weed seed bank management

Weed seed bank management

Rotation = oat – pea – wheat – canola
Non PFP = in-crop herbicide used
Std PFP = no in-crop herbicide used
CC = Chaff Cart all years
Disturbance = heavy harrows in the fall in the canola crop
Intensive = intensive management of weeds after the PFP crop in the pea crop, using chaff cart, disturbance, and trifluralin application prior to the pea crop

Preventing weed seeds from returning to the soil seedbank can help to avoid weed problems in future years. In one study modeling seedbank depletion (Jones and Medd, 2000), very low tolerance for weeds in the first few years brought the wild oat seedbank almost to zero after 15 years of chemical weed control and after 7 years of integrated weed management. In this study, herbicide use was increased for several years, but was the total herbicide use over 20 years was greatly reduced, especially when integrated weed management practices were used.

Table 2. Total density (+/- SE) of volunteer spring wheat in the field (plants/m 2 ) and in the soil seedbank (SB)(seeds/m 2 ) in canola stubble 2002-2004, in a Pesticide Free Production (PFP) rotation study (BRC).

Spring N fertilizer application


Weed seeds can be moved from field to field unwittingly, allowing weed species to be spread to new areas, causing new weed problems. Weed seed spread can be minimized by using clean seed and cleaning equipment between fields.

For some crops, harvest losses can be significant and resulting volunteer crops can be weed problems in future crops. For example, Gulden et al. (2003) found that the harvest losses of canola ranged from 9 to 55 times the normal canola seeding rate! Setting harvest equipment to minimize harvest losses is important.

Agronomic practices that improve the competitive ability of the crop compared to weeds can result in lower seed production by weeds that survive. Other practices such as clipping tall weeds above the crop canopy (see Other Mechanical Weed Control Practices ) or terminating crops early, either as a silage crop or green manure, can prevent weeds from successfully producing seed and returning it to the weed seedbank.

Keeping the weed seeds out

Chaff collection has the potential to reduce weed seed return and possible reduce the need for weed control. In a survey of Saskatchewan farms where chaff was collected, two-thirds of farmers reported being able to reduce herbicide use or eliminate at least one tillage operation per year, because of reduced weed pressure (Olfert et al., 1991). On the other hand, in a Brandon field study, chaff collection significantly reduced the amount of volunteer wheat in the subsequent years’ seedbank but had limited impact on the numbers of wheat plants emerging in the crop (Table 2).

After allowing weeds to grow for a short time, these weeds must be destroyed, usually with a tillage operation or application of a herbicide. (See section on Stale Seedbed in Spring Tillage)

The species composition and density of weed seed in the soil vary greatly and are closely linked to the cropping history of the land. Altering tillage practices changes weed seed depth in the soil, which plays a role in weed species shifts and affects efficacy of control practices. Crop rotation and weed control practices also affect the weed seedbank. Information on the influence of cropping practices on the weed seedbank should be a useful tool for integrated weed management. Decision aid models use information on the weed seedbank to estimate weed populations, crop yield loss, and recommend weed control tactics. Understanding the light requirements of weed seed may provide new approaches to weed management. Improving and applying our understanding of weed seedbank dynamics is essential to developing improved weed management systems. The principles of plant ecology must be integrated with the science of weed management to develop strategies that take advantage of basic plant responses in weed management systems for agronomic crops.

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Date and time: Sat, 15 Jan 2022 15:39:35 GMT