Generally, 2,4–Dichlorophenoxyacetic acid (2,4–D) has performed well as a selective herbicide for sweet corn. Sometimes, however, applications of 2,4–D presumably at recommended dosages have resulted in abnormal plant behavior. In certain instances reduced yields have resulted.

Individual herbicides and all double combinations of imazaquin, imazethapyr, and imazapyr were applied alone and in combination to the foliage of pitted morningglory plants in order to evaluate potential influences on translocation. Unlabeled imazethapyr at 5.62 μg plant−1 stimulated basipetal translocation of both 14C-imazaquin and 14C–imazapyr. Unlabeled imazaquin at 7.49 μg plant−1 also increased basipetal translocation of 14C–imazethapyr but did not influence 14C–imazapyr translocation. No combination affected the amount of 14C herbicide remaining in treated leaves or moving into foliage above treated leaves. Unlabeled imazapyr at 0.11 μg plant−1 did not affect movement of either imazaquin or imazethapyr.

Wild oat (Avena fatua L.) control and wheat (Triticum aestivum L.) injury with barban (4-chloro-2-butynyl m-chlorocarbanilate)-aqueous nitrogen combinations were evaluated in the field and greenhouse. The addition of aqueous nitrogen at volumes as low as 5 L/ha increased wild oat control with barban. The greatest increase in wild oat control with barban-aqueous nitrogen combinations was obtained on soil low in nitrogen. Wild oat control with barban-aqueous nitrogen combinations was not influenced by spray volume or nitrogen source. Aqueous nitrogen applications several days prior to barban were more effective than when the two were applied together. Wheat was generally quite tolerant of barban-aqueous nitrogen combinations; however, some injury was observed in 1974.

Polyacrylamide electrophoresis and spectroscopic methods were used to characterize biotypes A and B itchgrass [Rottboellia exaltata L.f. # ROOEX] and their F2 progeny. Electrophoretic analyses of F2 progeny showed that differences between these two biotypes are multiallelic. Spectrophotometric data indicated differences between the photosynthetic apparatus of the two biotypes. These differences may reflect different abilities to adapt to varying light conditions and infer that these biotypes promote survival of the species by increasing the number of environmental nitches that R. exaltata can occupy.

Annual applications for 4 years of 2,6-dichlorobenzonitrile (dichlobenil), N,N-dimethyl-2,2-diphenylacetamide (diphenamid), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 3-amino-2,5-dichlorobenzoic acid (chloramben), and 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) to a red raspberry (Rubus sp. ‘Newburgh’) planting had no direct deleterious effect upon the raspberry plants. Dichlobenil, simazine, and paraquat gave excellent weed control. Weed competition in control plots seriously reduced yields. Shoot development was delayed when dichlobenil was applied near the time of normal bud break.

Studies were conducted on the effects of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] on autotrophic growth (no sugar), heterotrophic growth (with sugar), and oxygen evolution and uptake and on the effects of MSMA (monosodium methanearsonate) on autotrophic growth and oxygen evolution and uptake by the unicellular green alga Chlorella pyrenoidosa Emerson strain (University of Texas). Two methods of analysis (probit and kinetic) were used to characterize the dosage-response of Chlorella to these herbicides. All measurements of Chlorella response to fluometuron were satisfactorily characterized by probit analysis, but only autotrophic cell number was adequately characterized by kinetic analysis. The fluometuron concentrations giving 50% inhibition on the probit plot were as follows: autotrophic cell number, 2.4 × 10−6M; chlorophyll at 400 nm, 3.3 × 10−6M; heterotrophic cell number, 2.4 × 10−6M; oxygen evolution, 20 × 10−6 M. The response of the alga to MSMA was stimulatory instead of inhibitory. Since this stimulation did not consistently range between 10 and 90% of the control, it was not possible to characterize the MSMA dosage-Chlorella response using either type of analysis.

In preemergence application of six different substituted urea herbicides on coriander (Coriandrum sativum L.) and tomato (Lycopersicum esculentum Mill.), the monohalogenated compounds were more effective in the destruction of the plants than their dihalogenated counterparts. The relative difference in effectiveness was much greater in the resistant coriander which appears to take up less dihalogenated than monohalogenated herbicide. In postemergence application, the dihalogenated herbicides generally were slightly more toxic than their monohalogenated counterparts.

The effects of tobacco thrips (Frankliniella fusca Hinds) control and herbicides on peanut (Arachis hypogaea L. ‘Florigiant’) canopy development and competition with large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were examined in field experiments during 1983 and 1984. Greater early-season peanut canopy development generally occurred when tobacco thrips were controlled with aldicarb [2-methyl-2-(methylthio) propionaldehyde-O-(methylcarbamoyl)oxime]. Tobacco thrips control did not affect large crabgrass dry weights or peanut seed yields with no herbicide, alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], vernolate (S-propyl dipropylcarbamothioate) + benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] + alachlor, and handweeding + sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one}. Averaged across weed control levels, large crabgrass dry weights with and without aldicarb were 320 and 310 g/m2 in 1983, and 260 and 250 g/m2 in 1984, respectively. Peanut seed yields with and without aldicarb were 1550 and 1630 kg/ha in 1983, and 2870 and 2920 kg/ha in 1984, respectively.

Eight triazolopyrimidine sulfonanilides were tested for metabolic stability in a number of crop and weed species. These data, along with in vitro determinations of activity (I50) against acetolactate synthase, successfully described the in vivo activity of these compounds in a two-parameter model. Whole plant activity increased with increasing compound stability and decreasing I50 (r2 =.78, N = 36). The difficulty in obtaining metabolic stability data during a structure optimization program prompted a study with substituent parameters in models of in vivo activity. Models describing whole plant activity in jimsonweed were developed using a series of 5-methyl triazolopyrimidine sulfonanilides that differed only in ortho and meta substituents on the aniline ring. The I50 term and clogP were most important to jimsonweed activity. Hence, in vitro activity (I50) may be a useful component of whole plant structure activity models to aid in identification of barriers to in vivo performance.

Puccinia coronata infection increased absorption of 14C-glyphosate in quackgrass 3 days after inoculation (DAI) when compared to 0,6,9, or 12 DAI. Days after inoculation had no effect on glyphosate translocation out of treated leaves until 9 to 12 DAI when 89% of the absorbed 14C-glyphosate was retained within the infected leaf. In contrast, only 43% was retained in leaves treated at 0 DAI. In other studies, 14C-glyphosate absorption increased linearly from 21 to 35% 12 to 96h after treatment (HAT). Differences between control and rust-infected plants were not significant. Sixty-three percent of absorbed 14C-glyphosate translocated out of control leaves by 96 HAT, while only 10% translocated out of rust-infected leaves. Additionally, 28 and 4% of the 14C absorbed was recovered from the rhizomes of control and rust-infected plants, respectively.

The competitive effects of pale smartweed (Polygonum lapathifolium L.) were studied on cabbage (Brassica oleracea L. ‘K-Y’) which was transplanted into rice (Oryza sativa L.) fields either 3 to 12 days before or 5 days after rice was harvested. Competitive effects were determined at weekly intervals from the time beds were formed around the cabbage at 5 days after rice harvest. Where cabbage was transplanted before rice harvest, at a time before pale smartweed germination, cabbage yields were reduced when weeds were allowed to grow for more than 4 weeks from the time the beds were formed. Where cabbage was transplanted at 5 days after the rice was harvested at a time when parts of pale smartweed had emerged, cabbage yields were reduced when weeds were allowed to grow for only 2 or more weeks after the beds were formed. Also, where weeds were removed at the beginning but allowed to grow at a later date, yield was reduced when cabbage was not kept weed-free for a minimum of 4 weeks.

Greenhouse studies suggested that dog mustard was less competitive than wheat, but of similar competitiveness to flax. In field studies, dog mustard growth and development were markedly affected by crop competition. Competition from flax and wheat reduced dog mustard leaf area, shoot dry weight, plant height, and seed production compared with the weed grown on summer-fallow. Dog mustard was a prolific seed producer when grown in the absence of interspecific competition. On summer-fallow, dog mustard produced as many as 79,100 seeds plant−1 when moisture was not a limiting factor. However, average seed production was 19,400 and 8000 seeds plant−1 in 1994 and 1995, respectively.

Dark-incubated common purslane (Portulaca oleracea L.) seed synthesize very little protein and essentially no nucleic acids. Dark-incubated seed incorporate only 14 × 10−3 nmoles 14C-leucine/mg protein/12-h dark. In contrast, seed exposed to 12-h light following 24-h dark incubation incorporate 365 × 10−3-nmoles 14C-leucine/mg protein/12-h light. Once dormancy is broken by exposure of seed to light, initiation of radicle protrusion occurs at 12 h. Protein synthesis gradually increases with time in the light and precedes nucleic acid synthesis which is associated with radicle protrusion. During the 12-h lag period preceding radicle protrusion protein synthesis increases significantly by 3 to 9 h in light, RNA synthesis by 9 h in light, and DNA synthesis by 12 h in light. After 12 h in light, 32P can be detected in all nucleic acid fractions, DNA and RNAs.

The possibility of an interaction between (2,4-dichlorophenoxy)acetic acid (2,4-D) and frost-injured plants of spring wheat (Triticum aestivum L., var. Manitou) was investigated. Application of 2,4-D was made either a few hours prior to the frost or at varying periods following the frost. Although there was no statistical evidence of any interaction between the frost and 2,4-D, yields of grain tended to be lowest when plants were exposed to both frost and herbicide. On the basis of results obtained, it was concluded that there is no great risk of severe damage occurring to frost-damaged spring wheat plants if they are treated with 2,4-D within a short period of being exposed to frost.

Experiments were conducted in controlled environment chambers to evaluate the effects of temperature and soil water content on the time of dissipation of commercial (CF) and starch encapsulated (SE) atrazine formulations to one-half the original concentration (T50). SE samples were also analyzed for the amount of atrazine remaining within the starch particles (percent encapsulation). The dissipation of CF atrazine was affected by changes in temperature and soil water content. SE atrazine dissipation was most influenced by changes in soil water content rather than temperature. Independent of soil water, there was no atrazine dissipation from any formulation at 15 C. The T50 for CF atrazine at 20% soil water content was 53.4 and 29.9 d for 25 and 35 C, respectively. At 20% soil water content, all SE treatments gave a T50 greater than 60 d. The percent starch encapsulation at 20% soil water content was greater than or equal to 55.8 and 30.4% for SE large and SE small, respectively. This high level of encapsulated atrazine accounts for the reduced SE dissipation observed at 20% soil water content. At 40% soil water content, the dissipation of CF and SE small atrazine were not different for either 25 or 35 C. Compared to the CF, the SE large formulation extended the T50 by 7.4 and 6.7 d at 25 and 35 C, respectively. At 40% soil water content, there was no encapsulated atrazine present in SE formulations 60 DAT.

The theme for our meetings this year is “A Positive Concern for Society.” It is in this context that I will talk about “Weed Science in Perspective.” In doing so, we need to consider where we are, where we have been, and where we are going.

The emergence of Sorghum bicolor seedlings and the dormancy status and survival of S. bicolor seeds buried in soil in the midwestern United States were studied from 1992 to 1995. Possible causes of seed mortality were also investigated. Emergence of seedlings from seeds buried in November averaged less than 2%, compared with 28% from seeds buried in March. Seeds showed little ability to survive winter, with more than 80% dying between November and March and virtually none surviving a second winter. Many seeds exhibited signs of cold damage. Further evidence of the effect of cold was the decreased mortality of seeds protected somewhat from the cold. The decline in the viability of seeds was modeled well by negative exponential curves with an exponent of between 0.011 and 0.016.

Sugarcane (Saccharum interspecific hybrids) grown without cultivation but maintained relatively weed-free with herbicides and hand hoeing, produced yields of sugarcane/ha and sugar/ha in the plant, first-ratoon, and second-ratoon crops that were 100%, 95%, and 88%, respectively, of the yield of sugarcane cultivated two to four times annually. Standard cultural practice involves at least two cultivations, namely, the off-barring and the fertilizational cultivations. Additional cultivations did not substantially increase yield. When sugarcane yield was affected either by cultivation or herbicide treatment, stalk population rather than stalk weight was affected the most. Johnsongrass [Sorghum halepense (L.) Pers.] and annual weeds were controlled effectively in both cultivated and non-cultivated sugarcane with broadcast, preemergence application of fenac [(2,3,6-trichlorophenyl)acetic acid] at 5 kg/ha or terbacil (3-tert-butyl-5-chloro-6-methyluracil) at 1.8 kg/ha. Purple nutsedge (Cyperus rotundus L.), however, was controlled only with a combination of fenac or terbacil and periodic cultivation.

Crabgrass, the universal lawn weed, has been the object of much research in the past few years. Lawn owners, cotton and vegetable growers, and golf course keepers have long been fighting this pest. Today, chemical eradication is rapidly displacing costly, difficult, and often ineffective mechanical control methods.

The persistence of picloram (4-amino-3,5,6-trichloropicolinic acid) was measured each spring over an 8-yr period following repeated annual applications at rates ranging from 0.020 to 0.070 kg/ha. Picloram residue levels were proportional to rate of application but averaged approximately 45% of the original levels when measured 12 months following application and declined to 10% 24 months after application ceased. Control of wild buckwheat (Polygonum convolvulus L.) was good with major population declines over the test period. Crop tolerance and yields were not affected at rates of 0.035 kg/ha or less.