Studies were conducted to determine the effect on photosynthesis, the absorption, and the metabolism of simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] in two biotypes of common groundsel (Senecio vulgaris L.). Simazine inhibited photosynthesis in the susceptible (S) plants, but resistant (R) plants were unaffected. When the herbicide was removed from the S biotype after 24 hr, photosynthesis resumed. Both biotypes absorbed the herbicide equally well and were unable to metabolize simazine during 96 hr. The greatest concentration of 14C activity (80 to 90%) was located in the chloroform-soluble fraction of the foliage of each biotype and was identified as simazine. Small amounts of radioactivity (10 to 15%) occurred in the water-soluble fraction, but there was no differential increase in water-soluble simazine metabolites. A different mechanism of resistance than previously reported for triazine-resistant plants may be operative in one groundsel biotype.

Buds of locally collected yellow nutsedge (Cyperus esculentus L.) tubers are formed only at the six most apical nodes with a 1/3 phyllotaxy. The oldest bud is largest. Bud size grades to the small apical bud. Veins of the rhizome are continuous through the tuber to each bud, root, and leaf. Buds break dormancy in acropetal order, starting with the oldest bud. If the tubers and buds remain undisturbed, usually only two buds break dormancy and grow into shoots.

The incidence of puncturevine (Tribulus terrestris L.) carpels and viable seed recovered from soil samples varied inversely and linearly with depths to 24 cm. Soil type and texture and method of tillage influenced the gradients of carpel distribution and their rate and degree of vertical migration. Evidence for enforced, induced, and innate dormancy in puncturevine seed is presented. Most seed germinated from depths of less than 4 cm in cultivated, sandy loam and clayloam soils. The intra-carpel pattern of seed germination was such that seed located nearest the stylar end of two, three, and four-seeded carpels tended to germinate first, with the other seed tending to follow in order of their position in the carpel from the stylar to the receptaclar end. However, all possible combinations of intra-carpel germination patterns occurred under field conditions.

Tomato (Lycopersicon esculentum Mill. ‘Fireball’), white bean (Phaseolus vulgaris L. ‘Seaway’), and tobacco (Nicotiana tabacum L. ‘Delhi 34’ and ‘White Gold’) were pretreated with herbicides at one of three rates prior to fumigation with ozone at 0, 7.5, 15, or 30 pphm (parts per hundred million) for two 1.5-hr period. The plants were harvested 5 to 7 days after ozone fumigation, dried, and weighed. The natural logarithms of the dry weight data were subjected to multiple regression analysis to test for synergistic or antagonistic interactions between ozone and the various herbicides. Synergistic phytotoxicity was definitely observed for pebulate (S-propyl butylethylthiocarbamate) and possibly for chloramben (3-amino-2,5-dichlorobenzoic acid) in combination with ozone on tobacco ‘White Gold’ and ‘Delhi 34’, respectively. For most of the other combinations (chloramben, trifluralin α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) or monolinuron (3-(p-chlorophenyl)-1-methoxy-1-methylurea) on white bean, diphenamid (N,N-dimethyl-2,2-diphenylacetamide) or trifluralin on tomato, chloramben on tobacco ‘White Gold’, and pebulate on tobacco ‘Delhi 34’) the phytotoxicity in the presence of ozone was additive and no interaction was indicated. An antagonistic interaction between ozone and benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) was indicated on the two cultivars of tobacco.

The effects of twelve substituted dinitroaniline herbicides on soybeans [Glycine max (L.) Merr., ‘Corsoy’], velvetleaf (Abutilon theophrasti Medic.), and giant foxtail (Setaria faberi Herrm.) were evaluated under field conditions in 1971 and 1972; and the relative persistence of herbicide residues in soil was determined by field bioassay. Of the herbicides tested, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), and benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2, 6-dinitro-p-toluidine) reduced soybean stands in 1971. Only dinitramine reduced soybean stands in 1972 when applied in low rates, but all of the herbicides except CGA-10832 (N,N-propyl-N-cyclopropylmethyl-4-trifluoromethyl-2,6-dinitroaniline) and chlornidine [N,N(2-chloroethyl)-2,6-dinitro-4-methylaniline] reduced soybean stands at high rates. Overall, oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), dinitramine, and BAS-3921 H[N-propyl-N-(2-chloroethyl)-2,6-dinitro-4-trifluoromethylaniline] provided the best velvetleaf control; while trifluralin, benefin, CGA-10832, and BAS-3921 H produced the most satisfactory giant foxtail control. In 1972, residues of seven of the herbicides caused injury to oats planted over the plot area 355 days after the original herbicide application. The greatest oat injury was caused by trifluralin and oryzalin. Oats were not injured, however, from dinitramine residues when planted only 75 days after the herbicide application.

The relative phytotoxicities of 12 substituted dinitroaniline herbicides to soybeans [Glycine max (L.) Merr ‘Corsoy’], velvetleaf (Abutilon theophrasti Medic.), and either giant foxtail (Setaria faberi Herrm.) or foxtail millet [Setaria italica (L.) Beauv.] were compared under greenhouse and laboratory conditions. In these studies, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) was most toxic to each species. Dinitramine, trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), and BAS-3921 H [N-propyl-N-(2-chloroethyl)-α,α,α-trifluoro-2,6-dinitro-p-toluidine] were most inhibitory of soybean shoot growth, while oryzalin (3,5-dinitro-N4,N4-dipropyl-sulfanilamide), dinitramine, and BAS-3921 H were most inhibitory of root growth. Similarly, dinitramine, oryzalin, nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], and BAS-3921 H inhibited velvetleaf shoot growth; and oryzalin, dinitramine, chlornidine [2,6-dinitro-N,N-di(2-dichloroethyl)-p-toluidine], nitralin, and GS-39985 (N-n-propyl-N-tetrahydrofurfuryl-4-trifluoromethyl-2,6-dinitroaniline) reduced root growth. All of the herbicides except oryzalin and nitralin inhibited foxtail millet shoot growth, while all of the herbicides reduced root growth.

Various soybean [Glycine max (L.) Merr. ‘Amsoy’] losses during harvesting with a combine were studied in relation to different weed densities, weed species, and growing weeds (early harvest) versus desiccated weeds (late harvest). Average soybean losses from shattering and stubble, stalk, and threshing losses were 7.8, 0.9, 2.0, and 1.4% of total yields, respectively. All harvest losses except threshing losses were significantly greater on late as compared with early harvested soybeans. The major loss from weeds in soybeans was reduced yields due to competition; whereas, harvesting losses were associated with high soybean yields and low weed yields. Soybean harvesting losses were 19% greater on plots containing a predominance of broadleaf compared with grass weeds. Average harvesting losses of 12.1% of total soybean yields ranged with treatments from 8.8 to 15.5%. Average gathering losses were 10.7% and threshing losses 1.4% of total soybean yields.

Six vegetable crops were greenhouse-grown to maturity in three Maryland soils treated with up to 500 ppm of arsenic (As) added as sodium arsenate. Phytotoxicity of arsenic residues was highest on Lakeland loamy sand and lowest on Hagerstown silty clay loam. Correlations between available arsenic and plant dry weight indicated that crop sensitivity proceeded as follows: green beans (Phaseolus vulgaris L. ‘stringless greenpod’) > lima beans (Phaseolus linensis L. ‘Fordhook 242’) spinach (Spinacia oleracea L. ‘Longstanding Bloomsdale Savoy’) > radish (Raphanus sativus L. ‘Champion’) > tomato (Lycopersicon esculentum Mill. ‘F-7’) > cabbage (Brassica oleracea L. var. capitata L. ‘Jersey Wakefield’). Residues in the total dry plant at the available arsenic level at which growth was reduced 50% (GR50) were highest with radish (43.8 ppm) and spinach (10.0 ppm). Residues in the dry-edible portion increased to 76.0 ppm arsenic for unpeeled, washed radish at the GR50 point. The soil at the GR50 level for radish contained about 19 ppm of available arsenic from a 50 ppm arsenate treatment to Lakeland loamy sand and a 100 ppm treatment to Hagerstown silty clay loam and to Christiana clay loam.

Overseeded rough bluegrass (Poa trivialis L. ‘Danish common’) and Italian ryegrass (Lolium multiflorum Lam. ‘Gulf’) maintained under putting green conditions were more susceptible to benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) and DCPA (dimethyl tetrachloroterephthalate) than creeping bentgrass (Agrostis palustris Hud. ‘Penn-cross’), red fescue (Festuca rubra L. ‘Dawson’), or perennial ryegrass (Lolium perenne L. ‘Medalist II’). February applications of 1.68 or 3.36 kg/ha of benefin and 6.72 or 13.44 kg/ha of DCPA caused significantly more discoloration and reductions in density than equivalent rates applied in March or April. Benefin was more injurious than DCPA to all overseeded species as judged by quality or density. DCPA caused significant delays in the breaking of dormancy of bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifdwarf’].

Greenhouse and field studies were used to evaluate crop protectants with herbicides in order to obtain selective, broad-spectrum weed control in sorghum [Sorghum bicolor (L.) Moench ‘RS 626’]. Of the herbicides evaluated alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide] was the only one causing sorghum injury that could be moderated with crop protectants. The crop protectant anhydride (1,8-napthalic anhydride) was most effective in reducing alachlor injury when applied as a seed treatment at 0.5% (w/w). Storage of anhydride-treated seed for 1 year did not increase anhydride damage to sorghum seedlings. Preplant applications of alachlor, incorporated into the soil, caused four times more injury to sorghum than did the same rate applied preemergence. Combinations of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and alachlor did not increase sorghum injury or alter the effects of the crop protectants. In the field, anhydride was the most effective crop protectant used. Crop protectant R-28725 (2,2-dimethyl-3-dichloroacetyloxazolidine) at 0.5% w/w to sorghum seed and at 0.6 kg/ha as a tank mix was effective in reducing sorghum injury at the lower alachlor rates. Crop protectant R-25788 (N,N-diallyl-2,2-dichloroacetamide) was the least effective of those studied; however, seed treatment at 0.5% w/w was more effective than the tank mixes.

Activated carbon, applied over the seeded row in a band 2.5 cm wide, protected grasses from herbicides applied preemergence. The carbon rate required to protect the grasses varied with the grass species, the herbicide, and the rate of herbicide application. Most of the herbicides controlled weeds effectively between the rows. The herbicides usually controlled weeds less effectively within the carbon bands. Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] was inactivated most readily by the carbon and showed the greatest safety margin on the crop species. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], and terbacil (3-tert-butyl-5-chloro-6-methyluracil) required higher carbon rates for crop protection than diuron and showed a much narrower safety margin on crops. Use of this technique made possible the effective control of weeds during establishment and, subsequently, the production of high quality seed in the first seed crop.

Fumigation of tomato (Lycopersicon esculentum Mill. ‘Sheyenne’) with low levels of O3 had little effect on root absorption, translocation, or conversion of diphenamid (N,N-dimethyl-2,2-diphenylacetamide) to water-soluble conjugates. However, the proportion of specific conjugates was markedly altered in O3-fumigated plants. Twenty-four hours after treatment, the predominant conjugates formed in nonfumigated and fumigated tomato were the β-glucoside (MDAG), and the β-gentiobioside (MDAGB), respectively, of N-hydroxymethyl-N-methyl-2,2-diphenylacetamide. The ratio MDAG:MDAGB was 8.2:1.0 in nonfumigated tissue and 0.6:1.0 in O3-fumigated tissue. This marked shift toward production of the more polar MDAGB was accompanied by a trend toward increased production of methanol-insoluble residues. A compound having limited stability was extracted from tomato; its probable structure was N-hydroxymethyl-N-methyl-2,2-diphenylacetamide (MODA). It is a postulated intermediate in the formation of MDAG and MDAGB from diphenamid.

We have shown by means of laboratory experiments with a wide range of soil types that the decomposition rate of picloram (4-amino-3,5,6-trichloropicolinic acid) in soil is dependent on soil temperature and moisture content and to no significant extent on organic matter, sand, silt, clay, pH, or initial concentration. A fractional order rate law (0.8) describes the disappearance rate best. It was not possible to develop a suitably precise equation for prediction of loss rate as affected by the above soil and climatic factors. Application of the Arrhenius equation to the data indicates an activation energy of 5.4 kcal/mol for the decomposition of picloram in soil, thus suggesting that the reaction is biological rather than chemical.

The degradation rates of 2,4-D [(2,4-dichlorophenoxy)acetic acid], dichlorprop [2-(2,4-dichlorophenoxy)propionic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], silvex [2,(2,4,5-trichlorophenoxy)propionic acid], dicamba (3,6-dichloro-o-anisic acid), and picloram (4-amino-3,5,6-trichloropicolinic acid) were determined in three soils. Herbicide breakdown was proportional to herbicide concentration, so half life of the various herbicides was calculated from linear regression of the logarithm transformed residue data. The average half life for 2,4-D, dichlorprop, silvex, 2,4,5-T, dicamba, and picloram were, respectively, 4 days, 10 days, 17 days, 20 days, 25 days, and greater than 100 days. The rate of degradation of 2,4-D was the same in all three soils, but for the other herbicides it was consistently faster in soil removed from under grass vegetation than from under trees.

Nitrate reductase activity of seed leaves and the first three true leaves of tall morningglory [Ipomoea purpurea (L.) Roth] was shown to increase rapidly initially then gradually decrease. The greatest level of reductase activity of each true leaf was reached at the fourth to fifth day after unfolding. A subsequent leveling off of enzyme activity corresponded to the acceleration of leaf growth. Leaf nitrates were correlated with enzyme activity. The sum of leaf activities was used to estimate the total reductive capacity of the plant leaf tissue at each sampling date.

The reduction in root yield (Y) of sugarbeets (Beta vulgaris L.) caused by specific densities (X) of kochia [Kochia scoparia (L.) Schrad.] was predicted by using the linear equation Y = 4.30 + 1.81 X. This equation was most accurate when the kochia density was 20 plants or less per 30.5 m of row. In 28 of 30 weed-control systems, where kochia densities ranged from 0.2 to 16.5 plants per 30.5 m of row, the predicted yield reductions were within 5% of the actual yield reductions.

A 2-year experiment was conducted to determine the time interval between flowering and viable seed production in common milkweed (Asclepias syriaca L.). A high percentage of seeds harvested 6 weeks after flowering germinated. Seeds harvested 6 and 7 weeks after flowering resulted in seedlings with significantly shorter radicles and hypocotyls than seeds harvested 8 weeks after flowering. There was a close association between seed weight and radicle and hypocotyl length. Common milkweed produced viable seeds 5 to 6 weeks after flowering.

Wild watermelon (Citrullus vulgaris Schrad. var. citroides Bailey) is a widespread problem in cotton (Gossypium hirsutum L.) and grain sorghum [Sorghum bicolor (L.) Moench] planted on sandy soils. Preplant herbicide treatments did not suppress wild watermelon emergence, dry matter, or melon production. Preemergence application of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] suppressed growth and controlled the weed. However, propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine] controlled and nearly eliminated melon production. Although postemergence application of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] was effective, most postemergence treatments gave erratic control, probably because of differences in vigor from seedlings emerging from varying depths. There was no difference in emergence from seed planted 2.5 to 10 cm deep. However, emergence was lower from seed planted 20 cm deep and seedlings were less vigorous from seed buried 10 cm or deeper.

Seeds of yellow foxtail [Setaria lutescens (Weigel) Hubb.], ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], common cocklebur (Xanthium pensylvanicum Wallr.), jimsonweed (Datura stramonium L.), velvetleaf (Abutilon theophrasti Medic.), and giant ragweed (Ambrosia trifida L.) were buried in the soil November 20 and 21, 1966 at Urbana, Illinois for noting emergence of seedlings from April 1 through August 18, 1967. Similarly, seeds of yellow foxtail, ivyleaf morningglory, jimsonweed, velvetleaf, giant ragweed, common ragweed (Ambrosia artemisiifolia L.), and Pennsylvania smartweed (Polygonum pensylvanicum L.) were buried on October 25, 1968 for emergence observations from April 1 to August 18, 1969. Pennsylvania smartweed, giant ragweed, and common ragweed had large flushes of germination from early April through early May, with no emergence after June 1. Velvetleaf displayed similar early flushes and had additional small flushes of emergence in late May or June. Yellow foxtail seedlings also emerged in April and May in 1969 and in May and June during both years. Common cocklebur seedlings emerged abundantly in April and May but less abundantly in June. Ivyleaf morningglory and jimsonweed displayed flushes of emergence sporadically after May 1. Flushes of emergence for all species which occurred after May 1 were preceded by sufficient rainfall to bring the surface 10 cm of soil to field capacity. Cumulative heat units in the soil above 10 C were not correlated with initiation of emergence for any species. The early emergence was attributed to stimuli from general soil warming while emergence after May 1 was stimulated by favorable soil moisture from rainfall.