Annual losses of weed seeds due to predation in organic cereal fields

Abstract

Summary1. Post-dispersal seed losses in annual arable weed species are poorly quantified, but may be of significance for natural population control, especially if they can be manipulated. We hypothesized that weed seed predation on the soil surface was significant, so we measured rates in the field to estimate annual seed losses due to predation. 2. Temporal patterns of weed seed losses due to predation ('demand') as well as weed seed production ('supply') were measured from May to June until harvest in August 1999 and 2000 during 2-week exposure periods in four organic cereal fields in the Netherlands. The proportion of weed seeds lost to predators M i (number of seeds consumed per number of seeds exposed per 14 days) was measured, using cards containing seeds of Stellaria media , Chenopodium album or Avena fatua . Seed production, Y i (number of seeds per m 2 per 14 days), was measured in 2000, using seed traps. 3. Annual seed loss due to predation,  (number of seeds consumed per number of seeds produced per year), was calculated based on M i and the exposure period of seeds to predators, starting with seed shed and ending with seed burial. The importance of the length of the exposure period on total seed loss was explored using a model. 4. The temporal trend in M i was consistent among farms and years: high in June and early July, lower in the second half of July and negligible in August and after harvest. Total seed production varied considerably among fields, i.e. 800-16 000 seeds per m 2 per year. The timing of peak seed production also varied substantially. 5. Calculated  ranged from 32% to 70%, when assuming continuous exposure of seeds to predators from seed shed till crop harvest. When exposure was limited to 2 or 4 weeks after seed shed,  decreased to 18-57% or 28-67%, respectively. Differences between fields and weed species were mainly due to differences in the timing of seed shed. 6. Synthesis and applications. Our results suggest that seed predation in organic cereal fields is an important factor shaping the population dynamics of arable weeds. A combination of environmental conditions (hot and dry weather) and agricultural practices (an early crop sowing) can advance weed phenology and postpone seed burial, resulting in higher proportions of weed seed loss to predation in cereals.

Postdispersal Weed Seed Predation by Crickets in a Rice Paddy Field after Irrigation Water Recedes

“…The mesh was fixed by sticking it to poles set up at 2 m intervals, while the bottom of the mesh was fixed to the soil surface by metal stakes at 0.5 m intervals. The activity density of crickets and invertebrate seed predation were investigated within the field using adhesive traps (10 × 16 cm cockroach traps, Earth Chemical Co., Ltd., Tokyo, Japan) and seed cards 20,21 , respectively, that were set on the inter-row space at distances of 0, 5, 10 and 15 m from the field edge (Fig. 1).…”

“…Recently, the number of quantitative studies of activity density of invertebrate seed predators 3,5,6,18,23 , weed seed predation by invertebrates 5,6,7,18,20,21,22,23 and the impact of seed predation on weed population dynamics 22 in upland fields have increased, primarily in Europe and the United States. However, knowledge of postdispersal weed seed predation in paddy fields remains very limited 4 .…”

“…Postdispersal seed predation by invertebrates, including crickets and carabid beetles, is one of the main causes of weed seed mortality, and may contribute to biological weed control in farmlands 7,9,10,18,20,21,22,25 . Recently, the number of quantitative studies of activity density of invertebrate seed predators 3,5,6,18,23 , weed seed predation by invertebrates 5,6,7,18,20,21,22,23 and the impact of seed predation on weed population dynamics 22 in upland fields have increased, primarily in Europe and the United States.…”

The use of insects in integrated weed management

“…The episodic nature of weed seed predation over the course of a year makes the estimation of annual seed loss due to seed predation in the fi eld highly variable and subject to error without careful repeated measurement ( Westerman et al, 2003 ). From ten published datasets, Davis et al (2011) estimated that annual seed losses due to invertebrates averaged 40% and ranged from 8% to 70% depending on the weed species and the agronomic context.…”

Effects of different methods to control the parasitic weed Phelipanche ramosa (L.) Pomel in processing tomato crops

“…These objectives are mutually dependent. The seed bank in the soil can only be reduced when the new seed input is smaller than the output, through successful germination, pathogens, seed predation, or natural death of the seeds (Lonsdale, 1993;Westerman et al, 2003;van Mourik et al, 2005;van Mourik and Stomph, 2011).…”