A generalised individual-based algorithm for modelling the evolution of quantitative herbicide resistance in arable weed populations.

Background: Simulation models are useful tools for predicting and comparing the risk of herbicide resistance in weed populations under different management strategies. Most existing models assume a monogenic mechanism governing herbicide resistance evolution. However, growing evidence suggests that herbicide resistance is often inherited in a polygenic or quantitative fashion.

Resistance to PPO-inhibiting herbicide in Palmer amaranth from Arkansas.

Background: The widespread occurrence of ALS inhibitor- and glyphosate-resistant Amaranthus palmeri has led to increasing use of protoporphyrinogen oxidase (PPO)-inhibiting herbicides in cotton and soybean. Studies were conducted to confirm resistance to fomesafen (a PPO inhibitor), determine the resistance frequency, examine the resistance profile to other foliar-applied herbicides and investigate the resistance mechanism of resistant plants in a population collected in 2011 (AR11-LAW B) and its progenies from two cycles of fomesafen selection (C1 and C2).

Results: The frequency of fomesafen-resistant plants increased from 5% in the original AR11-LAW-B to 17% in the C2 population.

US grower perceptions and experiences with glyphosate-resistant weeds.

Background: A survey of 400 growers of maize, soybeans and cotton was made in the United States to determine perceptions, experiences and management practices with glyphosate-resistant weeds. The survey included growers in the north (corn belt) and south (cotton belt) of the USA in spring 2006.

Results: Interestingly, 24 and 39% of northern and southern growers, respectively, assumed they had glyphosate weed resistance on their farm.

Activity of mesotrione on resistant weeds in maize.

Mesotrione is a new callistemone herbicide that inhibits the HPPD enzyme (p-hydroxyphenylpyruvate dioxygenase) and introduces a new naturally selective tool into weed-management programmes for use in maize. Mesotrione provides control of the major broad-leaved weeds, and it can be used in integrated weed-management programmes depending on the grower's preferred weed-control strategy. At post-emergence rates of 150 g AI ha-1 or less, mesotrione provides naturally selective control of key species that may show triazine resistance (TR), e.