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weed seed retention

Combines are the most important seed dispersal mechanism for weeds in our cropping system. While a small amount of seed may leave the field with grain, most weed seed that enter the combine with the crop are either spread throughout the field or carried to other fields. Harvest weed seed control (HWSC) involves modifying combines to prevent weed seed present at harvest from being added to the field’s seedbank. Waterhemp is the weed likely to drive the adoption of HWSC in Iowa. For HWSC to be effective, waterhemp must retain the majority of seed prior to harvest.

Nearly 80% of the waterhemp seed was retained by plants on Oct. 15, the final collection date (Figure 2). The rate of seed drop increased over time, thus delays in harvest will result in less waterhemp seed entering the combine. Weed scientists at the University of Illinois conducted more detailed research with waterhemp over three growing seasons. Seed retention declined to 80% on Sept. 24, Oct. 6, and Oct. 12 in the three years. Researchers in Australia used computer models to simulate the benefit of HWSC in herbicide resistance management. Capturing 50% of weed seed via HWSC delayed the evolution of resistance by 10 years compared to when all weed seed was returned to the seed bank. These findings indicate that HWSC could be an effective tool for managing waterhemp.

The continued evolution of herbicide resistant weeds is driving the need for alternative management tactics. HWSC is a tool that can be incorporated into our current production system easier than many other strategies. Research at Iowa State University will evaluate how to best adapt this strategy to Iowa’s production system.

Figure 2. Retention of waterhemp seed, Boone, IA, 2019. USDA Crop Progress Reports.

I conducted a simple demonstration to evaluate seed retention on waterhemp growing in soybean at the ISU AEA Research Farm near Boone, IA. Three waterhemp plants, ranging from 42 to 48 inches in height, were selected. Two trays were placed under each plant on Sept. 17 (Figure 1). Every 7 days the trays were emptied and seed cleaned from other material in the trays. After four weeks of seed collection (Oct 15) the plants were harvested and seed remaining on plants was collected and cleaned. I assumed that the traps captured 50% of the seed shed by plants. Seed quantity was determined by weight rather than counts, and seed loss was calculated by the cumulative amount of seed in the trays compared to total seed production.

Subject Editor:: Matt Liebman, Iowa State University, Ames, USA

The peer review history for this article is available at https://publons.com/publon/10.1111/wre.12438

Department of Plant and Environmental Sciences, University, of Copenhagen, Taastrup, Denmark

Abstract

Christian Andreasen, Department of Plant and Environmental Sciences, University of Copenhagen, Højbakkegaard Allé 13, DK 2630 Taastrup, Denmark.

Department of Plant and Environmental Sciences, University, of Copenhagen, Taastrup, Denmark

Correspondence

Christian Andreasen, Department of Plant and Environmental Sciences, University of Copenhagen, Højbakkegaard Allé 13, DK 2630 Taastrup, Denmark.

Figure 12. Seed retention (>15 cm from the surface) of winter weeds in a wheat crop. Maximum seed production (seeds/m 2 ) by these species is also given as text.

Figure 4. Persistence of turnip weed seeds placed on the soil surface or buried at 2 cm.

Turnip weed, button grass, bladder ketmia and sesbania pea produced a significant number of seeds (Figures 12 and 13), which were found to persist longer than 3.5 years (Figure 11). These characteristics enhance the adaptive potential of such weed species to become problematic and hard-to-control weeds. However, high seed retention and differential maturity periods between crops and weeds provide an opportunity for controlling such weed species through HSWC practices. Crop topping and desiccants may also be possible options in some crops.

Seed retention

Manalil S, Ali HH, Chauhan BS (2018) Germination ecology of Sonchus oleraceus L. in the northern region of Australia. Crop and Pasture Science 69:926-932

Figure 10. Persistence of seasbania pea seeds placed on the soil surface or buried at 2 cm.

Figure 2. Persistence of common sowthistle seeds placed on the soil surface or buried at 2 cm.

Winter weeds (common sowthistle, Mexican poppy and turnip weed) were established in a wheat crop. The crop was planted in May 2016 and May 2017 at a seeding rate of 60 kg/ha in 18 cm row spacing using a tyne seeder. Plots were sprinkle irrigated four times on alternate days starting from seeding to ensure good crop and weed emergence. Seed traps (4 trays/plot) were placed in the field to determine the temporal pattern of seed shed in different weed species. Seeds collected in these traps were retrieved carefully from seed maturity until harvest at a weekly interval to quantify the rate of seed shed. For common sowthistle, seed dispersal was computed based on the numbers of flower heads that dispersed or remained on the plant at the time of harvest.