This work is an endeavor to aid researchers located in remote areas as well as researchers who may have experienced difficulties in the regulation of controlled environment chambers. Descriptions of the maintenance and use of controlled environment chambers contained herein were compiled over an 8-year period of experience with four chambers. Although the physical characteristics of the controlled environment chambers described are dissimilar from many, the causes and remedies of malfunctions are general and typical of those found in many controlled environment chambers. Several protective devices for expensive equipment are described as well as several common malfunctions and their remedies.

Results were based on plant response with light levels in energy units, in accord with use of the spectrum by plants. Dry weight yields of control plants, and reductions of yields by 2,4-dichlorophenoxyacetic acid (2,4-D) below those of control plants were greatest in red light, followed by pink, yellow, white, green, and blue light, in that order. Sucrose mixed with 2,4-D or applied alone to plants altered the combined light-herbicide effect but little. Differences in concentration of 2,4-D affected respiration more than photosynthesis, as measured by CO2 exchange under different light qualities. In spectral effects, pink light caused greatest reduction of photosynthesis by 2,4-D at 500 ppm, while greatest promotion of respiration occurred under red light with 2,4-D at 1000 ppm.

Cluster tarweed (Madia glomerata Hook.) is an annual which occupies rangeland from Saskatchewan to N. Arizona at medium to high elevations. In the laboratory dried tarweed plants and leachates from them reduced the germination of intermediate wheatgrass (Agropyron intermedium (Host) Beauv.) and radish, and caused high proportions of abnormal seedlings. The inhibitory agent(s) was highly water soluble, dialyzable, stable to boiling, drying, and prolonged storage in solution, destroyed by ashing, and not affected by pH 4 to 7. In soil in the greenhouse, tarweed leachates and dried tarweed significantly reduced growth of wheatgrass seedlings. In the field, tarweed infestation reduced the establishment and growth of wheatgrass sown in it in proportion to the stand of tarweed.

Band applications of residual preemergence herbicides were equal to timely shallow cultivations for the control of annual weeds in corn, and were superior when wet weather delayed or interfered with early shallow cultivations. The average corn yield reduction of 7.4 bushels per acre from weed competition observed over a 13 year period, suggested that under average conditions the net cost of herbicide treatment would be less than the value of corn lost through failure to control weeds.

It has been shown that extracts of various weeds and crop plants inhibit germination and seedling growth (1, 4, 5, 7). In early experiments (7) it appeared that extracts of leafy spurge (Euphorbia esula) were particularly effective. For this reason it was of interest to more fully characterize the composition of leafy spurge. The present communication summarizes the results of qualitative paper chromatographic determinations for amino acids and sugars.

The herbicide 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) was selective for sugar beets (Beta vulgaris L.). In preemergence treatments, sugar beets tolerated pyrazon at rates up to 6 lb/A, but at this level some mortality occurred. On the other hand, some weed species were susceptible to levels as low as 2 lb/A. Between emergence and the cotyledon stage, both beets and weeds were quite susceptible and the phytotoxicity of pyrazon increased with increasing temperature. In the late cotyledon stage, beets were resistant to pyrazon in aqueous suspension and partially susceptible to an oil-water suspension. Beets in the two to four-leaf stage tolerated an oil-water herbicidal combination, while lambsquarters (Chenopodium albium L.) and redroot pigweed (Amaranthus retroflexus L.) remained susceptible up to the six to eight-leaf stage. Rape (Brassica napus L.) was of intermediate susceptibility. In general, preemergence treatments were the most promising but could be replaced by postemergence treatments of pyrazon in an oil-water emulsion.

The herbicide 0-(2,4-dichlorophenyl) 0-methyl isopropylphosphoramidothioate (DMPA) applied either as a preemergence spray or in mixture with the alkanolamine salt of 4,6-dinitro-orthosec-butylphenol (DNBP) at the “ground-cracking” (emergent) stage increased the yield of peanuts from 1960 to 1965. Average yield increases from DMPA treatments for the 5-year period were highly significant statistically if DMPA treated peanuts were compared with peanuts either cultivated, handweeded, or sprayed with standard herbicide mixtures.

Successful use of selective herbicides is dependent upon differences in susceptibility between the crop and the weeds. Often the cause and magnitude of these differences is not completely known. Intelligent use of a chemical requires some knowledge of the margin of safety between the weed and the crop. Beneficial modifications of existing chemicals or methods of application could be most efficiently accomplished if the cause of the differences in susceptibility to the chemical were known. The alkanolamine salts of 4,6–dinitro o secondary butylphenol (hereinafter referred to as DNBP) have shown variability in their toxicity to various plant species. This investigation is concerned with the degree and possible causes of this variability.

Pesticide drift studies were conducted in which two formulations were sprayed simultaneously to eliminate meteorological differences. One formulation was traced with Brilliant Sulfo Flavine (BSF) dye and the other with Rhodamine B (RhB) dye. Combined drift from both formulations was caught downwind on Mylar sheets. A filter fluorometer was used to analyze the deposits. By proper selection of a light source, primary filters, and secondary filters, the BSF was excluded while the RhB was analyzed, and vice versa. Concentrations below 1.0 μg/L were accurately measured.

A field study was conducted to develop systems using cultural and chemical methods for control of bermudagrass (Cynodon dactylon L.) in cotton (Gossypium hirsutum L.). Several control options were promising. On areas prepared either with a moldboard plow or a disk, the sodium and magnesium salts of dalapon (2,2-dichloropropionic acid) at 4.7 kg/ha directed to 25-cm-high cotton and repeated at the 40-cm height or the ethyl ester of difenopenten {4-[4-[4-(trifluoromethyl)phenoxy] phenoxy]-2-pentenoic acid} directed to 15-cm-high cotton and repeated at the 30-cm height, with either standard or close cultivation as needed, provided good bermudagrass control. On areas prepared with a moldboard plow, the isopropyl amine salt of glyphosate [N-(phosphonomethyl)glycine] at 4.4 kg/ha over-the-top as a fall application with cultivation as needed was promising.

We applied 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) to quackgrass (Agropyron repens L. Beauv.) at different stages of growth and subjected these treated plants to different light regimes. After paraquat and light treatment, foliage was removed and the reduction in regrowth was measured as evidence of paraquat movement and its effect on the regenerative potential of the rhizomes. Paraquat or a toxic metabolite moved in quantity from point of leaf application. Sufficient basipetal movement occurred in both the dark and light to significantly affect regrowth. As quackgrass plants matured and developed more foliage, the effect of paraquat treatment increased (i.e., the regrowth capacity of the plants and the regenerative ability of their rhizome buds decreased). A period of darkness (24 hr) after paraquat application and before exposure of treated plants to light did not affect numbers of plants killed but did decrease rate of regrowth. Treated quackgrass foliage showed extensive paraquat injury when placed in light for 48 to 72 hr after treatment; but only parts of treated leaves were killed. Leaving treated foliage intact greatly increased the number of plants killed.

Chemical analyses for carbohydrates, fats, and protein and C14O2 tracer techniques were employed to study the influence of repeated applications of amine methylarsonate (hereinafter referred to as AMA) on food reserves in purple nutsedge (Cyperus rotundus L.). Purple nutsedge plants were grown under greenhouse conditions and treated at 3-week intervals with an aqueous solution of AMA. Chemical analyses suggested that repeated applications of AMA accelerated starch hydrolysis in tubers but had little effect on the fat and protein content. The disappearance of starch was correlated with an increase in the arsenic (hereinafter referred to as As) content of tubers following repeated applications. In leaf tissue, applications of AMA significantly reduced the sugar content and increased the protein content. Tracer studies on the rate of C14O2 fixation and evolution suggested that, in general, AMA-treated plants had a higher rate of utilization of the products of photosynthesis than untreated plants. Apparently, the carbohydrate fraction of food reserves was utilized in preference to fats and protein.

Rhizomes develop from the crowns of yellow nutsedge (Cyperus esculentus L.) shoots and the tips transform into shoots or tubers. Transformation of primary rhizomes developed by the original shoot of a plant is a valid index of plant response to treatment when compared with the transformation of all rhizomes (primary, secondary, tertiary, and others), developed by a plant under treatment.

The relationship between trifluralin dosages detected in the soil at seeding, initial crop injury, and subsequent recovery of spring wheat during the growing season was investigated in field experiments in 1986 and 1987. As the amount of trifluralin in the soil increased, both crop density and dry matter production decreased such that at 1 kg/ha the two were reduced by 37 and 50%, respectively, early in the season. As the season progressed, crop growth rates (CGRs) of wheat in trifluralin-treated plots exceeded those of wheat in the untreated plots. Maximum CGRs occurred between Zadok's growth stages 30 and 45 where trifluralin levels in the soil were 0.3 to 0.5 kg ai/ha at seeding. Recovery from trifluralin injury was characterized by enhanced net assimilation rates of surviving plants, increased tillering and greater dry matter production per plant. Wheat seed yield was only weakly correlated with trifluralin levels in the soil at seeding. From a linear regression model it was determined that a 35% reduction in plant dry weight from the trifluralin injury at the beginning of tillering would result in no more than a 10% reduction in seed yield at final harvest.

Percentage canopy reduction of threadleaf snakeweed [Gutierrezia microcephala (D.C.) Gray] and common goldenweed [Isocoma coronopifolia (Gray) Greene] was substantially greater when sprays were applied during the spring of a year characterized by above-average rainfall than in a drought year. Applied at 2 kg/ha or less, 2,4-D [(2,4-dichlorophenoxy)acetic acid] only partially controlled threadleaf snakeweed in either year. Picloram (4-amino-3,5,6-trichloropicolinic acid) or triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} gave satisfactory control of threadleaf snakeweed at 0.5 or 1 kg/ha, depending upon year of application, whereas these treatments were effective against common goldenweed only in the “wet” year. Herbicide 3,6-dichloropicolinic acid tended to be less effective against either species than picloram or triclopyr. Approximately 1 and 2 yr after herbicides were applied, standing forage crop increased 37 and 25 kg/ha, respectively, with each percentage point reduction of threadleaf snakeweed canopy cover.

Greenhouse studies were conducted to investigate the absorption, translocation, and metabolism of foliar-applied [14C]halosulfuron-methyl in cucumber, summer squash, pitted morningglory, and velvetleaf. Cucumber and summer squash were treated at the 4-leaf stage, whereas velvetleaf and pitted morningglory were treated at 10 cm. All plants were collected at 4, 24, 48, and 72 h after treatment (HAT) for absorption and translocation studies and an additional 96-HAT interval was included in the metabolism study. Absorption did not exceed 45% in summer squash, whereas it plateaued around 60% in velvetleaf and cucumber and reached 80% in pitted morningglory 72 HAT. None of the four species translocated more than 23% of absorbed halosulfuron out of the treated leaf. Translocation in cucumber and summer squash was predominantly basipetal, while acropetal movement prevailed in velvetleaf. No significant direction of movement was observed for pitted morningglory. Negligible translocation occurred toward the roots, regardless of plant species. Of the total amount of [14C]halosulfuron-methyl absorbed into the plants at 96 HAT, more than 80% remained in the form of the parent compound in velvetleaf, summer squash, and pitted morningglory, whereas less than 20% was detected in cucumber. Rapid and high herbicide metabolism may explain cucumber tolerance to halosulfuron-methyl, while lack of metabolism contributes to summer squash and velvetleaf susceptibility. Pitted morningglory tolerance may be due to limited translocation associated with some level of metabolism, but further research would be needed to investigate other potential causes.

Additions of surfactants to the isooctyl ester of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) and the dimethylamine of 3,6-dichloro-o-anisic acid (dicamba) generally did not increase absorption or translocation of the herbicides when they were applied to foliage of five hardwood species and loblolly pine (Pinus taeda L.). Adjusting pH of the formulations to 3, 6, or 9 with a buffering solution had small and inconsistent effects upon absorption and translocation.

Zoysia germplasm exhibit different levels of sensitivity to fluazifop-P-butyl, but the genetic factors responsible for such differences are unknown. Segregation patterns of the fluazifop-P-butyl tolerance trait were studied under greenhouse conditions. In total, 244 F1 lines were generated from multiple crosses between the tolerant line 5337-2 (non–target site tolerance) and three more-sensitive lines (123, 252, and 5330-23). Progeny segregation showed that fluazifop-P-butyl tolerance within zoysiagrass (Zoysia spp.) is expressed as a quantitative trait with a wide range of intermediate phenotypes between parental phenotypes. Transgressive segregation was extensive and largely favored susceptibility in most families, but was especially evident for 5337-2 × 123 and 5337-2 × 5330-23. The segregation patterns for biomass reduction and percent injury were different within reciprocal crosses and among three different family crosses. Reciprocal effects were observed in growth reduction for 5337-2 × 5330-23, in percent injury at 3 wk after the treatment (WAT), and for 5337-2 × 252 at 6 WAT. This indicated that fluazifop-P-butyl tolerance was not completely controlled by nuclear genetic factors in 5337-2 and maternal/cytoplasmic inheritance was also partially responsible. These results suggested that fluazifop-P-butyl tolerance may be attributed to multiple genetic mechanisms, which could present a challenge for future breeding efforts because of the difficulty of fixing multiple traits within a breeding population.

Edamame [Glycine max (L.) Merr.] differs from grain-type soybean in several aspects, one being that edamame seeds are 65% to 100% larger than grain-type soybean seed. Crop seed size has implications for weed management in grain-type soybean; however, the extent to which this observation holds true for edamame is unknown. Because weed interference continues to be a barrier to domestic edamame production, the objective was to quantify the effect of edamame seed size on the crop’s ability to tolerate weed interference (CT) and the crop’s ability to suppress weeds (WSA). Five edamame cultivars plus one grain-type cultivar were each sorted to create “small” and “large” seed size classes. Seed lots were included in a split–split plot design, whereby an additional experimental factor was presence or absence of velvetleaf (Abutilon theophrasti Medik.). Crop and weed emergence and growth were monitored through 8 wk after emergence (WAE). Crop plants from large seed had higher tolerance to A. theophrasti than plants from small seed, as evidenced by crop height, area, and biomass. Edamame seed size had little effect on WSA; however, crop cultivars differentially reduced A. theophrasti leaf area and biomass at 4 and 8 WAE. While both seed size and edamame cultivar influence early-season crop competitive ability, the magnitude of these factors on CT and WSA underscores the importance of considering them not as stand-alone tactics but rather as useful additions to a more comprehensive integrated weed management system.

At germination, seedlings may be encouraged by the surrounding vegetation. This facilitation was studied in dandelions in a manipulative experiment to determine whether a nurse plant, either maple trees or alfalfa, assisted in the germination of dandelion seeds and whether there was a difference in germination when additional moisture (irrigation) was provided on top of rainfall. Seeds were sown into 33-cm2 “arenas” and surrounded by plastic collars, which prevented the seed from being eaten by predators. Germination was recorded at 1- to 2-d intervals, and the percentage of the seeds that germinated and their time to 50% germination (T50) was calculated. The nurse plant was consistently associated with seed germination. Compared with bare ground, the germination percentage was lower under tree cover, whereas T50 was shorter under the cover of herbaceous plants (alfalfa). The values for the germination percentage and T50 were similar under tree and herb nurse plants when the soil was irrigated. Nurse plants facilitated germination via their effects on understory humidity. Facilitating the germination of dandelions through the presence of nurse plants contributes to their propagation in crops.