27 Ate Today? Thank a Farmer. Better Farming | February 2024 weed watch #3. Ragweed (Ambrosia spp.) Characteristics: Beyond being the bane of allergy sufferers, ragweed plants can grow multiple branches with deeply lobed leaves. Impact: Each ragweed plant is prolific, producing thousands of pollen grains and affecting both corn and soybean yields. Control Measures: Herbicides with multiple modes of action can stall ragweed’s advance. Regular scouting and timely intervention are also key. The advent of soybeans resistant to dicamba or 2,4-D should help to control this weed in 2024. #4. Annual nightshade (Solanum spp.) Characteristics: This weed boasts heart-shaped leaves and produces small berries that can contaminate grain shipments. Impact: Direct competition and grain contamination are two-fold challenges posed by nightshade. Lynch warns that “if found in IP soybeans, the soybeans will probably be refused. This is because there once was a seed treatment that had the same colour as beans stained with nightshade berries. Buyers not wanting to take a chance just refused to accept beans stained with nightshade berries.” Control Measures: Lynch says that “in IP soybeans you need an herbicide pre-emerge that has good control of nightshade. Then you have to be prepared to come back with a post emergent herbicide. In corn there are lots of options.” #5. Volunteer corn (Zea mays) Characteristics: While corn is a staple crop, plants that grow in subsequent seasons from unharvested seeds can become weeds themselves. Impact: A weed is a plant growing out of place. Corn in a soybean field or volunteer corn in a corn field can be trouble. To make things worse, volunteer corn in soybeans can host corn rootworm and making crop rotation to control rootworm ineffective. Control Measures: Selective herbicides can target volunteer corn. Choose hybrids with good standability and harvest corn before ear drop. Lynch: “If you have a lot of fallen corn ears, mouldboard ploughing buries these ears to prevent them from germination next year.” #6. Fleabane (Conyza spp.) Characteristics: These are tall weeds with small flowers, often growing in clusters. Impact: Glyphosate-resistant varieties are especially troublesome, impacting yields of both corn and soybeans. Control Measures: Herbicides containing 2,4-D or dicamba are often recommended. There are numerous other herbicides to use. Lynch: “A quick check of OMAFRA’s program to select herbicides by crop and by weed makes controlling this weed easy. Layering residual herbicides can prevent fleabane seeds from germinating.” #7. Chickweed (Stellaria media) Characteristics: A lowgrowing weed, chickweed has small, star-shaped flowers and thrives in cooler climates. Impact: Primarily competing in the early growth stages, chickweed can be a direct threat to wheat. As well, it is a host for soybean cyst nematodes. A good stand of chickweed in the spring is an attractive place for armyworm or cutworm adults to lay their eggs. Control Measures: Pre-emergent herbicides, especially when combined with early mowing, can effectively control chickweed. Crop rotation with non-host crops disrupts its lifecycle. Integrated Weed Management (IWM) A holistic approach: Combating these threats requires a more holistic strategy than merely reaching for the herbicide sprayer. IWM emphasizes combining chemical, cultural, and mechanical methods. Diversification: Both in terms of crops and herbicides. Diverse rotations can reduce weed seed banks, and using a variety of herbicides can prevent resistance. Scouting: Regular field checks can identify weed threats early, allowing timely intervention. Mechanical Controls: Tillage, mowing, and even hand- weeding can be effective, especially when integrated with other control measures. Conclusion With a nuanced understanding of these annual adversaries and a strategic approach to their management, Ontario producers can confidently look forward to the 2024 growing season. The foundation lies in knowledge, timely action, and integrated strategies. BF (Editor’s Note: Online sources were used in researching this article.) JJ Gouin - stock.adobe.com Mahato Photography-Wirestock Creators - stock.adobe.com avoferten - stock.adobe.com Oskanov/iStock/Getty Images Plus Oleh Marchak - stock.adobe.com
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