The feasibility of using the spurge hawkmoth (Hyles euphorbiae L., Lepidoptera: Sphingidae), as a biological control agent on leafy spurge (Euphorbia esula L.) was evaluated. Studies relating adult hawkmoth emergence from the pupal stage and spring growth of leafy spurge plants showed that the plants would provide food and oviposition sites for the insect. Two generations of the insect may occur each year. Winter temperatures at approximately 2.5 cm below the soil surface or in the litter would result in some mortality of hawkmoth pupae. Pupal release programs indicated that protection from insect and rodent predators was necessary for adult emergence to occur. Predator determination using 32P indicated two specimens of Calosoma calidum Fab. and two specimens of Formica subsericea Say as possible predators. Predator determination using pitfall traps showed that several species listed by Canadian researchers as predators were present in leafy spurge stands in Nebraska. At this time it appears the spurge hawkmoth will not become a valuable biological control agent for leafy spurge in Nebraska.

Leaching of EPTC (S-ethyl dipropylthiocarbamate) plus R-25788 (N,N-diallyl-2,2-dichloroacetamide) through columns of four soils resulted in the separation of R-25788. Separation of R-25788 from EPTC was greater in coarser than in finer textured soils. When soil columns were placed under drying conditions for 6 days after leaching, R-25788 moved upward in the columns faster than EPTC.

Several chemicals were evaluated in the laboratory for their ability to inhibit growth of hydrilla [Hydrilla verticillata (L.f.) Royle] from tubers. Fenac [(2,3,6-trichlorophenyl)acetic acid] and dichlobenil (2,6-dichlorobenzonitrile) were effective in controlling regrowth in outdoor aquaria. In field tests, hydrilla regrowth was controlled for over 13 months by single applications of 34 kg/ha rates of fenac and over 48 months in one of three replicates treated with 11 kg/ha dichlobenil. Regrowth occurred in controls within 2 to 6 months. There were no differences in the number of viable propagules found in hydrosoil before and 13 months after treatments. Regrowth occurred from root-stocks and from tubers. Regrowth was associated with disappearance of the herbicides from water.

Fosamine [ethyl hydrogen (aminocarbonyl)phosphonate] acted as a chemical inhibitor of shoot growth for periods of up to 3 yr following a single summer application to honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] trees. Anatomical study of field, greenhouse, and seedling mesquite indicated that the inhibition of primary and secondary growth caused by fosamine was due to a general cessation of nuclear activity in apical meristems and in the vascular and cork cambia of this species.

Twenty years after aerial application of 2.24 kg ae/ha of the butoxy ethanol ester of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] to release grass stage longleaf pine (Pinus palustris Mill.) seedlings, stocking was the same for each of three treated and control 4-ha plots. Treated plots, however, had significantly greater tree diameter (10%), taller trees (17%), and more merchantable tree volume/ha (40%). Merchantable tree volume differences 20 yr after treatment represent an 8 yr growth advantage for treated plots.

Cotton (Gossypium hirsutum L. ‘Stoneville 213’) was grown with densities of sicklepod (Cassia obtusifolia L.) or redroot pigweed (Amaranthus retroflexus L.) ranging from 0 to 32 weeds/15 m of row. Regression of seed cotton yields on weed density revealed a linear decrease in yield with increasing weed densities. In the 3 yr these studies were conducted, losses in hand harvested yields of seed cotton ranged from 34 to 43 kg/ha for each sickledpod plant/15 m of row and 21 to 38 kg/ha for each redroot pigweed plant per 15 m of row. Under comparable weed densities, yields of seed cotton differed only slightly when hand harvested or mechanically harvested. Mechanical harvesting efficiencies of cotton were reduced only at higher densities of weeds. The percentage of trash in cotton generally increased with increasing density of weeds. Neither sicklepod nor redroot pigweed affected cotton grade or micronaire.

Dwarf spikerush [Eleocharis coloradoensis (Britt.) Gilly], a perennial aquatic plant, is composed of many individual rosettes connected by rhizomes. Each rosette has needlelike culms attached to a stalk, a crown with an apical meristem, and many fibrous roots. It reproduces by achenes, subterranean tubers, and crown tubers. Dwarf spikerush achenes were harvested three times in 1 yr after the water level had been manipulated to promote flowering. The annual yield of achenes following this treatment was 79 kg per ha. Subterranean tubers began to form in September and formation was maximum in October. Individual plants grown for 1 yr developed an average of 351 tubers. Maximum density of tubers formed in hydrosoil was 7 per cm2. Longevity studies showed that the percentage germination of achenes and tubers decreased, respectively, from 48 to 32% and from 100 to 46% when stored wet at 4 C for 4 yr. Plants grown for 6 months from a single subterranean tuber, rosette, or achene spanned 150, 127, and 99 cm, respectively. The species thrived in a wide range of water qualities and on soft hydrosoils largely made up of silt, clay, and organic matter. On plants immersed in 0 to 100% sea water for 1 month, culms were injured in 30% sea water and killed in 40% sea water. Surviving plants showed some new growth after transfer to fresh water. Some tubers were incubated in diluted sea water. They germinated in solutions up to 80% sea water. Plants grown in water under different light intensities grew best at the maximum of 3,900 lux. More rosettes, culms, and inflorescences were produced with a 14-h photoperiod than 11- or 17-h photoperiod. Dwarf spikerush displaced other species by invading them when growth of the other plants was suppressed. The erect crowded culms of dwarf spikerush mechanically resisted incursion of other aquatic plants.

Buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} may be useful for selective weed control in corn (Zea mays L.) but injures corn seedlings at high rates. Greenhouse studies were initiated to test potential antidotes for buthidazole injury to corn seedlings. NA (1,8-naphthalic anhydride) and CDAA (N,N-diallyl-2-chloroacetamide) were the most effective of six chemicals evaluated. A ratio of 1:3 (buthidazole: CDAA) appeared to be optimal for the protection effect. CDAA appeared to be more effective than NA. Since both CDAA and NA offered limited protection but R-25788 did not, this action appears to be through a different mechanism than the one proposed for the thiocarbamate or acetanilide herbicides. The other chemicals tested were R-25788 (2,2-dichloro-N,N-diallylacetamide), R-29148 (2,2-dimethyl-5-methyl-dichloroace-tyloxazolidine), carboxin (2,3-dihydro-5-carboxanilido-6-methyl-1,4-oxanthiin) and gibberellin (GA3). Seven herbicides, members of the acetanilide, thiocarbamate, and dinitroaniline groups, were also tested for their antagonistic interactions but none offered protection.

Under greenhouse conditions, postemergence herbicide effectiveness was greater when barnyardgrass [Echinochloa crus-galli (L.) Beauv.] plants were 5-or 10-cm tall as compared to 15-or 20-cm tall. Absorption of 14C-glyphosate [N-(phosphonomethyl)glycine] decreased from 58% of applied to 47% as plant height increased from 5 to 15 cm, and an additional reduction (to 32% of applied at 5 cm) occurred when terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] was added to glyphosate. Translocation of 14C-glyphosate was reduced in older plants or when terbutryn was added to glyphosate. Water stress studies included soil moisture levels of 10, 20, 30, and 40% moisture (PW). Herbicide treatments were less effective at soil moisture levels below field capacity (30 PW). When soil moisture was 10 PW (-37 bar) absorption of 14C-glyphosate was greatly reduced in plants treated at both 7.5-and 15-cm heights with or without terbutryn. At 10 PW only 15 to 20% of applied 14C was absorbed whereas at 40 PW, absorption was over 45% and 62% with and without terbutryn, respectively. The addition of terbutryn to glyphosate resulted in decreased translocation for all soil moisture levels except the 20 PW treatment at the 15-cm height. Translocation of 14C was greatly reduced for plants in soils at 10 PW for both herbicide treatments.

Residue of picloram (4-amino-3,5,6-trichloropicolinic acid) aerially sprayed onto a central Arizona chaparral stand was markedly reduced in the surface 7.6 cm of soil from a fall burn conducted 5 weeks later. Brush control was also reduced.

Uptake and translocation of 14C-buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} in corn (Zea mays L.) and redroot pigweed (Amaranthus retroflexus L.) were studied following both foliar and root treatments under greenhouse and growth chamber environments. Following foliar application, 14C-buthidazole was absorbed by the leaves of corn and redroot pigweed seedlings in similar amounts. Translocation occurred only toward the tip of the treated leaves in corn, whereas in redroot pigweed the 14C moved both acropetally and basipetally. Rapid uptake by the roots and rapid movement to the leaves via the xylem seems to be the main pathway of uptake and translocation of 14C-buthidazole supplied to the roots of redroot pigweed plants. Uptake by both the roots and the emerging coleoptile and transport to the foliage seems to be the pattern of absorption and translocation of buthidazole in corn following preemergence application. Differences in absorption did not appear to be an important factor contributing to selectivity of buthidazole between corn and redroot pigweed. However, translocation of 14C-buthidazole supplied to the roots was faster to the redroot pigweed shoots than to corn shoots.

Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] was evaluated in field experiments at rates from 0.6 to 4.5 kg/ha for control of volunteer wheat (Triticum aestivum L. ‘Hyslop’, ‘Stephens’) in fall-planted perennial ryegrass (Lolium perenne L. ‘Cropper’, ‘Pelo’, ‘Pennfine’, ‘Omega’). Ethofumesate applied at 1.7 kg/ha or more in mid-November to wheat in the one-to three-leaf stage eliminated the wheat. Wheat was not eliminated when ethofumesate was applied preemergence soon after planting or when applied at the end of November to wheat in the four-leaf to four-tiller stage. In four experiments in which wheat was present, ethofumesate significantly increased perennial ryegrass seed production. In one experiment in which wheat was not present, ethofumesate did not affect perennial ryegrass seed production. Ethofumesate applied in the fall at rates to 4.5 kg/ha to newly-seeded perennial ryegrass or to well-established bentgrass (Agrostis tenuis Sibth. ‘Highland’), Kentucky bluegrass (Poa pratensis L. ‘Newport’), and Italian ryegrass (Lolium multiflorum Lam.) did not adversely affect germination of the following seed crop.

In field studies conducted in 1971 through 1977 weed yields were higher in EPTC (S-ethyl dipropylthiocarbamate) and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide]-treated areas as compared to handweeded plots. Weeds present in EPTC-and alachlortreated areas did not result in a significant field bean (Phaseolus vulgaris L. ‘Great Northern 59’) yield reduction as compared to hand-weeded plots. For every 1000 kg of dry weeds present in field beans there was a corresponding decrease in field bean yields of 208 kg/ha. Weed yields produced in plots treated with alachlor, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), EPTC, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), and profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] were significantly less when herbicides were incorporated with the rotary tiller as compared to incorporation with the spike-tooth harrow. Incorporation method was not as critical with butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine], with spike-tooth harrow incorporation of herbicides providing similar weed control to that obtained with the rotary tiller. Weed densities and yields were higher in plots seeded with field bean determinate variety ‘Great Northern 1140’ than in plots seeded with indeterminate variety ‘Tara’, when either EPTC or alachlor were applied preplant and incorporated. Neither field bean variety competed well with weeds when no herbicide was used.

Purposefully introduced plants that have become weeds cost the United States millions of dollars annually by reducing yields of crops and livestock, clogging navigable and recreational waterways, reducing productivity and value of grazing lands, poisoning humans and livestock, and increasing weed control costs. Research is in progress to develop methods of intercepting foreign plants that might be toxic to livestock if introduced on western ranges and pastures. Methods of intercepting include identifying poisonous plants from seed inventories, chemical analysis, chemotaxonomic investigations of biochemical relationships between related taxa, and feeding suspected plants to laboratory and domestic animals.

In closed vapor exposure chambers, foliar injury on tobacco (Nicotiana tabacum L. ‘Speight G-28’) seedlings was caused by vapors arising from soils in which technical grade benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) or its commercially-formulated emulsifiable concentrate had been incorporated. The emulsifier alone did not cause injury. Dosages of the herbicide ranged from 0.84 to 6.72 kg/ha or 13.1 to 104.8 ppmw in the concentration in soils, and the lowest dosage was sufficient to induce the foliar injury. Leaves which developed during the exposure were markedly shortened, narrowed, and thickened, distorted in shape, and had an extremely poor lamina expansion and abnormal venation pattern. Severity of the foliar injury increased as the herbicide dosage and soil moisture increased, and as the soil organic matter content decreased. Leaves which were partially expanded before the exposure were affected much less. When exposed to vapors of 14C-benefin, plant seedlings readily absorbed radioactive materials by its entire foliage including the stem tip with a few tiny developing leaves. More than half of the 14C absorbed and adsorbed during a 3-day exposure was recovered by CHCl3 wash of leaves and appeared to be retained by the wax and cutin layers, and also by lipoidal secretion substances of the numerous trichomes on the leaf surface. There was a small fraction of unabsorbed or loosely retained 14C material on the surface of the leaves and stem tip, which was removed by water. That not recovered from H2O and CHCl3 washes appeared to be distributed in the internal tissues. Little acropetal translocation appeared to occur from the expanded leaves toward the stem tip. There was no translocation of 14C-benefin into roots of plants where only a single leaf was exposed to the radioactive vapors.

Mulching the soil with polyethylene sheets before sowing during the hot season, increased the soil temperatures, which resulted in the control of soil-borne pathogens and weeds. This method was tested in a field heavily infested with Egyptian broomrape (Orobanche aegyptiaca L.). Soil was irrigated and mulched for 36 days during August–September 1977, prior to sowing carrot (Daucus carota L. ‘Nantes Tip Top’) seeds. Mulching increased soil temperatures by 8 to 12 C, up to 56 C in the top 5 cm. In the non-mulched plots the carrot plants became stunted due to heavy parasitization with broomrape and they were completely destroyed by the end of the season. In contrast, broomrape and other weeds were controlled in the mulched plots and the carrot plants grew normally. This effect was less pronounced in the border rows of the mulched plots. Mulching also greatly reduced the infestation of other weeds. Egyptian broomrape was also controlled in two other field experiments with carrots and eggplants (Solanum melongena L. ‘Black oval’). As compared with fumigation, this new method of control is economical, simple, nonhazardous, and does not employ toxic materials.

Various chemical and cultural treatments were evaluated for smutgrass [Sporobolus poiretii (R.&S.) Hitchc], control and their effects on pangolagrass (Digitaria decumbens Stent.) and bahiagrass (Paspalum notatum Flügge). Herbicide treatments were dalapon (2,2-dichloropropionic acid) at 1.7, 3.3, and 5.0 kg/ha with Sunoco HE spraying oil at 0, 9.4, 19.0 and 37.0 L/ha. Five weeks after herbicide treatment plots were clipped (clipped vs. nonclipped) and fertilized (0 vs. 112 kg/ha N). Increasing dalapon from 1.7 to 5.0 kg/ha increased smutgrass control and decreased the number of smutgrass plants/plot. Pangolagrass ground cover generally increased with fertilization, as the rate of dalapon increased up to 3.9 kg/ha. Bahiagrass ground cover decreased with rates of dalapon above 1.7 kg/ha. Increasing the rate of oil increased bahiagrass ground cover after 90 days. Nitrogen applied 5 weeks after dalapon treatment and semi-annually for 5 yr generally decreased ground cover of smutgrass and bahiagrass, but increased pangolagrass. Clipping treated smutgrass plants increased pangolagrass and bahiagrass ground cover while decreasing the ground cover of smutgrass.

Afterripening requirements and the possible occurrence of endogenously controlled germination rhythms in downy brome (Bromus tectorum L.) were investigated in the laboratory. Afterripening temperatures from 0 to 50 C, maintained for periods of 4 to 28 days, had little effect on the percentage and rate of downy brome germination when seeds were incubated at 15 and 20 C. However, at 30 C germination temperature, the percentage and rate of germination were significantly increased by short periods (4 to 7 days) of afterripening at 50 C. Similar results occurred at 20 to 40 C afterripening temperatures after 14 to 28 days exposure. In general, high temperature afterripening conditions (40 to 50 C) initially increased downy brome germination at 30 C incubation temperature, but prolonged exposure tended to decrease germination. No endogenously controlled germination rhythms were observed in downy brome caryopses.

Field experiments were conducted over a 2-yr period to study the comparative morphological development of cogongrass [Imperata cylindrica (L.) Beauv.] ecotypes from 15 different locations throughout the three main regions of Iraq. Plant height and density of stands varied more than 2-fold. The number of flowering heads varied 11-fold for plants collected from the different locations. Mature leaf-blades varied in width from 4.7 to 6.9 mm. These distinct variations indicate the existence of different ecotypes of cogongrass in Iraq.

Two series of experiments were conducted from 1976 through 1978 on Marvyn loamy sand in central Alabama to determine the competitive relationship of yellow nutsedge (Cyperus esculentus L.) with cotton (Gossypium hirustum L. ‘Stoneville 213’). In the first series of experiments yellow nutsedge was left undisturbed or removed from plots to give periods of competition of 0, 2, 4, 6, 8, 10, and 25 weeks. Seed cotton yield was reduced 2 of 3 yr with full season (25 week) competition, but was unaffected by shorter periods of competition in all years. Main stem diameter of cotton was also reduced 2 of 3 yr when competing full season while main stem height was reduced in only 1 of 3 yr with full season competition. In the second series of experiments yellow nutsedge densities were monitored in 48 individual plots and regression analysis showed yields of seed cotton were consistently reduced with full-season competition. Yellow nutsedge shoot densities ranged from zero to 93 shoots/m2 (measured 13 cm on either side of the drill) and approximately 18 kg/ha of seed cotton were lost for each additional yellow nutsedge plant per m2.