Studies were conducted to determine if mesotrione alone or in mixtures with low rates of atrazine would control Canada thistle. In the field, mesotrione applied alone did not adequately control Canada thistle, although smaller plants in the rosette stage of growth were more susceptible than plants in the bolting stage. A mixture of mesotrione at 105 g ai ha−1 and atrazine at 280 g ai ha−1 improved control of Canada thistle over that with mesotrione alone. In the greenhouse, mixtures of mesotrione plus atrazine at 560 g ha−1 reduced Canada thistle regrowth more than mesotrione alone or mesotrione plus 280 g ha−1 atrazine. Mesotrione plus atrazine mixtures increased the rate of tissue necrosis compared with the slower development of bleaching symptoms normally associated with mesotrione alone. Uptake, translocation, and metabolism of 14C-mesotrione in Canada thistle were generally slow, and results did not explain the increased control associated with mesotrione plus atrazine mixtures. However, higher levels of absorption and translocation and reduced root metabolism of mesotrione in rosette stage plants compared with bolting plants may explain the greater susceptibility to mesotrione in the rosette stage. The changes in symptomology and increased control with mixtures of mesotrione and atrazine were likely due to the interrelationship between the modes of action of these herbicides.

It is well known that ammonium sulphate (AMS) overcomes the antagonistic effect of cations found in hard water on glyphosate activity. In this paper we examine the effect of AMS on glyphosatetrimesium activity when sprayed in deionised water and following hydroponic application to roots of two tolerant broadleaved weeds (Abutilon theophrasti Medik and Convolvulus arvensis L) and one susceptible grass (Sorghum halepense L). The increase in activity from foliar sprays with AMS was greatest on A theophrasti, followed by C arvensis, with no signi®cant improvement on S halepense. Following root treatment of the same weed species, glyphosate-trimesium showed a marked increase in activity against A theophrasti with AMS, with lower levels of enhancement on the other two species. This matched the higher calcium content of A theophrasti (3.1% dry weight) compared to C arvensis (1.5%) and S halepense (1.0%).Scanning electron microscopy and X-ray microanalysis were used to identify the presence of antagonistic elements (Mg and Ca) on leaf surfaces of A theophrasti. Misting of leaf surfaces promoted the leaching of substances rich in calcium from within the leaf on to the surface. In addition, species such as A theophrasti have specialised trichomes known as chalk glands which are a source of cations. Data are presented which show that, in uptake studies with [ 14 C]glyphosate-trimesium, anomalous results may be found unless an acidi®ed wash solution is used to remove residual surface material, which remains as an insoluble deposit with aqueous methanol washing. It is proposed that the reduced potency shown by glyphosate on certain species such as A theophrasti can be partially explained by the interaction of the herbicide anion with antagonistic cations both on and within the plant.

The biological potential of pinoxaden and its active principle pinoxaden dione in terms of grass weed control and tolerance in cereals was fully exploited by inclusion of the safener cloquintocet-mexyl in the formulation in combination with a specific and tailor-made tank-mix adjuvant based on methylated rape seed oil.

The closely related sulphonamide safeners, metcamifen and cyprosulfamide, were tested for their ability to protect rice from clodinafop-propargyl, a herbicide normally used in wheat. While demonstrating that both compounds were equally bioavailable in planta, only metcamifen prevented clodinafop from damaging seedlings, and this was associated with the enhanced detoxification of the herbicide. Transcriptome studies in rice cultures demonstrated that whereas cyprosulfamide had a negligible effect on gene expression over a 4 h exposure, metcamifen perturbed the abundance of 590 transcripts. Changes in gene expression with metcamifen could be divided into three phases, corresponding to inductions occurring over 30 min, 1.5 h and 4 h. The first phase of gene induction was dominated by transcription factors and proteins of unknown function, the second by genes involved in herbicide detoxification, while the third was linked to cellular homeostasis. Analysis of the inducible genes suggested that safening elicited similar gene families to those associated with specific biotic and abiotic stresses, notably those elicited by abscisic acid, salicylic acid, and methyl jasmonate. Subsequent experiments with safener biomarker genes induced in phase 1 and 2 in rice cell cultures provided further evidence of similarities in signalling processes elicited by metcamifen and salicylic acid.

Herbicides increase crop yields by allowing weed control and harvest management. Glyphosate is the most widely-used herbicide active ingredient, with $11 billion spent annually on glyphosate-containing products applied to >350 million hectares worldwide, using about 8.6 billion kg of glyphosate. The herbicidal effectiveness of glyphosate can depend upon the time of day of spraying. Here, we show that the plant circadian clock regulates the effectiveness of glyphosate. We identify a daily and circadian rhythm in the inhibition of plant development by glyphosate, due to interaction between glyphosate activity, the circadian oscillator and potentially auxin signalling. We identify that the circadian clock controls the timing and extent of glyphosate-induced plant cell death. Furthermore, the clock controls a rhythm in the minimum effective dose of glyphosate. We propose the concept of agricultural chronotherapy, similar in principle to chronotherapy in medical practice. Our findings provide a platform to refine agrochemical use and development, conferring future economic and environmental benefits.