Global expansion in the cultivation of genetically engineered (GE) crops has raised concerns about the adventitious presence of GE seeds in non-GE and organic products. Flax is the second most important oilseed crop in western Canada and is currently being evaluated as a potential platform for the production of bio-products. Before transgenic flax is released for commercial production, mitigation measures must be identified to reduce the adventitious presence in subsequent crops. To quantify adventitious presence of volunteer flax in spring wheat and to identify the efficacy of herbicide treatments on mitigating volunteer flax adventitious presence, research was conducted at four locations during 2005 and 2006 in central Alberta. To simulate artificial volunteer populations, flax was seeded prior to wheat at a target population of 150 plants m−2. In the untreated control, volunteer flax seed yield was 135 kg ha−1, which resulted in adventitious presence of 8.57% in spring wheat. When left uncontrolled, volunteer flax reduced wheat yields ∼57% and resulted in volunteer flax seed production of 4,755 seeds m−2. A single PRE treatment of glyphosate or glyphosate plus tribenuron reduced volunteer flax density from 39 to 4 and 6 plants m−2, respectively, seed production from 4,755 to < 58 seeds m−2, and volunteer flax seed viability from 55 to < 40%. POST herbicides, fluroxypyr plus MCPA and fluroxypyr plus 2,4-D, reduced volunteer flax seed production as low as 0.6 and 0.0 seeds m−2, respectively, adventitious presence to 0.64 and 0.03%, respectively, and seed viability to ≤ 10%. Combination of glyphosate applied PRE followed by fluroxypyr plus 2,4-D or by thifensulfuron plus tribenuron plus quinclorac applied POST reduced adventitious presence of volunteer flax in wheat to near 0%. These treatment combinations were also effective for reducing volunteer flax fecundity to 0.0 and 7.1 seeds m−2, respectively, and volunteer flax seed viability to 0 and 5%, respectively. This study demonstrated that with effective mitigation strategies, seed mediated gene flow from GE volunteer flax can be reduced.

The absorption and translocation of foliarly applied 14C-labeled (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T-1-14C) in winged elms (Ulmus alata Michx.) as affected by season of application, air temperature, and soil moisture were determined by autoradiography of bark samples and liquid scintillation counting of leaf tissue. Treatments at 3-week intervals throughout the growing season showed highly variable trends in absorption and translocation within and between growing seasons. Seasonal variations in the absorption of 14C-2,4,5-T were similar to the variations in translocation. Translocation into the stem closely correlated with absorption into the leaves. Higher daily temperatures of 24 to 40 C appeared to enhance absorption and translocation. Variations in soil moisture showed little effect on absorption; whereas, a decrease in soil moisture reduced translocation from leaves to roots.

Studies were conducted to determine the stage of growth at which curly dock (Rumex crispus L.) and broadleaf dock (Rumex obtusifolius L.) can propagate vegetatively from a rootstock. Curly dock plants were grown from seed in the greenhouse and phytotron under long-day conditions. Curly dock seedlings were capable of regrowth from a rootstock 47 days from seeding in the greenhouse. Some of the phytotrongrown plants attained this capacity 31 to 38 days after seeding; while all demonstrated this ability at 41 days. Broadleaf dock produced flower stalks within 38 days in phytotron studies but was not capable of regeneration during this same period of time. Broadleaf dock was capable of regrowth from a rootstock approximately 51 days after seeding in the phytotron.

In field experiments conducted from 1985 to 1987 in Mississippi and Arkansas, jimsonweed was successfully controlled with the fungus Alternaria crassa (Sacc.) Rands. Conidial applications of the fungus provided an average of 96% control in Mississippi, and 87% control in Arkansas. Mycelial formulations were less effective than conidial applications overall, but during periods of favorable environmental conditions, weed control provided by the mycelial formulations was similar to that provided by conidial preparations. These results indicate that Alternaria crassa has potential as a mycoherbicide for controlling jimsonweed.

The movement of biologically active levels of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide] was followed by monitoring photosynthetic activity of plant parts after application of the herbicide. Bentazon was applied to roots, stems, petioles, portions of the canopy, and portions of individual leaves of 4- to 24-day-old common cocklebur (Xanthium pensylvanicum Wallr.) at rates comparable to field application rates. Application of bentazon anywhere on the plant either slowed or stopped photosynthesis in leaves acropetal to the point of application. Contact of bentazon with stems, petioles or roots contributed to the phytotoxicity of the herbicide.

Field violet germination occurred during May to early July and again during September to November in Nova Scotia (N.S.), Canada. Germination occurred from October until early April in the North Carolina (NC) piedmont. Germination was stimulated by tillage. Seed collected in N.S. and in NC germinated optimally in the dark under a temperature regime of 15/5 C, on an 8/16 h thermoperiod. Germination at constant temperatures decreased with increasing temperatures, from 5 to 25 C. Seed collected in NC was capable of germinating at a higher constant temperature of 25 C than seed collected in N.S. Germination of seed collected in NC was partially inhibited by constant irradiance with a photosynthetic photon flux density of 100 μM m−2 s−1 (400 to 700 nm). Seed did not germinate when exposed to constant red or far-red irradiance.

In field and greenhouse experiments, liquid or granular formulations of EPTC (S-ethyl dipropylthiocarbamate) applied by hand directly in the row with seed of alfalfa (Medicago sativa L. ‘Vernal’), controlled grass seedlings in bands, usually 5 to 8 cm wide, without injuring alfalfa significantly. Grass was similarly controlled selectively when a mixture of alfalfa seed and clay granules, similar in size to alfalfa seed and containing 10% EPTC, was seeded mechanically.

Some genetic and physiological aspects of seed germination of wild and weedy sunflowers were investigated in order to analyze their population differentiation in seed characteristics. Seed germination of six populations classified on the basis of morphology as Helianthus exilis Gray, H. exilis-bolanderi hybrids, and H. bolanderi Gray was studied under red light at 20 C. The average germination of the three groups respectively were 56, 63, and 42%. Germinability of individual plant progenies derived from populations of H. bolanderi and H. exilis was studied under red and far-red light combined with the pretreatments at two temperatures (10 and 20 C). Average germination per progeny reached a maximum of 59% with red light and 10 C in H. bolanderi. Far-red light promoted germination of H. bolanderi but was ineffective with H. exilis. The homogeneity of populations within each taxon and the fact that germinability differences among the H. bolanderi progenies were consistent over replications, suggest a genetic component of variation. However, progenies obtained by crossing selected individuals that germinated under certain light and temperature treatments, were not significantly correlated in germinability with that of their parents. Inheritance of germination characteristics appears to be complex and highly dependent on the environmental conditions.

An experiment was established in 1961 to determine the influence of bearmat (Chamaebatia foliolosa Benth.) competition on ponderosa pine (Pinus ponderosa Laws.) survival and growth. Ponderosa pine seedlings were planted in bearmat which was: (A) untreated, (B) sprayed with a mixture of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and (C) eliminated by a combination of herbicide, clipping sprouts, and trenching to prevent root and rhizome invasion. Ponderosa pine survival after 19 yr averaged 9%, 66%, and 90%, respectively, for the three treatments. Tree height after 19 yr averaged 1.6, 1.9, and 5.7 m for treatments A, B, and C, respectively. Soil moisture use was initially less on the herbicide-treated than on the untreated plots, but bearmat quickly sprouted after application to compete with the pine seedlings for moisture. After 19 yr the bearmat was more dense and appeared to be more vigorous on the sprayed plots than on those receiving no treatment. We estimate that 75% reduction in net wood production could result after 50 yr on this site from bearmat competition.

Twenty-two sweet potato [Ipomoea batatas (L.) Lam.] clones with a wide range in metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] tolerance were used to establish narrow sense heritability estimates (h2) using a greenhouse procedure. The heritability estimates were obtained from simple linear regressions (h2 = 2b) of injury rating, shoot fresh weight, and change in shoot fresh weight of offspring against the same responses of parents at metribuzin concentrations of 0, 0.3, and 0.6 ppm in the potting medium and averaged data for the two concentrations. These values ranged from 0.85 to 1.0, indicating that a recurrent mass selection process should be an appropriate approach to developing metribuzin-tolerant cultivars. Several highly tolerant clones were identified.

Control of natural infestations of dogfennel [Eupatorium capillifolium (Lam.) Small # EUPCP] and woolly croton (Croton capitatus Michx. # CYNCP) in a bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA] – dallisgrass (Paspalum dilitatum Poir. # PASDI) sward ranged from 20 to 100% with surface-applied tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N-dimethylurea}. In general, efficacy increased with rate of application from 0.6 to 1.1 kg ai/ha, and with time to 107 days after treatment. Only 0.6 kg ai/ha controlled less than 90% of the weeds during the growing season. Dry matter yields of desirable forage ranged from 60 to 290 kg/ha more with tebuthiuron treatment than in the untreated check. There were no consistent differences in forage quality among treatments, which indicates that tebuthiuron had no detrimental effects upon the bermudagrass or dallisgrass.

The concentration of N,N-dimethyl-2,2-diphenylacetamide (diphenamid) required to cause 50% growth inhibition (I50) of the shoots or roots in soil, or the roots in a bioassay, was determined for several species. of the plants tested, grasses were the most sensitive, while Solanaceae were among the most tolerant to diphenamid. Based on shoot inhibition, the sensitivity difference between the sensitive foxtail millet (Setaria italica L.) and the tolerant pepper (Capsicum frutescens L.) was 150 fold. Highly significant correlations among the I50 values indicate that any of the three methods would be satisfactory for measuring the sensitivity of species to diphenamid.

Trifluralin a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) applied at 1.12 kg/ha inhibited lateral root development on field-grown pecan (Carya illinoensis (Wang.) K. Koch) seedlings. In a greenhouse study, inhibition of lateral roots, club-shaped radicles, and restricted penetration of tap roots resulted when pecans were planted in soil treated with 1.0 ppm trifluralin. When pecans were planted above soil treated with trifluralin, normal root development occurred only in the soil which had not been treated. Lateral roots were inhibited in the trifluralin-treated soil. Pecan nuts from trifluralin plots were smaller than those collected from controls, but other factors of quality were statistically equal or superior to nuts harvested in plots which had been treated with 2-chloro-4,6-bis-(ethylamino)-s-triazine (simazine) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). The smaller nut size was attributed to lateral root inhibition by trifluralin early during nut development.

Laboratory and greenhouse studies were conducted to determine the mobility and bioactivity of thiobencarb on a Pahokee muck, Everglades muck, and Immokalee sand. On all soils > 93% of thiobencarb remained in the upper 1 cm after leaching during unsaturated flow. During saturated flow the retardation factor (RT) of thiobencarb on an Immokalee sand was 68, 20, 2, and 1 with 0, 25, 50, and 75% by volume methanol in 0.01 N CaCl2, respectively. There was a significant log-linear relationship (r2 = 0.97) between the Freundlich adsorption values (Kf) estimated from RT values and the percentage by volume methanol of the leachate. In general, thiobencarb in combination with overhead irrigation reduced lettuce vigor and plant dry weight on an Immokalee sand more than with subsurface irrigation.

Temperature changes prior to picloram application affects its activity in leafy spurge. Absorption of 14C picloram was directly correlated with temperature changes; each 1 C increase in air temperature 24 h before treatment resulted in a 1% increase of 14C-picloram absorption in leafy spurge and vice versa. The greatest 14C-picloram absorption averaged 47% of applied 14C when the temperature increased from 18 C to 24 or 30 C 24 h before treatment compared to 33% when temperatures were constant. Translocation of 14C picloram was more sensitive than absorption to temperature changes with 4.3 and 1% of applied 14C-picloram translocated to the roots when the plants were maintained at 12 and 30 C, respectively. Even though absorption increased directly with temperature, 14C-picloram translocation to the root system declined as temperature increased.

Experiments in controlled-environment chambers indicated that high temperature, 30 C, increased the phytotoxicity of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) to wild mustard (Sinapis arvensis L. # SINAR) and redroot pigweed (Amaranthus retroflexus L. # AMARE) compared to low temperature, 10 C, during and after treatment. Bromoxynil phytotoxicity generally was higher at relative humidities of 90 to 95% compared to 40 to 60%, but relative humidity had less influence on bromoxynil phytotoxicity than did temperature. A simulated rain immediately after bromoxynil treatment reduced control of both species, but the reduction was of no practical importance for wild mustard. The data indicate that wild mustard and redroot pigweed control would be reduced by bromoxynil application during a period of low temperatures or to plants in advanced growth stages.

In recent years, chemical control methods have been discovered for most common annual weeds with the notable exception of wild oats. Isopropyl N-phenyl carbamate (IPC) and isopropyl N-(3–chlorophenyl)-carbamate (CIPC) appeared promising in 1950 when they successfully controlled wild oats in barley at University Farm, Saint Paul, Minnesota. In the spring of 1951, investigations were started in an attempt to evaluate these two chemicals further for selective use in field crops.

The present importance of the discipline of weed control is outlined. More acres in the United States are treated today for weed control than for the control of insects or plant diseases, despite disparity in personnel engaged; e.g., a total in the North Central region of 44 men in weed control, 176 in entomology and 177 in plant pathology.

A relatively simple method for screening and evaluating chemicals for algicidal properties has been developed which embodies spray application of chemicals and greenhouse culture conditions. The method utilizes equipment and facilities common to the majority of industrial herbicide screening programs.

Wild oat is the most important weed in Argentine barley and one of the worst weeds in wheat and barley worldwide. During 1997 and 1998, field experiments were performed to determine the response of wild oat to N fertilizer at planting and at early tillering at 55 kg ha−1 with and without the use of diclofop-methyl. Seedling emergence and survival rate, individual fecundity, and preharvest seed dispersal rate of wild oat were assessed. The effect on the individual growth of wild oat was also studied. N fertilizer increased both wild oat seedling survival rate and fecundity, especially when it was applied at early tillering. However, the effect of N fertilization was negligible with diclofop-methyl treatment. In addition, the application of N fertilizer reduced the seed dispersal rate immediately before crop harvest. Quantification of the effects of each agronomic practice, such as N fertilization, is useful to develop simulation models that predict the population dynamics. When N was applied at sowing, the annual growth rate of the wild oat population was almost 25% lower than when applied at early tillering.