Thomas Karp Pavlychenko's pioneering investigations on the root systems of crops and weeds and the results of his research on weed biology and ecology at the University of Saskatchewan in the 1930's and 1940's provided the foundation for many of the principles of modern weed science. His classical studies in which he quantified the distribution and length of roots of many plant species continue to be regarded as being of unsurpassed caliber. In addition to his work in the areas of crop ecology and plant competition, Pavlychenko is also noted for his many contributions relating to the cultural and chemical control of weeds. In this paper, a brief chronicle of Pavlychenko's life and major accomplishments during his remarkable career at the University of Saskatchewan and later with the American Chemical and Paint Company is presented.

Optimum germination of fringed sagebrush (Artemisia frigida Willd.) occurred at alternating temperatures of 10 to 20 C. Seeds were able to germinate (15%) in NaCl concentrations of 5000 ppmw. Light was important in seed germination; however, its absence could be overcome by adding 30 ppmw GA3 (gibberellic acid) to the germination medium. Optimum pH for germination was between 5.8 and 7.0. Depth of planting influenced seedling emergence; the greatest emergence occurred when seeds were planted on the soil surface; emergence was lower when seeds were buried at any depth in the soil. Osmotic potentials of −13 bars and greater reduced germination, but 6% of the seeds germinated at −15 bars. Fringed sagebrush seedlings tolerated average plant water potentials of −10 to −19 bars and died when water potentials were decreased to −22 bars. Mature fringed sagebrush plants were capable of producing from 16500 to 190000 seeds/plant.

The organophosphate insecticides, malathion [S-1,2-di (ethoxycarbonyl)ethyl O, O-dimethyl phosphorodithioate], parathion (O, O-diethyl O-4-nitrophenyl phosphorothioate) and diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate) combined with bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], caused severe injury to soybean [Glycine max (L.) Merr. ‘Corsoy′] and navy bean (Phaseolus vulgaris L. 'Seafarer′). Postemergence tank – mixture applications of bentazon with organophosphate or carbamate insecticides, or soil-applied organophosphate insecticides prior to bentazon treatments, did not interact with bentazon to injure corn (Zea mays L. ‘Great Lakes Hybrid 4122′). Technical grade malathion interacted with bentazon to the same extent as formulated malathion. Combination treatments of malathion with bentazon resulted in the same degree of injury whether they were applied as tank mixtures or split applications 48 h apart.

Oat (Avena sativa L. ‘Elgin′) and soybean (Glycine max L. ‘Evans′) were treated with 14C-diclofop-methyl {methyl ester of 2-[4-(2,4-dichlorophenoxy)phenoxy] propionic acid]} or 14C-diclofop alone or in combination with 2,4-D [(2,4-dichlorophenoxy)acetic acid] or bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and 14C-2,4-D alone or in combination with diclofop-methyl or diclofop. More radioactivity was recovered in the treatment zone after 14C-diclofop-methyl applications, alone or in combination, than after similar 14C-diclofop treatments in oat and soybean. Basipetal movement of radioactivity was 4 and 1% and acropetal movement was 1 and 4% in oat and soybean, respectively, regardless of the diphenyl ether treatment or time. Addition of 2,4-D or bentazon did not reduce translocation of radioactivity from 14C-diclofop-methyl treatments in either plant species. Basipetal movement of radioactivity from 14C-diclofop-methyl was greater than from 14C-diclofop in both oat and soybean. The addition of diclofop-methyl or diclofop did not affect the pattern or amount of 14C-2,4-D radioactivity translocated. In oats, radioactivity appeared to accumulate within the intercalary meristematic region with 14C-2,4-D and 14C-diphenyl-ether applications. Diclofop-methyl at 1 kg/ha applied either to an entire oat plant at the three-leaf stage or the apical meristemic region resulted in plant mortality. The extent to which transport contributes to diclofop-methyl efficacy is questioned.

Alfalfa (Medicago sativa L.), beans (Phaseolus vulgaris L.), corn (Zea mays L.), potatoes (Solanum tuberosum L.), spring wheat (Triticum aestivum L.), and sugarbeets (Beta vulgaris L.) were severely injured and had reduced foliage dry weights when grown in soil containing 0.10 ppmw or more terbacil (3-tert-butyl-5-chloro-6-methyluracil). Activated carbon at 150 kg/ha prevented a significant loss in weight of beans and corn in soil containing 0.10 ppmw terbacil and fully protected potatoes in soil containing 0.19 ppmw terbacil. Carbon at 300 kg/ha fully protected sugarbeets and prevented a significant weight loss in alfalfa in soil containing 0.19 ppmw terbacil. Carbon at 600 kg/ha did not protect wheat from 0.19 ppmw terbacil.

The influence of water stress on toxic alkaloid concentrations in threadleaf groundsel (Senecio longilobus Benth.) was investigated in a controlled environment by monitoring leaf xylem water potential during a 32-day period, and then analyzing for alkaloid concentration by plant part. Total plant alkaloid concentration increased with increasing severity of water stress. The most severe water stress (−2.0 MPa) for the 32-day period increased alkaloid concentration by 4.6 times, compared to the least stress imposition (−1.0 MPa). Averaged across watering regimes, alkaloid concentrations (percent dry weight) were highest in threadleaf groundsel roots (0.088%) and occurred in similar concentrations in stems (0.046%) and leaves (0.050%). These results indicate the importance of considering the influence of plant water stress when investigating secondary plant compounds.

To determine the competitiveness of common cocklebur (Xanthium pensylvanicum Wallr.) with cotton (Gossypium hirsutum L. 'Stoneville 213′), experiments were conducted on a Lucedale fine sandy loam from 1978 through 1980. Common cocklebur dry weight increased with increasing density up to 16 plants/15 m of row. No further increase in dry matter occurred beyond this density. Regression analysis showed that common cocklebur produced an average of 342 kg/ha of dry weight for each plant per 15-m row. Seed-cotton yields decreased as weed density increased up to 16 common cocklebur plants/15 m of row. Regression equations revealed yield losses ranging from 72 to 115 kg/ha for hand-harvested seed cotton and 57 to 90 kg/ha for machine-harvested seed cotton for each common cocklebur plant/15 m of row. Cotton stem diameter and height were reduced by weed competition in the same manner as seed cotton yields, but reductions were not as pronounced, indicating that these parameters were not good indicators of common cocklebur competition.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) killed nearly 100% of the wild garlic (Allium vineale L.) plants when applied in spring, but was less effective when applied in the fall. Treatment in the spring with paraquat consistently killed more wild garlic plants than treatments at any other date. Eradication of a wild garlic infestation was achieved after applications for three successive springs. Near eradication was achieved with two annual applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Among herbicides evaluated postemergence on wild garlic, mefluidide (N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide}, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene], bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], asulam (methyl sulfanilylcarbamate), and picloram (4-amino-3,5,6-trichloropicolinic acid) were not effective for controlling wild garlic. Glyphosate [N-(phosphonomethyl)glycine] and a mixture of cyperquat (1-methyl-4-phenylpyridinium) and 2,4-D ester reduced wild garlic populations by over 60%.

Analysis of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] in soil solution after application of 0.5 or 1.0 ppmw revealed up to five-fold differences among three Alabama soils (Lucedale fine sandy loam, Decatur silty clay loam, and Sacul loam). Differences in fluometuron in soil solution were attributed to variable organic matter present and clay fractions. Fluometuron concentration in soil solution for each soil correlated well with control of four broadleaf weed species in a field experiment.

Soybeans [Glycine max (L.) Merr.] are often the replacement crop when cotton (Gossypium hirsutum L.) is abandoned because of stand failure in the southern United States. Injury from cotton herbicides may be reduced if the soybean planting is delayed more than 4 weeks after cotton planting or if the original herbicide-treated area is fully tilled and a new seedbed formed. Planting delay intervals were compared with five cotton preemergence herbicides on Calloway silt loam at one location. Seedbed-preparation methods were included in a similar experiment at two locations on Sharkey silty clay. Herbicides compared were fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone], cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, perfluidone {1,1,1-trifluoro-N-[2-methyl-4-phenylsulfonyl)phenyl] methanesulfonamide}, fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. Seedbeds compared were no-till and conventional (fully tilled). Soybean planting delays after cotton planting were 20, 29, and 56 days (first year), and 15 and 29 or 15 and 30 days (second year). We found in the 2-yr studies that fluridone severely damaged soybeans both years. Fluometuron and diuron also caused damage the second year when we experienced wet, cool conditions in the spring. Most injury occurred on the clay, with yield reductions occurring even after the 30-day delay. Norflurazon was most injurious at this location. The no-tillage planting method resulted in the least herbicide injury on the silt loam and the conventional tillage method was better on the clay. Detailed studies with fluometuron under incubation conditions showed that degradation was inhibited most by low temperatures and high soil moisture.

Showy crotalaria (Crotalaria spectabilis Roth) was grown in a controlled-environment greenhouse with a day/night temperature of 32/26C at full sunlight and under 40, 60, or 90% shade. Shading significantly reduced height, dry-matter accumulation, leaf production, leaf-area expansion, axillary-branch development, reproductive development, and the partitioning of plant biomass into stems. Shading increased the partitioning of plant biomass into leaves and the leaf area ratio. Constant shading or shading from 0 through 25 days after planting reduced the leaf area duration (LAD) proportionally more than the net assimilation rate (NAR). Shading from 25 to 67 days after planting reduced NAR and LAD equally. In other experiments reducing the day/night temperature below 32/26C significantly reduced plant height, leaf area, and the rate of leaf production. Dry-matter production decreased significantly at temperatures below 29/23C, because of substantial reduction in LAD. Showy crotalaria flowered and produced seed at temperatures ranging from 23/17C to 32/26C. The results indicate that the geographical distribution of showy crotalaria in the United States probably will continue to increase.

Thirty compounds that are precursors, analogs, derivatives, or fragments of strigol were prepared and tested for their activity as witchweed [Striga asiatica (L.) Kuntze] seed-germination stimulators. Five compounds showed significant stimulatory activity. Among these were 5-ethoxy-3-methyl-2(5H)-furanone, 3-hydroxy-2,6,6-trimethylcyclohex-1-ene-1-carboxaldehyde, a two-ring analog of strigol, and two isomers of a three-ring analog. Several of the other 25 compounds showed slight and/or non-reproducible activity when dimethylsulfoxide was used as the carrier at 0.1% (v/v) in aqueous solutions. Compounds with such diverse structures as trimethylcyclohexenes, furanones, and bicycloheptenones were among those that possessed some stimulatory activity.

Four herbicides were applied in the spring and fall over a 3-yr period to Kentucky bluegrass [Poa pratensis (L.) ‘Common′] in the Mountain Region and bermudagrass [Cynodon dactylon (L.) Pers. ‘Common′] in the Piedmont Region of Georgia at different frequencies of treatments for summer and winter weed control. Large crabgrass [Digitaria sanguinalis (L.) Scop.] was controlled throughout the 3-yr period from spring treatments of bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] at 11.2 kg/ha and oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] at 4.5 kg/ha in the first year followed by 5.6 kg/ha for bensulide and 2.3 kg/ha for oxadiazon the following 2 yr. To control large crabgrass with benefin (N- butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) it was necessary to apply 3.4 kg/ha for 2 consecutive yr before rates could be reduced to 1.7 kg/ha. Oxadiazon was the only herbicide that controlled goosegrass [Eleusine indica (L.) Gaertn.] completely. Control was excellent throughout the 3-yr period when oxadiazon was applied at full rate in the spring of the first year with no additional treatments during the following 2 yr. Optimum control of winter weeds was obtained throughout the 3-yr period when herbicides were applied at full rates for the spring and fall treatments the first year followed by one-half rates at similar dates the following 2 yr. Bensulide treatments increased cover of corn speedwell (Veronica arvensis L.) and hop clover (Trifolium agrarium L.); DCPA (dimethyl tetrachloroterephthalate) and benefin increased spur weed (Soliva spp.) and wild parsnip (Pastinaca sativa L.); and oxadiazon increased wild parsnip and thymeleaf sandwort (Arenaria serpyllifolia L.).