Herbicide Kochia

The development of herbicide-resistant weeds has also been an influence on the selection of herbicides used on field corn or soybean. Weed resistance now affects nearly every decision a farmer makes about herbicide selection either a farmer is trying to control resistant weeds or is selecting herbicides that may reduce the possibility of weed populations becoming resistant. The adoption of the imidazolinone- and sulfonylurea-tolerant com hybrids mentioned above was in part a response to the presence of atrazine-tolerant pigweeds or kochia in many fields. However, a recent decrease in die use of imidazolinone and sulfonylurea herbicides can also be attributed to the development of populations of weeds that have become resistant to these herbicides. 

For example, kochia is normally very sensitive to atrazine and can often be controlled with l.lkg/ha (llb/A) along railroads and on farm lands. However, Burnside et al. (1979) reported that after 13 years of atrazine use, Union Pacific personnel were applying up to 15 kg/ha (13 lb/A) with poor control. These high rates are no longer allowed for atrazine uses. The use of mixtures of triazines and herbicides with alternate modes of action has been an effective management strategy to control weeds resistant to triazines. 

Until the mid-1990s, multiple-resistance (i.e., resistance to more than one herbicide mode of action within the same biotype) had not been reported within North America. However, Foes et al. (1996) found a kochia biotype from western Illinois resistant to atrazine and several ALS-inhibiting herbicides. Lopez-Martinez et al. (1996) reported that a triazine-resistant Echinochloa species found in atrazine-treated com also showed cross-resistance to quinclorac. Clay and Underwood (1989) and Clay (1989) reported that one triazine-resistant biotype of American willowherb was also resistant to paraquat from a hop garden in the United Kingdom treated annually for 25 years with simazine and paraquat. 

The first ALS-resistant weeds were reported in 1987 when prickly lettuce (Mallory-Smith, 1990 Mallory-Smith et al, 1990b) and kochia (Primiani et al, 1990) control failures occurred in Idaho and Kansas, respectively, after 5 consecutive years of chlorsulfuron use. The kochia biotype proved to be cross-resistant to six other ALS-inhibitor herbicides, including sulfonylureas and imidazolinones. Within 5 years, sulfonylurea-resistant kochia had been identified at 832 sites in 11 states of the United States and in three Canadian provinces (Saari et al, 1994). ALS inhibitor-resistant kochia and Russian thistle have become widespread problems in cereal-producing regions of northwestern United States and Canada. The mobility of these tumble weeds as plants with mature seeds or pollen carried by wind has undoubtedly contributed to the rate at which resistance has spread. 

Devine et al. (1991) and O Donovan et al. (1994) reported that chlorsulfuron-resistant chickweed populations were also resistant to other sulfonylurea herbicides. Primiani et al. (1990) reported cross-resistance to several sulfonylurea and imidazolinone herbicides in chlorsulfuron-resistant kochia. Lovell et al. (1996a) also documented that chlorsulfuron-resistant kochia biotypes from Idaho and Montana were cross-resistant to imazethapyr. 

Multiple-resistance mechanisms, defined as resistance due to more than one mode of action or class of herbicide, have been reported in several ALS-resistant weed biotypes - including false cleavers, wild oat, common waterhemp, kochia, rigid ryegrass in Australia (Powles and Matthews, 1992 Preston and Mallory-Smith, 2001), and wild radish (Walsh etal, 2004a). 

Tierney and Talbert (1995) found that the best treatments for control of both ALS-resistant and susceptible common cocklebur were triazine herbicides (i.e., atrazine, cyanazine, and metribuzin). Tonks and Westra (1997) reported that mixtures including ALS inhibitors gave no better control of ALS-resistant kochia from Colorado and Kansas than the nonsulfonylurea herbicides alone. 

Application time Herbicides used Kochia Smooth pigweed Palmer amaranth Common cocklebur Common tall waterhemp... 

Primiani, M.M., J.C. Cotterman, and L.L. Saari (1990). Resistance of kochia (Kochia scoparia) to sulfonylurea and imidazolinone herbicides. Weed Technol., 4 169-172. 

Saari, L.L., J.C. Cotterman, and M.M. Primiani (1990). Mechanisms of sulfonylurea herbicide resistance in the broadleaf weed Kochia scoparia. Plant Physiol., 93 55-61. 

Nalewaja JD and Matysiak R Spray carrier salts affect herbicide toxicity to kochia (Kochia scoparia), Weed Technology 7(1) 154-8 (1993). 

Resistant biotypes being reported in the early 1990s were selected by chlorsul-furon or metsulfuron-methyl in wheat-growing areas or by sulfometuron-methyl in non-crop areas. While resistance of Lolium rigidum to ALS-inhibitors was attributed to enhanced herbicide metabolism [50] it was shown, for Lolium perenne and dicotyledonous species like Stellaria media, Kochia scoparia, Scdsola iberica and Lactuca serriola, that resistant biotypes had a mutated ALS with reduced susceptibility to ALS-inhibitmg herbicides [51-53]. The IC50S for sulfonylureas, which were determined in vitro with ALS isolated from Stellaria media, Salsola iberica and Lolium perenne, increased 4- to 50-fold in the resistant biotypes. Smaller increases, about 2- to 7-fold, were determined in the same biotypes for the imidazo-linone herbicide imazapyr [53]. 

Selection of multiple resistance after sequential use of different herbicides has been described for a biotype of Kochia scoparia from North America. Many years... 

Fig. 2.5.18. Sensitivities of ALS from SU-resistant kochia to ALS-inhibiting herbicides. The data is for a kochia that has a mutation of...

Uses Postemergence herbicide used to control weeds such as chickweed, dogfennel, foxtail, kochia, nightshade and yellow mustard, in strawberries, beet crops and spinach. 

Uses Selective preemergence or postemergence herbicide used to effectively control a wide variety of broad-leaved weeds (such as bindweed, jimsonweed, kochia, mustards, pigweeds, sesbania, smartweed and velvet-leaf) in tolerant erops (com, grain sorghum, maize, rice and soybeans). 

Table ni. Characterization of the Response of Susceptible (S) and Resistant (R) Kochia Biotypes to Sulfonylurea, Triazolopyrimidine sulfonanilide, and Imidazolinone Herbicides (adapted from ref. 2. and Saari, L. L. Cotterman, J. C. Primiani, M. M. 1990, Plant Phvsiol. (in press)). 

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