As an alfalfa grower, noticing brown spots popping up on the leaves of your lush green plants can be alarming. But don’t panic – those unsightly spots are likely a result of a common fungus called common leaf spot. While not usually devastating, uncontrolled infections can reduce yields and forage quality. Catching and treating leaf spot early is key to keeping your alfalfa healthy and productive.
In this article, we’ll cover what causes common leaf spot how to identify it, and effective treatment options. Arm yourself with the knowledge to diagnose and treat this troublesome disease in your alfalfa crop. With timely intervention you can minimize losses and continue harvesting high-quality alfalfa.
What Causes Brown Spots on Alfalfa?
The fungus Pseudopeziza medicaginis is responsible for the development of common leaf spot in alfalfa. Spores of this fungus survive the winter on diseased alfalfa debris left on the soil surface. In spring when weather is cool and moist, spores spread through rain splash onto lower leaves, infecting the plant.
Small, water-soaked spots first appear on infected leaves. These spots then enlarge into tan lesions with dark brown borders. Severe infection causes leaves to yellow and drop prematurely. When conditions are favorable, the disease spreads rapidly defoliating plants from the bottom up.
Prolonged wet, cool weather promotes common leaf spot development. Dense plant stands and poor air circulation also increase disease spread. Stressed plants are more vulnerable to infection.
How to Identify Common Leaf Spot
Learning how to recognize common leaf spot is vital for effective management. Watch for these key signs:
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Small, circular or irregularly shaped tan lesions on leaves, surrounded by dark brown or purple margins. Lesions may coalesce into large necrotic patches
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Spots first develop on lower leaves near the soil. Disease progresses up the plant during extended wet periods.
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Heavily infected leaves turn yellow or brown and drop off leaving bare lower stems. Defoliation proceeds upwards as disease advances.
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Tiny black fungal fruiting bodies may be visible in the center of older spots.
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Infected plants become stunted and unthrifty in appearance.
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Disease is most severe during cool, wet spring weather and reoccurs in fall. Hot, dry summer conditions temporarily suppress symptoms.
Learning to differentiate common leaf spot from other alfalfa diseases like downy mildew will help diagnose problems accurately. Contact local crop advisors if you need assistance identifying diseases. Prompt and proper identification is key for effective management.
How to Prevent and Treat Common Leaf Spot
The best offense against leaf spot is a good defense. Integrating preventive practices into your alfalfa management plan is crucial for reducing disease impact. Here are some tips:
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Select resistant varieties – Plant alfalfa cultivars rated as having resistance to common leaf spot to avoid problems.
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Provide good air movement – Thin stands and avoid overcrowding to allow airflow and rapid drying of leaves.
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Control weeds – Weeds like mustard and shepherd’s purse harbor the leaf spot fungus. Keep them in check.
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Remove debris – Promptly chop/incorporate alfalfa stubble after harvest. Remove volunteer plants and destroy debris to reduce inoculum.
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Avoid stress – Prevent stresses like compaction, low fertility, and waterlogging that make plants more vulnerable.
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Scout fields – Monitor for early leaf spot symptoms and treat as needed before damage is severe.
If common leaf spot is detected, fungicide application at the first sign of disease can help protect plants. Repeated application is often needed, especially during prolonged cool, wet weather when the fungus is active. Always follow label directions on proper fungicide use.
With proactive management focused on prevention, common leaf spot doesn’t have to spell disaster for your alfalfa production. Scout diligently and know when to pull the trigger on protective fungicide treatments. By staying vigilant and responding quickly at the first sign of spots, you can keep this troublesome disease from overrunning your alfalfa crop.
A closer look at leaf diseases of alfalfa
Jim Isleib, – December 07, 2011
This third of three articles on alfalfa diseases includes common leaf diseases in Michigan and other problems sometimes confused with alfalfa leaf disease.
Many diseases can impact alfalfa leaves in Michigan, resulting in interference with photosynthesis and early defoliation. 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.
Leaf diseases of alfalfa tend to become more severe after flowering begins, so harvesting at no later than 10 percent flower, or earlier, is a good cultural practice to minimize leaf disease losses. Seeding alfalfa with a companion, or “nurse,” crop can also increase the incidence of leaf and stem diseases. Alfalfa varieties are screened for root and crown disease resistance by seed companies and universities. However, leaf and stem disease resistance ratings are not widely available, except for anthracnose.
Caused by the fungus Psuedopesziza medicaginis, this disease results in both early- and late-season defoliation. Cool and moist (or very humid) weather or alfalfa under a heavy companion crop can increase severity. Low fertility and acidic soil seems to make this disease worse. Symptoms include small, circular spots, brown or black in color, developing first on lower or inner leaves. Tiny, cup-shaped fungal fruiting structures appear in the center of fully developed spots on the upper leaf surface. 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. It appears mainly in spring and fall during cool, moist or very humid weather. Young leaflets on rapidly growing plants have light green blotches and may twist, or curl, downward if the disease is severe enough. The underside of leaflets may have a pale, violet, downy growth. Symptoms disappear during warm, dry weather, but can come back in the fall. The fungus overwinters in crop residue and can be seed borne.
Caused by the fungus Stemphylium botryosum, this disease is also called “target spot.” It is most common in lush stands following warm, wet weather and when harvest is delayed. The most noticeable symptom is formation of oval-to-elongate brown lesions with lighter centers, enlarging to form concentric light and dark brown zones. A single, large lesion can cause a leaflet to yellow and drop. Older lesions can be covered with a soot-like mold. The disease overwinters on old, infected stems, or on seed.
Caused by the fungus Leptosphaerulina briosiana, this disease is also called “pepper spot” and is most common in cool, wet weather on young leaves and petioles of recently cut stands. It produces small, reddish-brown to black spots, enlarging to form oval-round tan spots with a darker border. These spots can merge and kill the entire leaf. Dead leaves often cling to the stem for some time.
Other alfalfa leaf diseases include:
- Spring black stem and leafspot (see previous alfalfa stem disease article)
- Summer black stem (Cercospora) and leaf spot (see previous alfalfa stem disease article)
- Yellow leaf blotch
- Bacterial leaf spot
- Alfalfa mosaic virus
- Rust
Non-disease alfalfa leaf problems include:
- Insect injury: Potato leafhoppers cause “hopperburn,” a v-shaped yellowing of the leaf.
- Herbicide injury: Triazine carry-over in new seedings was common before the prevalence of glyphosate-resistant corn hybrids and Dicamba/2,4-D injuries can occur.
- Nutrient deficiencies: Boron – top leaves are bunched and yellow-reddish in color. Can be mistaken for hopperburn. Phosphorus – causes yellowing of leaves and is most common in low or high pH soils. Sulfur – upper leaves turn pale yellow, most likely on sandy, low organic matter soils. Magnesium – most likely on acid, sandy soils. Area between leaf veins turns yellow-white with plant stunting. Symptoms move from older to newer plant growth.
See the first article of this series, “Be familiar with root rot diseases of alfalfa,” for more information on certain root rot diseases, and the second article, “Gain knowledge on stem diseases of alfalfa,” for more information on certain stem diseases.
- Leaf and Stem Diseases of Alfalfa, RPD #301, University of Illinois Extension.
- Pest Management in Wisconsin Field Crops, A3646, University of Wisconsin Extension.
- MSU Extension Bulletin (archived) E-1422 “Alfalfa Diseases I.”
Brown Spots On Houseplant Leaves: Uncovering The 6 Causes And Ultimate Solutions! #plantcaretips
FAQ
What are the brown spots on alfalfa leaves?
How do you treat brown spot disease on plants?
What causes alfalfa to turn brown?
Why does my plant have random brown spots?
What causes brown spots on leaves?
Brown spots on leaves are typically caused by a variety of fungal diseases called leaf spot diseases. Plants that receive too much water or not enough airflow and sunlight are more likely to develop brown spots on their leaves due to moist conditions.
What causes brown spots on the face?
Brown spots are caused by the overproduction of melanin in your skin. Melanin is the pigment that gives your skin, hair and eyes their color. Age spots are caused by overactive pigment cells. Ultraviolet (UV) light speeds up the production of melanin.
Why does my houseplant have brown spots?
Although there are many reasons your plant may have brown spots, most of them include Overwatering, sunlight, and excessive fertilizer, the most common is Leaf Spot Disease. Leaf Spot is a limited discolored common fungal or bacterial infection that plagues houseplants.
Why are my plants turning brown?
If the leaves of your plants are turning brown, the most likely reason is that they’re not getting enough water when plants don’t get enough water, their leaves wilt and turn brown. The best way to prevent this is to water your plants regularly, giving them enough water so that the soil is always moist (but not wet).