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- Author or Editor: C. L. Elmore x
The perennial Brassicaceae specie Rorippa sylvestris has been described as a weed in Scandinavian forest nurseries and in Irish, Canadian, and American nurseries. It was first introduced into Philadelphia, Pennsylvania in about 1818 and has been reintroduced repeated since. It produces little seed unless there are two different introductions together because they are self incompatible. Propagation is principally by rhizome segments from soil or ornamental propagation material. Greenhouse studies to evaluate the depth of emergence of rhizome pieces indicated that 3-cm segments would routinely emerge from depths of at least 24 cm. Allocation to shoot, roots, stems or shoots form rhizomes varied greatly by depth. The greatest shoot weight was from shallow depths with increasing new shoots from rhizomes and stem weights from deeper depths. Preemergence control was excellent with dichlobenil granules at 3 or 6 lb/A, isozaben at 1 or 2 lb/A and the geotextile/herbicide (Biobarrier). The geotextile (Typar) fitted as collars alone were not effective. Trifluralin incorporated into the surface 2 inches at 2 lb/A was effective but did allow some emergence. Trifluralin plus isoxaben or oryzalin plus isoxaben were also effective at rates of 2 plus 0.5, 4 plus 1, or 6 plus 1.5 lb/A, or 3 plus 1, 4.5 plus 1.5, or 6 plus 2 lb/A, respectively, of the two herbicide combinations. Metolachlor at 3, 4.5, or 6 lb/A was ineffective for preemergence control of 3 cm rhizome pieces. Post emergence control was not commercial with 2,4-D, triclopyr, clopyralid or a combination of the latter two, when treated in the 6 to 8 leaf stage with 0.25% or 0.5% solutions. Once creeping field cress is established in ornamentals it is very difficult to control.
Soil solarization, alone and combined with metam sodium (MS), was evaluated as an alternative to methyl bromide and chloropicrin (MBC) fumigation, the standard soil disinfestation technique in the California strawberry (Fragaria ×ananassa Duch.) industry. Tests were conducted in two consecutive annual production cycles in Irvine, Calif., an environment representative of the coastal strawberry production area. Solarization treatments were applied from late July through September for October plantings. Treatments were equally effective in reducing baited populations of Phytophthora cactorum [(Lebert and Cohn) J. Schröt] (1989-90) and P. citricola Sawada (1990-91) when compared to pathogen survival in nontreated soil. Solarization and MBC reduced Verticillium dahliae Kleb inocnlnm in 1989-90, but MBC gave superior control in 1990-91. Solarization significantly controlled annual weeds, but was less effective than MBC. In 1989-90, solarization alone increased strawberry yield 12 % over the yield of nontreated plots; when combined with MS, yield increase was 29%, equivalent to that achieved with MBC fumigation. Treatments were equally effective in increasing yields in the 1990-91 test. Chemical names used: sodium N -methyldithiocarbamate (metam sodium), chloropicrin nitrotrichloromethane (chloropicrin).
Weed competition reduced the growth of young peach and plum rootstoeks. Heavy sprinkler irrigation increased the phytotoxicity of simazine to young Prunus rootstoeks. Recovery from severe foliar injury occurred during the season and normal growth resulted at the lower rates of simazine. No detrimental residual effect on tree growth was noted during the following season.
Principal hosts of the misletoe Phoradendron flavescens (Pursh.) Nutt. that infests black and English walnut trees in California are common cottonwood and California buckeye, but it also occurs on many other trees. The mistletoe usually becomes established in new growth or roughened areas along the older stems and crotches of branches of the host trees (2).
The control of annual weeds in young prune orchards increased growth. The degree of foliar expressed phytotoxicity did not result in decreased tree growth. Simazine gave long lasting weed control and the most foliar symptoms on prunes, but superior tree growth. Simazine and dichlobenil produced more foliar symptoms than diphenamid, but less indication of growth reduction.
A number of pre-emergence soil residual herbicides were tested at 2 locations on varieties of young peach, plum, cherry, pear and walnut rootstocks. The greatest variation in response resulted from differences in location. Important differences in varietal response were also obtained with the various herbicides in light soils. Simazine appeared sufficiently safe to trees in heavier soil but gave variable weed control. Diuron gave about the same degree of weed control but more safety than simazine on young trees. Of the uracil herbicides tested, DP-733 was the least toxic to the fruit tree species tested, while bromacil and isocil were generally the most toxic, except to peach trees. Of the commercial uracil herbicides, only DP-732 (terbacil) was of sufficient interest for further study.