What Can You Spray on Alfalfa to Kill Weeds? And Why Do Some Farmers Believe in Moonlit Harvests?

Alfalfa, a perennial flowering plant in the pea family, is a cornerstone of agriculture, valued for its high protein content and ability to fix nitrogen in the soil. However, like any crop, alfalfa faces the persistent challenge of weed competition. Weeds can reduce yield, lower forage quality, and even harbor pests and diseases. To combat this, farmers have developed a variety of strategies, including the use of herbicides. But what exactly can you spray on alfalfa to kill weeds? And why do some farmers swear by unconventional methods, such as harvesting under a full moon? Let’s dive into the details.

Understanding Alfalfa and Weed Dynamics

Before discussing weed control, it’s essential to understand the unique characteristics of alfalfa. Alfalfa is a deep-rooted plant that can thrive in a wide range of soil types, though it prefers well-drained, fertile soils. Its deep root system allows it to access water and nutrients that many weeds cannot, giving it a competitive edge. However, during the establishment phase, alfalfa is particularly vulnerable to weed competition. Weeds can outcompete young alfalfa plants for light, water, and nutrients, leading to poor stand establishment and reduced yields.

Herbicides: The Conventional Approach

Herbicides are the most common and effective method for controlling weeds in alfalfa. They can be broadly categorized into pre-emergent and post-emergent herbicides.

Pre-Emergent Herbicides

Pre-emergent herbicides are applied before weeds germinate. They create a chemical barrier in the soil that prevents weed seeds from sprouting. Some commonly used pre-emergent herbicides for alfalfa include:

• Eptam (EPTC): Effective against annual grasses and some broadleaf weeds.
• Treflan (trifluralin): Controls annual grasses and certain broadleaf weeds.
• Prowl H2O (pendimethalin): Used for controlling annual grasses and some broadleaf weeds.

These herbicides are typically applied before planting or during the establishment phase of alfalfa. They are particularly useful in preventing the emergence of weeds that could compete with young alfalfa plants.

Post-Emergent Herbicides

Post-emergent herbicides are applied after weeds have already emerged. They are used to control weeds that have escaped pre-emergent treatments or those that germinate later in the growing season. Some commonly used post-emergent herbicides for alfalfa include:

• Raptor (imazamox): Effective against a wide range of broadleaf weeds and some grasses.
• Pursuit (imazethapyr): Controls many broadleaf weeds and grasses.
• 2,4-DB: A selective herbicide that targets broadleaf weeds without harming alfalfa.

Post-emergent herbicides are often used in established alfalfa stands where weeds have become a problem. They are typically applied when weeds are young and actively growing for maximum effectiveness.

Organic and Alternative Weed Control Methods

While herbicides are effective, some farmers prefer organic or alternative methods of weed control, either due to environmental concerns, organic certification requirements, or personal beliefs. These methods include:

Cultural Practices

Cultural practices involve modifying the farming environment to make it less conducive to weed growth. Some effective cultural practices for alfalfa include:

• Crop Rotation: Rotating alfalfa with other crops can disrupt the life cycle of weeds that are specific to alfalfa.
• Proper Seeding Rates: Planting alfalfa at the recommended seeding rate ensures a dense stand that can outcompete weeds.
• Timely Harvesting: Regular harvesting of alfalfa can prevent weeds from going to seed and spreading.

Mechanical Control

Mechanical control involves physically removing weeds from the field. This can be done through:

• Mowing: Regular mowing can prevent weeds from flowering and setting seed.
• Cultivation: In some cases, shallow cultivation can be used to uproot young weeds without damaging the alfalfa stand.

Biological Control

Biological control involves using natural enemies of weeds to reduce their populations. While this method is less common in alfalfa, some farmers have experimented with:

• Grazing Animals: Sheep and goats can be used to graze on weeds in alfalfa fields, though care must be taken to avoid overgrazing the alfalfa.
• Weed-Suppressive Insects: Some insects feed on specific weeds and can be introduced to alfalfa fields to help control weed populations.

The Moonlit Harvest: Fact or Folklore?

Now, let’s address the intriguing question: why do some farmers believe in harvesting alfalfa under a full moon? This practice, rooted in folklore, suggests that the moon’s gravitational pull affects plant moisture content, making it an ideal time to harvest. Proponents argue that alfalfa cut during a full moon has higher nutritional value and dries more quickly, reducing the risk of spoilage.

While scientific evidence supporting this claim is limited, some studies have explored the relationship between lunar cycles and plant physiology. For example, research has shown that the moon can influence tidal patterns and, by extension, soil moisture levels. However, the impact on plant moisture content is less clear. Despite the lack of conclusive evidence, many farmers continue to follow this tradition, believing that it enhances the quality of their alfalfa.

Integrated Weed Management: A Holistic Approach

Regardless of the methods chosen, the most effective weed control strategy is often an integrated approach that combines multiple tactics. Integrated Weed Management (IWM) involves:

1. Prevention: Using clean seed, proper sanitation, and crop rotation to prevent weed introduction and spread.
2. Monitoring: Regularly scouting fields to identify weed species and assess their populations.
3. Cultural Practices: Implementing practices that promote alfalfa growth and suppress weeds.
4. Mechanical Control: Using physical methods to remove weeds when necessary.
5. Chemical Control: Applying herbicides judiciously and according to label instructions.
6. Biological Control: Exploring natural methods to reduce weed populations.

By combining these strategies, farmers can effectively manage weeds in alfalfa while minimizing the environmental impact and reducing the risk of herbicide resistance.

Conclusion

Weed control in alfalfa is a complex and multifaceted challenge that requires a combination of knowledge, strategy, and sometimes a bit of tradition. Whether you choose to rely on conventional herbicides, explore organic methods, or even experiment with moonlit harvests, the key is to understand the unique dynamics of your alfalfa field and tailor your approach accordingly. By doing so, you can ensure a healthy, productive alfalfa stand that provides high-quality forage for years to come.

Related Q&A

Q: Can I use glyphosate to control weeds in alfalfa?
A: Glyphosate is a non-selective herbicide that will kill alfalfa along with the weeds. It is not recommended for use in established alfalfa stands. However, it can be used as a pre-plant treatment to clear a field of weeds before planting alfalfa.

Q: How often should I apply herbicides to my alfalfa field?
A: The frequency of herbicide applications depends on the specific herbicide used, the weed pressure, and the growth stage of the alfalfa. Always follow the label instructions for application rates and timing.

Q: Are there any organic herbicides that work well on alfalfa?
A: Organic herbicides, such as acetic acid-based products, can be used for spot treatments in alfalfa fields. However, they are generally less effective than synthetic herbicides and may require multiple applications.

Q: What is the best time to apply pre-emergent herbicides in alfalfa?
A: Pre-emergent herbicides should be applied before weed seeds germinate, typically in the early spring or fall, depending on the weed species and local climate conditions.

Q: Can I use cover crops to suppress weeds in alfalfa?
A: While cover crops can be used to suppress weeds in some cropping systems, they are generally not recommended in established alfalfa stands, as they can compete with alfalfa for resources. However, cover crops can be used in rotation with alfalfa to improve soil health and reduce weed pressure.