Weed seed banks reflect past weed populations and management practices and are the source of weed infestations to come. The factors affecting weed seed germination, however, are often poorly understood. Depleting the soil seed bank and influencing germination patterns are common goals of enduring cultural weed management practices. Greater understanding of the factors influencing the germination of weed seeds could facilitate the development of more effective cultural weed management practices through either suppressing germination or encouraging germination at times when seedlings can be readily controlled. Such cultural methods may contribute to overcoming problems such as feral crops (e.g., weedy rice), crop volunteers, and the evolution of herbicide resistance in weeds that have, in some systems, increased to a point where the lack of sustainable practices is a threat to productivity. Weed seed germination is commonly influenced by light exposure, soil moisture, burial depth through tillage, the use of mulches, fire for land clearance, and flooding of the soil. Harnessing these factors to influence germination can serve as major entry points for improved weed management. Diverse crop production systems provide a wide range of examples to illustrate how recent advances in the understanding of the responses of weed seed germination can be used to develop new and sustainable cultural management of weeds. Crop management practices, such as adopting no-till crops or delaying tillage, that increase weed seed exposure to predators (ants, beetles, etc.) could be incorporated into integrated weed management programs. Retention of crop residue on the soil surface under no-till systems can suppress weed seedling emergence, delay the time of emergence, and allow the crop to gain an advantage over weeds, and reduce the need for control. Rotation of tillage or crop establishment system could also be adopted to deflect the “trajectories” of likely weed population shifts. In rice, flooding after herbicide application or hand weeding can largely prevent the growth of weeds and reduce the need for further interventions.

The role of seed ecology in improving weed management strategies in the tropics

This is the publisher’s final pdf. The published article is copyrighted by the Weed Science Society of America and can be found at: http://wssajournals.org/loi/wees. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work.

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Herbicide Resistance: Toward an Understanding of Resistance Development and the Impact of Herbicide-Resistant Crops

Biogas residues as fertilisers – Effects on wheat growth and soil microbial activities

Summary In relatively short-term studies it is often difficult to identify the factors that are important in determining the patterns of emergence for different weed species. When results from longer-term studies are averaged over years, they demonstrate that some weed species follow characteristic, and potentially predictable, patterns of annual emergence. In recent years, our understanding of the seasonal changes in dormancy and germination behaviour, and the interaction of these processes with the environment, has advanced considerably. In particular, the capacity for computer-based statistical analysis and the ability to handle large datasets has made it possible to use this information in a predictive way. Currently, there are several approaches to developing predictive weed emergence modelling. Some researchers have taken an empirical approach, seeking to identify correlations between environmental variables and observed emergence patterns. Others have taken a reductionist approach, subdividing the emergence process into its component stages of dormancy, germination and pre-emergence growth, to work towards achieving an eventual understanding of the physiological processes involved. Despite recent advances, a number of major challenges remain (e.g. population variability, dormancy and the quality of the input data) that must be overcome before these emergence models can be implemented in practice. The level of complexity and degree of parameterization incorporated within such models must also be addressed in relation to the intended use of the model.

Predicting weed emergence: a review of approaches and future challenges

Phosphorus nutrition of terrestrial plants

Information on responses of weeds to various soil fertility levels is required to develop fertilizer management strategies as components of integrated weed management programs. A controlled environment study was conducted to determine shoot and root growth response of 23 agricultural weeds to N fertilizer applied at 0, 40, 80, 120, 180, or 240 mg kg−1 soil. Wheat and canola were included as control species. Shoot and root growth of all weeds increased with added N, but the magnitude of the response varied greatly among weed species. Many weeds exhibited similar or greater responses in shoot and root biomass to increasing amounts of soil N, compared with wheat or canola. With increasing amounts of N, 15 weed species showed a greater increase in shoot biomass, and 8 species showed a greater increase in root biomass, compared with wheat. Ten weed species exhibited increases in shoot biomass similar to that exhibited by canola, and five weed species showed greater increases in root biomass than did c...

https://bioone.org/journals/weed-science/volume-51/issue-4/0043-1745(2003)051[0532:DROWST]2.0.CO;2/Differential-response-of-weed-species-to-added-nitrogen/10.1614/0043-1745(2003)051[0532:DROWST]2.0.CO;2.pdf

Differential response of weed species to added nitrogen

Information on nitrogen fertilizer effects on crop–weed competitive interactions might aid in developing improved weed management programs. A controlled environment study was conducted to examine the effect of three N rates on the competitive ability of four weed species grown with wheat. The four weed species were chosen to represent species that varied in their growth responsiveness to nitrogen (N): Persian darnel (low), Russian thistle (low), redroot pigweed (high), and wild oat (high). Wheat and each weed species were grown in a replacement series design at N rates of 60, 120, and 240 mg N kg−1 soil. The competitive ability of the low N-responsive species, Persian darnel and Russian thistle, was not influenced by N rate, supporting our hypothesis that N rate would have little effect on the competitiveness of species responding minimally to N. Conversely, the competitiveness of the high N-responsive species redroot pigweed progressively improved as N rate increased. However, wild oat competiti...

Nitrogen Fertilizer Rate Effects on Weed Competitiveness is Species Dependent

Information on weed responses to soil fertility levels is needed to aid development of fertilizer management strategies as components of integrated weed management programs. A controlled environment study was conducted to determine shoot and root growth response of 22 agricultural weeds to fertilizer phosphorus (P) applied at 5, 10, 20, 40, or 60 mg kg−1 soil. An unfertilized control was included. Wheat and canola were included as control species. Shoot and root growth of all weeds increased with added P, but the magnitude of the response varied greatly among species. Many weeds exhibited similar or greater responses in shoot and root biomass to increasing amounts of soil P compared with wheat or canola. With increasing amounts of P, 17 weed species increased shoot biomass more than wheat, and 19 weed species increased shoot biomass more than canola. However, only 10 weed species exhibited greater increases in root biomass than canola, and no weed species increased root biomass more than wheat wi...

Weed species response to phosphorus fertilization

In summer, 2011, we investigated suspected glyphosate-resistant (GR) kochia in three chem-fallow fields (designated F1, F2, F3, each farmed by a different grower) in southern Alberta. This study characterizes glyphosate resistance in those populations, based on data from dose–response experiments. In a greenhouse experiment, the three populations exhibited a resistance factor ranging from 4 to 6 based on shoot biomass response (GR50 ratios), or 5 to 7 based on survival response (LD50 ratios). Similar results were found in a field dose–response experiment at Lethbridge, AB, in spring 2012 using the F2 kochia population. In fall 2011, we surveyed 46 fields within a 20-km radius of the three chem-fallow fields for GR kochia. In the greenhouse, populations were screened with glyphosate at 900 g ae ha−1. Seven populations were confirmed as GR, the farthest site located about 13 km from the three originally confirmed populations. An additional GR population more than 100 km away was later confirmed. Po...

https://bioone.org/journals/Weed-Science/volume-61/issue-2/WS-D-12-00140.1/Glyphosate--and-Acetolactate-Synthase-InhibitorResistant-Kochia-iKochia-scoparia-i/10.1614/WS-D-12-00140.1.pdf

Glyphosate- and Acetolactate Synthase Inhibitor-Resistant Kochia (Kochia scoparia) in Western Canada

Information on phosphorus (P) fertilizer affecting crop–weed competitive interactions might aid in developing improved weed management systems. A controlled environment study was conducted to examine the effect of three P doses on the competitive ability of four weed species that were grown with wheat. Two grass and two broad-leaved weed species were chosen to represent the species that varied in their growth responsiveness to P: wild oat (medium), Persian darnel (low), round-leaved mallow (high), and kochia (low). Wheat and each weed species were grown in a replacement series design at P doses of 5, 15, and 45 mg P kg−1 soil. The competitive ability of the low P-responsive species, Persian darnel and kochia, decreased as the P dose increased, supporting our hypothesis that the competitiveness of species responding minimally to P would remain unchanged or decrease at higher P levels. As expected, the competitiveness of the high P-responsive species, round-leaved mallow, progressively improved as the P dose increased. However, wild oat's competitive ability with wheat was not affected by the P fertilizer. The results suggest that fertilizer management strategies that favor crops over weeds might deserve greater attention when weed infestations consist of species known to be highly responsive to higher soil P levels. The information gained in this study could be used to advise farmers of the importance of strategic fertilizer management in terms of both weed management and crop yield.

Randall N. Brandt

Papers

Differential response of weed species to added nitrogen

Nitrogen Fertilizer Rate Effects on Weed Competitiveness is Species Dependent

Weed species response to phosphorus fertilization

Glyphosate- and Acetolactate Synthase Inhibitor-Resistant Kochia (Kochia scoparia) in Western Canada

Phosphorus fertilizer effects on the competition between wheat and several weed species