Tubers of purple nutsedge (Cyperus rotundus L.) were soaked in distilled water, 9.3 × 10−6M 6-benzylamino-9 (tetrahydropyran-2yl)-9 H-purine (SD8339), or 1.39 × 10−7M kinetin and sprouted in darkness. Excised plants from tubers sprouted in sand culture were grown in half-strength Hoagland solution in 50-ml erlenmeyer flasks enclosed with aluminum foil. The leaves and upper part of the stem of each plant were exposed to an illumination of 32 klux. Rhizomes as well as untreated and treated tubers were exposed to red (R), red followed by far-red (R-FR), or red followed by far-red and red (R-FR-R) monochromatic light. R, R-FR, and R-FR-R illuminations of rhizomes from untreated tubers and plants produced basal bulbs while dark controls did not. Pfr did not revert to Pr. Dark controls produced significantly fewer basal bulbs than did rhizomes of untreated tubers and plants exposed to R, R-FR, or R-FR-R illuminations. There was no significant difference between R, R-FR, and R-FR-R illuminations. Tubers treated with SD8339 or kinetin produced basal bulbs in darkness but untreated tubers did not. Rhizomes of tubers treated with SD8339 or kinetin and exposed to R illumination produced basal bulbs. There was a significant difference in the number of bulbs produced by SD8339 or kinetin treatments and R illumination in contrast with the water controls in darkness. The effect of R illumination was similar to that of SD8339 or kinetin.

The application of individual droplets of an aqueous solution of As-74-labeled arsenic acid to the leaves, petioles, green stems and stalks of greenhouse-grown cotton plants (Gossypium hirsutum L. cv ‘Deltapine’) enabled the estimation of 100 ppm of As as the minimum effective internal concentration (MEIC) of arsenic from arsenic acid needed for the desiccation of cotton leaves. The spray application of arsenic acid to cotton plants (cv Lankart) in the field was calculated to have an overall efficiency of below 5 percent for this particular spraying operation. The application of aqueous arsenic acid to the abraded stalks of greenhouse-grown cotton plants (cv G-272) resulted in translocation of approximately 87% of the recovered arsenic so that treatment half-way around the stalk produced 70% desiccation. Treatment with sufficient quantities around the entire stalk resulted, in most cases, in complete desiccation and prevention of regrowth.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] provided adequate preemergence weed control on direct-seeded or transplanted tomato (Lycopersicon esculentum Mill.) on Plainfield sand and Drummer silty clay loam soils. Metribuzin demonstrated selective postemergence activity in the field but in glasshouse studies tomato cultivars had a wide range of tolerance to metribuzin applied to the foliage. Tomatoes were more susceptible to injury when they were less than 10-cm tall. Metribuzin was more effective in controlling broadleaf weeds than grass weeds, but grass control was acceptable with higher rates. Ultraviolet light decomposed metribuzin and weed control was improved when metribuzin was incorporated into the soil after application. Metribuzin treatment increased fruit yields. No metribuzin activity was found in the plots by the end of the growing season.

The distribution pattern of MCPA ([(4-chloro-o-tolyl)oxy] acetic acid) on leaf surfaces of three species was studied using the cathodoluminescence detection mode of a scanning electron microscope. On low-wax-content sugarbeet (Beta vulgaris L.) leaves MCPA concentrated in the depressions over the anticlinal cell walls when applied at high volumes (748 and 374 L/ha). At low volumes (23 L/ha), numerous small deposits of MCPA were randomly distributed over both anticlinal and periclinal walls. These distinct patterns were independent of herbicide concentration. Regardless of spray volumes, MCPA remaining on the waxy leaf surfaces of cabbage (Brassica oleracea L.) coalesced into small thick deposits. Large spray drops from high application volumes shattered on impact with the stellate hairs of turkey mullein (Eremocarpus setigerus Benth.) resulting in some MCPA reaching the leaf surface. Spray drops from low application volumes did not shatter but lodged on the hairs with very little reaching the leaf surface.

Arsenic as MSMA (monosodium methanearsonate) was applied to three soil types over a 6-year period. Percentage recovery of applied arsenic averaged 67, 57, and 39% in Hart-sells fine sandy loam, Decatur silt loam, and Dothan loamy sand soils, respectively. Essentially all of the arsenic recovered in the soils occurred in the plow layer with no evidence of leaching into deeper zones. Batch-equilibrium and soil-column studies in the laboratory indicated that the rate of MSMA movement through the surface horizon would be fastest in Dothan loamy sand and slowest in Decatur silt loam.

The plant hormones gibberellic acid (GA) and benzyladenine (BA) stimulated the development of dipeptidase activity in distal-half cotyledons of squash (Cucurbita maxima Duch. ‘Chicago Warted Hubbard’). The herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), and naptalam (N-1-napthylphalamic acid) inhibited the development of dipeptidase activity in this tissue. Herbicide concentrations which inhibited the development of this enzyme activity about 30% were used for the herbicidehormone interaction study. The addition of GA or BA counteracted the inhibition induced by 2,4-D and naptalam. Neither hormone grossly altered the inhibition induced by dicamba; however, BA did significantly reduce the inhibition caused by dicamba.

The basis for selectivity of phenmedipham (methyl-m-hydroxycarbanilate m-methylcarbanilate) and desmedipham (ethyl m-hydroxycarbanilate carbanilate) on wild mustard [Brassica kaber (DC.) L.C. Wheeler ‘pinnatifida’ (Stokes) L.C. Wheeler], redroot pigweed (Amaranthus retroflexus L.), and sugar beet (Beta vulgaris L.) was studied by evaluating spray retention, absorption, translocation, and metabolism. Total photosynthesis in wild mustard was severely inhibited in less than 5 hr after foliar application of either herbicide and did not recover. Total photosynthesis in sugar beet was slightly inhibited but recovered after 24 hr. Photosynthesis in redroot pigweed recovered from a treatment of phenmedipham but did not recover when treated with desmedipham. Differences in spray retention or foliar absorption did not explain selectivity. Within 5 hr after herbicide application, redroot pigweed had translocated more desmedipham than phenmedipham from the site of absorption and had metabolized a large amount of the phenmedipham but little desmedipham. The key factor explaining selectivity appeared to be at the initial detoxication reaction of the parent compound.

Weed species or genera previously and currently targeted for biological control with phytophagous insects or phytopathogens in the United States (including Hawaii) and Canada are listed. The current status of and natural enemies involved in national, federal, state, and university biological control projects are reported.

Three annual plant species — erect plantain (Plantago erecta Morris), common chickweed [Stellaria media (L.) Cyrill.], and silver hairgrass (Aira caryophyllea L.)—are commonly found and may dominate a unique flora on areas sprayed with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in cismontane rangelands of California. The basis of this phenomenon is shown to be temperature-related germination requirements, novel seed characteristics, and lack of competition.

Near isogenic strains of okra, super okra and normal leaf cotton (Gossypium hirsutum L.) were grown in rows spaced 25, 50, and 100 cm apart and were sprayed with various combinations of trifluralin (α,α,α,trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and fluometuron [1,1-dimethyl-3-(α,α,α,-trifluoro-m-tolyl)urea]. Neither row spacing nor leaf type had any effect on early season weed control. Late season control was better with normal and okra leaf types than with the super okra leaf type. Weed control was significantly better with additional postemergence application of herbicides than with only preplant and preemergence applications. Although the cotton varied in opening date with herbicide programs there was no difference in total yield.

Picloram (4-amino-3,5,6-trichloropicolinic acid), 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and dicamba (3,6-dichloro-o-anisic acid) were sprayed at 0.28 kg/ha on honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] and huisache [Acacia farnesiana (L.) Willd.] seedlings 1, 2, 4, 8, 12, and 16 weeks after emergence from seed under greenhouse conditions. Picloram or 2,4,5-T killed 73% or more of the honey mesquite up to 8 weeks after emergence, but the percent killed declined thereafter. Picloram killed more than 90% of the huisache seedlings when applied from 1 to 8 weeks after emergence. Less than 60% of the honey mesquite or huisache seedlings were killed with dicamba at any treatment date. Clipping the plants at the soil level resulted in high mortality (96 to 100%) of both species 1 to 2 weeks after emergence. Treating regrowth of clipped 1-year-old honey mesquite and huisache with 0.28 kg/ha of picloram, dicamba, or 2,4,5-T produced results similar to those obtained from plants grown from seed.

Eurasian watermilfoil (Myriophyllum spicatum L.) has invaded over 81,000 hectares in the Chesapeake Bay, 2,023 hectares in TVA reservoirs, and upwards of 32,000 hectares in Currituck Sound, North Carolina. Now it is causing concern in Florida because of its invasion of the Crystal-Homosassa River basin. In Yugoslavia and Pakistan, entomologists working on PL-480 grants found some 25 insect species feeding on eurasian watermilfoil. These species are potentially useful for the biological control of the weed in the United States.

The rates of degradation of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], the isopropyl analog [4-ammo-6-isopropyl-3-(methylthio)-as-triazin-5(4H)-one], and the cyclohexyl analog [4-amino-6-cyclohexyl-3-(methylthio)-as-triazin-5(4H)-one] in soil were determined under laboratory and field conditions. First-order kinetics best described the rate of degradation of the three herbicides. At 5 and 20°C, metribuzin and the isopropyl analog degraded more slowly than the cyclohexyl analog. At 35°C, the rates of degradation for all three herbicides were similar. The calculated half lives were approximately 329, 44, and 16 days for the three herbicides at 5, 20, and 35°C, respectively. Rates of 1.12 and 2.24 kg/ha, applied in the field, remained in the upper 5 cm of the soil profile, and the pattern of herbicide degradation followed that found in the laboratory study at 20°C.

Weeds in corn (Zea mays L.), cotton (Gossypium hirsutum L.), peanuts (Arachis hypogaea L.), and soybeans (Glycine max (L.) Merr.), grown continuously or in rotation, were controlled with either cultural or herbicidal programs designed for broad-spectrum control. The herbicidal program initially selected for each group was used each year from 1968 to 1971. Herbicides controlled more weeds than cultural practices in all cropping sequences. Weeds were almost eliminated, judging by percent ground cover at harvest time, in five of the eight cropping sequences in each of the last three years of the experiment. Although several rotations drastically reduced the number of weeds, the composition of the weed population was not altered significantly. When cultural weed control practices were used, the cropping sequence and rainfall influenced the level of weeds present at harvest time. More weeds were present at harvest in corn grown continuously and in sequence than in the other crops. In addition to three or four cultivations, we used a yearly average of 86 manhours/ha of hand-hoeing in corn and 195 manhours/ha of hand-hoeing in cotton during the first 6-week period after planting to keep these crops weedfree until the last cultivation. The cropping sequence did not affect the amount of hand-hoeing required in these crops. In general, cropping sequence did not affect crop yield.

Application of the ethylene-releasing agent ethephon (2-chloroethylphosphonic acid) as a lanolin paste to stems of honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockrell] caused the development of abnormal periderm, cortical, and xylem tissues in a localized portion of the stem within 1 cm of the treatment site. Ethephon inhibited secondary wall deposition in xylem parenchyma cells, whereas normal vessel element differentiation was unaffected. Similar changes in xylem formation occur in ethephon-treated huisache [Acacia farnesiana (L.) Willd.]. Ethephon and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] applied separately to honey mesquite and huisache stems have similar inhibitory effects on parenchyma cell differentiation but differ markedly in their effects on vessel element formation.

The toxicity of several toluidine and thiocarbamate herbicides to johnsongrass [Sorghum halepense (L.) Pers.] rhizome tissue was determined by a triphenyl tetrazolium chloride (TTC) assay. Rhizome sections were incubated in herbicide solutions for 24 hr and then in TTC solution for 24 hr. The amount of reduced TTC was a quantitative measure of herbicide toxicity. Concentrations of the different herbicides required to cause 100% tissue injury indicated that the order of decreasing herbicide toxicity was: USB-3584 (N3,N3-diethyl-2,4-dinitro-6-trifluoromethyl-1,3-phenylendiamine); trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine); benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2-6-dinitro-p-toluidine); nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline]; San-9789 [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazione]; and A-820 (Nsec-butyl-4-tert-butyl-2,6-dinitroaniline). In another study CGA-11607 (N-ethyl-N-tetrahydrofurfuryl-4-trifluoromethyl-2,6-dinitroaniline); AN-5647 [N,N-bis(2-chloroethyl)-2,6-dinitro-p-toluidine]; and CGA-10832 (Nn-propyl-N-cyclopropylmethyl-4-trifluoromethyl-2,6-dinitroaniline) were less toxic than trifluralin to johnsongrass rhizomes. Complete tissue injury caused by the thiocarbamates occurred in the same concentration range (10−3 to 10−2M) as the toluidine herbicides. At a concentration required for complete kill the toxicity in decreasing order was: EPTC (S-ethyl dipropylthiocarbamate); vernolate (S-propyl dipropylthiocarbamate); butylate (S-ethyl diisobutylthiocarbamate); and pebulate (S-propyl butylethylthiocarbamate). R-25788 (N,N-diallyl-2,2-dichloroacetamide) at 6.7 × 10−5 M had no effect on vernolate, EPTC, or pebulate activity; but it increased the toxicity of butylate to johnsongrass rhizome tissue.

The relative adsorption of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), triallate [S-(2,3,3-trichloroallyl)-diisopropylthiocarbamate], and diallate [S-(2,3-dichloroallyl)diisopropylthiocarbamate] was studied on several adsorptive surfaces. The herbicides were strongly adsorbed, with the following general trend: activated charcoal > peat moss > wheat straw (Triticum aestivum L.) ∼ cellulose triacetate > cation exchange resin > anion exchange resin > silica gel ∼ cellulose powder > kaolinite ∼ montmorillonite. Trifluralin and triallate were readily desorbed from montmorillonite by water, with miniminal desorption for peat moss, cellulose triacetate, and wheat straw.

In a 3-year field study in corn (Zea mays L.), several herbicides and combinations were studied for the control of yellow nutsedge (Cyperus esculentus L.), giant green foxtail [Setaria viridis var. major (Gaud.) Posp.], and fall panicum (Panicum dichotomiflorum Michx.). Best yellow nutsedge control (87 to 88%) resulted from applications of 4.48 kg/ha of either alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] preplant incorporated or atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] preplant incorporated plus atrazine postemergence with a phytobland oil. Between 72 to 83% control of yellow nutsedge resulted from applications of 2.24 kg/ha of alachlor, 4.48 kg/ha of butylate (S-ethyl diisobutylthiocarbamate), and combinations of atrazine plus butylate. Greater than 90% control of giant green foxtail and fall panicum resulted from butylate plus atrazine or alachlor; postemergence applications of atrazine resulted in significantly less control of fall panicum or giant green foxtail.