Resistance to quinclorac in R E. phyllopogon involved at least two mechanisms: (a) insensitivity along the response pathway whereby quinclorac induces ethylene production; (b) enhanced β-CAS activity, which should enable greater HCN detoxification following quinclorac stimulation of ethylene biosynthesis. This unveils new resistance mechanisms for this multiple-resistant biotype widely spread throughout California rice fields.

When irradiated in paddy-field water, propanil (PRP) undergoes photodegradation by direct photolysis, by reactions with OH and CO, and possibly also with the triplet states of chromophoric dissolved organic matter. Irradiation also inhibits the nonphotochemical (probably biological) degradation of PRP. The dark- and light-induced pathways can be easily distinguished because 3,4-dichloroaniline (34DCA, a transformation intermediate of considerable environmental concern) is produced with almost 100% yield in the dark but not at all through photochemical pathways. This issue allows an easy assessment of the dark process(es) under irradiation. In the natural environment, we expect PRP photodegradation to be important only in the presence of elevated nitrate and/or nitrite levels, e.g., [NO] approaching 1 mmol L (corresponding to approximately 60 mg L). Under these circumstances, OH and CO would play a major role in PRP phototransformation. Because flooded paddy fields are efficient denitrification bioreactors that can achieve decontamination of nitrate-rich water used for irrigation, irrigation with such water would both enhance PRP photodegradation and divert PRP dissipation processes away from the production of 34DCA, at least in the daylight hours.

This study focused on the dissipation of propanil and 3,4 dichloroaniline (3,4 DCA) over time in the soil, field water, inlet water, and outlet water of paddy fields under three management systems: conventional water seeding (CON), conventional water seeding with supplied liquid manure (LMA), and dry seeding (DRY). Propanil dissipation in water was also investigated under laboratory conditions. The field study was conducted from 2004 to 2006 at Vercelli, northern Italy. Propanil and 3,4 DCA showed rapid dissipation in water and soil environments both in the field and in the laboratory. Under controlled conditions, chemical hydrolysis was not detected for either compounds for up to 100 d at pHs of 5, 7, and 9. In the laboratory, the half-life of propanil in irrigation water was 1.1 d; its half-life in soil was routinely measured at <1.0 d (between 0.17 and 1.77 d). 3,4 DCA was found to persist much longer. Measured in all three study years at 50 d after treatment, its concentration ranged between 44 μg kg (CON) and 140 μg kg (DRY). Propanil and 3,4 DCA concentrations in paddy water were particularly high in samples collected at 4 d (2004) and 2 d (2005) after treatment. Maximum concentrations were 54.4 μg L (CON) for propanil (2005) and 113.7 μg L (LMA) for 3,4 DCA (2004). The concentrations of propanil and 3,4 DCA in inlet water were never above 1.1 and 0.3 μg L, respectively, whereas the highest concentration of each compound in outlet water was in samples collected first after treatment in 2005 and 2006. Both chemicals dissipated rapidly in all the soil-water environments but displayed no important differences among the three management systems. In conclusion, propanil and 3,4 DCA did not persist longer in paddy fields. A risk of water network contamination by these compounds may occur only early after herbicide spraying. A water-holding period after herbicide spraying may reduce this risk.

Weeds that have become resistant to herbicides may threaten rice production. Rice cultivation is mainly carried out in coastal and river delta areas that often suffer salinity problems. The aims of this study were to evaluate the effects of salinity upon germination and the root and shoot seedling growth of Italian weedy rice and cultivated rice (Oryza sativa), and to find a possible correlation between salinity and herbicide resistance. Seed germination tests were conducted in Petri dishes on four imazamox-sensitive and one resistant weedy rice populations and two rice varieties: Baldo (conventional) and CL80 (imidazolinone-resistant Clearfield® variety). Different salt concentrations were tested: 0, 50, 100, 150, 200, 250, 300, 350 and 400 mM NaCl. Germination percentage, germination speed, seedling root and shoot length were affected by increasing the salt concentration in all tested populations and varieties. The germination percentage was in general more affected in resistant weedy rice and CL80. In resistant weedy rice this was partially compensated by a faster germination up to 100 mM. In terms of seedling root and shoot length, CL80 and Baldo showed the highest tolerance to salt; resistant weedy rice was not able to produce seedling roots and shoots at concentrations > 300 mM.

The effect of elapsed time between spraying and first leaching event on the leaching behavior of five herbicides (terbuthylazine, S-metolachlor, mesotrione, flufenacet, and isoxaflutole) and two metabolites (desethyl-terbuthylazine and diketonitrile) was evaluated in a 2011-2012 study in northwest Italy. A battery of 12 lysimeters (8.4 m(2) long with a depth of 1.8 m) were used in the study, each filled with silty-loam soil and treated during pre-emergence with the selected herbicides by applying a mixture of commercial products Lumax (4 L ha(-1)) and Merlin Gold (1 L ha(-1)). During treatment periods, no gravity water was present in lysimeters. Irrigation events capable of producing leaching (40 mm) were conducted on independent groups of three lysimeters on 1 day after treatment (1 DAT), 7 DAT, 14 DAT, and 28 DAT. The series was then repeated 14 days later. Leachate samples were collected a few days after irrigation; compounds were extracted by solid phase extraction and analyzed by high-performance liquid chromatography and gas chromatography-mass spectrometry. Under study conditions, terbuthylazine and S-metolachlor showed the highest leaching potentials. Specifically, S-metolachlor concentrations were always found above 0.25 µg L(-1). Desethyl-terbuthylazine was often detected in leached waters, in most cases at concentrations above 0.1 µg L(-1). Flufenacet leached only when irrigation occurred close to the time of herbicide spraying. Isoxaflutole and mesotrione were not measured (<0.1 µg L(-1)), while diketonitrile was detected in concentrations above 0.1 µg L(-1) on 1 DAT in 2011 only.