Effect of Seeding Rate on Dose Response of Wild Mustard (Sinapis arvensis) to Fluthiacet-Methyl

Abstract

Concern over the development of herbicide-resistant weeds has led to interest in integrated weed management systems that reduce selection pressure by utilizing mechanical and cultural weed control practices in addition to herbicides. Increasing crop seeding rate increases crop competitive ability and thus can enhance herbicide efficacy. However, it is unknown how increasing the seeding rate affects an herbicide’s efficacy. The objective of this study was to examine the interaction between increasing seeding rate and herbicide dose to control weeds. To meet this objective, the herbicide fluthiacet-methyl was applied to field-grown lentil, with Indian mustard, a proxy for wild mustard, used as a model weed. The experiment was a factorial design with four lentil seeding rates and seven herbicide rates. Overall the herbicide dose response was altered by changing lentil seeding rate. Increasing lentil seeding rate decreased the weed biomass production when herbicides were not applied. In two of the four site-years, increasing lentil seeding rate lowered the herbicide ED50, the dose required to result in a 50% reduction in weed biomass. Increasing the crop seeding rate altered the dose response to provide greater weed control at lower herbicide rates compared with normal crop seeding rates. Increased seeding rates also resulted in higher and more stable crop seed yields across a wider range of herbicide dosages. These results suggest that dose–response models can be used to evaluate the efficacy of other weed management practices that can interact with herbicide performance.

Wheat Density Alters but Does Not Repress the Expression of a Fluroxypyr-Resistant Kochia (Bassia scoparia) Phenotype

“…The estimated doses required to achieve 50% visible control (ED 50 ), reduce kochia biomass by 50% (GR 50 ), or reduce kochia plant survival by 50% (LD 50 ) relative to the untreated control for each corresponding population and crop density, were extracted. The ED 50 and LD 50 values were regressed against wheat density using linear regression to assess the relationship between wheat density and phenotypic response to fluroxypyr treatment [19]. The relative differences (estimated ratios or R/S) in ED 50 , GR 50 , or LD 50 among the putative resistant populations (RockyView18 and Vulcan17) and the susceptible control [Lethbridge18(S)], and among the crop densities, were determined and compared using a t-test at α = 0.05 [40].…”

“…The kochia biomass DW data did not pass the lack-of-fit test for nonlinear regression (i.e., p < 0.05), although visualization of these data shows greater variability in response of RockyView18 to fluroxypyr rate compared with Lethbridge18(S), and a consistent biomass reduction in response to increasing wheat interference when fluroxypyr rates were inadequate for complete control (Figure S2). Augmented herbicide performance in response to increased crop seeding rate has been well documented in wheat and other crops [17][18][19]30]. For example, a range of post-emergence herbicides were more effective at reducing wild oat (Avena fatua L.) biomass and seed in the soil seedbank when wheat was seeded at 150 kg ha −1 compared with 75 kg ha −1 [18].…”

“…Resistance to multiple herbicide sites-of-action in kochia limits options for herbicidal control [3,14,15], creating a need for integrated weed management programs that exploit non-chemical weed control strategies. Cultural management tools used to increase crop competitive ability can interact with and augment herbicide efficacy [16][17][18][19]. One of the easiest, most effective, and consistent ways to improve crop competitive ability is to increase seeding rates [20,21].…”

“…The weed-suppressive effects of increased wheat plant densities have been well documented [17,18,[22][23][24][25][26][27][28][29]. Increased crop seeding rates interact with herbicide performance resulting in improved weed management [17][18][19]30]. Thus, cultural weed management tools such as increased seeding rates, when implemented in combination with herbicides, could enhance management of herbicide-resistant kochia.…”

Cultural weed management practices shorten the critical weed-free period for soybean grown in the Northern Great Plains

“…The importance of plant densities to crop productivity, particularly under weed interference, is well known in soybean (Arce et al 2009;Nice et al 2001) and other crops (Ball et al 1997;Fradgley et al 2017;O'Donovan et al 1999). The doseresponse work by Redlick et al (2017a) eloquently showed the trade-off between plant densities and herbicides for effective weed management and the importance of plant stand densities for improving herbicide efficacy and reducing the necessity for herbicides for weed management in lentil (Lens culinaris Medik.) (Redlick et al 2017b).…”