Soil incorporated into the tuber zone of purple nutsedge (Cyperus rotundus L.) at 1 to 9 kg/ha, O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide (bensulide) inhibited the growth of roots on plants developing from these tubers. The inhibitory effect was temporary and occurred only when bensulide was in intimate contact with the tubers and developing plants. When tubers were removed from bensulide-treated soil, washed, and replanted in untreated soil, root growth was normal. The production of shoots from tubers planted in bensulide-treated soil apparently was not affected, but shoot-growth was retarded when root growth was suppressed. When bensulide was incorporated into the upper 5-cm layer of soil, the shoots of nutsedge plants developing from tubers located below this layer grew through the treated soil with no adverse effect; the roots of these plants developed from basal bulbs below the layer of treated soil and were normal. Leaching bensulide-treated soil with 37.6 hectare-cm of water did not move enough bensulide into the soil to cause inhibitory growth effects on purple nutsedge.

Under Texas conditions, the potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram) usually was more effective than the isooctyl ester formulation for control of live oak (Quercus virginiana Mill.), yaupon (Ilex vomitoria Ait.), winged elm (Ulmus alata Michx.), huisache (Acacia farnesiana (L.) Willd.), and honey mesquite (Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell). Possible reasons for the difference in effectiveness of picloram formulations were studied in the laboratory. Extensive degradation of the ester of picloram (96%) occurred in open Petri dishes after 72 hr exposure to ultraviolet (uv) light, compared to a loss of 26% for the salt of picloram. Forty-five percent of the isooctyl ester of picloram was lost at high temperatures (60 C), whereas only 2% of the potassium salt of picloram was lost after 1 week at 60 C from open Petri dishes in a dark oven. Application of the ester to soils reduced thermal and ultraviolet light degradation losses compared to losses from open Petri dishes. Loss of the ester was greater when applied in diesel oil to Petri dishes than in either water or paraffin oil. The salt of picloram leached most after 12.5 cm simulated rainfall in soil columns to the 17.5 to 30-cm level (907 μg), followed by the acid (360 μg), and last the isooctyl ester (0 μg). However, considerable acid (161 μg) was recovered at the 32.5 to 45-cm depth from the isooctyl ester treatment exposed to wet soils for 3 days, indicating hydrolysis of the ester to acid.

Plants of curly dock (Rumex crispus L.) were subjected to soil temperatures of 10, 15, 26, and 35 C in a growth chamber. A soil temperature of 10 C was most favorable for root growth and production of large seeds. The highest yields of seeds and fruit were obtained at 26 C. Significant reductions in seed and fruit production, wt per 100 seeds, plant height, and growth rate occurred at 35 C. The total germination of mature seeds was not affected by soil temperature, but the seeds ripened at 26 and 35 C germinated faster than those from the 10 and 15 C treatments.

Plant litter that covers the soil surface acts as a layer of insulation moderating temperature and moisture, and creating favorable microsites for germination and the establishment of annual weed species in rangeland communities. Litter cover is an important factor in succession among annual species which culminates in dominance by downy brome (Bromus tectorum L.) and medusahead (Taeniatherum asperum (Sim.) Nevski) in these communities.

Better field bindweed (Convolvulus arvensis L.) control was obtained from granular formulations of 2,3,6-trichlorobenzyloxypropanol (hereinafter referred to as HRS 587), 4-amino-3,5,6-trichloropicolinic acid (picloram), (2,3,6-trichlorophenyl)acetic acid (fenac), and 2,3,6-trichlorobenzoic acid (2,3,6-TBA) than with equivalent amounts of liquid formulations. Two years after application, a granular formulation of picloram at 1 lb/A was as effective as a liquid formulation at 3 lb/A. One and 2 years after application, granular formulations of HRS 587, fenac and 2,3,6-TBA at 10 lb/A gave field bindweed control equal to that obtained with 20 lb/A of liquid formulations of these chemicals. Incorporation did not greatly affect the toxicity of either the liquid or granular formulations of the four herbicides. Increased effectiveness of granular formulations appeared to be associated with longer persistence in the soil.

Thirty variously substituted benzonitriles and derivatives applied at equimolar exponential rates were evaluated for their phytotoxic properties in nutrient solution. The order of activity of the variously substituted benzonitriles and derivatives was dissimilar to the benzoic acids and phenoxyalkylcarboxylic acids. Several of the materials evaluated were as active as, or more active than 2,6-dichlorobenzonitrile [dichlobenil]; namely, the 2,6-dibromobenzonitrile, 2,6-dichloro-β-benzaldoximeacetate, 2-bromo-6-chlorobenzonitrile, 2,3,4-trichlorobenzonitrile, and 2,3,5-trichlorobenzonitrile.

Preplanting application of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), reduced the number of monosodium methanearsonate (MSMA) applications needed for the control of johnsongrass (Sorghum halepense (L.) Pers.). The combined effect enabled weed control to be completed before cotton (Gossypium hirsutum L.) began to bloom, and hence without causing damage to the crop.

Addition of ammonium nitrate greatly increased the absorption of solutions of the isooctyl ester of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) by sweetgum (Liquidambar styraciflua L.), post oak (Quercus stellata Wangenh.), red maple (Acer rubrum L.), and loblolly pine (Pinus taeda L.) leaves. Phosphoric acid alone and mixed with ammonium nitrate caused less increase. Ammonium nitrate speeded translocation of the herbicide in post oak but not in the other species.

The phenology of reproduction was highly variable among 23 selections of medusahead (Taeniatherum asperum (Sim.) Nevski). Selections with markedly early and late maturity were observed. The phenology generally was consistent during 4 years of testing at Reno, Nevada, and during 2 years at Davis, California. Individual selections differed greatly in phenology between two locations. Some of the selections exhibited phenotypic plasticity in phenology when grown in competition with other weeds.

Combinations of copper sulfate pentahydrate (hereinafter referred to as CSP) at 1.0 ppmw copper plus 0.1 to 2.0 ppmw 6,7-dihydrodipyrido-(1,2-a:2′,1′-c)pyrazinediium ion (diquat) resulted in higher accumulations of copper in hydrilla (Hydrilla verticillata Casp.), egeria (Egeria densa Planch.), and southern naiad (Najas guadalupensis Spreng. Magnus) when compared to plants which received only CSP. A contact period greater than 24 hr was necessary before the higher amounts of copper were detected in those plants treated with the combinations. Water samples from outdoor, plastic pools 7 days after treatment with CSP at 1.0 ppmw of copper plus 1.0 ppmw of diquat contained 25% less copper than pools treated with CSP. Samples of hydrilla and southern naiad removed 7 days after treatment of the pools with the combination contained 77 and 38% more copper, respectively, than samples from those pools treated with only CSP.

The fine structure of the chloroplasts of bean (Phaseolus vulgaris L., var. Tendercrop) was grossly altered by treatment with 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) when plants were grown in a treated medium. Alterations occurred first at the leaf margins and preceded visual symptoms. Chloroplasts became spherical and swollen rather than discoid, clumped rather than peripherally arranged, and were totally devoid of starch. Grana formation was inhibited; the thylakoids became swollen and perforated, and they ultimately disintegrated. Concomitant with grana inhibition was the increase in size and number of lipid globules. Occasional breakage of the outer chloroplast membrane was observed. It is proposed that these changes result because pyrazon inhibits thylakoid structural protein formation.

Field bindweed (Convolvulus arvensis L.) was sprayed with a mixture of (2,4-dichlorophenoxy)acetic acid (2,4-D) and 4-amino-3,5,6-trichloropicolinic acid (picloram). A mixture of picloram and 2,4-D each at 0.01 lb and 0.001 lb/A killed tops of plants faster than 2,4-D alone or picloram alone at the same rates. Higher rates of 1 lb/A picloram plus 1 lb/A 2,4-D and 0.1 lb/A picloram plus 0.1 lb/A 2,4-D were not consistently synergistic or antagonistic. The percent of plants which produced new growth were 0 for picloram alone at 1 lb/A, 20 for a mixture of 2,4-D and picloram each at 1 lb/A, and 40 for 2,4-D alone at 1 lb/A. Other rates of 0.1 lb/A, 0.01 lb/A, and 0.001 lb/A did not control regrowth of field bindweed. Application of unlabeled picloram simultaneously with 14C-2,4-D increased translocation of 14C-2,4-D, but the reverse was not true.

Potassium azide (KN3) was shown to have potential use as a soil fumigant based on the evidence that azide killed dormant seeds in laboratory and field experiments. Volatility was an important factor in the dissipation of KN3; an acid environment greatly increased volatility probably due to rapid conversion to HN3, whereas soil type exerted little influence on vapor loss. Increasing the soil moisture decreased volatility due to water solubility of NH3. KN3 was leachable and weakly adsorbed in various soil types and at different pH levels. From experiments using stoppered flasks to exclude volatility, it was concluded that the dissipation of KN3 was a chemical phenomenon accelerated by elevated temperatures. KN3 dissipated rapidly from an acid soil whether autoclaved or non-autoclaved; however, alkaline soils prevented dissipation of KN3. Apparently, KN3 is converted to HN3 before it is decomposed. Diffusion within the soil was restricted and occurred only in an acid soil. Covering the soil with plastic immediately after application reduced volatility and increased the biological activity of KN3.

Relatively pure stands of eight weed species were maintained under field conditions on a Goldsboro loamy sand at Lewiston, North Carolina, for all or part of a 6-year period. Herbicides evaluated as preemergence surface treatments for these species were 2-sec-butyl-4,6-dinitrophenol (dinoseb), isopropyl m-chlorocarbanilate (chloropropham), 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea (diuron), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and 3-amino-2,5-dichlorobenzoic acid (amiben). S-ethyl dipropylthiocarbamate (EPTC) and a,a,a-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) were evaluated as preemergence incorporated treatments. The first four herbicides were evaluated in 1961, 1964, and 1966 while the last three were evaluated in 1962, 1963, and 1965. A series of rates was used for each chemical with three replications. With the exception of diuron which failed to control goosegrass (Eleusine indica (L.) Gaertn.), all of the herbicides provided at least a moderate degree of control of goosegrass, smooth crabgrass (Digitaria ischaemum (Schreb.) Muhl.), and redroot pigweed (Amaranthus retroflexus L.) at the respective typical field use rates. In general, trifluralin and amiben gave the best grass control and dinoseb the poorest. None of the herbicides effectively controlled common cocklebur (Xanthium pensylvanicum Wallr.) or ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.). Trifluralin and EPTC did not control Pennsylvania smartweed (Polygonum pensylvanicum L.), common ragweed (Ambrosia artemisiifolia L.), and common lambsquarters (Chenopodium album L.). Chloropropham was ineffective on common ragweed. Simazine, chloropropham, and amiben controlled Pennsylvania smartweed while diuron, simazine, dinoseb, and amiben were especially effective on common lambsquarters. Distinctive patterns of nematode infestations were observed as a function of weed species.

Fumitory (Fumaria officinalis L.) achenes were subjected to various treatments to induce germination and to study dormancy. Complete pericarp removal, partial seed coat removal, puncturing the seed coat, heat treatment, red and far-red light treatments, and germination temperature treatments did not break dormancy. Low-temperature after-ripening for 60 days at 4 C dormant fumitory achenes resulted in 90 to 95% germination. Water leaching of fumitory achenes increased the time required for successful after-ripening and the water leachate stimulated Avena coleoptile cylinder elongation. Wild oat (Avena fatua L.) embryo germination was inhibited by high concentrations of fumitory achene leachate and stimulated slightly by lower concentrations. High concentrations of the leachate inhibited epicotyl and radicle growth of pre-sprouted lettuce (Lactuca sativa L.) seedlings and lower concentrations markedly stimulated radicle growth.

Three tractor cultivations that severely pruned the root systems of hand-weeded plots of sweet corn [Zea mays L. var. rugosa Bonaf., Iochief] grown on a Codorus-Elkton silt loam under extreme drought conditions did not reduce the yield of marketable ears when irrigation totalling 2 acre-inches was applied during pollination and ear-filling. Pre-emergence application of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine [atrazine] to the soil surface without cultivation reduced brace root growth and yields significantly in the year of most severe drought. These effects of atrazine were avoided when the herbicide treatments were supplemented with tractor cultivations that covered the brace root zone of the corn plants with soil.

Imbibition of pretreated velvetleaf (Abutilon theophrasti Medic.) seed was most rapid when the chalazal region was wetted, but submergence of the chalaza in water delayed seed germination. Respiratory measurements indicated that the seed coat did not inhibit gas exchange under our experimental conditions. Effects of 2,4-dinitrophenol on germination indicated that radicle emergence and radicle growth were distinct processes, and that radicle emergence was more sensitive to low concentrations of the uncoupler.

Pretreatment of potato (Solanum tuberosum L., var. Russet) tuber discs in pH 5.5 buffer significantly reduced uptake of picloram (10−3M). Tissue pretreated in buffer at 7 C subsequently absorbed more picloram than tissue pretreated at 25 C. Inclusion of cetyl trimethyl ammonium bromide (hereinafter referred to as CTAB) (2 × 10−4M) in the treating solution caused a significant increase in picloram uptake in tissues that were not pretreated in buffer. The reduction in uptake caused by buffer pretreatment was effectively reversed when CTAB was included in the treating solution. The results suggest that picloram uptake by potato tissue is related to the availability of the quaternary ammonium binding sites provided by membrane phosphatides.

In a 3-year field study, from 51 to 1% of seed of velvetleaf (Abutilon theophrasti Medic) planted at 1 and 6-inch depths, respectively, produced established plants. Utilizing a microplot technique, 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and the ammonium salt of 3-amino-2,5-dichlorobenzoic acid (amiben) were applied at 2 and 3 lb/A, respectively, at soil depths of 0, 2, and 4 inches. Velvetleaf seed were planted at depths of 1, 2, and 3 inches. Compared with the number of plants establishing in untreated plots, surface-applied amiben reduced the number of established plants 39, 23, and 29% from seed planted at depths of 1, 2, and 3 inches, respectively. Amiben at or below seed depth gave over 95% control, and when applied below the soil surface but above the seed, 86% control. Atrazine, surface-applied, reduced weed establishment 33, 62, and 85% from seed planted at depths of 1, 2, and 3 inches, respectively. When atrazine was at, below, or above the seed but below the soil surface, control was 96% or higher.

The effect of dimethyl tetrachloroterephthalate (DCPA) applied during the establishment of Tifgreen bermudagrass (Cynodon dactylon (L.) Pers. X C. transvaalensis Burtt-Davy) on subsequent winter injury was studied. DCPA treatments to plots sprigged in July or later increased winter injury. DCPA applied in July, August, or September to plots planted in June resulted in approximately 15% of the turf being killed during the winter; however, DCPA applied before the middle of June did not significantly influence winter injury. Significant increases were found in total nitrogen, nitrate, amino acids, and protein of stolons harvested from DCPA-treated plots. These data suggest that DCPA treatments applied during establishment resulted in a less winter hardy condition by maintaining vegetative growth into the normal period of winter hardening.