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.

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.

Dwarf amaranth (Amaranthus macrocarpus Benth.) is a problematic broadleaf weed in many crops in Australia; however, no information is available on the germination ecology of this species. Seeds from two populations of this species were collected from Hillston, NSW, Australia (D-P-01), and Yandilla, QLD, Australia (D-P-02). Seeds were germinated at a range of constant (20 to 45 C) and alternating temperatures (30/20, 35/25, 40/30, and 45/35 C day/night). For the constant temperature treatments, the highest germination occurred at 35 C for D-P-01 (89%) and D-P-02 (82%). Germination was higher at the alternating day/night temperature of 40/30 C for both populations D-P-01 (91%) and D-P-02 (85%). Seed germination of both populations was stimulated by light, which indicates a great amount of emergence of A. macrocarpus can occur on bare ground such as crop seed beds. Results also revealed that this species tolerates a moderate level of salinity and can germinate in slightly alkaline soil conditions. The emergence of this species was highest (47%) for the seed buried at 0.5-cm depth in grey cracking alkaline soil compared with seed buried at the same depth in acidic red soils. These results suggest that soil inversion by tillage to bury weed seeds below their maximum emergence depth could serve as an important tool for managing A. macrocarpus. The results from this study will help in developing more sustainable and effective integrated weed management tactics for the control of this weed and weeds with similar responses in summer cropping systems.

When clay granules containing chlorpropham (isopropyl m-chlorocarbanilate) were applied to the surface of moist soil, the herbicide gradually moved to the atmosphere as a vapor and little entered the soil. Chlorpropham killed seedlings of field dodder (Cuascuta campestris Yunck.) and largeseed dodder (C. indecora Choisy) effectively whether it contacted them in the soil or in the air above the soil.

Multiple applications of several preemergence herbicides were evaluated for weed control and for phytotoxicity to gladiolus (Gladiolus X hortulanus L.) grown from cormels in 1984 and 1985. Oryzalin [4-(dipropylamino)-3,5-dinitrobenzenesulfonamide] consistently provided acceptable control of southern crabgrass [Digitaria ciliaris (Retz.) Koel. # DIGSP], goosegrass [Eleusine indica (L.) Gaertn. # ELEIN], and smooth pigweed (Amaranthus hybridus L. # AMACH) and had minimal effect on gladiolus plant growth even after four applications. Pronamide [3,5-dichloro (N-1,1-dimethyl-2-propynyl)benzamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] provided erratic weed control and reduced yields of gladiolus corms.

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.

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.

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.

We developed a technique to measure the projected leaf area of plants any time during the day or night. “Projected leaf area” is the leaf area seen from directly above, and is the area most likely to intercept herbicide spray from an over-the-top application. The technique involves photographing a plant and a reference square of known area from directly overhead using a light-tight box containing a flash unit. Negative images thus obtained are reflected (by means of a slide projector and mirror) onto filter paper lying on a glass stage. The projected leaf area is determined by planimetry of the negative image of the leaves and the reference square. The projected leaf area can be compared to the actual total leaf area after one determines the latter with a conventional area meter.

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.

A nonphytotoxic paraffinic oil at 2.5, 5, and 10% (v/v) or a blended alkylaryl sulfonate surfactant at 0.5, 1, and 2% (v/v) did not enhance the activity of propanil (3′,4′-dichloropropionanilide) at 1.7, 3.4, and 6.7 kg/ha applied as a foliage spray in aqueous systems on barnyardgrass [Echinochloa crus-galli (L.) Beauv.] or rice (Oryza sativa L. ‘Starbonnet’). Time and rate of applying propanil affected control of barnyardgrass. Barnyardgrass control and rice yield were best with treatments of 3.4 or 6.7 kg/ha of propanil to four-leaf grass plants. Propanil at 6.7 kg/ha controlled tillering and jointing barnyardgrass well enough to increase grain yields over those of untreated rice.

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 performance of four sequential weed management models that assumed either low or high risk was compared to the performance of two sugarbeet consultants, one who assumed low risk and the other high risk. Weed management recommendations were performed over one growing season at two locations, each with several levels of weed populations. Recommendations for preplant, postemergence, and layby herbicide treatments or late-season handweeding differed among the four weed management levels. The high-risk management level was labor intensive and the low-risk management level was herbicide intensive. Weed populations at harvest, recoverable sucrose, and net return above weed control costs were not different among the four weed management levels. Weeds can be controlled in sugarbeets by employing weed management practices based on bioeconomic modeling.

The effects of twelve soil metabolites of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] on soybean [Glycine max (L.) Merr.] growth, yield, and seed oil and protein content were determined. The metabolites included oxidative dealkylated, reduced nitro group, benzimidazole, azoxy, azo, oxidized, and hydroxylated derivatives of trifluralin. When applied at 0.22 kg ai/ha and incorporated 7.5 cm deep, no individual metabolite had a significant adverse effect on growth or yield. Three of the metabolites significantly decreased seed oil content and two of the metabolites significantly increased seed protein content. These effects are not considered important in that the differences, while statistically significant, are very small. Also, the amounts of metabolites applied greatly exceeded those expected to be found after many years of continuous use of trifluralin. Potential accumulation of individual metabolites from long-term use of trifluralin does not appear to adversely affect soybean growth, yield, or quality.

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 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.

Three preemergence and four postemergence herbicides were compared for control of prickly sida (Sida spinosa L.) in soybeans (Glycine max Merrill) and for level of phytotoxicity to soybeans. As a preemergence herbicide, chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxyl-1-methylurea] provided better control of prickly sida than did linuron [3-(3,4-dichlorophenyl)-1-methoxyl-1-methylurea] which was more consistently effective than was naptalam (N-1-naphthylphthalamic acid) plus dinoseb (2-sec-butyl-4,6-dinitrophenol). Chlorbromuron applied as a preemergence treatment caused slight crop injury. In most cases preemergence treatments followed by cultivation were effective in providing season-long control. The descending order of effectiveness for prickly sida control by the postemergence herbicides was: chlorbromuron metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] > prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] > dinoseb. Prometryne as a postemergence treatment following a preemergence herbicide increased prickly sida control more consistently than dinoseb used as the postemergence treatment. However, prometryne caused more crop injury than did dinoseb.

Comparison of soybean yields from the weedy and weed free checks show that prickly sida caused only 9 to 14% yield losses in soybeans.

The effect of herbicide rates on weed control and crop yield is the subject of countless and ongoing research projects. Weed seed banks receive very little attention in comparison. The seed bank resulting from 3 yr (2006 to 2008) of single herbicide rates in a cropping system where glyphosate/glufosinate and corn/soybean were rotated or not was evaluated in a field located in St-Augustin-de-Desmaures, Québec, Canada. Field plots under conventional tillage were seeded in corn every year, or corn and soybean (1 yr). These plots received the same herbicide every year or various glyphosate/glufosinate 3-yr sequences. Subplots were sprayed with a single POST application of the recommended rate of glyphosate (900 g ae ha−1) or glufosinate (500 g ai ha−1) or lower rates. Subplots received the same full (1.0×, recommended) or reduced (0.5×, 0.75×) rate every year. After crop harvest in 2008, soil cores were extracted and the weed seed bank was evaluated. Including soybean in the cropping system resulted in lower seed banks compared to those under continuous corn cropping. Including glufosinate in a glyphosate herbicide sequence increased weed seed banks due to the lower efficacy of the glufosinate rates tested at reducing the seed bank of annual grasses. Higher herbicide rates translated into lower seed banks, up to a certain rate. After 3 yr, the lowest seed bank (full glyphosate rates every year) still had 4,339 ± 836 seeds m−2 and was higher than the initial seed bank (2,826 ± 724 seeds m−2).

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.