Blackgrass (Alopecurus myosuroides Huds.) and silky windgrass [Apera spica-venti (L.) P. Beauv.] are becoming a significant problem in Europe. Due to the development of herbicide-resistant biotypes and unwanted side effects of herbicides, there is a need for new integrated weed management strategies to control weeds. Therefore, reducing weed infestations by targeting seed production during crop harvest should be considered. In 2017 and 2018, we estimated the fraction of the total seed production of A. myosuroides and A. spica-venti in a field that potentially could be collected by a grain harvester during winter wheat (Triticum aestivum L.) harvest. Twenty plants of each species were surrounded by a porous net before flowering to trap shed seeds during reproductive development. Seeds were collected and counted weekly up until and immediately before wheat harvest, and the ratio of harvestable seeds to shed seeds during the growing season was determined. Alopecurus myosuroides produced on average 953 seeds plant⁻¹ in 2017 and 3,337 seeds plant⁻¹ in 2018. In 2017 and 2018, 29% and 37% of the total A. myosuroides seeds produced, respectively, were retained on plants at maturity. Apera spica-venti produced on average 1,192 seeds plant⁻¹ in 2017 and 5,678 seeds plant⁻¹ in 2018, and retained 53% and 16% of the seeds at harvest, respectively. If a grain harvester potentially collected approximately 30% of the total seed production of the two grass weeds and removed or killed them, it would reduce seed input to the soil seedbank. However, such methods cannot stand alone to reduce weed pressure.

If seeds retained on weeds at crop harvest could be collected and removed by the combine harvester, weed infestation could be reduced in the following years. We estimated the proportion of weed seeds that could be removed at oat harvest. The seed production and shedding pattern of Fallopia convolvulus, Sinapis arvensis, Spergula arvensis and Stellaria media, were assessed in two spring oat fields in Denmark during 2018 and 2019. Ten randomly chosen plants of each species were surrounded by a porous net before flowering. The start time of seed shedding was recorded, and the seeds were collected from the nets and counted weekly until oat harvest. Just before harvest, the retained seeds on the weed plants were counted. The ratio between harvestable seeds and shed seeds during the growing season was determined. On average 260, 195, 411 and 316 seeds plant⁻¹ were produced by F. convolvulus, Sinapis arvensis, Spergula arvensis and S. media, respectively, of which in average 44%, 67%, 45% and 56% of the seeds were retained on the plants at harvest. There was a strong, positive correlation between the weed biomass and the total seed production.

Reusing soil can reduce environmental impacts associated with obtaining natural fresh soil during road construction and analogous activities. However, the movement and reuse of soils can spread numerous plant diseases and pests, including propagules of weeds and invasive alien plant species. To avoid the spread of barnyardgrass in reused soil, its seeds must be killed before that soil is spread to new areas. We investigated the possibility of thermal control of barnyardgrass seeds using a prototype of a stationary soil steaming device. One Polish and four Norwegian seed populations were examined for thermal sensitivity. To mimic a natural range in seed moisture content, dried seeds were moistened for 0, 12, 24, or 48 h before steaming. To find effective soil temperatures and whether exposure duration is important, we tested target soil temperatures in the range 60 to 99 C at an exposure duration of 90 s (Experiment 1) and exposure durations of 30, 90, or 180 s with a target temperature of 99 C (Experiment 2). In a third experiment, we tested exposure durations of 90, 180, and 540 s at 99 C (Experiment 3). Obtaining target temperatures was challenging. For target temperatures of 60, 70, 80, and 99 C, the actual temperatures obtained were 59 to 69, 74 to 76, 77 to 83, and 94 to 99 C, respectively. After steaming treatments, seed germination was followed for 28 d in a greenhouse. Maximum soil temperature affected seed germination, but exposure duration did not. Seed premoistening was of influence but varied among temperatures and populations. The relationships between maximum soil temperature and seed germination were described by a common dose–response function. Seed germination was reduced by 50% when the maximum soil temperature reached 62 to 68 C and 90% at 76 to 86 C. For total weed control, 94 C was required in four populations, whereas 79 C was sufficient in one Norwegian population.

Eradication of alien invasive species in the soil with steam as an alternative to chemical fumigation may allow contaminated soil to be reused. We have investigated steam disinfestation of soil to combat invasive plant species in three experiments including different temperatures and exposure durations using a prototype stationary soil-steaming device. The experiments included effects on seed germination of bigleaf lupine (Lupinus polyphyllusLindl.), ornamental jewelweed (Impatiens glanduliferaRoyle), and wild oat (Avena fatuaL.; one population from Poland and one from Norway), as well as effects on sprouting rhizome fragments of Canada goldenrod (Solidago canadensisL.) and Bohemian knotweed (ReynoutriaxbohemicaChrtek & Chrtková). In Experiment 1, we tested four different soil temperatures of 64, 75, 79, and 98 C with an exposure duration of 90 s. In Experiments 2 and 3, we tested exposure durations of 30, 90, and 180 s and 90, 180, and 540 s, respectively, at 98 C. Seed pretreatment of 14 d cooling forL. polyphyllusandI. glandulifera, no seed pretreatment and 12-h moistening forA. fatuapopulations, and 5- and 10-cm cutting size forR. xbohemicawere applied. Our results showed germination/sprouting was inhibited at 75 C forI.glandulifera(for 90 s) and 98 C for the other species; however, longer exposure duration was needed forL.polyphyllus. While 30 s at 98 C was enough to killA.fatuaseeds andS.canadensisandR. xbohemicarhizome fragments, 180-s exposure duration was needed to killL.polyphyllusseeds. The results showed promising control levels of invasive plant propagules in contaminated soil by steaming, supporting the steam treatment method as a potential way of disinfecting soil to prevent dispersal of invasive species.