The future of weed science, and indeed of all of modern agricultural science and technology, is in jeopardy today because the public does not clearly understand their importance. As a result, decisions may be made and actions taken that can, and will if continued, most certainly destroy our complex and highly productive agricultural systems where one worker annually provides food for more than 46 people. We can improve prospects for the future by effective action.

I have chosen to begin with the proposition that more energy is expended for the weeding of man's crops than for any other single human task. Because it is one of man's principal occupations, the burden is intricately woven into the fabric of his family and community life and to lift it from the tangled skeins of his existence so that we may examine it, or judge it, is well nigh impossible. In the writings of Aristotle, there are these words which seem appropriate to the task ahead, “The search for Truth is in one way hard and in another easy, for it is evident that no one can master it fully nor miss it wholly.”

Greenhouse and field experiments were conducted to compare the response of cucumber (Cucumis sativus L. ‘Ashley’), muskmelon (Cucumis melo L. ‘Delicious 51’), watermelon (Citrillus vulgaris L. ‘Charleston Grey’), and three winter squashes (Cucurbita moschata Duch. ex Poir. ‘Butternut’, Cucurbita pepo L. ‘Table Queen’, and Cucurbita maxima Duch. ‘Boston Marrow’) to 3-amino-2,5-dichlorobenzoic acid (chloramben) and six of its analogs (ammonium salt, amide, mixed salts, methyl ester, hydroxy propyl ester, and butoxy ethyl ester). There were little differences among the analogs except the amide was generally nontoxic to all test crops and weeds. Great differences in growth were noted among species. When chloramben was incorporated in the soil, cucumber and watermelon were very susceptible to all analogs except the amide. Muskmelon was tolerant of all analogs. Squashes exhibited variable susceptibility with ‘Butternut’ the least tolerant, ‘Table Queen’ intermediate, and ‘Boston Marrow’ quite tolerant of the analogs. Separation of exposure of the germinating and emerging seedling on the basis of root or shoot showed cucumber to be most susceptible to root exposure but also susceptible to shoot exposure. Muskmelon and ‘Boston Marrow’ squash were susceptible to root exposure but not to shoot exposure. Muskmelon was not susceptible to either hypocotyl or cotyledon exposure, but cucumber was susceptible to both these treatments. All three species were severely injured by postemergence sprays of chloramben.

An extensive search of the literature and records was conducted to determine when and how johnsongrass (Sorghum halepense (L.) Pers.) was introduced into the United States. Previous authors surmised that johnsongrass was imported from the Mediterranean area, but my search revealed that no agriculturist from the United States had worked in the Mediterranean region before 1840. Although Dr. James B. Davis assisted the Turkish Empire in cotton culture in the 1840's, there is evidence that johnsongrass was grown throughout the Southeast by 1830 if not before. Documentation of the initial introduction and distribution was hampered by the use of more than 40 common names for this weed in the nineteenth century. At least eight different Latin names were used to identify johnsongrass in the 1800's. The use of johnsongrass as a common name on a national basis resulted from a letter written by Herbert Post of Selma, Alabama, in 1874 to George Vasey, an employee of the U. S. Department of Agriculture in Washington. In 1880, John Haralson of Selma, Alabama, wrote to D. L. Phares of Woodville, Mississippi, that johnsongrass was the common name used in his area. These letters were published in the Monthly Report of the U. S. Department of Agriculture and in Farmers Book of Grasses, respectively; the wide attention that these received resulted in the common name of johnsongrass. The name was derived from that of William Johnson, a farmer of Marion Junction, Alabama, who presumably introduced it into Alabama. By the late nineteenth century, the presence of johnsongrass was almost nationwide. Many reports testify to the severity of the problem caused by this weed in the late 1800's. Its pernicious nature led to the first Federal appropriation specifically for weed control in 1900, and to the first report on johnsongrass control, prepared by C. R. Ball in 1902.

The metabolism of 3′,4′-dichloropropionanilide (propanil) to 3,4-dichloroaniline (hereinafter referred to as 3,4-DCA) and N-(3,4-dichlorophenyl)glucosylamine (hereinafter referred to as 3,4-DCAG) was quantitatively modified in rice (Oryza sativa L. ‘Nato’) by temperature and day length. The propanil, 3,4-DCA, and 3,4-DCAG content of rice was determined 1, 2, 5, and 8 days after root treatment with 92 μM propanil. Plants were grown and treated under long-day (16 hr) and short-day (12 hr) conditions with day temperatures of 32, 27, or 21 C and night temperatures of 21 C. Absorption and metabolism of propanil were most rapid under high temperature and long day conditions. A mean value of 0.75 μmoles total of aniline equivalent per plant was obtained. Greater quantities of 3,4-DCA and 3,4-DCAG were recovered from plants in high temperature, long day environments. An average of 47% of the propanil plus water-soluble metabolites in rice was in root tissue. Conditions favoring high growth rates and transpiration increased the percentage in the shoots. Because of the increased tissue mass at high temperatures, mean concentrations of propanil plus water-soluble metabolites in plant tissue were reduced from 0.18 to 0.12 μmoles/g dry weight.

Wild buckwheat (Polygonum convolvulus L.), leafy spurge (Euphorbia esula L.), yellow foxtail [Setaria glauca (L.) Beauv.], and wild oat (Avena fatua L.) hydroxylated, in a 7-day period, 2 to 7% of the (2,4-dichlorophenoxy)acetic acid-1-14C (2,4-D-1-14C) absorbed. Only a trace of hydroxylation products was detected in wild mustard [Brassica kaber (DC.) L. C. Wheeler var. pinnatifida (Stokes) L. C. Wheeler], perennial sowthistle (Sonchus arvensis L.), and kochia [Kochia scoparia (L.) Roth]. The investigation was limited to hydroxylation on the para-position of the herbicide. The predominant product, 2,5-dichloro-4-hydroxyphenoxyacetic acid, was detected in all weed species studied. Also found in measurable amounts in some species were 2,3-dichloro-4-hydroxyphenoxyacetic acid and 2-chloro-4-hydroxyphenoxyacetic acid. The hydroxylation rate on the number four carbon of the ring did not account for the variation in susceptibility exhibited by these plants.

Foliar-spray and radioisotope herbicidal studies were conducted near Tucson, Arizona, to study factors influencing absorption, translocation and toxicity of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in creosotebush [Larrea tridentata (DC.)Cov.]. Maximum absorption and translocation of 14C-labeled 2,4,5-T occurred approximately 30 days after initiation of effective summer rains and coincided with maximum total killing of creosotebush. This occurred during the full-flowering to mid-fruiting stage of phenological development, overlapped the period of old leaf drop, and was due in part to the generally greater basipetal translocation of radioactive 2,4,5-T from old leaves, flowers, fruits, and young bark than from young leaves. Translocation of radioactive 2,4,5-T was relatively slow, 1 to 5 cm per hour, and basipetal movement ceased after 18 to 24 hr, following which the 2,4,5-T largely disappeared from the vascular tissues of the stem. Absorption of 2,4,5-T by the leaves was low during dormancy and may have limited herbicidal effects during this period, but it was not a factor during the season of high susceptibility.

The movement and adsorption of soil-applied 14C-labeled 2,4-bis(isopropylamino)-6-(methylthio-s-triazine (prometryne) and 1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea (fluometuron) in the presence of 0.01 and 0.5 N CaCl2 were studied. The soils were Ca++-saturated Eufaula loamy fine sand and Norge loam. In equilibrium adsorption studies, fluometuron adsorption was decreased and prometryne adsorption was increased by increasing the CaCl2 concentration from 0.01 to 0.5 N. The mobility of prometryne in the two water-saturated soils was decreased by an increase in CaCl2 concentration. Fluometuron mobility was unchanged by the two CaCl2 concentrations in Eufaula, but was greater in Norge at the higher CaCl2 concentration. The adsorption of each herbicide in the flowing system was less than that predicted by the distribution coefficient. Differences in CaCl2 concentration do not appear to influence the mobility of the two herbicides sufficiently at the soil-water flow rate used in this study to require changes in current field application practices.

The herbicide 4-amino-3,5,6-trichloropicolinic acid (picloram) was applied to several bermudagrasses (Cynodon spp.). Most of the grasses were susceptible to picloram; however, some were resistant and recovered within 16 months from the initial treatment. There were no detectable metabolites of 14C picloram in bermudagrass (C. dactylon (L.) Pers. ‘U-3’) or common Kentucky bluegrass (Poa pratensis L.). Also, there were no abnormal changes in cells of swollen nodes of picloram-treated bermudagrass that could explain the selective herbicidal injury of picloram on bermudagrass.

In greenhouse studies, magnesium-deficient tomato (Lycopersicon esculentum Mill.) plants were more susceptible to 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) than normal plants when grown under continuous light. Under a 12-hr photoperiod, magnesium-atrazine interactions were not significant. Magnesium deficiency and continuous light each caused reductions in chlorophyll content in tomatoes. A combination of these two conditions caused an additive reduction in chlorophyll content and also caused the greatest susceptibility to atrazine. The influence of magnesium on atrazine toxicity may be due to its effect on chlorophyll content rather than a direct effect on atrazine action.

Thirteen prominent species decreased 40% or more after applications of (2,4-dichlorophenoxy)acetic acid (2,4-D) at 2.2 kg/ha. Four of the “most-susceptible” species [gumweed (Grindelia squarrosa (Pursh) Dunal), fringed sagebrush (Artemisia frigida Willd.), drummond milk vetch (Astragalus drummondii Dougl. in Hook.), and hairy goldaster (Chrysopsis villosa (Pursh) Nutt.)] are considered undesirable and two of them [bluebells (Mertensia lanceolata (Pursh) A. DC.) and evening-primrose (Oenothera coronopifolia Torr. & Gray)] desirable. The other seven species of this group are quite unimportant for cattle. Therefore, spraying mixed-grass prairie with 2,4-D improves range condition and increases forage production.

The influence of mineral nutrition on the parasite-host relationship of witchweed (Striga lutea Lour.) and sorghum (Sorghum vulgare Pers. ‘Texas Bighead’) was investigated in greenhouse and growth chamber studies. Sorghum was grown in Eustis loamy sand, either infested or not infested with witchweed, and treated with one of three levels of mineral nutrients. Witchweed reduced host-shoot yields by about 70% at the low nutrient levels and by about 45% at the highest nutrient level. Witchweed produced seed at all nutrient levels, whereas the host produced seed at the highest level only. Increased nutrition also increased witchweed yields. Regardless of nutrient level, an early attack by witchweed was more destructive to the host than a late attack. Growth of witchweed in soil also was studied after the parasite was detached from the host or the host shoot was removed. When only the host shoot was removed, (a) witchweed growth was inhibited; (b) feeding of sucrose to witchweed did not restore parasite growth; (c) mineral nutrients were toxic to the parasite; and (d) high relative humidity around witchweed protected it from the nutrient toxicity. High relative humidity enhanced survival of the detached parasite but markedly inhibited growth of witchweed in the intact parasite-host relationship.

A reduction in soybean (Glycine max (L.) Merr.) yield of 25% (1968) to 30% (1969) resulted from one smooth pigweed (Amaranthus hybridus L.) per ft in 30-inch rows. A giant foxtail (Setaria faberii Herrm.) infestation of one plant per ft in 30-inch rows reduced yield 13% in 1969. Harvesting before weeds were desiccated resulted in significant threshing and separating losses as speed was increased from 1 to 2 and 3 mph. Stubble, lodging, and stalk losses were more than double in the pigweed and foxtail plots when compared to the weed-free plots after weeds were desiccated by frost.

Small field plots, 18 by 18 cm in size, were treated with S-(2,3,3-trichloroallyl)diisopropylthiolcarbamate (triallate) at rates equivalent to 2.8 kg/ha at five sites in Saskatchewan. After one growing season (5 months) the residues remaining in the 0 to 5 and 5 to 10-cm levels of soil were determined by gas chromatographic analysis. At all locations 16 to 27% of the applied herbicide was found in the top 5 cm while negligible residues were detected at the 5 to 10-cm level.

Nineteen herbicides in various formulations were tested preemergence and postemergence for control of western bracken (Pteridium aquilinum (L.) Kuhn var. pubescens Underw.). Excellent suppression was obtained for 1 year with fall applications of granular formulations of 2,6-dichlorobenzonitrile (dichlobenil) at 6.7 and 10.1 kg/ha, 4-amino-3,5,6-trichloropicolinic acid (picloram) at 2.2 kg/ha, and 3,6-dichloro-o-anisic acid (dicamba) at 4.5 to 9.0 kg/ha. Bracken recovered rapidly after 1 year of suppression by dichlobenil, but other herbaceous species were killed. Bracken recovered considerably the second growing season after application of picloram or dicamba, although morphological effects were noticeable for 2 to 3 years, particularly from dicamba. No visual injury to grasses was apparent from picloram. Some injury to orchardgrass (Dactylis glomerata L.) was noted from dicamba.

The adsorption of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) from aqueous solution by charcoal varied widely with the type of charcoal tested. However, adsorption in solution was directly related to the deactivating properties of the charcoals for the two herbicides in soil. Several charcoals deactivated residues of 0.3 ppmw of atrazine and 1.0 ppmw of diuron when they were present at concentrations of 30 to 50 ppmw in the soil. Activation of the charcoal was essential for the adsorption and deactivating properties. A simple laboratory test was developed for assessing activated charcoals for use in deactivation studies in soil.

Single topical applications of monosodium methanearsonate (MSMA) affected cotton (Gossypium hirsutum L.) growth more than did similar disodium methanearsonate (DSMA) applications. There was usually no difference in yield among rates and dates with single applications of DSMA. Single applications of MSMA at later dates and higher rates reduced yields. Repeated topical applications of MSMA reduced yields and affected boll weight, lint percentage, number of seed per boll, and fiber fineness as compared with these properties of cotton treated once with MSMA. Response of cotton to MSMA was related to the number of applications and rate of herbicide. Repeated applications of DSMA affected cotton yield, lint percentage, and number of seed per boll less than did MSMA.

Repeated postemergence treatments of 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), or 2-sec-butyl-4,6-dinitrophenol (dinoseb) can be applied to soybeans (Glycine max (L.) Merr.) without severe injury to the foliage throughout the growing season. However, multiple treatments of 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) resulted in more foliar injury early in the season than from similar treatments of chloroxuron, linuron, or dinoseb. Chlorotic veination appeared in the upper leaves of soybeans treated with prometryne late in the season, and injury was greater from multiple applications than from a single application. Chloroxuron and dinoseb resulted in stem injury which increased with repeated applications. Seed yields were lower from plots treated with repeated applications of prometryne compared with untreated plots or plots treated with a single application. Multiple applications of chloroxuron, linuron, or dinoseb did not affect seed yields. Soybean stands were significantly lower in 1 year from three or four applications of linuron and four applications of prometryne compared with fewer applications of each herbicide. Seed quality was best in dinoseb-treated plots and poorest in prometryne-treated plots regardless of the number of applications.

Field studies indicated that D(-) (3-chlorophenylcarbamoyloxy)-2N-isopropylpropionamide (RP-11755) at 3 lb/A controlled dodder (Cuscuta spp.) in alfalfa (Medicago sativa L.) as well as or better than the standard treatment, isopropyl m-chlorocarbanilate (chlorpropham) at 6 lb/A. Control from 2-sec-butyl-4,6-dinitrophenol (dinoseb) at 12 lb/A (amine or phenol form) sometimes was equal but never superior to that from chlorpropham. Greenhouse studies indicated that vapors toxic to dodder seedlings evolved from soil treated with dinoseb (amine or phenol form) but not from soil treated with RP-11755.

The fate of 2,4-dichlorophenyl p-nitrophenyl ether (nitrofen) in the foliage of rape (Brassica campestris L. ‘Echo’), redroot pigweed (Amaranthus retroflexus L.), and green foxtail (Setaria viridis (L.) Beauv.) was investigated with the aid of 14C-nitrofen. Only limited amounts of the label were translocated in these species. Plants treated with 14C-nitrofen under high light conditions produced several labelled compounds of different molecular size and chromatographic properties. The time at which these compounds were first detectable depended on light intensity. At least two of these compounds are lipid-nitrofen conjugates or nitrofen polymers and others may be formed by cleavage of nitrofen at the ether linkage.