The three major needs in training weed scientists for a career in the agricultural industry are an understanding and appreciation for the screening and evaluation process, a thorough knowledge of the Environmental Protection Agency (EPA) registration requirements and procedures, and a clear picture of the scientific job opportunities available in the total industry, not just in chemical companies. These needs should be fulfilled during the early part of undergraduate studies so the student can design a program to prepare him/her for industry positions after B.S., M.S., or Ph.D. studies.

Accelerated biodegradation of herbicides in soils can be demonstrated in the laboratory either by treating soil samples with a herbicide under conditions favorable for microbial growth or by sampling field soils soon after herbicidal treatment. Quantitative measurement of accelerated degradation of thiocarbamates in field soils is complicated by the difficulty both of obtaining a proper untreated soil and of obtaining a representative sample by proper mixing of treated soil. Both bacteria and fungi degrade thiocarbamate herbicides, and examples of either class of organisms can be isolated by suitable selection and enrichment conditions. The enzymes involved in the initial steps of thiocarbamate biodegradation seem labile and have not been characterized. Studies of accelerated biodegradation of pesticides should measure the disappearance of the parent or active herbicide using chemical analyses or bioassays. Measuring accelerated biodegradation by determining metabolites (including CO2) is complicated by potential formation of other products, by incorporation of radioactivity into soil microflora, and by complex kinetics partly due to co-metabolism of the herbicide. Additional index words: EPTC, butylate.

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.

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.

Those preparing for a career in weed science extension are expected to take formal courses in weed science and related subject matter. They should gain experience in conducting and interpreting research. They also can benefit from formal courses and experience to develop communication skills for technology transfer. Such courses as psychology, journalism, photography, and public speaking should be considered. Along with research and teaching assistantships, educational institutions should establish extension assistantships to help those preparing for a career in weed science extension.

Research conducted since 1979 in the north central United States and southern Canada demonstrated that after repeated annual applications of the same thiocarbamate herbicide to the same field, control of some difficult-to-control weed species was reduced. Laboratory studies of herbicide degradation in soils from these fields indicated that these performance failures were due to more rapid or “enhanced” biodegradation of the thiocarbamate herbicides after repeated use with a shorter period during which effective herbicide levels remained in the soils. Weeds such as wild proso millet [Panicum miliaceum L. spp. ruderale (Kitagawa) Tzevelev. #3 PANMI] and shattercane [Sorghum bicolor (L.) Moench. # SORVU] which germinate over long time periods were most likely to escape these herbicides after repeated use. Adding dietholate (O,O-diethyl O-phenyl phosphorothioate) to EPTC (S-ethyl dipropyl carbamothioate) reduced problems caused by enhanced EPTC biodegradation in soils treated previously with EPTC alone but not in soils previously treated with EPTC plus dietholate. While previous use of other thiocarbamate herbicides frequently enhanced biodegradation of EPTC or butylate [S-ethyl bis(2-methylpropyl)carbamothioate], previous use of other classes of herbicides or the insecticide carbofuran (2,3 -dihydro-2,2 -dimethyl-7-benzofuranyl methylcarbamate) did not. Enhanced biodegradation of herbicides other than the thiocarbamates was not observed.

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.

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.

The influence of previous herbicide applications on the degradation rate of butylate [S-ethyl bis (2-methylpropyl)carbamothioate], EPTC (S-ethyl dipropyl carbamothioate), alachlor [2-chloro-N-(2,6-diethyl-phenyl)-N-(methoxymethyl)acetamide], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] was measured. Degradation studies were conducted on soils with zero to eight previous applications of butylate, zero and six consecutive annual applications of alachlor, and zero to seven previous applications of metolachlor. Previous applications of alachlor or of metolachlor did not affect the rate of degradation when the same herbicide was reapplied. Soils with previous butylate-use history had more rapid degradation of butylate or EPTC than soils with no previous butylate applications. Because soil sterilization reduced 14CO2 evolution to a low level, soil microorganisms could be the primary mechanism of butylate degradation. There was no difference between butylate or EPTC degradation rate in soils treated previously with butylate. Butylate could not be detected 28 days after treatment in soils previously treated with butylate, whereas soils not previously treated with butylate still contained biologically active butylate. Dietholate (O,O-diethyl O-phenyl phosphorothioate) added to butylate generally reduced the rate of butylate degradation in soils previously treated with butylate, but the butylate concentration always was lower in soils treated previously with butylate than in soils without previous butylate applications. Weed control in the field showed rapid loss of butylate and EPTC in soils with previous butylate treatment and that dietholate reduced the rate of butylate and EPTC degradation.

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.

Quackgrass [Agropyron repens (L.) Beauv. #3 AGRRE] infests farms and gardens throughout the northern United States, southern Canada, almost all of Europe—its native home—and parts of Asia. It grows in Alaska, extends above the Arctic Circle in Norway, and plagues coffee plantations in New Guinea. While quackgrass occurs in every state in the United States, it is rarely a troublesome crop weed in the South.

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.

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.

Although the word “xanthium” may conjure up visions of the exotic Far East, it is the generic name of spiny cocklebur (Xanthium spinosum L. #3 XANSP) and common cocklebur (X. strumarium L. # XANST). A familiar weed of fields and roadsides, cocklebur may have originated in the Mediterranean region and has plagued farmers and shepherds since Biblical times. Common cocklebur was considered a beneficient herb in ancient times. Its roots, seeds, and leaves were used as a diuretic and as a tonic to purify the blood. North American Indians used the leaves of spiny cocklebur to counteract hydrophobia.

Imazaquin (Scepter) is a new, broad spectrum herbicide that is being marketed under the trademark Scepter® herbicide by American Cyanamid Co., Princeton, NJ. It can be applied preplant incorporated (PPI), preemergence (PE) or over-the-top postemergence (POST) in soybean. Crop tolerance is excellent with all methods of application. Imazaquin was tested in the United States in 1984 and 1985 under an Experimental Use Permit (EUP). Section 18 Emergency Exemptions also were granted by the Environmental Protection Agency (EPA) in 1985 for control of sicklepod (Cassia obtusifolia) in five southern states. Imazaquin was registered by the EPA for use in the United States on soybean, in March, 1986, and was sold in 23 states that year. Marketing in four additional states in 1987 was approved by the EPA in October, 1986.

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.