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weed seed bank management

In temperate cropping systems, cover crops have been evaluated for their potential to promote the fatal germination of weed seeds. For example, Mirsky et al. (2010) reported declines in weed seedbanks by encouraging fatal germination associated with soil disturbance in cover crop treatments. Cover crops stimulated weed seed germination and the germinated weeds were either suppressed by the cover crop or controlled by subsequent tillage and preempted weed seed rain. The stimulative effect of certain cover crops has been proven particularly helpful in the management of parasitic weeds. In upland DSR fields in East Africa, green manure ( Crotalaria ochroleuca, M. invisa, and Cassia obtusifolia) exhibited a potential to induce the suicidal germination of S. asiatica ( Kayeke et al., 2007 ). The cover crops in this case served as a false-host by stimulating the germination of Striga without providing conditions necessary for survival.

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Leonard P. Gianessi , in The Triazine Herbicides , 2008

2.5.2 Stimulating Fatal Germination With Crop and Cover Crop Rotations

Weed seedbanks are an ever-present component of agricultural land, and resources directed to understanding, interpreting, and predicting seed germination potential can improve agricultural production.

Adusumilli N. Rao , . David E. Johnson , in Advances in Agronomy , 2017

To illustrate the direct relationship between the weed seedbank and in-crop weeds, a study by Rahman et al. (1996) studying the number of emerged weeds vs. the number of viable weed seeds in the soil found a clear, almost one-to-one relationship ( Fig. 5.9 ). Clearly, the larger the weed seedbank, the larger the population of in-crop weeds.

Richter et al. (2002) have reviewed the use of models to evaluate the dynamics of herbicide resistance and to develop suitable anti-resistance strategies. Herbicide resistance is impacted by a high initial frequency of resistance alleles in a population, out-breeding, dominance of inheritance, a short persistence of the seed bank in the soil, and the lack of a fitness penalty for resistant versus susceptible biotypes of a weed species, along with agronomic factors having a positive influence on weed development. The occurrence of herbicide-resistant weeds in a field usually means the loss of an effective control measure. This is particularly serious if resistance develops in species for which there are few if any effective alternatives. As a rapid increase in the development of herbicides with new modes of action is not likely, and since economic and environmental conditions often will not support cultural control measures or alternative cropping systems, it is important to manage resistance wisely in order to avoid further loss of herbicides.

Remember that none of these strategies can be expected to eliminate the weed seed bank, and also that you may need to change seed bank management strategy as the seed bank itself changes. The reason the weed seed bank is so difficult to manage is because it contains not only many seeds, but many different kinds of seeds, with typically 20 to 50 different weed species in a single field. In other words, the grower may have to deal with 20 to 50 different plant survival strategies! Thus, there will almost always be some weeds that tolerate, or even thrive on, whatever combination of seed bank management strategies the farmer adopts.

One way to estimate a field’s weed seed bank is to wait and see what weeds emerge during the first season. However, knowing something about seed bank content before the season starts can help the farmer prevent severe weed problems before they develop. Davis (2004) recommended the following simple procedure for scouting the weed seed bank:

Weed seeds can reach the soil surface and become part of the soil seed bank through several avenues. The main source of weed seeds in the seed bank is from local matured weeds that set seed. Agricultural weeds can also enter a field on animals, wind, and water, as well as on machinery during activities like cultivation and harvesting (explored further in Keeping New Weedy Invaders Out of the Field).

Challenge of Weed Seed Bank Diversity

Use these strategies to maximize losses (withdrawals) from the weed seed bank:

Incorporated green manures or surface residues of cover crops can reduce the establishment of small-seeded weeds through allelopathy and/or physical hindrance. Thus, these practices can provide a measure of selective weed control for transplanted or large-seeded crops, which are tolerant to the stresses imposed by cover crop residues. This selectivity does not apply to small-seeded, direct sown vegetables like carrots and salad greens, which are at least as sensitive to these cover crop effects as small-seeded weeds.

Cultivation efficacy—weed kill—can vary considerably based on equipment, soil conditions, weed growth stage, and operator experience. Eighty percent mortality would be considered quite respectable, a level of weed control far less than that achieved with most herbicides. Therefore, without the “big hammer” of selective herbicides to remove heavy weed populations from standing crops, effective measures to reduce weed seed banks become vital for the organic farmer.

Because soil microorganisms can play a role in weed seed decay, maintaining a high level of soil biological activity through good organic soil management might be expected to shorten the half-life of weed seed banks. In addition, incorporation of a succulent legume or other cover crop may either stimulate weed seed germination by enhancing soil nitrate N levels, or promote weed seed or seedling decay as a result of the “feeding frenzy” of soil microorganisms on the green manure residues. However, the potential of these practices as weed seed bank management tools requires verification through further research.

In agricultural systems, weed seedbanks provide insights into cropping and management history as well as potential weed problems. Seedbank management is an integral part of a long-term weed management system. In this article, we propose a framework for managing weed seedbanks by putting weed seedbanks into the context of populations and communities. Early in the plant invasion process, it is possible to eradicate or contain the weed species through intensive focused management. Weed populations that become established and pose unique or extreme problems should be managed using population-based strategies such as targeted removal or trap crops. Established weed populations that pose no specific problem should be managed as part of the weed community using a variety of strategies such as tillage, crop rotation, cover crops and mulches, soil solarization, and microorganisms.

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Weed Technology publishes original research and scholarship focused on understanding “how” weeds are managed. As such, it is focused on more applied aspects concerning the management of weeds.

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