Tolerance of Some Garden Flowers to Selected Preemergence Herbicides

Abstract

Alachlor G and EC, chloropropham G, and napropamide G at 4.4 and 8.8 kg/ha and trifluralin G at 4.4 kg/ha were applied to chysanthemum, aster and portulaca and all materials except trifluralin to gladiolus after field planting. Weed population and plant quality data were taken twice during the growing season. Alachlor G or EC provided the best weed control followed by napropamide. Control by trifluralin was acceptable but weed suppression by chloropropham was not. Alachlor, napropamide, chloropropham and trifluralin cause no significant injury to portulaca, aster or gladiolus. All formulations of alachlor produced significant damage to the chrysanthemum while napropamide, chloropropham and trifuralin were safe. A wide variety of annual flowers are grown for seasonal color in commercial and residential landscapes and for cut flower production. Weed competition in such plantings causes a serious reduction in growth (Newman and Binning, 1974) and detracts from the aesthetics of the planting and overall landscape. Handweeding is a major maintenance cost for such plantings. Ahrens (1974) reported hoeing costs in chrysanthemum fields to be over $1000/ha. The cost for present day operations has increased dramatically due to inflation and is compounded by the varied sizes and shapes associated with annual beds as opposed to field rows. The diversity of species used for outdoor annual and perennial gardens serve to further complicate chemical weed control. Several trials conducted in the past have found species tolerance to herbicides highly variable (Newman and Binning, 1974; Bing, 1982, 1983a). Four species of flowers of particular interest in landscapes include: chrysanthemum (Chrysanthemum x morifolium Ramat.); gladiolus (Gladiolus x hortulanus Baily); aster (Callistephus chinesis (L.) Nees); and portulaca Journal Article 83-190-J, Kansas State University Agricultural Experiment Station. This content downloaded from 207.46.13.148 on Sun, 11 Sep 2016 04:33:42 UTC All use subject to http://about.jstor.org/terms VOLUME 88, NUMBERS 3-4 147 (Portulaca grandiflora Hook). Chrysanthemums are planted for a fall color display and are field-grown for retail sales. A large number of cultivars have been selected and named. Gladioli are grown commercially as cut flowers from corms (Bing, 1979) and as landscape annuals. Asters are also grown for cut flowers and as annual bedding plants. Portulaca is a low growing landscape annual tolerant of dry, hot conditions. Chrysanthemum has been shown to be tolerant of DCPA, diphenamid, trifluralin, chloropropham, and napropamide (Bing, 1982). DCPA, dephenamid, trifluralin, EPTC and chloramben are currently recommended for use with this species (Smith, 1982). Ahrens (1974) reported injury to chrysanthemum from emulsifiable concentrate formulation of alachlor (4.4 kg/ha) and a slight reduction in growth and later flowering due to granular application to the cultivar 'Chapel Bell'. Root dips of activated carbon were not totally effective in protecting chrysanthemums from alachlor. No injury occurred when 2.2 kg/ha alachlor was applied to field planted rooted cuttings, however, 4.4 kg/ha caused moderate leaf curl in two established cultivars and stunted field plant rooted cuttings (Ahrens, 1973). Granular alachlor (4.4 kg/ha) did not injure seven cultivars when applied in August. Currently recommended herbicides for gladiolus include trifluralin, bensulide and DCPA (Smith, 1982). Napropamide (Wilfret and Burgis, 1977; Bing, 1979) and oxyflurofen caused leaf burn and greatly reduced corm production (Bing, 1979). Talbert et al. (1979, 1980) reported increasing injury to gladiolus with increasing rates of napropamide but found no injury for alachlor. Bing (1977) reported injury to cormels by alachlor at higher