Freshly-harvested seeds of several common weeds showed little or no promotion of germination by light. However, after burial for 6 months, germination becomes entirely dependent on exposure to light. Red light promoted the germination of the buried seeds, and this promotion was reversed by far-red light, indicating phytochrome involvement. Freshly-harvested seeds were made light-requiring by treatment with mannitol. The germination of these light-requiring seeds was promoted by red light, gibberellic acid (GA), acetylcholine (ACh), and adenosine 3′,5′-monophosphate (cyclic AMP). The phytochrome response may trigger ACh synthesis which causes the release of GA from a bound form and/or GA synthesis which enhances the production of cyclic AMP which initiates the germination response.

Fall panicum (Panicum dichotomiflorum Michx.) and Texas panicum (Panicum texanum Buckl.) were grown in the greenhouse under flooding treatments of 0, 6, and 9 days in 10 for 1 month. Fall panicum was more tolerant of flooded soil than was Texas panicum. Root development of Texas panicum was reduced by 50% under all flooding treatments. Herbage and root growth of fall panicum with flooding was similar to that on well-drained soil. Fall panicum root diameter was greater than that of Texas panicum, but both species increased under flooding. Tolerance of fall panicum to flooding may partially explain why it competes so well with crop plants during wet periods.

The absorption and translocation of 14C-labeled α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) and 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione methazole from nutrient solutions of various temperatures by (Arachis hypogaea L. ‘Starr’) seedlings were determined. The accumulation of trifluralin in roots at 24 hr after exposure to trifluralin was greatest at 21 C and decreased at higher temperatures up to 38 C. The amounts of trifluralin translocated and accumulated in hypocotyls, tops, and cotyledons were small but generally increased with temperature. The initial rate of absorption of trifluralin was greater in excised lateral root tips than in tap root tips, but there was a greater accumulation in excised tap roots at 24 hr. The initial rates of absorption were higher for excised lateral roots at high temperatures. Total absorption of trifluralin at equilibrium was not proportional to the initial rates of absorption but was highest at low (21 C) and high (38 C) temperatures for excised lateral roots. The absorption of methazole by roots and translocation to other plant parts increased linearly with temperature, and it tended to accumulate in the mature leaf tissue.

Hawaiian sugarcane cultivars (Saccharum L. hybrids) differed considerably in their tolerance to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). There was a greater concentration of diuron in the younger leaves of a sensitive cultivar, ‘H 53–263,’ compared with a tolerant cultivar, ‘H 50–7209′; degradation of diuron was more extensive in ‘H 50–7209′. The metabolites identified after applications of carbonyl-labeled diuron to the root system were 1-(3,4-dichlorophenyl)-3-methylurea (monomethyl-diuron) and 1-(3,4-dichlorophenyl)urea (demethylated diuron). Differences in diuron phytotoxicity to cultivars ‘H 53–263’ and ‘H 50–7209’ are at least partially explained by differences in the distribution and degradation of diuron.

Herbicides and mechanical methods of weed control were tested on 1 and 2-year-old peach trees (Prunus persica (L.) Batsch) on two soil types and locations. Several herbicide methods gave season-long weed control without detriment to growth or yield of peach trees. In general, a cultural system where herbicides were used in rows and 8-ft sodded strips maintained in row middles did not decrease the growth or yield of trees when compared to overall mechanical methods of weed control.

The theme for our meetings this year is “A Positive Concern for Society.” It is in this context that I will talk about “Weed Science in Perspective.” In doing so, we need to consider where we are, where we have been, and where we are going.

In field studies combinations of herbicides applied preplant, preemergence, or postemergence were compared for control of prickly sida (Sida spinosa L.) in cotton (Gossypium hirsutum L. ‘Stoneville 7A’). All plots received an application of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) incorporated into the soil prior to planting. Additional preemergence applications increased control of prickly sida 94% with 1,1-dimethyl-3-α,α,α-trifluoro-m-tolyl)urea (fluometuron) and 53% with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). Seven postemergence treatments evaluated were at least partially effective in controlling prickly sida. However, trifluralin applied preplant followed by fluometuron applied preemergence gave the most effective prickly sida control in combination with all post-emergence treatments. Prickly sida populations of 130 plants per square meter competed with cotton all season and reduced yield 41 and 37% in 1969 and 1970, respectively. Prickly sida did not appear to affect cotton grade or staple length.

Preplanting treatment of filter paper or soil containing α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) with any of a wide variety of plant lipids prevented the phytotoxic action of the herbicide in laboratory situations. The protective action of externally applied lipids was attributed to preventing sorption of trifluralin by seedlings. However, protection by internal lipids also appeared likely. A significant correlation (1% level) was demonstrated between seedling sensitivity to trifluralin and the lipid content of dry seeds of 11 weed and crop species. Artificially induced increases in the internal lipid content of wheat (Triticum aestivum L. ‘Mediterranean’) seed resulted in greater tolerance of seedlings to trifluralin. Therefore, it is hypothesized that selective phytotoxicity of trifluralin to young seedlings is determined in part by the amount of endogenous lipids available to trap trifluralin and keep it from its site of phytotoxic action. Tolerance above that predicted from seed lipid content was observed in a twelfth species of the study.

Growth chamber studies were conducted to determine the influence of several pretreatment radiation, humidity, and temperature regimes on the response of peas (Pisum sativum L. ‘Alaska’) and velvetleaf (Abutilon theophrasti Medic.) to foliarly-applied (2,4-dichlorophenoxy)acetic acid (2,4-D). Under the conditions of these studies, growing peas under solar or fluorescent-incandescent lamp radiation, in high or low humidity, or in temperatures between 10 and 25 C prior to treatment did not influence their response to 2,4-D. The response of velvetleaf to 2,4-D was slightly greater when pretreatment growth was under solar radiation rather than under fluorescent-incandescent lamps. Similarly, high pretreatment humidities and temperatures produced slightly greater responses to 2,4-D in velvetleaf than low pretreatment humidities and temperatures. Herbicide uptake and translocation were greater when pretreatment pea growth was under solar radiation, but spray retention and rate of 2,4-D metabolism were not affected by pretreatment radiation. This study indicates that pretreatment light, temperature, and humidity conditions play only a minor role in determining the response of peas and velvetleaf to 2,4-D.

Soybean (Glycine max (L.) Merr., ‘Hawkeye 63′) seedling segments from the zone of elongation and corn (Zea mays L., ‘Pioneer 3306) seedling segments were utilized to evaluate the antagonistic interaction of S-ethyl dipropylthiocarbamate (EPTC) and (2,4-dichlorophenoxy)-acetic acid (2,4-D). EPTC inhibited growth of the soybean and corn tissue, and 2,4-D in combination with EPTC caused an increase in growth compared to EPTC alone. The 2,4-D-enhanced growth in the presence of EPTC was due to an antagonism of the EPTC inhibition. Inhibition of soybean tissue growth by S-ethyl diisobutylthiocarbamate (butylate) also was antagonized by 2,4-D. Preincubation of soybean tissue in EPTC for 4 hr prior to the addition of 2,4-D did not prevent 2,4-D enhancement of growth. Conversely, the rate of growth was inhibited when EPTC was added after 4 hr of 2,4-D-enhanced growth. The addition of uridine to the incubation media with EPTC did not decrease the EPTC-inhibition of soybean tissue growth. This indicated that EPTC did not inhibit the synthesis of pyrimidine precursors. EPTC vapor losses from the incubation media reduced the inhibitory effect of EPTC to soybean tissue. Also, a growth reduction occurred when the amount of soybean tissue per unit of EPTC was increased.

Many speakers preface their remarks to a group such as this with the statement, “I am most happy to be here, and have the opportunity to discuss with you…”. I have deliberately avoided that opening remark in most talks, but in this case that bit of rhetoric is appropriate. I am indeed most happy to once again address that professional society with which I have been most closely and most happily associated.

Reserve carbohydrates of Dalmatian toadflax (Linaria dalmatica (L.) Mill.) in eastern Washington were at their highest levels in autumn at the end of the growing season, and the lowest point occurred at the beginning of flowering about June 15. A one-time removal of first-year floral stems (June 11, 1964) did not significantly lower reserve carbohydrates when measured in September, but similar clipping of floral stems the second year (June 16, 1965) did cause a significant reduction. Reserves were reduced by 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) at 1.12 or 1.68 kg/ha but were not reduced by 4-amino-3,5,6-trichloropicolinic acid (picloram) at the same rates. Combinations of equal weights of the two herbicides to total 1.12 or 1.68 kg/ha caused a significant reduction in reserve carbohydrates. The combinations of silvex and picloram appeared to have an additive toxic effect, but the reduction of reserve carbohydrates was no greater than that caused by silvex alone at 1.12 or 1.68 kg/ha. Lethal action of the herbicides did not appear to be caused by reserve carbohydrate depletion. Glucose and fructose were the major reducing sugars detected in chromatographic analysis.

The competitiveness of 10 soybean [Glycine max (L.) Merr.] cultivars to weeds, their tolerance to twice normal rates of commonly used soybean herbicides, and the soil residual properties of these herbicides were studied during 4 years at Lincoln, Nebraska. Three soybean cultivars showing the least percentage yield loss from weeds were ‘Harosoy 63′, ‘Amsoy’, and ‘Corsoy’; whereas cultivars showing the greatest yield loss were ‘Hawkeye 63′, ‘Shelby’, and ‘Lindarin 63′. The two herbicide treatments causing the greatest average soybean yield loss were 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) at 4.5 kg/ha and α,α,α-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 2.2 kg/ha. Cultivar selection was important in reducing soybean yield loss from herbicides as linuron at 4.5 kg/ha reduced yields 5% for ‘Harosoy 63’ to as much as 31% for ‘Ford’. ‘Neal’ oat (Avena saliva L.) yields showed 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) to be the most persistent herbicide in soil in this study followed by trifluralin. Plowing the soil eliminated the phytotoxicity of nitralin and trifluralin to subsequently planted oats.

A liquid scintillation counting solution was developed which optimized the direct assay efficiencies of 14C-labeled 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3,6-dichloro-o-anisic acid (dicamba), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) in soil. In this counting technique, 3-g soil samples containing 14C-labeled herbicide were placed directly into a liquid scintillation vial containing a phosphorescent counting solution. Samples were shaken and allowed to settle before assaying using a liquid scintillation spectrometer. This direct radioassay was as efficient or more efficient than double or single extraction processes. Automatic external standardization in conjunction with the liquid scintillation counter was an effective tool for estimating the 14C present in soil samples.

Three-day-old soybean (Glycine max (L.) Merr., ‘Hawkeye 63′) hypocotyl segments (0.5 to 1.5 cm below the cotyledons) were utilized to evaluate the effects of the antagonistic interaction of S-ethyl dipropylthiocarbamate (EPTC) and (2,4-dichlorophenoxy)acetic acid (2,4-D) on growth and nucleic acid synthesis. EPTC inhibited growth and RNA synthesis in soybean tissue. The addition of 2,4-D with EPTC was antagonistic to EPTC inhibition of growth and caused an increase in total RNA synthesis. Analysis of soybean tissue nucleic acids by methylated-albumin-kieselguhr(MAK) column chromatography showed that EPTC inhibited ribosomal-RNA (r-RNA), DNA like RNA (D-RNA), and tenaciously-bound-RNA (TB-RNA) synthesis. The combination of 2,4-D with EPTC caused an increase in D-RNA and TB-RNA synthesis compared to the EPTC treatment alone. The 2,4-D-enhanced synthesis of D-RNA and TB-RNA in the presence of EPTC appears to be the basis of the antagonism between EPTC and 2,4-D. Preliminary analysis of r-RNA indicated that EPTC preferentially inhibited the synthesis of 18S r-RNA more than 25S r-RNA and that 2,4-D had no effect on this selective inhibition.

When almost no broadleaf weeds were present, 0.56 kg/ha of the butoxyethanol ester and 0.84 kg/ha of the dimethylamine salt of 4-(2,4-dichlorophenoxy)butyric acid (2, 4-DB) caused no yield reductions of seedling alfalfa (Medicago sativa L.); but 0.56 kg/ha of 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) caused slight reductions. Rates of bromoxynil above 0.56 kg/ha caused significant yield reductions of alfalfa. Broadleaf weeds, when present, shielded alfalfa from the bromoxynil so that reduction in yields of broadleaf weeds and increases in alfalfa were similar to those obtained with 2,4-DB. At equivalent rates 3,5-dichloro-4-hydroxybenzonitrile (hereinafter referred to as chloroxynil) was less effective than bromoxynil for controlling broadleaf weeds and also was less injurious to alfalfa. When no weeds were present at time of application, bromoxynil at a rate of 0.56 kg/ha or greater and chloroxynil at 0.84 and 1.12 kg/ha significantly reduced yields of red clover (Trifolium pratense L.). When weeds were present bromoxynil did not reduce yields of red clover until the 1.12-kg rate was reached. Chloroxynil did not reduce yields at rates as high as 1.12 kg/ha. Excellent control of common lambsquarter (Chenopodium album L.) and common ragweed (Ambrosia artemisiifolia L.) was obtained, and no reduction in alfalfa or red clover occurred with 0.28 kg/ha of bromoxynil or chloroxynil mixed with 0.56 kg/ha of 2,4-DB ester.

The response of close-spaced, pickling cucumbers (Cucumis sativus L.) to preplant incorporation treatments of O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide (bensulide), N-butyl-N-ethyl α,α,α-trifluoro-2,6-dinitro-p-toluidine (benefin), and dimethyl tetrachloroterephthalate (DCPA) and preemergence applications of 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) and the methyl ester of 3-amino-2,5-dichlorobenzoic acid (chloramben) has been evaluated over a 2-year period. DCPA and nitralin gave the best overall weed control, while benefin and the methyl ester of chloramben were less effective in controlling weeds. The poorest weed control performance was observed with bensulide. Nitralin, DCPA, benefin, and the methyl ester of chloramben caused crop injury if leaching rains followed application. Despite early herbicide injury, yields were usually not adversely affected.

When the topic of this talk was first discussed, it was suggested that I might deal with developments in weed science outside the USA, but one had only to pause for a moment to realise that this was a hopelessly vast topic which could not usefully be dealt with in one presentation. I had, therefore, to choose between discussing the advances occurring in the more developed territories such as Europe and Japan and the advances or lack of advance in the less developed countries. It was natural enough for me to narrow my discussion to the developing countries, not only because of my personal experience in this sphere, but also because I believe there is a great deal to consider in this context which is of relevance to the theme for today, namely “a positive concern for society”.

Shoot apices of 7-day old foxtail millet (Setaria italica (L) Beauv.) seedlings treated with 2 and 20 mg/L of dimethyltetrachloroterephthalate (DCPA) were examined under the electron microscope. Cell division is interrupted. The nucleus and nucleolus do not disintegrate and chromosomes do not differentiate. Instead, giant nuclei and giant nucleoli occupy most of the cell volume in the meristematic regions. Several nucleolar caps form on the giant nucleolus; and in the advanced stages, they separate and are encircled by a nuclear membrane to form multiple nuclei. Other organelles are also affected. Cristae and thylakoid membranes of mitochondria and chloroplasts degenerate and multiple vacuoles form. Cell walls are markedly more osmophilic after DCPA treatment. Treated cells are less turgid than controls.

Foxtail millet [Setaria italica (L.) Beauv. ‘Empire’] and proso millet (Panicum miliaceum L. ‘White’) seedlings were grown in glass units to expose selectively either roots or shoots to vapors arising from soil containing a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin). The root and shoot growth of both species was inhibited by trifluralin vapors. Suppression of root and shoot growth increased as trifluralin application rates increased. In shoot exposure, vapors arising from soil treated with 5 ppmw of trifluralin were lethal to seedlings of both species. In root exposure, root growth of both species was severely suppressed at 20 ppmw, but shoot growth was unaffected. Phytotoxic effects resulting from a given concentration of trifluralin were more severe as greater carrier volumes were used for application. Trifluralin vapors arising from soil 16 to 22 days after treatment were still sufficient to cause shoot growth inhibition.