Assessing variability in fecundity of Amaranthus powellii using a simulation model

Abstract

Summary Estimates of weed fecundity and its variability are critical for the development of population dynamic models and for evaluating the long‐term consequences of weed management practices. The purpose of this research was to estimate Amaranthus powellii fecundity across years, seasons and competitive environments using a mechanistic model. Existing models were modified to account for weed responses to shade, and to dynamically simulate seed production among subthreshold densities of A. powellii. The model was parameterized and tested using five sets of field data in which A. powellii was grown either alone or with transplanted broccoli. The model overestimated A. powellii height, but predicted both dry weight and fecundity well. Mean simulated fecundity for A. powellii ranged from 0 to 268 000 seeds per plant depending on year, crop maturity date, relative time of emergence and location. Year‐to‐year variability in simulated fecundity was large with coefficients of variation ranging from 77 to 128 under low and high competitive environments respectively. Our results suggest that estimates of weed fecundity based on 1 or 2 years of empirical data may result in significant errors in population dynamic models, and that the use of economic optimum thresholds based on weed density alone entails considerable risks.

Crop Rotation, Cover Crop, and Weed Management Effects on Weed Seedbanks and Yields in Snap Bean, Sweet Corn, and Cabbage

“…For example, in 1997, weed biomass at the time of corn harvest in FC + CL treatments was 153 g m 22 , compared to only 4.4 g m 22 in FC treatments. Since Amaranthus species accounted for at least half of this dry weight, and reproductive effort among Amaranthus species can easily exceed 300 seeds g 21 (Brainard and Bellinder 2004), weed seed input in FC + CL treatments may have exceeded that of FC treatments by 20,000 seeds m 22 or more in 1997. However, this effect clearly did not occur in every year, since no difference in weed seedbank in these two treatments was observed in cycle 2 ( Figure 2B).…”

“…However, this effect clearly did not occur in every year, since no difference in weed seedbank in these two treatments was observed in cycle 2 ( Figure 2B). Large year to year variation in seed production in identically managed systems is not unusual due to variation in weed fecundity or efficacy of weed management practices in response to weather conditions (Brainard and Bellinder 2004).…”

When is the Best Time to Emerge—II: Seed Mass, Maturation, and Afterripening of Common Waterhemp (Amaranthus tuberculatus) Natural Cohorts

“…A simulation study assessing variability in Powell amaranth fecundity suggested that seed production occurs in relatively few high seed production environments, and seeds produced from those high-fecundity years have critical influence on the characteristics of the Powell amaranth seed bank (Brainard and Bellinder 2004). Given the much higher seed production reported (Wu and Owen 2014) and high levels of dormancy we observed in the current study, waterhemp seeds from 2010 cohorts are more likely to become part of the persistent soil seed bank than those produced in 2009, and thus will be more of a concern to farmers with regard to long-term waterhemp management.…”

Review of Glyphosate and Als-inhibiting Herbicide Crop Resistance and Resistant Weed Management

“…Additionally, growers need a very high degree of biological understanding to control weeds at the economic threshold (Coble 1994). New models are addressing the issue of herbicide-resistant weeds and seed production from a multiyear perspective, with more emphasis on managing weed seed production (Brainard and Bellinder 2004;Doyle and Stypa 2004).…”