Response of velvetleaf demographic processes to herbicide rate

Abstract

Field studies were conducted in 1995 and 1996 to determine the rate response of velvetleaf seedling survival, seed production, and shoot biomass to postemergence herbicides in corn and soybean. Dicamba and imazethapyr were applied to corn and soybean, respectively, at 1, ½, ¼, ⅛, 1/16, 1/32, and 0× labeled rates. Velvetleaf mature plant density was linearly related to seedling density, thus indicating that seedling survival was not density dependent, even after seedling densities exceeded 150 plants m−2. Seedling survival as influenced by herbicide was described by a dose–response curve in corn and soybean. In corn, seedling survival ranged from 0 to 48% across herbicide treatments and years. Seedling survival was greater at the ½× or lower herbicide rates than at the 1× rate. In soybean, maximum seedling survival was 61 and 14% in 1995 and 1996, respectively, and minimum seedling survival was less than 2% in each year. Seedling survival was less in 1996 than in 1995 because velvetleaf was infected with wilt in 1996. In soybean, seedling survival was 20 times greater when treated with herbicides at the ½× rate than when treated at the 1× rate in 1995, but seedling survival was similar when herbicides were applied at 1, ½, ¼, and ⅛× rates in 1996. Velvetleaf fecundity (seeds per plant) was dependent on mature plant density in 1995 but was density independent in 1996. Fecundity as influenced by herbicide was described by dose–response curves in corn each year and in soybean in 1995. In 1995, velvetleaf treated with herbicides at ½× and ¼× rates produced 20 to 30 times more seed per square meter than when treated with herbicides at the 1× rate. Differences in seed per square meter were exaggerated by high densities of velvetleaf. Seed per square meter did not differ between velvetleaf treated with herbicides at 1× or ½× rates in corn or soybean in 1996. Wilt infection of velvetleaf in 1996 was the likely cause of differences in herbicide performance between years. Herbicides at reduced rates were not effective at limiting seedling survival and seed production compared to 1× rates in the absence of wilt. As a result, long-term management of velvetleaf with herbicides at reduced rates likely will be difficult, especially in areas with high densities, unless integrated with other management practices.

The impact of altered precipitation variability on annual weed species

“…However, S. faberi biomass decreased with longer intervals, while C. album biomass either increased or remained unaffected. Previous research has shown a strong relationship between biomass and seed production for both species ( Bussan et al, 2000 ;Grundy et al, 2004 ), suggesting that increasing precipitation variation may impact the relative fi tness of these two species. The pronounced response of both species to interval length suggests that predicted changes in storm frequency and intensity ( Easterling et al, 2000 ;Weltzin et al, 2003 ;IPCC, 2007 ) could impact the overall abundance and species compo-[Vol.…”

Economic analysis of integrated weed management in field bean (Phaseolus vulgaris L.)

“…The use of sublethal herbicide dose could be promising as a strategy for decreasing the production costs and for environmental reasons, but results from other experiments indicate that this effect varies greatly, depending on the used herbicides and amount of weed species present in the fields (Bussan et al 2000, Zhang et al 2000. Results from the second year of our investigations are presented in Table 4 and Figure 2.…”

“…Profitable, alternative weed management systems are therefore needed to help farmers to solve this pressing environmental concern without greatly changing current farming practice. However, despite of many successful examples (Buhler et al 1995, Zoschke 1994, concern over the use of herbicides at below-labelled rates remains (Bussan et al 2000, Zhang et al 2000.…”

The Biology of Canadian Weeds. 141. Setaria faberi Herrm.

“…Bussan et al (2000) recorded seed production of up to 4000 seeds per plant in competition with soybean. In a soybean crop not treated with herbicides, the average seed production was about 600 seeds per plant (11 400 seeds m (2 ) (DeFelice et al 1989).…”