STUDIES ON WEED SPECIES OF THE GENUS POLYGONUM L.

Summary. Seeds of Polygonum persicaria from several sources, or from plants subjected to in lain treatments, were chilled for varying periods and incubated for a 3-week germination test period. Populations differed widely in seed weight and to some extent in the response to different periods of chilling. No relationship between this response and the climate of the locality of origin could be found. There was much variation in seed weight and germination behaviour between individual plants within populations. A total of four polymorphic seed categories were observed. The proportions of seeds in the two main categories varied widely between and within populations, and were affected by certain environmental factors. These factors also appeared to affect the degree of inter-plant variation in seed shape and germination behaviour.
Travaux sur les espàes indésirables du genre Polygonum L. V. Variations dans le poids des semences, leur comportement à la germination et leur polymorphisme chez P. persicaria L.     

THE INFLUENCE OF IRRIGATION, FERTILIZING AND MCPA ON THE COMPETITION BETWEEN SPRING CEREALS AND WEEDS

Summary. The average air-dry yield of weeds on fallow plots was about four times as large (2660 kg/ha) as the yield of weeds which developed among spring cereal crops (740 kg/ha). Application of fertilizers increased the number of weeds and their average weight on both irrigated and non-irrigated plots. Treatment with MCPA reduced the weed yield to 36% on fallow plots and to 26% on weedy cereal plots. It was more effective on fertilized plots than on unfertilized plots, but irrigation made little difference to its effectiveness. The space left by the destroyed weeds was mainly occupied by Agropyron repens . Oats were better able to compete with weeds than were wheat and barley. On unfertilized and non-irrigated plots spraying with MCPA (1-26 kg/ha) at the beginning of shooting significantly reduced the yields of weed-free barley. The yields of sprayed oats and wheat were also below the yields from the unsprayed although the reductions were not significant at the 5% level. However, on a number of fertilized and irrigated plots, both weedy and hand-weeded , on which the plants had better growing conditions, MCPA resulted in a significant increase in the grain yield of barley and oats.
Influence de l'irrigation, de la fertilisation et du MCPA sur la compétition entre céréales de printemps et mauvaises herbes     

Pathogenicity of Fusarium oxysporum f. sp. Cepae and its interaction with Pyrenochaeta terrestris on onion

Onion breeding lines known to be resistant to Pyrenochaeta terrestris showed, in several locations, root-pruning symptoms that have been usually associated with only the action of P. terrestris. Fusarium oxysporum f. sp. cepae was invariably isolated from affected roots and the stem-plate area of these pink-root-resistant lines. Symptoms not commonly associated with the action of Fusarium, including darkening of dry scales of yellow bulbs and a reddening of scales of white bulbs, were noted. Controlled tests were conducted to establish (a) the pathogenicity of four isolates of F. oxysporum f. sp. cepae, (b) the reaction of onion breeding lines to inoculation at various temperatures with both the pink root and the Fusarium bulb rot organism, and (c) the pathogenic interaction of F. oxysporum f. sp. cepae with P. terrestris. The Fusarium isolates were pathogenic over a wide range of temperatures (20 to 38°C.). Host reaction to the organisms in combination depended on the level of susceptibility that was the greater to one or the other organism. Resistance to one did not markedly modify susceptibility to the other when both were present. Resistance to F. oxysporum f. sp. cepae was found in several onion lines.Horticulturist, Pathologist, and Horticulturist, respectively, United States Department of Agriculture, Beltsville, Maryland, U.S.A.     

CHEMICAL AND BIOLOGICAL PROPERTIES OF TWO NEW HERBICIDES—IOXYNIL AND BROMOXYNIL

Summary. The preparation of ioxynil, bromoxynil, and their salts is described, and information on solubilities and stability to storage is summarized. Although the toxicology of the herbicides is to be reported in greater detail, a preliminary statement is made here. Evidence of herbicidat activity under glasshouse conditions is indicated briefly, and supports the conclusion that both compounds are effective when applied to the foliage of a wide range of dicotyledon weed species. Seedlings of some weed species resistant to the phenoxy alkanoic acids are controlled under glasshouse conditions at doses as low as 0.125 lb/ac, and ioxynil has a wider range of activity than bromoxynil at these low doses. Graminaceous species tolerate 4–8 lb/ac of both herbicides without injury, and certain leguminous crops tolerate one or other herbicide at doses of 0.5–0.75 lb/ac. The contact action of the herbicides is rapid, there are also slower systemic effects, and seed germination is inhibited. In susceptible species the level of post-emergence activity is shown to be influenced by the growth stage of the weed, the distribution of herbicide on the foliage, and environmental factors of which light intensity appears to be most important.
Propriétés chimiques et biologiques de deux nouveaux herbicides: ioxynil et bromoxynil