Red clover (Trifolium pratense L.) contains isoflavones that are of interest because of their benefits for human health as well as their adverse effects on the fertility of farm animals. A series of field experiments was conducted in Sainte-Anne-de-Bellevue, QC, Canada, to determine the effects of the environment, cultivar, plant maturity, plant part, and preservation method on the concentration of the two predominant isoflavones in red clover, formononetin and biochanin A. In a multi-year, multisite trial, the total isoflavone concentration in 10 cultivars ranged between 8,923 and 12,753 microg g(-1) of DM averaged across sites, harvests, and years. Despite strong environmental effects, the cultivar "Start" consistently had the lowest isoflavone concentrations, with few differences observed among other cultivars. Across stages of maturity, leaves were found to have the highest isoflavone concentration followed by stems and inflorescences (11,970, 4,896, and 3,297 microg g(-1) of DM, respectively). Changes in isoflavone concentrations with increasing maturity varied depending on the plant part. Overall, highest isoflavone concentrations were found in leaves and stems during the vegetative stages, with the formononetin concentration declining until plants initiated flowering, especially in stems, with concentrations then stabilized in both parts. Upon initiation, inflorescences contained similar isoflavone concentrations than leaves, but concentrations decreased rapidly during flower development to fall even below those observed in stems. Inflorescences then had isoflavone concentrations that were as much as 11 times lower than leaves. Fresh herbage contained higher formononetin and total isoflavone concentrations than did silage and hay (14,464, 12,200, and 11,604 microg g(-1) of DM, respectively). The isoflavone concentration in field-grown red clover is thus high but can be affected by a range of agronomic factors.

Flame weeding is often used for weed control in organic production and other situations where use of herbicides is prohibited or undesirable. Response to cross-flaming was evaluated on five common weed species: common lambsquarters, redroot pigweed, shepherd's-purse, barnyardgrass, and yellow foxtail. Dose-response curves were generated according to species and growth stage. Dicot species were more effectively controlled than monocot species. Common lambsquarters was susceptible to flame treatment with doses required for 95% control (LD95) ranging from 0.9 to 3.3 kg/km with increasing maturity stage. Comparable levels of control in redroot pigweed required higher doses than common lambsquarters, but adequate control was still achieved. Flaming effectively controlled shepherd's-purse at the cotyledon stage (LD95 = 1.2 kg/km). However, the LD95 for weeds with two to five leaves increased to 2.5 kg/km, likely due to the rosette stage of growth, which allowed treated weeds to avoid thermal injury. Control of barnyardgrass and yellow foxtail was poor, with weed survival > 50% for all maturity stages and flaming doses tested. Flame weeding can be an effective and labor-saving weed control method, the extent of which is partially dependent on the weed flora present. Knowledge of the local weed flora and their susceptibility to flame weeding is vital for the effective use of this method.

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IntroductionThe adoption of biotechnology-derived crop varieties continues to be rapid and encompasses all areas in the US. Planted acreage to these crop varieties was 252 million acres in 2006, up from 222 million acres in 2005. This is the initial year in the second decade of the commercial availability of biotechnology-derived crop varieties. The crop varieties are expanding in several ways worth mentioning. First, the varieties are being adapted to different locations and climatic zones so that producers have better choices of biotechnology-derived crops. Second, there is an expansion of the traits that the biotechnology-derived crops encompass, mostly related to insect pests. Finally, there is an increasing tendency to "stack" the traits, i.e. in a single variety including Roundup Ready weed control and insect control traits related to rootworms and bollworms.

Red clover (Trifolium pratense L.) contains high concentrations of isoflavones, compounds that have received much interest lately due to their presumed benefits for human health. In this experiment we tested the possibility to induce isoflavone production in the foliage of two greenhouse-grown red clover cultivars (ÔAzurÕ and ÔStartÕ) through the application of elicitor compounds. Foliar applications of different concentrations of acetic acid (50, 100, 250 and 500 mm), yeast extract (1, 2, 3 and 4 g l )1 ), and chitosan (125, 250, 500, and 1000 mg l )1 ) were carried out on plants at the late vegetative stage, which were harvested 2 or 8 days after spraying. Concentrations of genistein, daidzein, formononetin and biochanin A were determined by high performance liquid chromatography. The two cultivars differed in isoflavone concentrations, ÔAzurÕ having on average 36 % higher biochanin A, formononetin and total isoflavone concentrations than ÔStartÕ (P < 0.05). A cultivar · sampling date interaction (P < 0.1) reflected a 20 % increase over time in total isoflavone concentration with ÔAzurÕ, which was not observed with ÔStartÕ. Effects of elicitors were limited, contrasts indicating overall, 12, 14 and 15 % greater total isoflavone concentration in yeast extract (P < 0.1), chitosan (P < 0.05) and acetic acid (P < 0.05)-treated plants, respectively, than in untreated control plants. There were few differences between the various elicitors and none between concentrations of each elicitor.