Four field studies and two growth-chamber studies were used to evaluate the compatibility of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) in suspension fertilizer on corn (Zea mays L. ‘Pioneer 321’). Crop yields and tissue analyses were used to determine effects of atrazine on fertilizer availability. Visual and pictorial comparisons determined effects of fertilizer on atrazine phytotoxicity. Fertilizer-herbicide combinations compounded 230 days or sooner before application produced no change in atrazine phytotoxicity or fertilizer availability in growth chamber studies. Preplant-incorporated treatments displayed better fertilizer availability than preemergence treatments in the field. Preemergence treatments resulted in greater atrazine phytotoxicity under drought conditions. No problems of physical compatibility were encountered with the mixtures.

The acid and amine formulations of 2,4-dichorophenoxyacetic acid (2,4-D) can be extracted from soybean seed simultaneously or separately. The method consists of partitioning first between ethyl ether and citrate-phosphate buffer and then between carbon tetrachloride and citrate-phosphate buffer. Quantitative determination of the 2,4-D can be made by means of chromatography.

The full spectrum of herbicide resistance in a weed can vary according to the mechanistic basis and cannot be implied from the selective pressure. Common ragweed (Ambrosia artemisiifolia L.) is an important weed species of horticultural crops that has developed resistance to linuron based on either target site– or non–target site resistance mechanisms. The objective of the study is to characterize the cross-resistance to metribuzin of linuron-selected biotypes of A. artemisiifolia with target site– and non–target site resistance and determine its genetic basis. Crosses were made between two types of linuron-resistant biotype and a linuron-susceptible biotype, and the progeny were further backcrossed with susceptible plants to the third backcross (BC3) generation to determine their responses to both herbicides compared with parental lines. The target site–based linuron-resistant biotype was cross-resistant to metribuzin, and resistance to both herbicides was maintained at the same level in the BC3 line. In contrast, the linuron-selected biotype with a non–target site resistance mechanism was not cross-resistant to metribuzin. In addition, the BC3 lines deriving from the non–target site resistant parents had very low-level resistance. While the target site–resistance trait is maintained through multiple crosses, non–target site based resistance would be lost over time when selection is absent or insufficient to retain all genes involved in resistance as a complex trait. This would imply A. artemisiifolia biotypes with different mechanisms would need to be managed differently over time.

Populations of rigid ryegrass (Lolium rigidum Gaudin) from southern Australia have evolved resistance to the thiocarbamate herbicide prosulfocarb. The inheritance of prosulfocarb resistance was explored by crossing resistant (R) and susceptible (S) individuals. In all families within each cross, except 16.2, the response of the F1 was intermediate between the parents, suggesting that resistance is inherited as a single, partially dominant trait. For 16.2, the response of the F1 was more similar to the S parent, suggesting resistance may be a recessive trait in this population. Segregation at the discriminating dose of 1,200 g ai ha−1 prosulfocarb in population 375-14 fit the ratio (15:1) consistent with two independent dominant alleles; in population 198-15, it fit a ratio (13:3) for two independent alleles, one dominant and one recessive; and in population EP162, it fit a ratio (9:7) for two additive dominant alleles. In contrast, segregation of population 16.2 fit a ratio (7:9) consistent with two independent recessive alleles contributing to prosulfocarb resistance. Four different patterns of resistance to prosulfocarb were identified in different R populations, with inheritance as a dominant allele, dominant and recessive, additive dominant and as an independent recessive allele. This suggests there are several different mechanisms of prosulfocarb resistance present in L. rigidum.

Burning nettle is a noxious weed that commonly infests coastal California vegetable fields. Weed control programs for lettuce and fresh spinach grown in this area do not adequately control burning nettle, and escaped weeds that mature are highly problematic during hand weeding and harvesting. Information on the biology and ecology of burning nettle is limited, and work was conducted to develop information about this weed. The objectives of this study were to evaluate the effect of temperature on burning nettle germination and to determine its base temperature value, to characterize the germination pattern of this weed and seedbanks under local California coastal conditions, and to estimate the optimal timing for burning nettle removal by herbicides and physical methods. The upper optimal temperature for burning nettle germination was 22.8 C, but there was no difference in the final germination percentage between 4 and 22.8 C. The base temperature was determined to be 3 6 0.2 C, and this information allowed the development of temperature-based optimal control timing models. In the field, burning nettle emerged throughout the year without any seasonal pattern, and germinable seeds were also found in the seedbank throughout the year. Burning nettle was able to complete a growth cycle throughout the year in coastal California. Burning nettle has a short growth cycle that allows it to set viable seeds within 466 6 13 growing degree days (GDD), and this timing is critical for burning nettle removal by herbicides, cultivation, or hand weeding. The optimal timing for phenmedipham application at 180 g ai ha–1 was estimated to be 205 GDD. The germination and seedbank field studies indicate why burning nettle is so well adapted to the mild climate of coastal California. However, results presented here suggest strategies to reduce the burning nettle seedbank, improve its control, and allow more efficient lettuce and fresh spinach production.

Absorption and translocation of aminocyclopyrachlor (AMCP) was investigated in black walnut. Radiolabeled AMCP was applied foliarly as a free acid, and basally as a free-acid-formulated oil-soluble liquid and as a methyl ester emusifiable concentrate. Maximum absorption was 68% for the methyl ester, 47% for the free-acid oil-soluble liquid, and 8% for the free acid when evaluated as percent applied. When recovered AMCP was presented as Bq g−1, no difference was observed in AMCP absorption or translocation of 14C-labeled material out of treated plant parts. Recovery of applied radiolabeled material in the roots from basal applications was 5 to 11% 72 h after treatment (HAT), compared with 0.8% recovery from a foliar application. Regardless of chemical form or formulation type, comparable injury was observed within 72 HAT despite low levels of translocation.

The growth response of annual sowthistle (Sonchus oleraceus L.) to anticipated future climate conditions is currently unknown, and thus two parallel studies were conducted dealing with glyphosate-resistant (GR) and glyphosate-susceptible (GS) biotypes of S. oleraceus. The glyphosate efficacy study was conducted using different doses of glyphosate (0 [control], 180, 360, 720 [recommended dose], and 1,440 g ae ha−1) at two different moisture levels (well-watered and water-stressed conditions). In the second study, the growth and seed production of these biotypes were studied under different atmospheric carbon dioxide (CO2) concentrations (450 and 750 ppm) and under well-watered (100% field capacity) and water-stressed (50% field capacity) conditions. Results showed that the GR biotype survived (>68%) at 1,440 g ha−1, but for the GS biotype, no plant survived, and both biotypes were slightly (<10%) affected by moisture regimes. In the elevated CO2 condition, the GS biotype plants were >38% taller and produced >44%, >18%, and >21% more leaves, buds, and seeds, respectively, compared with the ambient CO2 concentration under both moisture regimes. The biomass also increased by 27% in comparison with the ambient CO2 concentration. For the GR biotype, plants at the elevated CO2 level, while they also grew 38% taller in comparison with the ambient CO2 concentration, the numbers of leaves, buds, and seeds and biomass were not affected by this increase in CO2. Results showed that there were minimal changes in response to glyphosate for GR and GS biotypes of S. oleraceus with or without moisture stress. Our study suggests that future climate change with elevated CO2 levels can affect the response of S. oleraceus to glyphosate, and such knowledge will be helpful for weed management in the future.

Rates of evaporation of dalapon acid and four low-volatile esters of dalapon from open dishes at 38C. in pounds per acre per hour, determined gravimetrically, were dalapon acid, 180; propyleneglycol bis ester, 27; diethyleneglycol bis ester, 1.6; dipropyleneglycol bis ester, 0.83; and triethyleneglycol bis ester, 0.61. Foliar applications on an acid equivalent basis were phytotoxic to seedling oats in the increasing order of propyleneglycol bis ester, acid, dipropyleneglycol bis ester, diethyleneglycol bis ester, sodium salt, and tripropyleneglycol bis ester. Relative phytotoxicities were not altered by subjecting plants to rapid drying after spraying. These compounds did not differ significantly in phytotoxicity when added to the rooting medium of germinating oat plants. The triethyleneglycol bis ester, and possibly other esters of dalapon, may offer practical advantages as herbicides other than those related to volatility.

The value of 2,4–dichlorophenoxyacetic acid (2,4–D) for control of broadleaved weeds is well known. It is equally well known that these chemicals can cause serious damage to certain crops. After 10 years of general use in agriculture it is well to review the extent to which 2,4–D has been a source of trouble and to examine regulatory policy with regard to 2,4–D.

Studies were conducted to compare weed growth under lighting systems composed of metal halide (MH) lamps and fluorescent-incandescent (FI) lamps. The MH lamps provided more light intensity and over a 6-week period caused plant dry weight to be 60 to 70% more than for plants exposed to the FI lamps. One week after emergence, all plants under the higher intensity MH lamps had larger stems and cotyledons or first true leaves. Six weeks after planting, weeds grown under the MH lamps had larger leaves, shorter internodes, thicker stems, and, in general, more pubescence than plants under the conventional lighting system. Growth habits of weeds exposed to the MH lamps were similar to those observed for field growth plants.

Winter applications of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or combinations of paraquat with diquat [6,7-dihydrodipydrido (1,2-α: 2′,1′-c) pyrazinediium ion], propham (isopropyl carbanilate), or pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl)benzamide], usually controlled both winter annual grass and broadleaf weeds in established white clover (Trifolium repens L. ‘New Zealand,’ ‘Louisiana S-1,’ and ‘Tillman’). Diquat controlled broadleaf weeds, but was less effective than paraquat or combinations of paraquat with diquat, propham, or pronamide for grass control. Dichlobenil (2,6-dichlorobenzonitrile) controlled weeds in some experiments. Pronamide and propham usually controlled grass weeds but not broadleaf weeds. In experiments in which clover seed production differed significantly, paraquat or combinations of paraquat with propham or pronamide usually resulted in higher yields than the check. Yields increased more often where treatments included paraquat.

A mechanism of action of the ethyl ester of quizalofop was determined in monocotyledonous and dicotyledonous plants. Quizalofop inhibited electron transport in both cucumber and corn chloroplasts. In corn, inhibition of electron transport was more pronounced under phosphorylating conditions. Half-maximal inhibition (I50) of ATP synthesis was achieved with a 75-μM concentration of quizalofop in coupled corn chloroplasts. Cucumber chloroplast ATP synthesis was not inhibited at herbicide concentrations up to 100 μM. Corn chloroplast fractions contained greater quantities of bound [U-14C] quizalofop ester following incubation in light and dark assays. Thin-layer radiochromatograms of 14C-labeled quizalofop showed no metabolism or degradation of parent ester incubated in light and dark chloroplast-mediated reactions. In our studies, it is apparent that the inhibitory action of quizalofop was due to the parent ester. The ester formulation of quizalofop appears to exhibit multiple activity in susceptible plant chloroplasts.

Forage legumes are often injured when herbicides, such as 2,4–dichlorophenoxyacetic acid (2,4–D), are applied to control weeds in fields of grain containing legume seedlings. At times the legume seedlings are not injured materially but in many instances the herbicide applications result in a moderate or even drastic thinning of the stand. Various factors have been suggested to account for the variability in results observed.

SHOOTMERISTEMLESS (STM) encodes a member of the class I KNOX homeodomain protein family that is required for meristem development and maintenance. We have isolated both genomic and cDNA clones of STM from the perennial weed leafy spurge. A comparison to other class I KNOX genes indicates that EeSTM represents an orthologue of AtSTM and not one of the other class I KNOX gene family members. 5′ rapid amplification of cDNA ends (RACE) indicated that the transcription initiation site is close to the start of translation and is conserved between arabidopsis and leafy spurge. Putative cis-acting elements were identified in the EeSTM promoter, including a tuber-specific sucrose-responsive element, which could play a major role in the expression of EeSTM in root tissue.

A miniature sprayer designed for primary screening of herbicides is described. It uses a drift-free flat fan nozzle at low pressure. It has negligible dead volume and a minimum of wetted surface. Total cost was about $10.00 in 1967.