herbicide resistance

Herbicides that inhibit HPPD have become very important. In North America, corn-selective HPPD herbicides have long been used and cases of HPPD herbicide-resistant weeds reported. 

With glyphosate currently under intense scrutiny worldwide from an environmental and health perspective, the paper’s authors contemplate possible scenarios of farming without our most important and popular herbicide.

The objective of this study was to determine whether a jungle rice population from the tropical Ord River region of northwest Australia was glyphosate-resistant and whether alternative herbicides labelled for jungle rice control were still effective. Seed samples collected from the field site were initially screened with glyphosate in the glasshouse, and surviving individuals were self-pollinated for subsequent glyphosate dose-response studies. Glyphosate resistance was confirmed, as the suspected resistant population was found to be 8.6-fold more resistant to glyphosate than a susceptible population-based on survival (LD50 of 3.72 kg ha21), and 5.6-fold more resistant based on biomass reduction (GR50 of 1.16 kg ha21).

Weed resistance to foliar herbicides has dramatically increased worldwide in the last two decades. As a consequence, current practices of weed management have changed, with increased adoption of soil-applied herbicides to restore control of herbicide-resistant weeds.

This paper outlines three case studies of weed species that have demonstrated a great propensity for HR gene flow: B. scoparia in western North America, Amaranthus palmeri S. Watson (Palmer amaranth) in the United States (U.S.), and Lolium rigidum Gaud. (annual or rigid ryegrass) in Australia. These three species share three common features: (1) a top troublesome and economically damaging weed in their respective jurisdictions; (2) high incidence of multiple resistance in populations; and (3) rapid expansion of resistance incidence across jurisdictions in a short period of time.

This review covers recent developments and trends in herbicide-resistant (HR) weed management in agronomic field crops. In countries where input-intensive agriculture is practised, these developments and trends over the past decade include renewed efforts by the agrichemical industry in herbicide discovery, cultivation of crops with combined (stacked) HR traits, increasing reliance on preemergence vs. postemergence herbicides, breeding for weed-competitive crop cultivars, expansion of harvest weed seed control practices, and advances in site-specific or precision weed management.

The increasing number of weedy species resistant to dinitroaniline herbicides warrants studies on the evolutionary factors contributing to resistance evolution, including genetic inheritance of resistance traits.

In this study, the researchers investigated the genetic control of trifluralin resistance in a well-characterised Lolium rigidum Gaud. (annual ryegrass) population from Western Australia. This population was purified to contain plants homozygous for the Val-202-Phe α-tubulin mutation, and used as the resistant (R) parents and crossed with susceptible (S) parents to produce eight reciprocal F1 families.

Synthetic auxin herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D), are widely used for selective control of broadleaf weeds in cereals and transgenic crops.

The obvious evolutionary reality is that persistent use of harvest weed seed control (HWSC) is a selection pressure for any mechanisms enabling L. rigidum seed to avoid HWSC. For example, seed shatters before grain harvest or a greater percentage of retained seed at a height below that at which the crop is cut in the harvesting operation.

In Australia, triazine herbicides have routinely controlled the Vulpia species (Vulpia bromoides, Vulpia myuros, and Vulpia fasciculata; collectively referred to as silvergrass). However, a simazine-resistant silvergrass biotype, collected from Pingelly in the Western Australian grain belt in 2014, has been confirmed.