Phytotoxic compounds from plants and microorganisms represent a wide range of chemistries and mechanisms of action that have potential in the design and development of new herbicides. Although several natural products of higher plants have been patented as herbicides, none have been developed commercially. Many microbial products have been patented as herbicides and several have been or are being developed, including bialophos {L-2-amino-4-[(hydroxy)(methyl)phosphinoyl] -butyryl-L-alanyl-L-alanine} and glufosinate [L-2-amino-4-(hydroxyl)(methyl)(phosphinoyl)-butyric acid]. The new tools of molecular biology and biotechnology are making natural products more attractive alternatives in herbicide discovery programs.

Soybean-based [Glycine max (L.) Merr.] and petroleum-based crop oil concentrates were equally effective as spray adjuvants for control of quackgrass [Agropyron repens (L.) Beauv. #3 AGRRE] with the butyl ester of fluazifop {[±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} and sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}. With favorable growing conditions at application in 1983 and 1985, an adjuvant concentration of 1% (v/v) with these herbicides was adequate for quackgrass control. Unfavorable growing conditions at application in 1984 resulted in unacceptable quackgrass control, and spray volume did not affect control. However, increasing the adjuvant concentration to 4% (v/v) with either herbicide applied in a spray volume of 70 L/ha nearly doubled quackgrass control. In 1983 and 1985, equal or greater quackgrass control with each herbicide was achieved with spray volumes as low as 35 L/ha compared to 280 L/ha.

The relatively new micro-encapsulated formulation of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine] were soil-applied for yellow nutsedge (Cyperus esculentus L. #3 CYPES) control in cotton (Gossypium hirsutum L. ‘Acala SF-2’). Both herbicides at rates of 1.68 to 3.36 kg ai/ha provided 60 to 80% control of yellow nutsedge for 6 weeks. Although control declined to 50 to 70% by cotton harvest, plots treated with herbicides usually yielded more seed cotton than cultivated control plots. Yields were similar from herbicide-treated and hand-weeded plots. Fewer tubers were counted in herbicide-treated than in cultivated-control plots in the fall. Based on yellow nutsedge control and seed cotton yields, alachlor and diethatyl could be helpful in controlling nutsedge and protecting cotton yields.

Field experiments were conducted to examine the effect of tillage on atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] persistence in the soil and soybean [Glycine max (L.) Merr.] injury. Tillage systems evaluated were no-tillage, chisel plowing, and moldboard plowing. Reduced tillage systems, such as no-tillage or chisel plowing, resulted in greater soybean injury from atrazine residue than did moldboard plowing. Regardless of atrazine residue level, metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] resulted in the greatest injury to soybeans. Metribuzin application in combination with atrazine residue increased soybean injury under the chisel plowed system.

In field experiments, preemergence applications of bensulide {O,O-bis(1-methylethyl)S-[2-[(phenylsulfonyl)amino] ethyl] phosphorodithioate} or DCPA (dimethyl-2,3,5,6-tetrachloro-1,4-benzenedicarboxylate) at 11.2 kg ai/ha controlled smooth crabgrass [Digitaria ischaemum (Schreb. ex Schweig.)Schreb. ex Muhl. #3 DIGIS] selectively in turf. Granular and liquid formulations of bensulide performed similarly. Napropamide [N,N-diethyl-2-(1-naphthalenyloxy)propanamide] granules when applied alone at 1.1 to 3.4 kg ai/ha were partially effective, but when combined with 5.6 kg ai/ha bensulide, controlled smooth crabgrass for the entire season. Oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one} controlled crabgrass but temporarily injured the turf. Residual control of crabgrass the year after treatment was unacceptable for all treatments.

In field studies, mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} was most effective as an enhancing agent for bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and/or acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} when applied as a tank mixture compared to sequential applications. The influence of mefluidide rate on weed control was not consistent. Additives improved the control of several weed species evaluated, but mefluidide generally was only equal to petroleum oil concentrate (phytobland petroleum oil plus emulsifiers in an 83:17 ratio) as an enhancing agent for bentazon and/or acifluorfen.

Chlorsulfuron [2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-amino] carbonyl] benzenesulfonamide], applied at 9 to 560 g ai/ha to the soil surface, stopped shoot elongation of well established Canada thistle [Cirsium arvense (L.) Scop. #4 CIRAR] plants in the greenhouse. Root fresh weight decreased progressively as chlorsulfuron rate was increased when measured 1 month after treatment. In contrast, the number of visible root buds plus secondary shoots increased 1.9- to 2.3-fold between 9 and 67 g/ha chlorsulfuron 1 month after soil surface treatment. Despite more numerous root buds, the number of secondary shoots arising from adventitious root buds progressively decreased as chlorsulfuron rate was raised. Increases in the number of visible root buds were observed first between 3 and 4 weeks following soil application with 67 g/ha of chlorsulfuron, 2 weeks after shoot growth stopped.

Increasing the air temperature from 20 to 32 C, the water temperature from 21 to 30 C, and the wind velocity from 0 to 8 km/h increased the loss of EPTC (S-ethyl dipropyl carbamothioate) from water applied through a sprinkler by 24 to 138%. Decreasing the water temperature from 21 to 10 C decreased the loss of EPTC by 35 to 50%. Decreasing the water pressure or nozzle size by 33% or doubling the herbicide concentration did not affect the percentage of EPTC lost.

A non-linear dose-response model was used to analyze the response of tomato (Lycopersicon esculentum Mill.) and eastern black nightshade (Solanum ptycanthum Dun. #3 SOLPT) to acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, fluoroglycofen {carboxymethyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate}, fomesafen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide}, and lactofen {(±)-2-ethoxy-1-methyl-2-oxoethyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate}. The relative potency of these herbicides to both species was lactofen > fluoroglycofen > fomesafen > acifluorfen. Tomato was significantly more resistant to acifluorfen, fluoroglycofen, and lactofen than was eastern black nightshade, but there was no significant difference between species in response to fomesafen. At the rate required to reduce tomato weight by 10%, eastern black nightshade weight was reduced 48, 32, 20, and 5% by acifluorfen, fluoroglycofen, lactofen, and fomesafen, respectively.

The response of yellow nutsedge (Cyperus esculentus L. #3 CYPES) and Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] to combinations of low rates of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} and bentazon [3-(1-methylethyl)-(1H)-2,l,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was determined in a controlled environment chamber and on Canada thistle in the field. In the growth chamber, injury to yellow nutsedge was increased with 24 g ai/ha fluridone combined with 323 g ai/ha bentazon. Either 2.7 or 5.4 g/ha fluridone combined with 27 g/ha bentazon caused uniform injury to Canada thistle. In the field, the combinations of 5.6 g/ha fluridone with either 28 or 2800 g/ha bentazon was phytotoxic to Canada thistle.

A survey showed weed scientists agree that basic agronomy, crop production and plant-oriented courses are essential in weed science education. Although there was no consensus on the structure of a core curriculum or even on whether one was needed, they agreed that curricula must be constructed to fit student interests, goals, and abilities.

Although not all graduate students will teach in the classroom, all will use teaching skills in some aspects of their work. Graduate students can participate in activities that will prove useful in later teaching situations. They can prepare audio-visual materials or design and conduct experiments and demonstrations in the laboratory. Carefully selected and well-prepared graduate students can give lecture or laboratory presentations; however, care must be taken not to detract from the quality and continuity of the course from the standpoint of students who are enrolled for credit (and are paying for the course).

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.

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.

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.

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.