The inheritance of resistance to the auxinic herbicide dicamba was examined in a kochia population from Nebraska. An inbred, resistant line was developed by selection and selfing over seven generations to ensure any resistance alleles would be homozygous in the parents. An inbred, susceptible line was similarly developed, but without selection. Dose–response experiments with dicamba determined a glyphosate-resistant concentration required to inhibit dry weight accumulation by 50% (GR50) of 45 and 1,331 g ae ha−1for the susceptible and resistant populations, respectively. F1crosses were made between resistant and susceptible inbred individuals by hand-pollination, and the F1plants were selfed to produce F2plants. The F2population was screened with 280 g ha−1dicamba, a rate that could discriminate between susceptible and resistant plants. A total of eight F2families were screened twice. In the first screen, seven F2families segregated in a 3:1 ratio, consistent with a single dominant allele controlling resistance, and in the second screen six F2families segregated in a 3:1 ratio. F2individuals were selfed, the F3progeny were tested with 280 g ha−1dicamba, and the genotype of each F2parent was determined based on F3progeny segregation. F3family segregation was consistent with the F2parents having a 1:2:1 homozygous-susceptible:heterozygote:homozygous-resistant pattern, confirming that resistance to dicamba in kochia is likely conferred by a single allele with a high degree of dominance.
The resolved isomer of metolachlor, S-metolachlor, was registered in 1997. New formulations based primarily on the S-metolachlor isomer are more active on a gram for gram metolachlor basis than formulations based on a racemic mixture of metolachlor containing a 50:50 ratio of the R and S isomers. The labelled use rates of S-metolachlor-based products were reduced by 35% to give equivalent weed control to metolachlor. However, several companies have recently registered new metolachlor formulations with the same recommended use rates for weed control as S-metolachlor. This research was done to compare the soil behaviour and the biological activity of metolachlor and S-metolachlor in different soils under greenhouse and field conditions. Although K(d) ranged from 1.6 to 6.9 across the five soils, there were no differences in the binding of metolachlor and S-metolachlor to soil or in the rate of soil solution dissipation in a given soil. However, both greenhouse and field studies showed that S-metolachlor was 1.4-3-fold more active than metolachlor against Echinochloa crus-galli (L.) Beauv. in five different soils and that S-metolachlor was more active than metolachlor in three Colorado field locations. When the rates of metolachlor and S-metolachlor were adjusted for S isomer concentrations in the formulations, there were no differences between the formulations in field, greenhouse or bioassay studies. Thus herbicidal activity is due to the S isomers, with the R isomers being largely inactive.
High Avena fatua control costs have caused some Hordeum vulgare growers to use reduced rates of herbicides without fully understanding the consequences. Field studies near Moscow and Genesee, ID, were conducted to determine the effect of A. fatua density and PP-604 rate on A. fatua seed production in H. vulgare and on H. vulgare yield. PP-604 treatments were 25, 50, 100, 150, and 200 (minimum labeled rate) g ha−1, and five A. fatua densities ranged from 0 to 386 plants m−2. Visual A. fatua control was greater than 85% with 100 g ha−1 PP-604 at all locations. Data from 1998 were used to construct nonlinear exponential decay and parabolic models to describe the effect of reduced herbicide rates on viable A. fatua seed production and relative H. vulgare grain yield, respectively. At A. fatua densities of 42 to 138 plants m−2, 46 to 71% of the minimum labeled rate of PP-604 reduced seed production 95%. However, an estimated 140 to 235 seeds m−2 were produced at this level of control, which may not ensure a decline in the A. fatua population over the long-term. Hordeum vulgare grain yield was maximum when 70 to 85% of the minimum labeled rate was applied to A. fatua densities of 42 to 138 plants m−2. A higher rate of PP-604 likely will be required to ensure a decline in A. fatua populations over the long-term than needed to obtain maximum H. vulgare grain yield in a single growing season.
Growth analysis, absorption and translocation studies were conducted to compare a 1-aminomethanamide dihydrogen tetraoxosulfate (GLY-A) formulation of glyphosate with two isopropylamine (GLY-IPA-1, GLY-IPA-2) formulations of glyphosate on velvetleaf. The two isopropylamine formulations differed by the presence of a surfactant in the formulation, GLY-IPA-1 containing surfactant whereas GLY-IPA-2 did not. Four- to six-leaf velvetleaf was treated with GLY-A and GLY-IPA-1 and GLY-IPA-2 (0, 50, 67, 89, 119, 158, 280, 420, 560 and 840 g AE ha(-1)) with and without ammonium sulfate (AMS; 20 g L(-1)). GLY-A and GLY-IPA-2 included a non-ionic surfactant (2.5 mL L(-1)) in the spray solution at all herbicide concentrations. No additional surfactant was added to GLY-IPA-1. The IC50 value for GLY-A was 88 g AE ha(-1) compared with 346 and 376 g AE ha(-1) for GLY-IPA-1 and GLY-IPA-2 respectively in the absence of AMS. When AMS (20 g L(-1)) was added to the spray solution, the estimated IC50 values were 143, 76 and 60 g AE ha(-1) for GLY-IPA-1, GLY-IPA-2 and GLY-A respectively. Absorption of 14C-glyphosate into the third leaf of five- to six-leaf velvetleaf was three- to sixfold greater 72 h after treatment (HAT) when applied as GLY-A compared with GLY-IPA-1 and GLY-IPA-2 respectively in the absence of AMS. AMS (20 g L(-1)) increased absorption of 14C-glyphosate in all glyphosate formulations two- to threefold, but differences among the formulations remained. Approximately three- and sixfold more 14C-glyphosate applied as GLY-A had translocated out of the treated leaf compared with GLY-IPA-1 and GLY-IPA-2 respectively by 72 HAT. Adding AMS (20 g L(-1)) increased translocation of 14C-glyphosate out of the treated leaf approximately 2.5-fold for all three formulations. The increased efficacy of GLY-A versus GLY-IPA-1 and GLY-IPA-2 on velvetleaf is due to the greater rate of absorption and subsequent translocation of glyphosate out of the treated leaf. AMS increased the efficacy of all three formulations by increasing absorption and translocation of glyphosate in the plant.
Over the last 18 months, Syngenta has gone through a strategic realignment in order to optimally leverage the depth and breadth of our seed treatment and crop protection chemistries against our genetic and seed technology portfolio. Hilleshӧg has long been recognized as the disease tolerance provider, offering strong native tolerance and resistance to a wide array of pests and pathogens, including industry leading Cercospora, Rhizoctonia, and Curly Top tolerance. Additionally, Syngenta has offered the industry leading chemistries and seed treatments necessary for season long disease and weed control. Developing a "One Syngenta" approach to solving grower issues has allowed the sugar beet seed business access to all new seed technologies, molecular tools and GM platforms formerly limited to our corn and soybean business, launching our breeding efforts forward into the new millennium. Additionally by building working groups across business functions key weaknesses in one portfolio are quickly recognized and the gaps are filled with strengths from another. One Syngenta strategies and success stories will be addressed.
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