultivars tested. Both sethoxydim and fluazifop-P caused temporary growth reduction in ‘Hershey Red’. Foliar injury or growth reduction resulting from these herbicides was temporary, with no damage evident 6 weeks after application. Although adding either crop oil concentration or a nonionic surfactant increased phytotoxicity of fluazifop-P to Hinocrimson and Poukhanense, these adjuvants were not phytotoxic to azalea cultivars when applied alone.

A location in east Central Kansas with a history of continuous corn (Zea mays L.), EPTC (S-ethyl dipropyl carbamothioate) plus dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide) plus dietholate (O,O-diethyl O-phenylphosphorothioate) application, and shattercane [Sorghum bicolor (L.) Moench. #3 SORVU] was selected for herbicide efficacy investigations. Thiocarbamate herbicides applied before planting corn failed to control shattercane in 1 of 2 years. Adding dietholate did not improve EPTC efficacy in either year. Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] applied preplant failed to control shattercane both years. Treatments which included applications of alachlor at 2.2 kg ai/ha 7 or 10 days after preplant herbicide applications were made provided significantly better shattercane control than did preplant treatments.

Twenty field experiments were conducted in Oklahoma from 1983 through 1986 to evaluate the ethylthio analog of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one] for selective control of cheat (Bromus secalinus L. #3 BROSE), downy brome (Bromus tectorum L. # BROTE), and rescuegrass (Bromus catharticus Vahl. # BROCA) in winter wheat (Triticum aestivum L.). The ethylthio analog of metribuzin applied postemergence at 1.1 kg ai/ha before the weeds tillered controlled 91 to 100% of these Bromus spp. in winter wheat. Control of tillered Bromus spp. was less consistent. As Bromus spp. control increased, wheat yields increased, and dockage decreased. The herbicide was selective on wheat over a wide range of soils, including sands. Adding surfactant to very early postemergence applications of 0.6 kg ai/ha increased cheat control but injured wheat slightly. Surfactant use had little or no effect on dockage reduction and yields.

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.

The objective of this paper is to discuss ways to improve training of weed scientists for research, including student backgrounds, appreciation for total production systems, economics, computer science and technology, reassessment of technical subject matter areas, and practical experience.

Plantain, which weary toilers dig from their lawns, hoe from their gardens, or cultivate from their fields was brought to the United States to serve man. Originally considered a valuable medicinal herb and an edible green, it was grown in monastery gardens and was cultivated in botanic gardens. It still is raised as a crop for bird feed.

After 25 yr in research and teaching, I moved into administration about 2 yr ago. Thus I shall discuss with you the image of weed science as a recent outsider, which I consider myself. From this perspective, I want to point out both the positive and negative aspects of our weed science image. In other words, what are our strengths and weaknesses? Can we build on our strengths and overcome our weaknesses?

Professor Li has taught botany since 1940 at University of Nanking, Nanking, China, and weed science at Nanjing Agricultural University, Nanjing, China, since 1964. He developed and taught the school's first weed science course and he presently teaches botany, crop plant anatomy, and weed identification and control. Under his direction, programs in weed quarantine and biological weed control have been instituted and supported by the Ministry of Agriculture and the Bureau of Education (present name: Ministry of Agriculture, Animal Husbandry and Fishery). One of his prime targets has been the study of darnel and the biological control of dodder on soybeans. Professor Li is the supervisor of several graduate students for the Masters and Ph.D. degrees. While at Nanjing, he also has directed the establishment of the most complete herbarium of weeds and weed seeds in China. Currently, Professor Li is editing Weed Flora of China. In addition to publishing many weed texts and teaching short courses on weed identification and control within China, he is a member of the FAO Panel of Experts on Improved Weed Management.

If classical hierarchy were based on survival rather than riches, then weeds would rank just behind cockroaches. It is known all too well that weeds are the most tenacious of plants, and that they interfere very successfully with the productivity of crops valuable to man for food and fiber.

In the last two decades the weed species, diffuse knapweed (Centaurea diffusa) and spotted knapweed (C. maculosa) have gained prominence in the British Columbia interior. These aggressive species have invaded over 40,000 hectares (100,000 acres) of British Columbia range and forest land and are spreading at a rate of about 10% per year. Knapweed can reduce the native forage by as much as 80 to 90% and thus destroy the food supply for cattle and wild animals such as elk and deer. If the weeds spread to their ecological limit over 1 million hectares in British Columbia could be affected, causing an estimated agricultural loss of $13 million annually (Cranston, R. 1985, B.C. Min. of Agric. 85–1). The potential extinction of native plant and animal species is a cost too great to be measured.