Grid applications of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] pellets at 2.2 kg ai/ha or less did not effectively control honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell ♯3 PRCJG], blackbrush acacia (Acacia rigidula Benth. ♯ ACARI), lotebush condalia [Condalia obtusifolia (Hook.) Weberb. ♯ CNCOF], granjeno (Celtis pallida Torr. ♯ CETPA) or twisted acacia [Acacia tortuosa (L.) Willd.] growing as mixed stands on clay loam or clay soils. Efficacy of hexazinone apparently was affected little by variation in rainfall ranging from 35% less to 51% greater than the long-term average during the year of application. Apparent mortality of honey mesquite, granjeno, and lotebush condalia was increased by increasing the application rate from 2.2 to 4.5 kg/ha on clay loam soils. Control of honey mesquite, blackbrush acacia, and twisted acacia with 2.2 kg/ha was better when applied to sandy clay loam than to clay soils.

Greenhouse studies were initiated to determine the efficacy of four herbicide antidotes as protectants of corn (Zea mays L., ‘DeKalb XL72AA’ and ‘DeKalb XL67′) against injury from preemergence or early postemergence applications of the herbicides chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide}, fluazifop-butyl {butyl-2-[4-[5-(trifluoromethyl-2-pyridinyl)oxy] phenoxy] propanoate}, or BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexene-1-one}. NA (1,8-naphthalic anhydride) was the most effective of the four antidotes in protecting corn against injury from preemergence applications of chlorsulfuron. CGA-43089 [α-(cyanomethoxy)-imino-benzeneacetonitrile] and CGA-92194 [α-(1,3-dioxolan-2-yl-methoxy)-imino-benzeneacetonitrile] partially protected corn from chlorsulfuron injury, whereas R-25788 (N,N-diallyl-2,2-dichloroacetamide] was the least effective. R-25788 offered partial to good protection to corn against injury from preemergence applications of fluazifop-butyl and BAS 9052 OH. NA, or CGA-43089, and CGA-92194 partially protected corn from fluazifop-butyl injury but their efficacy against BAS 9052 OH injury to corn was limited. In general, all four antidotes offered better protection to the thiocarbamate-tolerant ‘XL72AA’ hybrid than to the thiocarbamate-susceptible ‘XL67’ hybrid. With the exception of NA, which partially protected corn from postemergence-applied chlorsulfuron, none of the four herbicide antidotes was effective in protecting corn against injury from postemergence applications of any of the three herbicides.

In greenhouse and field studies, sethoxydim {2-[1-(ethoxyimino)-butyl]-5-(2-ethylthio)-propyl]-3-hydroxy-2-cyclohexen-1-one} provided good control of quackgrass [(Agropyron repens L. (Beauv.) ♯ AGRRE] in potato (Solanum tuberosum L. ‘Russet Burbank’). Level of control with sethoxydim at 0.6 kg ai/ha in the greenhouse was improved by the addition of a surfactant at 1.0% (v/v) of spray volume. Removal of quackgrass shoots at 6 or 24 h after treatment resulted in decreased control at application rates of 0.6, 1.0, and 1.6 kg ai/ha. Application of sethoxydim at 1.2 or 1.6 kg ai/ha in the field gave excellent control of quackgrass when applied at either the three- or six-leaf stage. Cultivation at 2 days after treatment did not adversely affect level of control obtained. Sethoxydim did not cause any adverse effect on potato yield, but delaying application until the six-leaf stage of quackgrass resulted in yield loss due to quackgrass competition.

The growth of wild oat (Avena fatua L. ♯3 AVEFA) under different moisture regimes was investigated under field conditions and in a growth chamber. In the field, growth of wild oat under low moisture conditions (0.6 cm water per week – Regime 1) was significantly reduced compared to growth under high moisture conditions (2.5 cm water per week – Regime 2). Maximum reductions of 49, 33, and 38% were recorded in the leaf area, dry weight, and number of viable tillers, respectively. The growth of wild oat in soil watered daily to a soil moisture content (SMC) of 10% (water potential −6.5 bars) in the growth chamber was less than for plants in soil watered daily to 20% SMC (-0.3 bars). Maximum reductions of 55, 57, and 38% were recorded in the leaf area, dry weight, and number of viable tillers, respectively. Wild oat growth was more adversely affected by reducing the SMC from 20 to 10% after, rather than before, the four-leaf stage. By the last sampling date, stomatal diffusion resistance of the most severely water-stressed plants was 25 s·cm-1 compared to between 5 and 10 s·cm-1 for the plants receiving more water.

The germination of milkweedvine (Morrenia odorata Lindl. ♯3 MONOD) seed at 20 or 25 C was unaffected by a 12-h photoperiod. The 12-h photoperiod, however, decreased germination by 50% at 15 C. No germination occurred at 35 C regardless of photoperiod. By alternating 35 C for 12 h with 20 C for 12 h, the germination percentage was 57%. Seedling growth was maximum at alternating temperatures of 30/20 C. Optimum pH for germination and seedling growth was 7 and germination did not occur at pH levels below 6. Seed germination declined steadily at osmotic stress below −0.12 MPa; no germination occurred at −0.5 MPa. Seedling growth was not influenced by osmotic stress down to −0.18 MPa. Germination percentages of seeds kept under aerated water and nonaerated water were similar, but the seedling growth was greater in aerated water. Seedling emergence was maximum from depths of 0.5 to 2.5 cm, but no seedling emerged from 0 or 10 cm. Planting depth was negatively correlated (r = −0.7) with shoot growth but positively correlated (r = +0.98) to root growth.

Soil samples representing a time series from forest before clearing to land in cultivation for 20 yr were taken near Delta Junction, AK, to determine the changes that occur in the soil seed bank following clearing and agricultural use. The total number of seed was initially low in the forested sites but increased after 3 to 5 yr in cultivation due to seed production by native colonizers and by introduced weeds such as common lambsquarters (Chenopodium album L. ♯3 CHEAL). Viability of seed of several mature forest species was low. There was a shift from a seed bank dominated by native species in the forest and newly cleared sites to a seed bank dominated by introduced colonizers in the older fields. Although seed of introduced species increased in importance over time, native species, especially native colonizers, continued to be an important component of the seed bank throughout the 20-yr period represented.

In greenhouse studies, postemergence applications of 0.1 or 0.3 kg ai/ha mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} as a tank mixture with 0.3, 0.4, or 0.6 kg ai/ha acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, or as a pretreatment 3, 5, or 7 days prior to acifluorfen treatment, often increased injury to ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. ♯3 IPOHE], velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE), compared to the injury from either herbicide alone. All sequential treatments with 0.1 kg ai/ha mefluidide and 0.3 kg ai/ha acifluorfen increased injury and decreased dry weight of ivyleaf morningglory and velvetleaf when compared with 0.6 kg/ha acifluorfen alone.

The forage selection and grazing behavior of sheep in leafy spurge (Euphorbia esula L. ♯3 EPHES)-infested pastures was examined in a 3-month grazing study conducted during the summer, 1981. No definite preference for or avoidance of leafy spurge was detected. An initial 1- to 3-week avoidance was observed, followed by a steady increase in leafy spurge consumption. A maximum intake of 40 to 50% of the diet per animal was observed. Weight gain by ewes in pastures infested with leafy spurge was not significantly different from weight gain by ewes in pastures free of leafy spurge. Results from these studies indicate that leafy spurge may be classified as a forage for sheep. Sheep will consume a significant amount of vegetation while suffering neither harmful internal effects nor a significant loss of body weight. Sheep can be considered an effective biological control agent for leafy spurge.

In the greenhouse, glyphosate [N-(phosphonomethyl)glycine] at 0.6 kg ae/ha applied directly to seeds alone or seeds on the soil surface reduced germination and shoot dry weight of common rye (Secale cereale L. ♯3 SECCE). Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) applied similarly at 0.6 kg ai/ha reduced germination and shoot dry weight of downy brome (Bromus tectorum L. ♯ BROTE) and wheat (Triticum aestivum L. ‘Daws' ♯ TRZAX). Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one] at 0.6 kg ai/ha applied to seeds, soil, or seeds and soil had very little effect on germination, but significantly reduced shoot dry weight of common rye, downy brome, wheat, and jointed goatgrass (Aegilops cylindrica Host. ♯ AEGCY). Pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] at 0.6 kg ai/ha, and propham (isopropyl carbanilate) at 3.4 kg ai/ha plus extender (p-chlorophenyl-N-methylcarbamate) at 0.4 kg ai/ha substantially reduced shoot height and dry weight of all species, regardless of application method, with pronamide completely inhibiting shoot elongation and dry-weight production in three of the four species.

Various environmental factors were tested under laboratory conditions to determine their effects on germination of seeds of prickly sida (Sida spinosa L. ♯3 SIDSP). Neither freezing and thawing nor moist chilling at 5 C promoted seed germination. However, increasing the incubation temperature and subjecting seeds to wet-dry cycles enhanced germination; high temperatures were more effective than alternate wetting and drying. Shifting seeds from a lower to a higher temperature regime increased germination. Seeds shifted from 15/6, 20/10, 25/15, or 30/15 C to higher regimes of 20/10, 25/15, 30/15, 35/20, or 40/25 C germinated to greater percentages than did seeds kept continuously at the lower thermoperiods. With an increase in length of time seeds were at a lower temperature, there was an increase in the percentage that germinated after they were moved to a higher regime.

Jointed goatgrass (Aegilops cylindrica Host. ♯3 AEGCY) has a quantitative requirement for vernalization in order to flower. In greenhouse and field studies, increasing periods of vernalization progressively reduced the number of days needed for plants to mature following transfer from the cold treatment to favorable growing conditions. Plants that had been vernalized at 3 ± 2 C for 8 weeks as imbibed seed took 120 days to flower following transfer to the greenhouse. Unvernalized controls flowered 197 to 222 days after planting in the greenhouse. Lengthening periods of vernalization from 2 to 8 weeks increased the number of seedheads per plant and dry weight per seedhead. Vernalized plants partitioned more dry matter into seedheads than unvernalized controls. The ratio of seedhead dry weight to vegetative shoot dry weight increased with duration of vernalization, even though vernalization did not alter total shoot dry-matter production. In field studies, plants that were established in the fall flowered sooner and more synchronously after resumption of growth in the spring than those that were planted in the spring and flowered in the summer. Plants seeded after May failed to flower in the same summer.

The methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} applied at 0.8 to 1.4 kg ai/ha and incorporated prior to seeding winter wheat (Triticum aestivum L.) controlled downy brome (Bromus tectorum L. ♯ BROTE) better than when applied preemergence at 1.7 kg/ha in 2 of 4 yr. The emulsifiable concentrate and a granular formulation of diclofop performed similarly. Controlling downy brome improved wheat yields 3 of 4 yr. However, preplant-incorporated applications of diclofop at 1.4 kg/ha reduced wheat yield 1 of 4 yr. Greenhouse data indicated that diclofop dissipated more rapidly in moist soil than in air-dry soil.

Wild oat (Avena fatua L. ♯3 AVEFA) and Avena sterilis L. ♯ AVEST accessions from the United States were screened for tolerance to diallate [S-(2,3-dichloroallyl) diisopropylthiocarbamate], triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate], barban (4-chloro-2-butynyl m-chlorocarbanilate), diclofop {2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid}, difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium), flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine], and MSMA (monosodium methanearsonate). Some accessions were tolerant to more than one herbicide but none were tolerant to all herbicides. Tolerance to a herbicide was not restricted to certain areas of origin of the accessions, and tolerant accessions occurred even in locations that had not been treated previously with the herbicide. In general, accessions from Southern California and Arizona were shorter, produced more tillers, and required the least number of days to panicle emergence. However, accessions from within individual areas were nearly as variable in these characteristics as the entire 1200 accessions. Tolerance of accessions to flamprop, difenzoquat, MSMA, and diclofop was not due to low leaf surface area, since the tolerant accessions usually had the most leaf surface area. All the accessions tolerant to difenzoquat, MSMA, and flamprop, and three of the four accessions tolerant to diclofop, tillered less than the susceptible accessions.

A culture medium and environmental conditions were selected for ovule culture of velvetleaf (Abutilon theophrasti Medic. ♯4 ABUTH), which allowed development parallel to that occurring in vivo. Of the six nutrient media evaluated, the most suitable one contained an organic nitrogen source and was of high osmotic potential. A liquid medium with a pH of 5 to 7, and culture for 14 days at 25 C under green light (1.3 μmole·m-2·-1) encouraged good embryo and ovule development. No difference was recorded between polyethylene glycol 20000 and mannitol in the medium used for dehydration and subsequent imbibition of cultured mature ovules. To investigate the effects of maternal tissues, surgical alterations were performed on the testa and funiculus of immature velvetleaf ovules. The intact testa appears to be a barrier to nutrient absorption and reduces the fresh and dry weights and embryo length. Ovule and embryo development was significantly better if either the testa was nicked or the funiculus removed.

Seed size and weight significantly affected witchweed [Striga asiatica (L.) Kuntze = S. lutea Lour. ♯4 STRLU] seed germination, witchweed emergence, and host-parasitization. Witchweed seed were divided into four groups for testing; large (> 149 microns in diameter) and heavy (specific gravity greater than one) (LH), large and light (specific gravity less than one) (LL), small (< 125 microns in diameter) and heavy (SH), and small and light (SL). Germination percentages were 87, 84, 58, and 26 for LH, LL, SH, and SL, respectively. Corn (Zea mays L.) was planted in pots containing soil infested with these four seed categories. The total number of witchweed plants (submerged plus emerged) per pot containing LH, LL, SH, and SL witchweed seed was 65, 12, 0, and 0, respectively, and the number of witchweed plants that emerged was 19, 4, 0, and 0 per pot. There were no significant differences in shoot weights of corn grown in the pots either between kinds of witchweed seed infesting the soil or between plants grown in infested soil and plants grown in soil that did not contain witchweed seed. Roots of corn plants grown in soil infested with LH seed were significantly heavier than those grown in soil infested with any other seed class and heavier than those from soil that did not contain witchweed seed. No other seed class significantly affected root weight.

Witchweed (Striga asiatica Lour. ♯4 STRLU) seed remained viable for 6 yr under open-shelf laboratory conditions and for 14 yr when deep buried under field conditions. Seed kept in normal atmosphere of the laboratory for < 1 through 6 yr had the following germination percentages: 2, 95, 95, 94, 83, 38, and 7. Newly harvested seed will not germinate because of postmaturity ripening requirements. There were no viable seed after 7 yr of shelf storage in the laboratory. Seed buried in the field gave 60 to 90% germination the first season after production. Annual recovery and testing showed a gradual reduction in viability to 10% at year 14 for the deepest buried seed; shallower buried seed expired sooner. No germination occurred thereafter.

Picloram (4-amino-3,5,6-trichloropicolinic acid) and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} were the most effective herbicides for killing Macartney rose (Rosa bracteata Wendl.) on the Claypan Resource Area of Texas. At 4.5 kg/ha picloram (ae/ha) and tebuthiuron (ai/ha) as sprays killed 70% of the plants and as pellets 73 and 84% 1 yr after application, respectively. Bay Met 1486 {N-[5-(ethylsulfonyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}, 2,4-D [(2,4-dichlorophenoxy) acetic acid], 3,6-dichloropicolinic acid, glyphosate [N-(phosphonomethyl)glycine], hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid} were markedly less effective than either picloram or tebuthiuron. After 2 to 4 months, 2,4-D, picloram, picloram + 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and triclopyr reduced the Macartney rose canopy by at least 95%, but only picloram and tebuthiuron controlled Macartney rose after 3 yr. Sprays of glyphosate and hexazinone inhibited growth of grasses after 3 months. Most herbicide sprays reduced broadleaf cover for at least 3 months.

When grown without soybean [Glycine max (L.) Merr.] interference, eastern black nightshade (Solanum ptycanthum Dun.) planted in May produced as many as 7000 berries and 800000 seeds per plant. Eastern black nightshade planted in mid-July produced as many as 100 berries, but those planted in mid-August failed to produce berries. Eastern black nightshade produced less than 85 berries per plant when planted with soybeans in May, 0 to 3 berries per plant when planted into soybeans in June, and no berries when planted into soybeans in July. However, when soybeans were defoliated in July to simulate hail injury, eastern black nightshade that had been planted with soybeans in May produced up to 1600 berries per plant, and those planted into the defoliated soybeans in July produced up to 58 berries per plant. We suggest, therefore, that in vigorously growing soybeans, control of eastern black nightshade emerging in the row would only be required through June to prevent berry production. If, however, the soybean canopy were disturbed by hail or other factors, eastern black nightshade seedlings emerging in late July or early August might produce berries by soybean harvest.

The potential of several common weed species to produce adventitious shoots when the plants were excised approximately 1.0 cm below the cotyledonary node at the cotyledon growth stage and at the four true-leaf stage is reported. Indian jointvetch (Aeschynomene indica L. ♯3 AESIN), northern jointvetch [Aeschynomene virginica (L.) B.S.P. ♯ AESVI], and wild poinsettia (Euphorbia heterophylla L. ♯ EPHHL) produced adventitious shoots at both growth stages after shoot excision. Adventitious and vegetative regeneration of wild poinsettia damaged by herbicides was similar to that from decapitation.

Johnsongrass [Sorghum halepense (L.) Pers., ♯3 SORHA] dry weight and johnsongrass culms/ha at harvest were more negatively correlated with soybean yield reductions than the number of johnsongrass plants/ha present at 4 to 6 weeks after planting. However, plant numbers can be determined in sufficient time to implement control measures to prevent yield reduction. Prediction equations for estimating soybean yield at various johnsongrass populations are Ŷ = 1776 + 424e-.023x2 for 0.25-m row spacing and Ŷ = 1668 + 643e-.004x2 for the 1-m row spacing, where Ŷ = estimated yield and x = the number of johnsongrass plants/10 m2. Full-season heavy johnsongrass competition reduced soybean yields from 59 to 88%. Soybeans in the 1-m row spacing were more competitive with low johnsongrass densities than in the 0.25-m row spacing. The johnsongrass-free requirement for soybeans was 4 weeks after planting and soybeans could not tolerate heavy infestations of johnsongrass for more than 5 weeks without loss in yield potential. Application of sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 3 or 4 weeks after planting was effective in controlling heavy infestations of johnsongrass and preventing yield reductions due to competition.