With a corn (Zea mays L.) yield of 144 bu/A on weed-free plots, giant foxtail (Setaria faberii Herrm.) reduced corn yields 1, 2, 5, 7, and 18 bu/A, respectively, when removed when 3, 6, 9, and 12 inches high and at maturity. With a soybean (Glycine max L.) yield of 30 bu/A on weed-free plots, the same treatments reduced soybean yields 0, 0, 1, 2, and 18 bu/A, respectively. Giant foxtail competing with corn delayed tassel emergence but had little effect on moisture of grain or on shelling percent at harvest. The total dry matter produced per acre remained relatively constant whether the dry matter was made up of corn alone or corn and weeds. The greatest competitive effect of giant foxtail with soybeans occurred after the reproductive stage of soybeans began or after the weeds became sufficiently dense to reduce the light which soybeans received. Early-season competition had greater effect on corn than on soybeans. However, the taller growing corn competed better than soybeans with giant foxtail later in the season.

The phytotoxicity of N,N-dimethyl-2,2-diphenylacetamide [diphenamid], N-methyl-2,2-diphenylacetamide, 2,2-diphenylacetamide, and 2,2-diphenylacetic acid was studied on tomatoes [Lycopersicon esculentum Mill.], common lambsquarters [Chenopodium album L.], redroot pigweed [Amaranthus retroflexus L.], and rape [Brassica napus L.], by means of nutrient solution culture techniques. Diphenamid was the most phytotoxic; 2,2-diphenylacetic acid was the least active. Only minor differences in the arithmetical means of the phytotoxicity indices existed in the phytotoxicity of the N-methyl and amide analogs of diphenamid.

Several herbicides and herbicide combinations were investigated for desiccation, defoliation, and killing of tropical vegetation near Mayaguez, Puerto Rico. Hydroxydimethylarsine oxide (cacodylic acid) was one of the more effective defoliants on guava (Psidium guajava L.) within 2 weeks after treatment. However, several herbicide combinations including contact: growth-regulator types were more effective 1 month after spraying. Six months after treatment, herbicides containing (2,4-dichlorophenoxy)-acetic acid (2,4-D), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), or 4-amino-3,5,6-trichloropicolinic acid (picloram) were superior to contact herbicides in controlling regrowth. In a mixed tropical forest, most rapid desiccation and defoliation of vegetation was produced by 6,7-dihydrodipyrido (1,2-a:2′,1′c) pyrazinediium salt (diquat) within 2 weeks after treatment. At 1 month after treatment and longer, the 1:1 mixture of the butyl ester of 2,4-D:2,4,5-T and a 2:2:1 mixture of the isooctyl esters of 2,4-D:2,4,5-T:picloram were superior to other herbicides.

Field screening methods were developed which proved very reliable in accurately assessing the potential of herbicides during the first year of testing. Under conditions imposed by these methods, the herbicides usually exhibited maximum toxicity, thereby indicating which ones might be potentially hazardous in growers' fields when crop tolerance is lowered by adverse growing conditions. Of the 29 crop uses suggested by the data, 16 are registered by the USDA and are now in current use. Of these 29, 26 were indicated during the first year of testing and substantiated by data from an additional 1 to 4 years of testing.

Whitebrush (Aloysia lycioides Cham.) near Llano and Marble Falls, Texas was treated at 19 dates with broadcast applications of the potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram) as the 2% granules. At Llano, the average percentages of whitebrush plants killed with 1, 2, and 4 lb/A rates of picloram granules at five dates were 18, 52, and 87; however, at three dates, the 3 lb/A treatment killed 98% of the plants. Picloram granules were applied at 15 dates at Marble Falls where 1, 2, 3, and 4 lb/A rates averaged 17, 43, 68, and 79% of the whitebrush plants killed, respectively. Picloram was most toxic when applied during the cooler months, particularly when application was soon followed by rains. Broadcast sprays of the potassium salt of picloram were included at two dates and were more effective than granules. Most individual whitebrush plants were killed by one-third tablespoon of the 10% granule, or by 2 tablespoons of the 2% granule of picloram applied in an area 2 ft in diam at the base of the stem.

Isopropyl m-chlorocarbanilate (chlorpropham) at 6 lb/A, the standard treatment, usually controlled dodder (Cuscuta spp.) completely for 3 to 5 weeks. Of 27 other herbicides compared with chlorpropham, seven controlled dodder completely for longer periods (6 to 18 weeks), and nine for comparable or slightly shorter periods. Eleven controlled dodder only partially or completely for a period shorter than that from chlorpropham. The period of dodder control from chlorpropham was doubled when p-chlorophenyl N-methylcarbamate at 1.5 lb/A was included with it.

Turions of Hydrilla verticillata (Casp.) were treated with gibberellic acid (GA), napthaleneacetic acid (NAA), indoleacetic acid (1AA), 2-chloroethane phosphonic acid, 6,7-dihydrodipyrido(1,2,-a:2′, 1′-c)-pyrazinediium salts (diquat), 1,1′dimethyl-4,4′-bipyridinium salts (paraquat), mono-N,N-dimethylcocoamine salt of 7-oxabicyclo (2.2.1)heptane-2,3-dicarboxylic acid (cocoamine salt of endothall), or the dimethyl amine formulation of 2,4-dichlorophenoxyacetic acid (2,4-D). Germination and growth of subterranean turions was enhanced by GA and axillary turions by 1AA and 2,4-D. The herbicides exhibited little phytotoxicity to the propagules.

We modified a cereal huller to thresh seed of honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell]. The device threshes seed of other mesquite varieties, huisache [Acacia farnesiana (L.) Willd.], and other leguminous species.

Rates of photosynthesis, respiration, and transpiration of wheat (Triticum aestivum L., var. Gaines) were determined as functions of time, under controlled conditions of moderate soil water stress and soil temperature, after treatment of the roots with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). Air temperature, relative humidity, light intensity, and air movement were maintained constant. The rate of photosynthesis declined with time for all plants treated with diuron but not for the controls. No change in the rate of respiration was detected. The rate of transpiration decreased slightly immediately upon application of the diuron and then remained constant. The data indicate that soil temperature and soil water stress play important roles in the herbicidal action of diuron applied to the soil.

Antagonistic responses were noted on sorghum (Sorghum vulgare pers.) and giant foxtail (Setaria faberii Herrm.) using preemergence combinations of (2,4-dichlorophenoxy)acetic acid (2,4-D) and the carbamates S-ethyl dipropylthiocarbamate (EPTC), isopropyl m-chlorocarbanilate (chlorpropham), and 2-chloroallyl diethyldithiocarbamate (CDEC). Combinations of EPTC and (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) or 3,6-dichloro-o-anisic acid (dicamba) gave similar results. Effects of these combinations were mainly additive on four dicotyledonous species. Combinations of 2,4-D and N-1-naphthylphthalamic acid (naptalam) also were antagonistic on sorghum and giant foxtail but were additive on the remaining species. Eight other herbicide combinations were mainly additive on all six species.

A bioassay standard curve injury rating, using cucumbers (Cucumis sativus L.) as the indicator plant, was developed for quantitatively determining soil residues of 5-bromo-3-sec-butyl-6-methyluracil (bromacil), 6-dichloro-o-anisic acid (dicamba), 3(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), (2,3,6-trichlorophenyl)-acetic acid (fenac), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 2,4-bis(isopropylamino)-6-methoxy-s-triazine (prometone). The herbicide concentrations ranged from 0.001 to 2.187 ppmw. The presence of all the herbicides could be detected at 0.009 ppmw and the herbicides killed cucumbers at 2.187 ppmw. Cucumbers could be used to effectively measure a greater concentration range of fenac than the other herbicides. A highly significant negative correlation existed between injury rating and fresh plant weight. However, concentrations of the herbicides were more easily detected by a visual injury rating on abnormal growth characteristics than by fresh plant weight.

Discs of potato (Solanum tuberosum L.) tuber tissue were immersed in buffered (pH 4.0 to 8.0) solutions of 4-amino-3,5,6-trichloropicolinic acid (picloram) (5 × 10−4M to 5 × 10−3M) for 1 to 36 hr. Uptake of picloram during incubation, and leakage after return of the discs to untreated buffer, were determined by gas chromatographic analysis of extracts of the tissue and ambient buffer. Picloram absorption increased with concentration and with time up to 24 hr. Maximum uptake occurred at pH 4.0 and very little picloram was absorbed at pH 7.0 and 8.0. Both absorption and leakage were temperature dependent. The rate and extent of leakage was greatest at the highest concentration. Typically, more than 90% of the picloram absorbed from 5 × 10−3M was lost to fresh buffer within 12 hr.

The influence of repeated clipping of the shoots on the translocation of 14C-assimilates and 2,2-dichloropropionic acid 2-14C (dalapon) into the rhizome system of established johnsongrass (Sorghum halepense (L.) Pers.) was studied when regrowth was in the preboot, boot, and flowering stages. Radioautography and radio-assay procedures were used to follow the distribution of label within the plants. Plants defoliated three times prior to treatment showed no increase in basipetal translocation over plants defoliated once. As plants matured to the flowering stage, assimilate translocation into rhizomes increased. This increase was closely related to the degree of secondary rhizome growth occurring at time of label application. During preboot, assimilate movement was restricted to rhizome apices with very little retention in intervening tissue. Labeled dalapon followed a similar translocation pattern to that of assimilates. The role of assimilate translocation and storage as correlated with life cycle changes in carbohydrate nutrition of established johnsongrass is discussed.

Absorption of the isooctyl ester of (2,4,5-trichlorophenoxy)-acetic acid varied more than 20% in four woody species when incident light intensity was increased from 40 to 4,000 ft-c. Variations in translocation of the herbicide of 45 to 50% in post oak (Quercus stellata Wangenh.) and water oak (Quercus nigra L.) accompanied changes in illumination. Light intensity did not affect translocation in longleaf pine (Pinus palustris Mill.) or American holly (Ilex opaca Ait.)

The disappearance of 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) from soil was studied using Brassica species for bioassay and the spectrophotometer and chromogenic reagents for chemical determination. Loss of pyrazon from soil appeared to be an exponential function of time characteristic of the activity of soil microorganisms. On the other hand, non-biological degradation appeared negligible. Leaching of pyrazon appeared to be insignificant or minor. The greater part of the herbicide remained in the top 3 inches of soil.

Sugar beets (Beta vulgaris L., var. MSU 126 × 5460) were treated with 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) applied to the soil. The pyrazon was labeled with either 3H in the phenyl ring, or with 14C at the 4 and 5 positions of the pyridazinone ring. The disappearance of pyrazon and the appearance of metabolites in the soil and shoots were examined 1, 2, 4, 6, 8, 12, and 16 weeks after treatment. The total recoverable radioactivity decreased with time, but there was a greater loss of 3H-labeled compounds than 14C-labeled compounds from the soil. Thin-layer chromatography of the soil and shoot extracts revealed the presence of one metabolite in the soil and three metabolites in the plant. By co-chromatography with known pyrazon derivatives and by comparison of the labeling (14C, 3H, or both), the metabolites in the shoot were identified as N-(2-chloro-4-phenyl-3(2H)-pyridazinone)-glucosamine (hereinafter referred to as N-glucosyl pyrazon), 5-amino-4-chloro-3(2H)-pyridazinone (hereinafter referred to as ACP), and ACP-complex. The other moiety in the ACP-complex was not identified. The metabolite in the soil was identified as ACP, and was detectable 2 weeks prior to its appearance in the shoot, suggesting that it was absorbed from the soil.

Weed competition in this experiment had a more marked effect on sorghum [Sorghum bicolor (L.) Moench, var. RS 610] grain yields than did row spacings or sorghum populations. Sorghum grown in 20-inch, as compared to 40-inch, rows had higher grain and stover yields and lower weed yields and 1000-seed weight. Sorghum populations of 42,000 to 50,000 plants per acre produced higher grain and stover yields than populations of 26,000 to 28,000 plants per acre which had greater weed yields, heads per plant, seed weight per head, seed moisture at harvest, and 1000-seed weight. In hand weeded plots, sorghum yields were not affected by row spacing or sorghum population; but as weed competition increased, sorghum yields increased with narrower rows and higher plant populations. Sorghum yields were reduced 4, 12, and 18% by delaying weeding of plots 3, 4, and 5 weeks as compared with 2 weeks after planting. Weeds that did not emerge until 4 weeks after planting did not reduce sorghum yields.

Total petiolar fatty acid content of sicklepod (Cassia obtusifolia L.) treated with 0, 0.14, 0.28, 0.56, 1.12, 2.24, or 4.48 kg/ha S-ethyl dipropylthiocarbamate (EPTC) was measured by gas-liquid chromatography. Neither total petiole fatty acid content nor percentages of the various 53 identified constituents changed in relation to herbicide application. Isostearate (17.5%), stearate (5.7%), oleate (5.7%), linolate (9.8%), and arachidate (8.2%) accounted for 46.9% of the total petiole fatty acid content. Anteiso derivatives of C15 to C31 were identified and quantitated at concentrations of 0.25 to 2.00%. Petiole cuticle thickness decreased 35% as herbicide concentration increased to 4.48 kg/ha.

A survey has been made of the literature on biochemical characteristics of plants with particular emphasis on factors affecting photosynthesis. From these characteristics, plants have been divided into two groups, efficient and non-efficient. This division is justified on the basis of data published by numerous workers. A hypothesis has been developed that efficient plants often have been used in agriculture because of their high production, but efficient plants also are very competitive and the observation has been made that almost all weeds which have been tested are members of the efficient groups of plants. This hypothesis is discussed and some general conclusions have been advanced related to plant breeding, development of herbicides to inhibit specific biochemical reactions, ecology, and increasing food production.

The herbicide 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) had a ten-fold greater inhibitory effect on the growth of common lambsquarters (Chenopodium album L.) than on sugar beets (Beta vulgaris L.), Production of dry matter was inhibited by accumulations of pyrazon in the tissues. When these accumulations reached a level approximately twice that which affected dry matter production, plants wilted, collapsed, and died. Pyrazon failed to affect the structural integrity of either chlorophyll or the chloroplast, but inhibited the Hill reaction of chloroplasts isolated from both sugar beets and common lambsquarters. The I50 value was 6 × 10−6 M pyrazon. There was no difference between sugar beets and common lambsquarters in the degree of inhibition in oxygen evolution by leaf discs placed in pyrazon. When plants were cultured in vivo with pyrazon, the rate of oxygen evolution was correlated with herbicide accumulations in the leaf tissues. Sugar beet leaves contained only one-third to one-fifth the level present in common lambsquarters. The rates of respiration of roots and leaf discs of both species were not affected by pyrazon treatments in vivo or in vitro.