Yellow rocket (Barbarea vulgaris R. Br.) was effectively controlled in established alfalfa (Medicago sativa L.) by September 15 applications of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-tert-butyl-5-chloro-6-methyluracil (terbacil), and 2-sec-butylamino-4-ethylamino-6-methoxy-s-triazine (hereinafter referred to as GS 14254). White cockle (Lychnis alba Mill.) was more difficult to control, but simazine was the most effective herbicide. Herbicide applications in early October reduced reserve nonstructural carbohydrate accumulations in roots of yellow rocket by November 15 but not in white cockle. Alfalfa yields were not reduced by two consecutive autumn applications of the herbicides at rates that provided adequate control of yellow rocket and white cockle.

Two overhead applications of monosodium methanearsonate (MSMA) at either 4 + 4 or 4 + 2.5 lb/A were required for effective postemergence control of rhizome johnsongrass (Sorghum halepense (L.) Pers.) in ratoon sugarcane (hybrids of the genus Saccharum). Two applications of MSMA in the spring controlled 95% of the johnsongrass, whereas two applications of 2,2-dichloropropionic acid (dalapon) at 4.5 lb/A, the standard treatment, controlled only 70%. In heavily infested fields, sugarcane treated with MSMA also outyielded sugarcane treated with dalapon. Sugarcane tolerated MSMA applied before June; the yield of weed-free sugarcane treated with MSMA was not significantly less than that of the untreated control. However, most MSMA treatments, particularly those applied in late spring, caused temporary leaf chlorosis and stunting. Sugarcane sprayed with MSMA before June generally contained no more arsenic in the juice and bagasse at harvest than untreated sugarcane. Application of MSMA in June or August increased the arsenic content, and resulted in concentrations up to 0.45 ppm in juice, and up to 1.68 ppm in bagasse.

Rice (Oryza sativa L., var. Bluebonnet) bioassay was utilized to evaluate activity of several herbicide combinations at concentrations of each individual compound causing a 50% reduction in root length. Synergistic combinations were trichloroacetic acid (TCA) plus 1,1-dimethyl-3-phenylurea (fenuron); TCA plus 3-(p-chlorophenyl)-1,1-dimethylurea (monuron); TCA plus 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron); TCA plus 3-amino-s-triazole (amitrole); TCA plus 2,2-dichloropropionic acid (dalapon); and dalapon plus monuron. Additive results were obtained from combinations of TCA plus 1,2-dihydro-3,6-pyridazinedione (MH); dalapon plus fenuron; and dalapon plus diuron. MH and (2,4-dichlorophenoxy) acetic acid (2,4-D) exhibited antagonistic responses when combined with fenuron, monuron, diuron, dalapon, amitrole, and with each other. Antagonistic responses were obtained from combination of 2,4-D and TCA.

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.

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.

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.

Results from both growth chamber and field experiments indicate that root absorption of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) applied postemergence to small broadleaf weeds is not a requisite for their control. Though broadleaf weeds absorb toxic quantities of atrazine from wet soil, they can be killed by foliar absorption alone because all of their meristems are exposed to a foliar spray. They are particularly sensitive when foliar penetration is enhanced by high relative humidity and wet foliage.

Seeds of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] planted immediately after extraction from mature seed pods germinated 84% and after burial overwinter germinated 97%. Seedling emergence was limited to depths of less than 4 inches. Seedling roots developed adventitious buds capable of producing new shoots about 5 weeks after emergence. Preemergence and early postemergence treatments with 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) gave 100% control of seedlings in greenhouse experiments. Heavy natural infestations of honeyvine milkweed in corn (Zea mays L.) were controlled 95% with 2,4-(dichlorophenoxy)acetic acid (2,4-D) at 0.5 lb/A when treatments were made before the weed started climbing on corn stalks. Later treatments required higher rates of 2,4-D, the use of 2,4,5-(trichlorophenoxy)acetic acid (2,4,5-T), or the combination of 2,4-D plus 2,4,5-T for adequate control.

In the presence of relatively high but non-toxic levels of phosphate, the suppression of corn (Zea mays L.) or squash (Cucurbita maxima Duchesne) seedling growth in the dark by 3-amino-2,5-dichlorobenzoic acid (amiben) or 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) was enhanced. This effect was not due to increased uptake of either herbicide in the presence of the phosphate by roots of corn, squash, soybeans (Glycine max (L.) Merr.), or redroot pigweed (Amaranthus retroflexus L.). A proportional decrease in herbicide uptake with increasing herbicide concentration was most evident for amiben and atrazine uptake by the roots of soybean plants grown in the light.

Phytase activity increased 2 to 3 fold in barley (Hordeum vulgare L.), 6 fold in corn (Zea mays L.), and 12 fold in squash (Cucurbita maxima Duchesne) seedlings 2 days after the initiation of germination in the dark. Most of the phytase was found in the embryo of the seed, presumably in the cotyledon(s). Gibberellic acid and benzyladenine supplied during germination exerted only limited influence on the development of phytase in these seedlings. Of the herbicides studied, only sodium arsenite exerted an influence on phytase activity per se that was of physiological significance. The presence of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-amino-2,5-dichlorobenzoic acid (amiben), 2-chloro-N-isopropylacetanilide (propachlor), 2,6-dichlorobenzonitrile (dichlobenil), or α,α,α-trifluoro-2,6-dinitro-N-N-dipropyl-p-toluidine (trifluralin) in the culture solution during germination partially inhibited the development of phytase activity. The herbicidal inhibition was enhanced if potassium phosphate at a non-inhibitory level also was present in the culture solution. The interaction of atrazine and amiben with phosphorus was not due to increased internal concentrations of inorganic phosphorus to a level inhibitory to the development of phytase activity.

The herbicides 3-tert-butyl-5-chloro-6-methyluracil (terbacil) and isopropyl m-chlorocarbanilate (chlorpropham) showed greatly enhanced activity on giant foxtail (Setaria faberii Herrm.) and ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) when applied in an isoparaffinic oil rather than water. The activity of terbacil was enhanced but to a lesser extent when crop oil was added to a water carrier at a concentration of 10%. In field trials, similar enhancement of terbacil and chlorpropham activity was obtained on several weeds. Onions (Allium cepa L., var. Spartan Gem) in the “loop stage” were moderately tolerant and carrots (Daucus carota L., var. Royal Chantenay) were highly tolerant to chlorpropham at 4 lb/A applied in the isoparaffinic oil. Peppermint (Mentha peperita L.) and spearmint (Mentha spicata L.) were tolerant to terbacil applied in the oil at rates sufficient to give good weed control. The oil alone had no injurious effects on onions, carrots, peppermint, or spearmint. This enhancement in activity in greenhouse and field studies appeared to be due to increased penetration as shown by washing, speed of killing plants, and tracer studies. Tracer studies showed that within 2 hr after application, the isoparaffinic oil increased the penetration of chlorpropham more than eightfold in ivyleaf morningglory and more than fourfold in giant foxtail compared to a water carrier. This increase in penetration was even more striking with terbacil. After 4 hr, penetration was increased over 16 times in ivyleaf morningglory and over 18 times in giant foxtail, when applied in the oil rather than acetone. Chlorpropham and terbacil were translocated to the shoot apex of ivyleaf morningglory only when they were applied in the oil.

The herbicide 3-tert-butyl-5-chloro-6-methyluracil (terbacil) applied in an isoparaffinic oil caused, in susceptible ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.), rapid and nearly complete inhibition of photosynthesis, from which it never recovered. Photosynthesis in peppermint (Mentha peperita L.), a tolerant species, was decreased only temporarily. Terbacil was readily absorbed by leaves of both species; however, there was little or no movement out of the treated peppermint leaves. Terbacil was translocated out of the treated leaves of ivyleaf morningglory to the untreated leaves and shoot apex. It was metabolized in both species but at a higher rate in peppermint. Therefore, it appears that foliarly-applied terbacil may be bound in peppermint leaves and this, together with the higher rate of metabolism, may contribute to the tolerance of peppermint. Terbacil was readily taken up and translocated to the foliage of both species when applied to the roots. Again, it was metabolized in both plants but at a higher rate in peppermint. However, the rate of metabolism alone did not appear to be sufficient to account for peppermint tolerance to root-applied terbacil.

We applied 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) to quackgrass (Agropyron repens L. Beauv.) at different stages of growth and subjected these treated plants to different light regimes. After paraquat and light treatment, foliage was removed and the reduction in regrowth was measured as evidence of paraquat movement and its effect on the regenerative potential of the rhizomes. Paraquat or a toxic metabolite moved in quantity from point of leaf application. Sufficient basipetal movement occurred in both the dark and light to significantly affect regrowth. As quackgrass plants matured and developed more foliage, the effect of paraquat treatment increased (i.e., the regrowth capacity of the plants and the regenerative ability of their rhizome buds decreased). A period of darkness (24 hr) after paraquat application and before exposure of treated plants to light did not affect numbers of plants killed but did decrease rate of regrowth. Treated quackgrass foliage showed extensive paraquat injury when placed in light for 48 to 72 hr after treatment; but only parts of treated leaves were killed. Leaving treated foliage intact greatly increased the number of plants killed.

Chenopodium humile L. did not germinate under laboratory conditions while the pericarp was intact. Scarification, leaching, ethanol, gibberellic acid, and thiourea stimulated germination. Germination was enhanced by moderate temperature (30 C), and long days. Factors which stimulated germination shortened the time between planting and maturation under short-day conditions but did not promote flowering which was absent under long-day growing conditions. Water stress did not affect germination but hastened maturation.

Mixtures of 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) plus 2,2-dichloropropionic acid (dalapon) were applied to sugarbeets (Beta vulgaris L.) at three growth stages 1 year and six growth stages another year. The growth of tops and roots was retarded most when sugarbeets were treated in the two-leaf stage of growth. The weight of tops and roots was reduced 43 and 50%, respectively, 6 weeks following an application of a mixture of 3 lb/A each of pyrazon and dalapon. However, when these sugarbeets were sampled 2 weeks later, the tops and roots weighed only 4 and 12% less, respectively, than the untreated controls. Furthermore, the early suppression in the growth of sugarbeets for 3 to 8 weeks following herbicide treatment had no effect on final yield of roots, pounds of sucrose, or sucrose content at harvest.

Aqueous sprays of 4-ammo-3,5,6-trichloropicolinic acid (picloram) (1 lb aehg) were applied to individual plants in stands of burroweed (Haplopappus tenuisectus (Greene) Blake) and creosotebush (Larrea tridentata (DC.) Coville) August 27 to 31, 1965, to prepare the areas for seeding to fourwing saltbush (A triplex canescens (Pursh) Nutt.). By July 1967, 99% of the burroweed was dead, but 90% of the creosotebush was still alive. Samples of the surface ½ inch of soil, taken February 1, 1966, were planted to fourwing saltbush. Emergence and growth of fourwing saltbush were seriously reduced on soil taken from under the sprayed burroweed crowns. Growth of fourwing saltbush seedlings was retarded on soils from beneath sprayed creosotebushes, but emergence was not reduced significantly. The surface soil under sprayed burroweed crowns contained 0.11 ppm picloram 2 years after treatment, but the picloram test was negative on soils from the creosotebush area.

Studies were conducted on and in the vicinity of the U. S. Cotton Research Station at Shafter, California, to evaluate the prevalence of the insect Bactra verutana Zeller (Olethreutidae) and its potential for injury to yellow nutsedge (Cyperus esculentus L.). Field surveys during August 1966, and August and October 1967 revealed many infested yellow nutsedge plants. Other field studies indicated that the insect may significantly suppress the growth of yellow nutsedge, providing that the insect infestation is early, sufficiently severe, and present on both parent and subsequently emerging vegetative plants. Greenhouse studies further revealed that severely infested plants may survive to produce numerous vegetative plants and tubers. While Bactra verutana Zeller damaged yellow nutsedge plants late in the season, the absence of early infestation limited its usefulness as a biological control agent.

The effect of humidity on the rate and direction of translocation of stem-injected (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in bean (Phaseolus vulgaris L., var. Stringless Green-pod) seedlings was determined. A total of 0.75 μg of 14C-labeled 2,4,5-T was injected into the stem with a 1-μl syringe pipette. Translocation was determined by assaying the nutrient solution and plant parts for 14C. High relative humidities enhanced downward translocation to roots and nutrient solutions. About 41% of the applied 2,4,5-T was found in the nutrient solution after 2 days' treatment at about 95% relative humidity while only 23% was found when treatment was conducted at 20% relative humidity. Low humidity during treatment caused much more 2,4,5-T to be translocated upward to the primary leaves and young shoots of the seedlings and this effect was more pronounced in plants which were grown in low humidity prior to treatment. The results confirm the conclusions of others and show that the increased basipetal phloem transport of herbicides in plants under high humidity is not due to an effect on penetration of herbicides in leaf tissue.

Leaves of a number of plant species were surveyed for their CO2 compensation concentration which is one of the distinguishing characteristics used to classify plants on the basis of their photosynthetic capacity. Monocot genera with low CO2 compensation values are mainly limited to tribes of Chlorideae, Paniceae, Andropogoneae, Tripsaceae, and a part of Festuceae in Gramineae. Major grain crops, except corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), are primarily in the tribes of Hordeae, Aveneae, and Oryzeae, and have high CO2 compensation concentrations. Seven genera of dicots with low CO2 compensation occur in the four families of Amaranthaceae, Chenopodiaceae, Portulacaceae, and Euphorbiaceae. Major dicot crops are in the families Leguminosae and Malvaceae and have high CO2 compensation points. Low CO2 compensation concentration also is correlated with low carbonic anhydrase activity. Conversely, high CO2 compensation concentration plants have a high carbonic anhydrase activity. Data on the influence of light intensity and temperature on the rate of photosynthetic CO2 fixation in leaves from plants with high and low CO2 compensation concentration indicate differential responses of photosynthesis to these environmental factors. The data are interpreted as supporting a hypothesis for competition by specific plants.

Assimilate transport in purple nutsedge (Cyperus rotundus L.) was studied using autoradiographic technique. Results show the basic pattern of assimilate distribution was from areas of synthesis to areas of use or accumulation. The initial underground centers of high metabolic activity were replaced as these organs matured, by new centers of actively growing rhizomes, tubers, and roots. The planted tuber did not accumulate assimilates. Treatment of purple nutsedge plants with 2,6-dichlorobenzonitrile (dichlobenil) resulted in accumulation of assimilates in the tubers rather than in young underground tissues. Leaves of treated plants also accumulated labeled assimilate in excess of control plants. Assimilate accumulation in leaves of dichlobenil-treated plants resulted from the destruction of the phloem in the basal portions of the leaf-sheaths. An increase in tuber respiration accompanied an increase in accumulation of assimilates in dichlobenil treated tubers.