Weed seed banks can often become a large factor that can influence crop health and yield, particularly if left undealt with.
Weed seed banks consist of viable weed seeds lying dormant in the soil, waiting for the right conditions to germinate. These seeds can act as reservoirs for various pathogens, leading to the persistence and spread of diseases among crops.
Understanding how dormant weed seeds contribute to disease persistence can help growers develop crop protection strategies to manage weed seed banks effectively, leading to reduced disease pressure and more yield opportunity.
The nature and dynamics of weed seed banks
Weed seed banks are essentially collections of weed seeds that exist in the soil. These seeds can remain dormant for extended periods, depending on the species and environmental conditions.
These banks provide a continuous emergence of weeds even after control measures have been used. This persistent presence of weed seeds in the soil poses a significant challenge for farmers, as it necessitates ongoing weed management strategies.
The role of weed seed banks in disease persistence
Weeds are not just competitors for sunlight, nutrients, and water; they can also be carriers of harmful plant pathogens, including fungi, bacteria, and viruses.
When weeds become infected with these pathogens, they act as hosts, providing a continuous source of infection that can spread to nearby crops. This is particularly problematic as many weeds have a longer growing season than crops, offering a more extended period for pathogens to survive and proliferate.
Pathogen reservoirs
Weed seed banks can harbour pathogens through:
Direct pathogen carryover
Some pathogens can survive on or within weed seeds, remaining viable during the seed’s dormancy period. When the seed germinates, it can directly infect the new weed seedlings.
Indirect pathogen support
Weeds that emerge from the seed bank can become infected from the surrounding environment and then serve as a new source of pathogens, which can subsequently infect crops.
Weeds and pathogens
Canada Thistle (Cirsium arvense) and Fusarium oxysporum:
Canada Thistle is a weed that can host Fusarium oxysporum, which causes wilt diseases in various crops such as potatoes and tomatoes. Fusarium oxysporum can survive in soil and infect crops even after Canada Thistle is removed.
Wild Mustard (Sinapis arvensis) and Blackleg (Leptosphaeria maculans):
Wild Mustard is a weed that can harbour the fungal pathogen Leptosphaeria maculans, which causes blackleg in canola crops. This disease can lead to significant yield losses.
Wild Oats (Avena fatua) and Crown Rust (Puccinia coronata):
Wild Oats are known to host Puccinia coronata, the causal agent of crown rust disease in cereals such as wheat and barley. Crown rust can reduce grain quality and yield if not managed effectively.
Common Ragweed (Ambrosia artemisiifolia)and Sclerotinia sclerotiorum:
Common Ragweed can carry Sclerotinia sclerotiorum, a fungal pathogen that causes white mold disease in many broadleaf crops, including canola, sunflowers, and beans. This disease can lead to significant losses in crop production.
Managing weed seed banks to reduce disease pressure
Effective management of weed seed banks is essential to minimize the risk of disease persistence and spread. Here are several strategies to manage weed seed banks:
- Cultural practices
Crop Rotation: Rotating crops with different life cycles and growth habits can disrupt the life cycles of weeds and reduce the seed bank. For instance, rotating cereals with legumes can help manage specific weed species and their associated pathogens.
Cover Crops: Planting cover crops can suppress weed growth by outcompeting them for resources and creating a physical barrier. Cover crops can also enhance soil health, making conditions less favourable for pathogen survival.
- Mechanical control
Tillage: Proper tillage can help reduce the weed seed bank by burying seeds deep into the soil, where they are less likely to germinate. However, it must be used with care as excessive tillage can lead to soil erosion and degradation.
Weed Pulling and Mowing: Regularly removing weeds before they set seed can prevent the addition of new seeds to the seed bank. This method is labour-intensive but effective in small-scale situations.
- Chemical Control
Pre-emergence Herbicides: Applying pre-emergence and pre-seed burndown herbicides can prevent weed seeds from germinating and setting seed. Products like GoldWing herbicide, a pre-seed burndown herbicide , offer effective control over a broad spectrum of emerged weed species.
Post-emergence Herbicides: Using post-emergence herbicides to control weeds that escape pre-emergence treatments can help manage the seed bank. It is crucial to use herbicides correctly to ensure their effectiveness and prevent resistance development.
- Integrated Weed Management (IWM)
Canadian farmers face unique challenges due to the diverse climatic conditions across the country, which influence weed behaviour and pathogen prevalence. Initiatives for crop protection in Canada require integrated approaches to manage weed seed banks effectively.
Combining multiple control strategies is often the most effective approach to managing weed seed banks. Integrated Weed Management (IWM) involves using a combination of cultural, mechanical and chemical methods to manage weeds and their seed banks.
For instance, crop rotation and herbicide and fungicide use often help growers disrupt weed and pathogen life cycles. Canadian farmers are encouraged to use these strategies and others to manage weed populations efficiently.
Weed seed banks are a significant factor in the persistence and spread of crop diseases. These dormant weed seeds pose a continuous threat to crop health and productivity by serving as reservoirs for pathogens.
Understanding the dynamics of weed seed banks and their role in disease persistence allows farmers and agronomists to develop targeted and effective crop protection strategies.
