Keeping Lamb’s Quarters Out of Corn

 

Lamb’s-quarters (Chenopodium album) is a common and persistent weed that can pose significant challenges for corn growers. Effective management of this weed is essential to maintain optimal corn yields and ensure the health of the crop.

Identifying lamb’s quarters: Characteristics and growth patterns

Lamb’s quarters is a member of the Amaranthaceae family and can grow up to 1.5 meters tall. This plant has a distinctive appearance with triangular to diamond-shaped leaves that are often coated with a whitish, mealy substance, particularly on the undersides. The leaves are toothed and can vary in colour and size depending on the plant’s age and growing conditions.

It can also have small, green flowers that form dense clusters at the tips of the stems and produce a large number of small, black seeds that contribute to its persistence and widespread distribution.

Understanding the growth patterns and lifecycle of Lamb’s-quarters is crucial for effective weed management. It germinates in late spring to early summer when soil temperatures reach around 10°C (50°F). It has a rapid growth rate, often outcompeting crops for light, nutrients, and water. Lamb’s-quarters can produce several generations within a single growing season, with each plant capable of producing up to 75,000 seeds. These seeds can remain viable in the soil for many years, contributing to their persistence.

Impact of lamb’s quarters on corn yields Lamb’s-quarters can have a detrimental impact on corn yields due to its aggressive growth and competition for resources. The key ways in which it affects corn yields include:

• Competition for Nutrients: Lamb’s-quarters compete with corn plants for essential nutrients such as nitrogen, phosphorus, and potassium. This competition can lead to reduced nutrient availability for corn, resulting in stunted growth and lower yields.
• Water Competition: During dry conditions, lamb’s-quarters can outcompete corn for water, exacerbating drought stress and further reducing corn productivity.
• Light Competition: Lamb’s-quarters can grow taller than young corn plants, shading them and reducing their access to sunlight. This shading effect can hinder photosynthesis and weaken corn plants.

Its resistance to photosystem II inhibitors (triazines), ALS inhibitors, and suspected resistance to glyphosate makes this weed a serious threat to agricultural production systems across North America. Resistant weed problems often arise from producer practices, such as not rotating herbicides and relying too heavily on chemical management tactics. However, as with most weed species, the exact impact of common lamb’s-quarters competition is determined by weed density, the timing of crop and weed emergence, and, most importantly, environmental conditions.

Managing lamb’s quarters in corn fields

Due to its early emergence and rapid growth rate, common lamb’s-quarters is a successful competitor with corn.

Effective management of lamb’s-quarters requires an integrated approach that combines cultural, mechanical, and chemical control methods.

Cultural Control

• Alternate planting dates relative to weed emergence
• Plant to narrow rows and use higher seeding rates for greater crop competition
• Placing fertilizer with the crop (not the weed)
• Implement crop rotations that discourage summer annual weed success

Mechanical Control

Cover cropping and row cultivating, can help reduce herbicide dependence and effectively control seedling weeds. Common lamb’s-quarters seedlings are very small and fragile, and the seeds germinate in response to soil disturbance, stirring of the top 1 to 2 inches of soil is highly effective at controlling emerging seedlings during the first 4 to 6 weeks after planting.

Chemical Control

Using herbicides is a crucial component of managing lamb’s-quarters in cornfields. A combination of pre-emergence and post-emergence herbicides can provide effective control:

Pre-emergence Herbicides: Applying pre-emergence herbicides before or at the time of planting can help prevent lamb’s-quarter’s seeds from germinating. These herbicides create a chemical barrier in the soil that inhibits weed growth.

Post-emergent Herbicides: Post-emergent herbicides are applied after the corn and weeds have emerged. Using a broadleaf herbicide that targets lamb’s-quarters can help control established plants. Herbicides with glyphosate may not be effective against mature plants due to established herbicide resistance.

Monitoring and early detection techniques

Early detection and monitoring are essential for effective management of lamb’s-quarters. Regular scouting of cornfields can help identify lamb’s-quarter seedlings before they become problematic. Here are some techniques for monitoring:

• Field Scouting: Conduct routine field inspections, especially during the early stages of corn growth. Look for lamb’s-quarters seedlings and note their distribution and density.
• Mapping: Create weed maps to document the locations of lamb’s-quarters infestations. This information can guide targeted control measures and track the effectiveness of management strategies over time.
• Weed Thresholds: Establishing weed thresholds can help determine the economic impact of lamb’s-quarters and inform the timing of control measures.

Preventing herbicide resistance in lamb’s-quarters

Herbicide resistance is a growing concern in weed management. Preventing resistance in lamb’s-quarters requires adopting best practices for herbicide use:

• Herbicide Rotation: Rotate herbicides with different modes of action to prevent the development of resistance. Avoid relying on a single herbicide or mode of action repeatedly.
• Tank Mixing: Use tank mixes of herbicides with different modes of action to enhance control and reduce the risk of resistance.
• Integrated Weed Management: Combine chemical control with cultural and mechanical methods to reduce reliance on herbicides and manage weed populations more sustainably.
• Responsible Herbicide use: Follow label recommendations for herbicide application rates, timing, and conditions to maximize efficacy and minimize the risk of resistance.

Managing lamb’s-quarters in cornfields requires a comprehensive and integrated approach. By understanding the characteristics and growth patterns of lamb’s-quarters, corn growers can implement effective strategies to mitigate its impact on corn yields. Combining cultural, mechanical, and chemical control methods, along with regular monitoring and early detection, ensures effective management of this persistent weed. Preventing herbicide resistance through best practices and integrated weed management is essential for long-term control. By adopting these strategies, corn growers can keep lamb’s-quarters out of their fields and maintain healthy, productive crops.