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Abutilon theophrasti is a weed that is spreading worldwide and that has had to adapt to different combinations of environmental conditions. Wide interpopulation variability has been reported regarding dormancy and germination. This variability, controlled by the interaction of genetic diversity and maternal effect, could hinder the adoption of Integrated Weed Management (IWM) tools. A collaborative project was conducted to compare emergence dynamics of 12 European and North American populations under diverse environmental conditions. The main aim was to assess interpopulation variability and explain this according to environmental conditions in the seed collection sites. Seeds were sown at six experimental sites, and seedling emergence was monitored. The AlertInf model was tested to evaluate its ability to predict emergence dynamics of the different populations. A wide interpopulation variability was observed for emergence percentage and dynamics with consistent trends across sites and related to different seed dormancy levels. Populations from Catalonia, Iowa and Minnesota reached higher emergence percentage with earlier and concentrated emergence flushes probably due to low dormancy level, while populations from Croatia, Serbia and Hungary, given their low average emergence percentage, presented high dormancy levels. Good predictive accuracy of AlertInf model was obtained at the different sites, confirming the possibility of adopting it across a wide range of environmental conditions. Achieving a better knowledge of interpopulation variability can allow specific control strategies to be designed, facilitating the replacement of solely herbicide-based management with true IWM., Postprint (updated version)

Weed management is a major constraint in organic crop production. Propane flaming could be an additional tool for weed control in organic soybean production. The objective of this study was to investigate the response of soybean to broadcast flaming as influenced by propane dose and crop growth stage. We initiated a 2-year field study at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, NE using five propane doses applied at four growth stages of VC (unfolded cotyledons), VU (fully unrolled unifoliate leaves), V2 (second trifoliate stage) and V5 (fifth trifoliate stage). The propane doses tested were 0, 13, 24,44 and 85 kg ha(-1). Flaming treatments were applied utilizing a custom-built research flamer mounted on the back of a four-wheeler driven at a constant speed of 6.4 km h(-1). The response of soybean to propane flaming was described by using log-logistic models on the basis of visual ratings of crop injury, yield components (plants m(-2), branches plant(-1), pods plant(-1), seeds pod(-1) and 100-seed weight) and grain yield. In general, soybean at VC stage was the most tolerant whereas VU stage was the most susceptible to broadcast flaming resulting in the highest visual crop injury, and the largest loss of yield and its components. The maximum yield reductions with the highest propane dose were 19%, 96%, 54% and 30% for VC, VU, V2 and V5 stages, respectively. An arbitrarily assigned 5% yield reduction was evident with 55, 13, 21 and 47 kg ha(-1) propane for VC, VU, V2 and V5 growth stages, respectively, suggesting that soybean flamed at VC stage can tolerate higher dose of propane for the same yield reduction compared to other growth stages. It appears that flaming has a potential to be used effectively in organic soybean production when conducted properly at VC stage.

Farmers are interested to produce sweet maize under organic production systems and propane flaming could be a potential alternative tool for weed control in organic sweet maize production. Therefore, the objective of this study was to investigate the response of sweet maize to broadcast flaming as influenced by propane dose and crop growth stage. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, NE in 2008 and 2009 using five propane doses applied at three different growth stages of V2 (2-leaf), V5 (5-leaf) and V7 (7-leaf). The propane doses were 0, 13, 24, 44 and 85 kg ha(-1). The response of sweet maize to propane flaming was evaluated in terms of visual crop injury, effects on plant height, yield components (plants m(-2), tillers plant(-1), number of ears plant(-1), cob length and number of seeds cob(-1)) and fresh marketable yield. The response of different growth stages of sweet maize to propane doses was described by log-logistic models. Based on most parameters tested. V7 was the most tolerant while V2 was the least tolerant stage for broadcast flaming. The maximum yield reductions with the highest propane dose of 85 kg ha(-1) were 22%, 12% and 6% for V2, V5 and V7 stages, respectively. Furthermore, a 5% yield reduction was evident with 23,25 and 36 kg ha(-1) of propane for V2, V5 and V7 growth stages, respectively, suggesting that plants flamed at V7 stage can tolerate higher dose of propane for the same yield reduction compared to the other growth stages. We believe that flaming has a potential to be used effectively in organic sweet maize production if properly used.