Ten warm-season and seven cool-season weed species were grown in the glasshouse on Hartsells fine sandy loam taken from field plots that had been in long-term fertility studies. The soil pH was 5.9 and phosphorus (P) levels ranged from 8 to 95 kg/ha and the potassium (K) levels from 40 to 213 kg/ha. Growth response to P and K levels was measured by dry herbage yield. Redroot pigweed (Amaranthus retroflexus L.), jimsonweed (Datura stramonium L.), and Florida beggarweed [Desmodium tortuosum (Sw.) DC] were the most responsive warm-season weed species to P, whereas chickweed [Stellaria media (L.) Cyrillo] was the most responsive cool-season weed to P. Extreme P deficiency symptoms were evident on species giving a high response to P. P-deficient plants were severely stunted and exhibited a characteristic reddish-purple color. Showy crotalaria (Crotalaria spectabilis Roth), tall morningglory [Ipomoea purpurea (L.) Roth], sicklepod (Cassia obtusifolia L.), Carolina geranium (Geranium carolinianum L.), and coffee senna (Cassia occidentalis L.) were the most tolerant to low soil P. Redroot pigweed, jimsonweed, and Florida beggarweed were the most responsive warm-season weeds to K. Wild mustard [Brassica kaber (DC.) L.C. Wheeler var. Pinnatifida (Stokes) L.C. Wheeler] and annual bluegrass (Poa annua L.) were the most responsive cool-season weeds to K. Potassium deficiency symptoms were characterized primarily by severe stunting. Buckhorn plantain (Plantago lanceolata L.), Carolina geranium, and curly dock (Rumex crispus L.) were the most tolerant cool-season weeds to low soil K. Generally, weeds were more sensitive to low soil-test P than K.

The effects of common cocklebur (Xanthium pensylvanicum Wallr.) on soybean [Glycine max (L.) Merr.] yields, grades, and net returns were determined by regression analysis of data from 450 research plots from 1971 through 1973. Common cocklebur control from 0 to 100% was achieved by various combinations of preemergence and postemergence practices. Foreign matter in soybean seed samples was 0.7% with total common cocklebur control and 5.1% with no control. At least 70% control of common cocklebur was required to avoid deductions from gross harvested weights due to seed moisture levels exceeding 13%. Small discounts for damaged kernels occurred when common cocklebur control was less than 40%. With 100% common cocklebur control, the estimated US soybean grade was 1.3. Failure to control common cocklebur resulted in a predicted grade of 3.9. When adjusted for various weight discounts, soybean yields were 1170 kg/ha without control of common cocklebur and 1890 kg/ha for 100% control. Soybean yields were increased about 6% for each 10% increase in common cocklebur control. Net returns to land, management, and general farm overhead were $63/ha when common cocklebur was not controlled, and $119/ha with 95% control.

Two incorporation methods were used in applying eight dinitroaniline herbicides before planting cotton (Gossypium hirsutum L.) for 3 yr. Penoxalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] gave the best stands of cotton. Nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] and dinitramine (N4,N4-diethyl-a,a,a-trifluoro-3,5-dinitrotoluene-2,4-diamine) resulted in the poorest stands. In 2 of 3 yr, cotton stands were better where herbicides were incorporated by listing only rather than by disking before listing. The eight herbicides were equally effective in annual grass control when followed by postemergence applications of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. An-56477 [N,N-bis(2-chloroethyl)-4-methyl-2,6-dinitrobenzenamine] was least effective in controlling annual broadleaf weeds. In 1972, cotton yield was reduced when An-56477 was incorporated by disking. In the average cotton yields for six tests, An-56477 produced significantly lower yields than any other herbicide except butralin [4-(1,1-dimethylethyl-N-(1-methylpropyl)-2,6-dinitrobenzenamine]. No differences in cotton fiber properties or boll components were due to herbicides or method of application.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 1.1 and 2.2 kg/ha and paraquat + dinoseb (2-sec-butyl-4,6-dinitrophenol) at 1.1 + 0.7 kg/ha controlled redroot pigweed (Amaranthus retroflexus L.) and barnyardgrass [Echinochloa crus-galli (L.) Beauv.] in hops (Humulus lupulus L. ‘Yakima Cluster’) without reducing hop yield or the alpha and beta acid content of the hop cones. Three applications at about 3-week intervals were required to control weeds until harvest. Two applications controlled hop sucker growth. Paraquat at more than 0.6 kg/ha in the third application caused excessive reduction in hop sucker growth.

Spurred anoda [Anoda cristata (L.) Schlect.] seed germination averaged 0.5 to 3.0% for seeds buried in the field for up to 20 months under natural conditions. These same seeds averaged over 76% germination after scarification with concentrated sulfuric acid, indicating hard seed coat involvement in seed dormancy. Germination was unaffected by light variables but increased as temperature increased. Germination of scarified seed increased from 50% to 85% as temperature was increased from 18 C to 30 C. Spurred anoda developed more slowly than did cotton (Gossypium hirsutum L. ‘Coker 310′) for the first 45 days. After that spurred anoda grew more rapidly until by 60 days after emergence, the weed was larger than cotton as measured by shoot height and total leaf surface area. This difference in development between cotton and spurred anoda indicates postemergence directed sprays of herbicides might be useful as a control tool.

Six-week-old honey mesquite [Prosopis glandulosa (Torr.) var. glandulosa] seedlings were treated with various concentrations of ethephon (2-chloroethylphosphonic acid) and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] alone and in combinations to determine effect on stem mortality under greenhouse conditions. Ethephon alone at 0.05 g/L brought about defoliation and a reduction in xylem tissue formation but did not affect the histological development of the stem tissue. Treatment with 2,4,5-T alone at 3.2 g/L resulted in 40% stem mortality along with the formation of abnormal xylem tissue of reduced thickness. A combination of ethephon (0.05 g/L) and 2,4,5-T (3.2 g/L) significantly increased mesquite mortality. This was associated with a further reduction in xylem thickness, abnormal development of the xylem, abnormal positional relationships of vascular tissues, and initiation of adventitious roots. This study showed that ethephon in combination with 2,4,5-T was more effective than either treatment alone in promoting the disruption of the tissue systems of the stem and in increasing control of mesquite seedlings.

In greenhouse studies, Cyperus esculentus L. var. esculentus was less susceptible than C. esculentus L. var. leptostachyus Boeck. to preplant applications of 1.77 kg/ha of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] or 0.5 kg/ha of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5-(4H)one]. C. var. esculentus was more susceptible than C. var. leptostachyus to postemergence applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid] oil-soluble amine. C. var. esculentus had longer, slightly narrower, and more upright leaves; generally fewer but larger tubers; fewer rhizomes; and a lower frequency of flowers with less seeds per inflorescence than C. var. leptostachyus. Publications on C. esculentus should specify which variety was used.

Asulam (methyl sulfanilylcarbamate) at 3.3 or 4.5 kg/ha gave 54% and 61% control, respectively, when applied only to the initial infestation of rhizomatous johnsongrass [Sorghum halepense (L.) Pers.] in sugarcane (Saccharum interspecific hybrids). When applied both to the initial infestation and to the regrowth, 81% and 88% control, respectively, were obtained. Both the single and dual asulam treatments produced yields of sugar that were about double the yield of an untreated check and about 90% of the yield of a hand-weeded check. Sugarcane cultivars ‘CP 52-68′, ‘CP 65-357′, ‘CP 61-37′, and ‘L 62-96’ were highly tolerant to single applications of asulam at 4.5 and 6.7 kg/ha and to dual applications of asulam at 3.4 kg/ha. Some cultivars were moderately injured by dual applications of asulam at 4.5 kg/ha.

Maximum activity of isocitric lyase (EC 4.1.3.1) was reached at 24 hr incubation of afterripened (nondormant) prickly sida (Sida spinosa L.) seed. Enzyme activity declined gradually with incubation times in excess of 24 hr. Actinomycin D (Act D) at 5 μg/ml had essentially no effect on 24-hr germination but inhibited development of isocitric lyase activity 83%. Cycloheximide (CH) at 10 μg/ml inhibited 24-hr germination of punctured seed only 7% but inhibited development of isocitric lyase activity 76%. Seed incubated in water 12 hr before being transferred to Act D at 5 μg/ml for an additional 12 hr did not escape sensitivity to the antibiotic. Isocitric lyase activity was inhibited when assayed at 24 hr total incubation. In the reverse experiment, seed incubated in Act D 12 hr before being transferred to water, isocitric lyase activity at 24 hr was not affected. Apparently prickly sida seed lacked a performed mRNA for isocitric lyase and transcription and translation of the mRNA occurred shortly after initiation of radicle protrusion (~8 hr).

Soil-incorporated treatments of dichlobenil (2,6-dichlorobenzonitrile) at 4.5 or 9 kg/ha completely controlled field horsetail (Equisetum arvense L.) for 2 yr and at 9 kg/ha, control was 90 to 99% in the third year. Mulching with sawdust after surface application of dichlobenil gave similar results. In an area treated at 9 kg/ha and isolated from emerged field horsetail, there was no reappearance of field horsetail until 5.5 yr after treatment. Japanese holly (Ilex crenata Thunb.) and azalea (Rhododendron X ‘Rosebud’) planted a year after treatment made as much growth in treated as in adjacent untreated soil. Douglas fir seedlings [Pseudotsuga menziesii (Mirb.) Franco] made as much growth in treated as in untreated soil only when planted 2 yr after treatment. Strawberry (Fragaria X ‘Northwest’) plants made approximately 80% as much top growth in treated as in untreated soil when planted 2 yr after herbicide application.

In at least three metabolic processes in wheat (Triticum aestivum L. var. ‘Arthur’) shoots inhibitory activity can be related to the chemical structure of substituted pyridazinones. Inhibitory activities include: inhibition of the Hill reaction and photosynthetic CO2 fixation; inhibition of carotenoid biosynthesis accompanied by photodestruction of chlorophyll; and interference with the formation of chloroplast membrane polar lipids. The parent compound, pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], inhibits the Hill reaction and photosynthetic CO2 fixation. Trifluoromethyl substitution of the phenyl ring of pyrazon, mono-methyl substitution of the amine, or substitutions at both positions result in inhibition of carotenoid biosynthesis. However, both substitutions are required for maximum effect. Substitutions onto the molecular structure of pyrazon are also related to alterations in the formation of membrane polar lipids. Dimethyl substitution of the amine of pyrazon is related to a decrease in linolenic acid accompanied by an increase in linoleic acid without a shift in the relative proportion of saturated to unsaturated fatty acids of the membrane lipids. The trifluoromethyl substitution of the phenyl ring and mono-methyl substitution of the amine are related to a shift toward a higher proportion of saturated fatty acids of chloroplast membrane lipids. Results obtained with diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and with dark-grown wheat tissue indicated that activity of the pyridazinones on the formation of membrane lipids was probably not related to inhibition of the Hill reaction.

Three preemergence and four postemergence herbicides were compared for control of prickly sida (Sida spinosa L.) in soybeans (Glycine max Merrill) and for level of phytotoxicity to soybeans. As a preemergence herbicide, chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxyl-1-methylurea] provided better control of prickly sida than did linuron [3-(3,4-dichlorophenyl)-1-methoxyl-1-methylurea] which was more consistently effective than was naptalam (N-1-naphthylphthalamic acid) plus dinoseb (2-sec-butyl-4,6-dinitrophenol). Chlorbromuron applied as a preemergence treatment caused slight crop injury. In most cases preemergence treatments followed by cultivation were effective in providing season-long control. The descending order of effectiveness for prickly sida control by the postemergence herbicides was: chlorbromuron metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] > prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] > dinoseb. Prometryne as a postemergence treatment following a preemergence herbicide increased prickly sida control more consistently than dinoseb used as the postemergence treatment. However, prometryne caused more crop injury than did dinoseb.

Comparison of soybean yields from the weedy and weed free checks show that prickly sida caused only 9 to 14% yield losses in soybeans.

Fall panicum (Panicum dichotomiflorum Michx.) and witchgrass (Panicum capillare L.) emerged in naturally infested fields as early as April 30 and May 14, respectively. The shortest period between seeding and emergence was during the warmest period of the growing season. The number of days from emergence to heading decreased progressively for later seedings. After emergence witchgrass formed seedheads about 7 days earlier than fall panicum. Fall panicum emerging in the middle of July and witchgrass seedlings emerging July 25 produced mature seeds in the fall, shaded or not. Plant height, tiller number, and yield of both grasses were highest for plants emerging in May and June. Decreased light intensity delayed seed emergence, heading, and maturity of both grasses. Plant height, yields, number of tillers, and number of panicles also were decreased by shading. Fall panicum was a coarser plant than witchgrass and produced more tillers and panicles than witchgrass. Fall panicum and witchgrass seedlings emerging between June 23 and July 7 produced the most vigorous fast growing plants.

A mixture of diquat [6,7-dihydrodipyrido(1,2-α: 2′,1′-c) pyrazinediium ion] and copper sulfate pentahydrate was applied to artificial chinook salmon (Onchorhynchus tshawytscha Wal.) spawning channels to reduce excessive growths of algae [Cladophora glomerata (L.) Kutz]. Juvenile salmon were not harmed by the applications. A concentration of 100 ppb w/w diquat plus 150 ppb copper-ion was maintained for 3 hr. The alga was controlled satisfactorily for distances up to 0.5 km per treatment. Each treatment consisted of one to three applications, each made on consecutive days. Water temperature was 11.2 C during three winter applications and 15.5 C during a spring application. Diquat was rapidly sorbed out of the treated water to 3.8 ppb at 1.6 km. Copper-ion residues dissipated to 60 ppb at 1.6 km.

The tolerance of bermudagrasses ‘Tifway’, ‘Tifgreen’, ‘Tifdwarf’, ‘Ormond’, and ‘Floraturf’ [Cynodon dactylon (L.) Pers.] cultivars to repeated annual applications of oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] and butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] were evaluated over a 4-yr period. Oxadiazon treatments did not affect growth characteristics of these bermudagrasses. Butralin caused moderate to severe reduction in sod density. ‘Tifway’, ‘Ormond’, and ‘Floraturf’ were more tolerant to butralin than ‘Tifgreen’ and ‘Tifdwarf’.

A weevil [Rhinocyllus conicus (Froelich)] host specific to Carduus, Cirsium, Silybum, and Onopordum, was introduced into Gallatin County, Montana, for biocontrol of musk thistle (Carduus nutans L.). Releases were made in 1969, 1971, 1972, and 1973 on local musk thistle infestations. The insects became established and overwintered successfully. In 1974, R. conicus was found over a 1,280-km2 area of the county in seed heads of musk thistle. Weevil larvae severely infected the primary flowers, but only a few secondary and later flowers were attacked. Seed production from infected primary flowers was greatly reduced, and other factors influenced reduction of seeds from secondary and later flowers.

The movement and persistence of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and its degradation product, 3,4-DCA (3,4-dichloraniline) were studied in an orchard soil which had received diuron annually at the rate of 4.5 kg/ha for 7 yr. Accumulation of residues was not observed at significant levels although carry-over of the herbicide occurred between years. The bulk of the herbicide residue was confined to the upper 15 cm of soil. The degradation rate of diuron generally followed first-order kinetics and the residual levels of diuron in the soil were highly phytotoxic to oat (Avena sativa L.) plants during the 3 yr after the last application. The levels of 3,4-DCA were low in all soil samples (< 21 ppb) and its relative distribution in the soil profile was similar to that of diuron.

Growth chamber studies showed crabgrass [Digitaria sanguinalis (L.) Scop.] to be more tolerant than witchgrass (Panicum capillare L.) to simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Both grasses were more susceptible to simazine than to atrazine. The s-triazines were taken up by both weed species in equal quantities, but witchgrass translocated larger amounts of simazine and atrazine to the shoots. The greater sensitivity of witchgrass to simazine appeared to be due to the increased translocation of unchanged simazine to the shoots. Greater sensitivity of witchgrass to atrazine was attributed to increased translocation of atrazine to the shoots and less metabolism of the s-triazine to hydrophilic metabolites. It was concluded that the hydrophilic metabolites were the peptide conjugates formed by the enzyme glutathione-S-transferase.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] applied preemergence resulted in increased phytotoxicity with increasing soil pH. In the field, fall panicum (Panicum dichotomiflorum Michx.) control, number of dead corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] plants, and crop injury ratings increased, and plant height and grain yield decreased as the soil pH increased. In the greenhouse, corn and soybean grown in soil showed decreased dry weights due to metribuzin as pH increased. By contrast, the pH response to metribuzin was not evident in nutrient-sand culture, indicating that, in soil, pH affected the availability of metribuzin for plant absorption.

A clean-up procedure for soil and plant samples utilizing a non-ionic exchange resin column followed by treatment with lead acetate was developed for determining microgram quantities of hexaflurate (potassium hexafluoroarsenate) spectrophotometrically. The method is sensitive to 0.45 ppm with a standard deviation of 0.09 ppm with a recovery of better than 85%. Samples high in organic matter require this treatment to remove interfering substances. Soil samples containing little or no organic matter could be analyzed by using either the lead acetate treatment or the non-ionic exchange resin column. Soil and plant samples analyzed 5 to 7 yr following treatment of south Texas soils for pricklypear (Opuntia spp.) control were found to contain trace quantities of hexaflurate. Downward movement of hexaflurate is either very slow or plants continually assimilate the ion and redeposit it on the soil surface through decomposition of plant parts. The tri- and pent-oxide forms of arsenic did not interfere with analysis of the hexaflurate ion using the clean-up procedure.