Symptoms of wilt diseases of alfalfa have been observed in several fields in southeast Nebraska (Figure 1). The symptoms include wilting shoots, bleaching of leaves (Figure 2) and stems, and a reddish-brown discoloration of the center of the taproot (Figure 3). Several pathogens including the fungi Fusarium and Verticillium and the bacterium Clavibacter can cause wilt in alfalfa. Fusarium and Verticillium cause leaf bleaching; bacterial wilt is characterized by yellow-green foliage. Fusarium was isolated from samples submitted to the UNL Plant and Pest Diagnostic Clinic.
Symptoms became evident several weeks ago during the unusually warm, dry conditions that caused plants to undergo moisture stress. Growers noted yellowing of established alfalfa in low field areas and thought nighttime frost/freezing temperatures might have caused the injury.
Closer examination indicated the symptoms were not consistent with frost injury. Damaged plants were shorter than surrounding healthy green alfalfa, plant stand was sometimes reduced, and upper leaflets often had distinct white interveinal areas prior to leaflets becoming yellow (Figure 2).
These plants were near waterways in upper field areas as well as in lower elevation areas, and were consistent with high moisture areas conducive to fungal root disease development. Wilting plants are often the first symptom of these diseases, although interveinal white areas and yellowing plants preceded wilt in 2012. Other symptoms include bleaching of the leaf and stem, and a reddish tint to the leaves, especially with Verticillium wilt. In infected alfalfa, stress helps to express the symptoms. Roots have a dark reddish-brown streak in the stele (center of root) when infected with Fusarium wilt (Figure 3). Alfalfa wilt caused by Fusarium or Verticillium is often chronic, causing plants and stands to decline over time (Figure 1).
As an alfalfa grower it can be alarming to walk out and see your normally perky alfalfa plants looking weak and droopy in the field. Alfalfa wilting and drooping leaves are a sign that the plants are under duress. But what’s causing the issue and what can you do to perk up your limp alfalfa? In this article, we’ll explore the range of factors that can lead to dropped leaves and wilting stems, along with tips to bring your plants back to good health.
Overview of Reasons for Droopy Alfalfa
Many different factors can cause alfalfa plants to wilt and droop leaves downwards. The most common reasons include:
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Lack of water from drought stress or ineffective irrigation
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Excess water from over irrigation rain or flooding
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High or low temperatures beyond the ideal range
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Pest and disease damage impeding water movement
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Nutrient deficiencies disrupting plant functions
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Herbicide injury damaging cells
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Soil compaction limiting root development
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Cutting or grazing too severely
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Normal growth habit of some varieties
Diagnosing the trigger is essential for proper treatment to restore upright, healthy plants.
Environmental Stresses
Environmental conditions play a major role in alfalfa plant droop. Hot, dry weather can quickly wilt plants, as can overly wet soils.
Drought Stress
Lack of adequate water transpiration causes loss of turgor pressure in plant cells, leading to wilting and drooping. Ensure proper irrigation during dry periods.
Excess Moisture
Saturated soils limit oxygen availability to roots. Allow soils to dry somewhat between waterings and improve drainage if needed.
Temperature Extremes
Hot weather causes excess transpiration while cold temps can damage cell membranes. Select suitable alfalfa varieties for local climate. Provide shade cloth or frost protection when appropriate.
Herbicide Injury
Certain herbicides damage plant tissues, impairing water transport and causing wilting. Strictly follow label directions to avoid herbicide injury.
Diseases and Pests
Alfalfa plants can wilt downwards when infected by pathogens or attacked by hungry pests.
Fungal Diseases
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Anthracnose, Fusarium and Verticillium wilts clog water conductive vascular tissues.
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Phytophthora root rot damages the roots’ ability to take up moisture.
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Powdery mildew coats leaves in fungus, disrupting transpiration.
Bacterial Diseases
- Bacterial wilt also blocks water movement in the plant’s vascular system.
Pest Infestations
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Potato leafhopper feeding inhibits water movement, causing “hopperburn”.
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Heavy spider mite infestations lead to extensive leaf stippling damage.
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Alfalfa weevil larvae skeletonize leaves when feeding.
For diseases and pests, scout regularly and use insecticides, fungicides, or resistant varieties as needed.
Cultural Factors
Certain common crop management practices can also lead to limp alfalfa plants if improper.
Overcutting
Removing too much leaf area via grazing or mowing stresses plants. Allow proper recovery periods between cuttings.
Nutrient Deficiencies
Lack of nitrogen, phosphorus, potassium or other nutrients contributes to poor growth and wilting. Fertilize based on soil test results.
Soil Compaction
Dense soil layers prevent root penetration and function. Relieve compaction through deep tillage when required.
Variety Habit
Some alfalfa varieties naturally exhibit more droopy stems and leaves. Select more upright types if desired.
Diagnosing Drooping Alfalfa Plants
When alfalfa plants start looking droopy, determine the cause by:
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Checking soil moisture and assessing recent weather conditions
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Scouting thoroughly for disease symptoms or pest damage
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Testing soil nutrients and pH to see if deficiency is likely
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Reviewing recent field activities like irrigation, spraying, cutting schedules
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Monitoring differences related to characteristics like soil type or alfalfa variety
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Looking for patterns indicating spread from an initial source
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Comparing plant appearance to previous vigor or growth stage
Turn Droopy Alfalfa Around
Once the trigger becomes clear, take action to get your alfalfa standing upright again:
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Water thoroughly if drought stressed, allow soils to dry some before next watering
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Improve drainage from excess rainfall or overwatering
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Protect from temperature extremes with covers, shade, variety selection
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Rule out herbicide damage, be meticulous with applications
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Use integrated pest management – scout, spray, release beneficials
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Follow proper cutting schedules to minimize stress
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Test and amend soil nutrients based on recommendations
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Relieve compaction through deep tillage, controlled traffic flow
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Overseed or renovate stands if mortality exceeds 50%
Prevent Future Alfalfa Droop
A bit of prevention goes a long way to avoid stressed, drooping alfalfa plants:
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Select suitable varieties for local growing conditions
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Practice good irrigation management, avoid overwatering
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Scout regularly and treat pests early before heavy damage
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Test soils and fertilize appropriately to maintain nutrients
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Allow proper plant recovery between cuttings or grazing
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Reduce compaction with steps like rotation, cover crops, controlled traffic
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Follow all pesticide label instructions carefully
It’s worrying to see your alfalfa crop looking limp and weak. But don’t panic! Follow the tips above to diagnose the cause, provide solutions tailored to the trigger, and get your plants looking perky again. With careful management going forward, you can help your alfalfa thrive and stand tall.
Disease Resistance and Management
Differences in varietal resistance range widely in alfalfa. Several varieties provide only 31-50% resistance, and highly resistant (HR) varieties can range from 51% to 100%. Several Fusarium species can affect seedling alfalfa as well.
Fusarium and Verticillium wilt of alfalfa can be managed by planting resistant cultivars, crop rotation, weed control, pathogen-free seed, and harvesting younger stands before older, diseased stands.
Michael Rethwisch Extension Educator, Butler County Stephen Wegulo Extension Plant Pathologist
How to Start a Good Alfalfa Stand
FAQ
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