Oklahoma growers often wonder how quickly alfalfa can be rotated with the previous alfalfa crops. There is no single answer for this issue — it depends on other factors surrounding the system. Many producers believe the least amount of time to leave fields out of alfalfa before reestablishing is the number of years the stand was active. If a stand lasted six years—leave it out for six years. Currently, the recommended time is a two-year rotation to re-introduce alfalfa in a field is recommended. However, one year might be enough for some fields and two years might not be enough for others. Rather than relying on simplified and inaccurate over-generalizations, alfalfa producers can make more accurate decisions by understanding the soil-plant-weather relations pertinent to re-establishing alfalfa stands. The first step is to understand the factors that result in an unsuccessful alfalfa re-establishment. They are:
Autotoxicity is the first factor to be checked in fields before planning to re-seed alfalfa. In other words, a field with good soil moisture; fertility; absent of pests and diseases; and free of water ponding may still not be ready for re-seeding alfalfa if residues from old stands are still present in or on the soil. The goal of this fact sheet is to explain alfalfa autotoxicity and present an objective way to assess this issue in contrasting soil-weather scenarios.
Alfalfa autotoxicity is caused by substances produced by alfalfa plants that moves into the soil, inhibiting new alfalfa seedling root development. This leads to reduced vigor and seedling death. Those substances are secondary metabolites, medicarpins and phenolic compounds. Mature alfalfa plants accumulate them with the objective of defending themselves against pests and diseases attacks. Eventually, those metabolites escape to the soil, inhibiting new seedlings, consequently, allowing the existing plants to grown unimpeded. Unfortunately, those compounds can remain active in the soil for prolonged periods. Even though the old alfalfa stand is terminated, the compounds will continue to be active in the soil for months or years after termination. The breakdown of the metabolites will vary according to soil, weather and field practices. Therefore, timing to re-seed alfalfa vary by specific field.
As an alfalfa grower it can be concerning to see your upright green alfalfa plants start bending and falling over. A toppled alfalfa plant is clearly under duress. But don’t despair! By understanding the potential reasons for the droop, you can take action to get your alfalfa standing tall again.
4 Common Causes of a Flopped Over Alfalfa Plant
Here are some of the most frequent culprits for alfalfa stems going limp:
1. Insufficient Support
Alfalfa has a tall, slender stem that can get top heavy as the plant matures. Without adequate structural support, that stem is prone to buckling under the weight of the foliage and flowers above it
Adding stakes, trellises or other supports provides stability to keep the alfalfa plants upright. Just be sure not to bind the stems too tightly to avoid damage.
2. Water Imbalance
Too much or too little water can both make alfalfa stems go limp. Overwatering leads to saturated soil, poor root health, and weakened stems. Underwatering causes the plant to wilt.
Monitor soil moisture and maintain even hydration to keep those alfalfa stems rigid. Alfalfa thrives in moderately moist, well-draining soil.
3. Nutrient Deficiency
If nutrients like nitrogen, phosphorus, or potassium are lacking, alfalfa plants can become stunted and structurally unsound. The compromised stem strength leads to floppiness.
Test your soil to see which nutrients are needed. Amend soil with organic matter or use a balanced fertilizer to provide missing elements. This nourishes the plant from the roots up.
4. Pests and Diseases
Chewing insects, boring pests, and certain plant pathogens physically damage alfalfa plant tissues, weakening stems so they fall over more readily.
Inspect for signs like chewed leaves, sticky deposits, powdery growth, etc. Address any issues through proper identification, sanitation, natural predators, treatments, etc.
When to Take Action on a Drooping Alfalfa Plant
Don’t delay when you notice your alfalfa starting to sag and bend. Acting quickly improves your chances of getting it standing upright again.
Signs that it’s time to intervene on a droopy alfalfa plant include:
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Stems bending at 30 degrees or more from vertical
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Clear yellowing or browning of lower leaves
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Visible pest damage covering 25% or more of leaves
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Areas of soil appear overly dry or saturated
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White powdery substance visible on 30%+ of leaves
5 Tips to Get Your Alfalfa Standing Upright Again
Here are some tips to rehabilitate a floppy alfalfa plant:
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Stake it – Install stakes gently to support bent stems until they recover strength.
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Water carefully – Improve drainage if oversaturated. Water deeply if drought stressed.
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Feed regularly – Apply a balanced liquid fertilizer every 2-3 weeks to nourish the plant.
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Treat pests – Use insecticidal soaps, natural predators, or other remedies to control infestations.
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Prune damaged areas – Selectively remove sections of stem or foliage that are unsalvageable to promote new growth.
Preventative Care for Upright Alfalfa Plants
The best defense is a good offense when it comes to keeping alfalfa standing tall. Here are some proactive care tips:
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Choose disease-resistant alfalfa varieties when planting
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Maintain proper row spacing for airflow and light penetration
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Test and amend soil to optimal nutrient levels prior to planting
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Use crop covers to protect young plants from wind damage
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Scout regularly for early signs of pests or disease
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Control weeds to reduce competition for water and nutrients
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Avoid overwatering and improve drainage if soils stay soggy
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Fertilize according to soil test recommendations to prevent deficiencies
Limp, falling over alfalfa plants are never what you want to see as a grower. But don’t despair. With a bit of detective work to identify the cause, and taking prompt action to provide supports, tweak watering, treat pests, or make other fixes, you can get your alfalfa standing tall and healthy once again. Pay close attention to your plants, act at the first signs of trouble, and be diligent about preventative care for the best results.
Factors Affecting Persistence of Alfalfa Autotoxicity
The age of the alfalfa stand plays a major role in the levels of autotoxins released into the soil. One- to two-year-old stands have less potential of producing autotoxins than three- to five-year-old stands. Furthermore, certain parts of the alfalfa plant will produce different amounts of autotoxins. Leaves and flowers will produce more autotoxins than stems, roots and seeds. Chung and Miller (1995) found that water extracts of alfalfa leaves and flowers drastically reduced seedling germination by 26 and 38 percent, respectively; while water extracts of alfalfa stems (16 percent), seeds (12 percent) and roots (8 percent) had a lessened effect on alfalfa seed germination. This data set showed flower parts have the highest concentrations; consequently, alfalfa stands will have higher levels of autotoxins after flowering (reproductive stage). Hedge and Miller (1992) proved that reproductive-stage alfalfa plants extracts at concentrations as low as 20 grams per milliliter were enough to reduce seed germination. On the other hand, vegetative stage alfalfa plants started to decrease seed germination at a concentration of 60 grams per milliliter, which is three times higher.
The thickness of the alfalfa stand is another important aspect. The higher the density of alfalfa plants in a field, the higher the amount of autotoxin produced. According to Jennings (1999), the zone of influence of an old alfalfa plant on alfalfa seedlings extends to a radius of 16 inches. Alfalfa seedlings within 8 inches proximity to an old alfalfa plant will not survive. Seedlings within 8 to 16 inches will have reduced growth and those more than 16 inches away will not be affected. Based on these findings, it is conclusive that a stand with a plant population of 0.8 plants per square foot will have issues with autotoxins. On the other hand, an alfalfa field that contains large dead areas due to seedling failure and water ponding where plants less than one year old were present, can be re-seed with no autotoxin issues.
Think Twice Before Cutting Alfalfa This Fall | Beck’s Agronomy Update
FAQ
Why is my plant falling over?
What are the problems with growing alfalfa?
How long does alfalfa autotoxicity last?
Can you plant alfalfa back to back?
What causes alfalfa leaf disease?
Yield and quality suffer when disease problems become serious. Along with disease pathogens, other factors can damage alfalfa leaves. These include insect injury, herbicide injury and nutrient deficiency. Familiarity with symptoms of more common alfalfa leaf diseases and other problems can help producers identify and manage their crop.
What causes premature defoliation in alfalfa?
Premature defoliation results as the number of leaf spots increases. The disease overwinters in un-decomposed leaves on the soil surface. Caused by the fungus-like organism Peronospora trifoliorum, this disease seldom causes plant death in alfalfa stands, but affects yield and quality.
Why do alfalfa seedlings die?
As soon as the water came off, more alfalfa seed was flown onto moist clay-loam soils and the resulting stand was perfect. In another case, we observed a seedling field that died from seedling diseases due to cold, wet weather.
How does rain affect alfalfa?
Rainfall helps wash out the autotoxic compounds and microorganisms that help degrade the toxins. Any grower with a current alfalfa field should plan on making a field/crop assessment this fall, ideally after the final harvest of the season. A final assessment should be done to determine any liming, nutrient or reseeding needs.