Both purple nutsedge (Cyperus rotundus L. # CYPRO) and yellow nutsedge (C. esculentus L. # CYPES) are problem weeds in crops in many parts of the world. Yellow nutsedge is found in all U.S. states. Purple nutsedge is confined to the southern region of the United States, ranging from North Carolina across southern Arkansas and into southern California.

Field research was conducted to evaluate the performance of chlorsulfuron {2-chloro-N-[[4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} applied to established Canada thistle plants [Cirsium arvense L. scop. # CIRAR] in the spring or fall to young vegetative shoots, and in June to plants in the bud growth stage. Canada thistle shoot densities measured in the spring following chlorsulfuron applications the previous year were lower when chlorsulfuron was applied in the bud and fall growth stage as compared to applications made in the spring to young vegetative shoots. Suppression of Canada thistle shoots from chlorsulfuron application during the bud and fall growth stage increased with rate, and was greatest at 269 g ai/ha. Chlorsulfuron applied at 269 g/ha at the fall growth stage only partially controlled the root system of Canada thistle.

Glyphosate [N-(phosphonomethyl)glycine] toxicity to volunteer wheat (Triticum aestivum L.) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] was influenced more by carrier volume than application method. Glyphosate phytotoxicity increased when carrier volume was reduced with both application methods. When compared at equal carrier volumes, there was little difference in volunteer wheat or large crabgrass control when glyphosate was applied with a controlled droplet applicator or flat fan nozzles. Volunteer wheat and large crabgrass control with controlled droplet applicators was influenced by application factors. At a given carrier volume, application factors which yielded larger droplets generally resulted in superior vegetation control.

Field studies were conducted for 3 yr to determine the foliar activity of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} for control of common lambsquarters (Chenopodium album L. # CHEAL) in snap beans (Phaseolus vulgaris L. ‘Provider’ in 1983 and 1985 and ‘Green Crop’ in 1984). Control of 1 to 7 cm tall common lambsquarters varied between 75 and 100% with 0.28 kg ai/ha acifluorfen and frequently increased linearly with increases in acifluorfen rates to 0.84 kg/ha. Snap bean injury occurred each year and in 1985 was influenced by acifluorfen rate, stage of snap bean growth, and surfactant. Snap bean yields in 1983 were reduced linearly with increases in acifluorfen rates and in 1985 were reduced more from applications at the 1- to 2-trifoliolate leaf stage than at the 4- to 8-trifoliolate leaf stage. In the greenhouse, reductions in snap bean height from acifluorfen were related to application timing, surfactant and cultivar. Fresh weight reduction of snap beans was highest with the cultivar ‘Green Crop’ but was increased to both cultivars by early application timing and the addition of surfactant to the spray mix.

Economic performance of prescribed burning following aerial applications of tebuthiuron {N-[5-(1,1-dimethyiethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} pellets was estimated for Texas whitebrush (Aloysia gratissima [Gillies & Hook.] Troncoso # ALYLY)-dominated rangeland and for post oak (Quercus stellata Wangenh. # QUESL)-dominated mixed hardwood stands. Honey mesquite (Prosopis glandulosa Torr. # PRCJG) invasion largely negated differences in estimated beef production between treated and untreated pastures within 13 yr of controlling Texas whitebrush with tebuthiuron at 2 kg ai/ha. American beautyberry (Callicarpa americana L.) and other shrubs increased such that the woody canopy cover was 87% of the original canopy 7 yr after applying tebuthiuron at 2.2 kg/ha to a heavy cover of oaks-mixed hardwoods. Burning at 2- to 4-yr intervals after tebuthiuron applications suppressed invading shrubs and increased projected internal rates of return by about 2% for each burning, compared to herbicide application only.

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.

In 2 yr of field experiments, trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine], profluralin [N-(cyclopropylmethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)benzenamine], fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)benzenamine], ethalfluralin [N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine], and benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] controlled white campion [Silene alba (Mill.) E.H.L. Krause.# MELAL] during the establishment of birdsfoot trefoil (Lotus corniculatus L. ‘Leo’).

A low-volume (21.5 L/ha) spinning disc (controlled droplet applicator) and a high-volume (187 L/ha) boom-nozzle applicator were compared in applying tank mixtures of the weed pathogen Colletotrichum gloeosporioides (Penz.) Sacc. f. sp.] aeschynomene (henceforth designated C.G.A.) and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} for control of northern jointvetch [Aeschynomene virginica (L.) B.S.P. # AESVI] and hemp sesbania [Sesbania exaltata (Raf.) Rydb. ex A.W. Hill # SEBEX] in soybean [Glycine max (L.) Merr. ‘Tracy M’]. Application with a spinning disc did not increase control of either weed species over the boom-nozzle applicator. C.G.A. controlled northern jointvetch in 2 of 3 yr. Northern jointvetch control with the spinning-disc was poorer at lower rates in years of unfavorable environment. Acifluorfen at 0.56 kg ai/ha and applied with either applicator controlled hemp sesbania satisfactorily.

Percent soil organic matter content, as determined by standard chromic acid oxidations, was highly (r = 0.89) correlated with soil humic matter content, as determined by NaOH/DTPA (diethylenetriaminepenta-acetic acid)/alcohol extraction of 201 U.S. soils. Humic matter content of the soils was equally or better correlated (r = 0.89 to 0.97) with herbicide bioactivity, as measured in field experiments, than was percent organic matter content (r = 0.87 to 0.92). Regression equations provided allow herbicide rate recommendations for 80% weed control to be calculated based on soil humic matter or soil organic matter levels.

The effect of various growth regulators on seedling field bindweed (Convolvulus arvensis L. # CONAR) growth and control with herbicides was evaluated. Fourteen growth regulators were applied at 0.38 to 380 g/ha 7 days before herbicide application in greenhouse, growth chamber and field studies. Field bindweed seedlings pretreated with growth regulators were more effectively controlled by herbicides compared to those not pretreated in greenhouse evaluations. Abscisic acid [[R-(Z,E)]-(+)-5-(1-hydroxy-2,6-6-trimethyl-4-oxo-2-cyclohexane-1-yl)-3-methyl-2,4-pentadicenoic acid] (ABA), ancymidol [a-cyclopropyl-a-(p-methoxyphenyl)-5-pyrimidine methanol], cycloheximide {3-[2-(3,5-dimethyl-2-oxocylohexyl)-2-hydroxyethyl]glutarimide}, ethylenediamine tetraacetic acid [N,N′-1,2-ethanediyl-bis-(N-(carboxymethyl) glycine] (EDTA), and 1-naphthaleneacetic acid (NAA) increased field bindweed stem length. Ancymidol and gibberellic acid [ent-3α,10,13-trihydroxy-20-norgibberell-1,16-diene-7,19-dioc acid 19,10-lactone] (GA) increased root weight, and GA increased root length. Cycloheximide, ethephon [(2-chloroethyl)phosphonic acid] and MH (1,2-dihydro-3,6-pyridazinedione) decreased field bindweed root weight. Ancymidol, GA and IAA (indole-3-acetic acid) increased the number of shoots per plant of seedling field bindweed. Dicamba (3,6-dichloro-2-methoxybenzoic acid) efficacy was enhanced following field bindweed preconditioning with ethephon and IAA. Ancymidol and cycloheximide applied as pretreatments increased glyphosate [N-(phosphonomethyl)glycine] activity on seedling field bindweed. Ancymidol and IAA pretreatment improved field bindweed control with triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}. Herbicide-growth regulator combination treatments that increased field bindweed control in greenhouse and growth chamber studies did not increase top growth control in the field.

Two conventional greenhouses were modified into a containment facility for the study of foreign noxious weed species that could be dangerous to North American agriculture. The facility was designed for research on the biology, ecology, and weed control technology of foreign noxious weeds, without the escape of propagules. Two growth chambers and a germinator are located within the containment facility for evaluations under controlled environmental conditions. A standard operating procedure is followed to preclude the escape of weed seeds or propagules while minimizing restrictions to research. The facilities are locked and located in a secure fenced area to reduce the probability of accidental or intentional damage. Procedures for emergencies have been designed to facilitate aid without compromising the containment security. Knowledge concerning weeds that have the potential to threaten North American agriculture will be gained from research performed within this facility.

Field days on diagnosis of plant problems were conducted by Extension specialists at Michigan State University. The objective was to expose participants to a variety of plant growth problems. Techniques were developed to simulate crop injury from herbicide and fertilizer misapplication and environmental stress. Twenty demonstration plots each were established for corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.]. A specific problem was demonstrated in each plot. Two field days were held in 1985. One field day was conducted for agribusiness personnel and the other for Extension field staff. Promotion of the field days was a cooperative effort among Michigan Cooperative Extension Service, Michigan Pesticide Association, and Michigan Plant Food Council. Resource people conducting tours of the plots and leading discussions of the problems included a weed scientist, a soil fertility specialist, and a crop production agronomist. An evaluation survey indicated that this event was useful in furthering the understanding of plant growth problems. Based on the survey responses, future plant problem diagnosis field days are being planned in Michigan.

The family Cyperaceae includes approximately 3000 species, of which about 220 species are identified as weeds (Table 1). Nearly 42% of these weeds are in the genus Cyperus. An additional 43% are in three other genera, Eleocharis, Scirpus, and Fimbristylis. The remaining 15% are found in six other genera, Scleria, Kyllinga, Rhynchospora, Bulbostylis, Fuira, and Dichromena. Purple nutsedge (Cyperus rotundus L. # CYPRO) was identified as the world's worst weed based on the number of countries where it was reported as a serious, principal, or common weed. Competition with crops was the major factor in determining weediness. From the same report, yellow nutsedge (Cyperus esculentus L. # CYPES) ranked sixteenth. This contrasts with relative rankings of these two species in the United States where yellow nutsedge is more widespread than purple nutsedge.

Yellow and purple nutsedges (Cyperus esculentus L. # CYPES and C. rotundus L. # CYPRO) are herbaceous perennial weeds that are among the worst pests known. Holm et al. list purple nutsedge as the world's worst weed and yellow nutsedge as the sixteenth worst weed. Both weeds infest crop production areas in tropical and temperate climates, causing large losses in crop yields. While both species proliferate in the warm regions of the world, yellow nutsedge inhabits a wider range than purple nutsedge in the temperate areas, primarily because yellow nutsedge can tolerate colder temperatures. With such an extended range of habitation, many ecotypic variations of these species would be expected since they likely have adjusted to a multitude of local environments.

Ecological studies improve the understanding of crop losses caused by weeds and interactions among weeds and crops. Knowledge of weed-crop interactions can aid in developing more efficient weed management systems. Also, knowledge of the duration of weed interference and the length of the weed-free period required to prevent crop losses is essential for planning cost-effective control practices.

Cultural and mechanical methods are viable options for inclusion in any weed control program. Selection of weed control methods is determined by crop, cost, desired yield, weather, and labor availability. Yellow and purple nutsedge (Cyperus esculentus L. # CYPES and C. rotundus L. # CYPRO) have proliferated as production inputs have intensified. Nutsedge densities have increased largely due to reduced competition as better annual weed control and improved growing conditions have resulted.

Observations of the effects of living organisms on weeds dates from 1795 when an insect, Dactylopius ceylonicus, was introduced for drooping pricklypear (Opuntia vulgaris Miller) control over a vast area. Since that time, biological control of weeds employed mainly the classical strategy of introducing natural enemies from areas of co-evolution. Self-perpetuation and dissemination of these introduced enemies was essential to suppress successfully the weed below economic levels. This classical tactic is suited particularly for weeds that are distributed widely in less intensively cropped or noncropped areas. Guidelines to introduce foreign organisms for biological control of weeds in the United States have been established.