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Hannah Mathers, Ohio State University Extension, Horticulture and Crop Science |
Identification of the weeds in your nursery is extremely important. Certain families of weeds respond to certain herbicides and not others. An example is the Mustard family (Brassicaceae). Treflan does not control Mustards. Failure to recognize shepherds purse as a member of the Mustard family and use of Treflan for control would be a waste of time, money, and chemical (Mathers and Leidenfrost, 1995). Another example is with the Pink family (Caryophyllaceae). Many Pink family members are resistant to Ronstar. Members of the Pink family include a number of annuals, biennials, or perennials, including corn spurry (Spergula arvenis), chickweeds and stitchworts (Stellaria spp. and Cerastium spp.), bladder campion (Silene vulgaris), pearlwort (Sagina procumbens), and bouncingbet (Saponaria officinalis).
Most preemergents work on members of the Pink family, including Simazine, Diuron, Casoron, Surflan, and Kerb; however, use of Ronstar would lead to a lack of control. An example of a weed that has become resistant to certain herbicides is common groundsel (Senecio vulgaris), a prevalent weed and serious competitor in nurseries and landscapes. Strains of atrazine-resistant and glyphosate-resistant groundsel have emerged and are becoming an increasing concern. Other weeds with herbicide resistance are kochia, Russian thistle, prickly lettuce, wild oat, Italian ryegrass, Powell amaranth, and yellow starthistle.
Identification of weeds around the nursery is also very important. "Total farm weed control," including adjacent areas such as fence lines, roads, irrigation ditches, and around hoop-houses and other farm buildings, is essential. Most weeds invade the nursery from adjacent farm areas or field perimeters. Control of weeds from adjacent areas is a tough job for nursery managers. However, even if weed control in adjacent areas is unfeasible, identification of the potential weed species is still an option.
Identification to the family level often provides a large part of the information you need to identify the life cycle of the weed and which herbicide will be most effective. The first identification step at the family level is determining if your weeds are grasses, broadleaves, sedges, or rushes. There are several families of problematic broadleaf weeds that have species common in ornamental operations. In the Grass family (Poaceae), there are also numerous difficult ornamental weeds. The most common grassy weed is annual bluegrass. The Sedge family (Cyperaceae) and Rush family (Juncaceae) also have tough-to-control weeds but are not as common in ornamental culture within the western and Midwestern United States.