Alfalfa leaves turn yellow when the plant is stressed due to environmental factors or a negative change in its living conditions. Correctly diagnosing the cause of the color change is the first step toward appropriate treatment.
The most common causes of yellowing alfalfa leaves are overwatering, crown rot disease, poor nodulation, root rot, potassium deficiency, soil compaction and leaf spot disease.
In this article, we will discuss the different causes of yellowing alfalfa leaves and how to remedy each one.
What is Alfalfa?
Alfalfa is also called the queen of forage crops. It makes a great addition to your home garden and can even be grown in pots.
The plant is native to warmer climates and is grown as livestock fodder.
Alfalfa has many nutrients that are beneficial to humans, which aid in detoxifying the urinary tract, purifying the blood and liver, and maintaining the alkalinity of the human body.
Alfalfa is a perennial plant, meaning that it regrows every spring. It can grow up to three feet tall and three feet wide.
The leaves of the alfalfa have three narrow, oval leaflets, a hairy lower surface and a smoother upper surface.
Why are My Alfalfa Leaves Turning Yellow?
Overwatering
Alfalfa plants are quite tolerant of drought and only really need 18 to 36 inches of water each season.
When an alfalfa plant is overwatered and the roots are constantly in soggy soil, they will drown and possibly die, as they are unable to get oxygen from air in the soil. The roots will rot and become susceptible to opportunistic pathogens.
These infections can travel up from the roots and into the stem and leaves of the plant, one of the effects of which is the yellowing of the leaves.
Avoid overwatering your plant also to avoid a host of other possible infections.
Crown rot disease
If the leaves of your alfalfa are turning yellow, you can determine a lot about its condition by digging up the plant and cutting into the crown. If there is brown discoloration, the alfalfa may have crown rot.
Many soil-borne fungi can cause crown rot in alfalfa, and some varieties can recover from the affliction. If the infection is severe, it may affect the long-term health of the plant.
If you have observed crown rot in plants in a specific area of your garden, you may need to rotate your crops.
Root rot
The condition of root rot can be exacerbated by several pathogens in saturated soil.
The most damaging of these is the Phytophthora root rot, which attacks the root system in all stages of the plant’s life.
The Pythium and Aphanomyces organisms are also known to attack the feeder roots of mature alfalfa plants when the soil around them is soggy.
You can try to avoid these infections by choosing varieties that are resistant to the Aphanomyces and Phytophthora root rots. Unfortunately, no known alfalfa variety is resistant to the Pythium root rot. You can only do your best to avoid the infection by improving the drainage in your soil and making sure it is not compacted. All of these diseases thrive in these conditions.
Poor nodulation
Another cause of yellowing alfalfa leaves is poor nodulation. You can check for this cause by digging up the seedlings and washing off the roots to carefully examine their nodules.
Alfalfa seedlings can develop poor nodulation if they get root rot, or from poor viability of the Rhizobium bacterium on the seed.
Because poor nodulation can be traced back to root rot, avoid overwatering to avoid root rot, thus avoiding poor nodulation as well.
Soil compaction
Wet soil during the spring can result in soil compaction in your garden. You can determine if the yellowing of the alfalfa leaves is caused by soil compaction by digging up and examining the root system of the plants as well as the soil structure.
When the compaction is severe, the plant’s roots are unable to pass through the soil, significantly reducing the plants’ yields. The compacted soil will also make plowing and replanting the only option if your first alfalfa plants are severely affected by the compaction.
Avoid this problem by making sure the soil is not compacted when you plant the alfalfa in the first place.
Potassium deficiency
Alfalfa plants consume a lot of potassium from soil every year. You can test the potassium levels in your soil, and if the levels are low, apply potassium-rich fertilizer where you plan on growing the alfalfa.
One of the most obvious signs of potassium deficiency in alfalfa plants is the yellowing of their leaves.
If the alfalfa plants have a potassium deficiency, it does not necessarily mean that the soil is depleted of this nutrient. It is also possible that the soil has normal levels of potassium but it is just compacted, making it difficult for the roots to absorb the potassium in it. This deficiency can also go hand in hand with root rot. Root rot, caused by overwatering, severely compromises the plants ability to effectively absorb nutrients and minerals.
In order to avoid potassium deficiency, avoid overwatering to prevent root rot, so that the plant can easily take up potassium from the soil.
Potato leafhopper
The potato leafhopper is a pest that feeds on alfalfa plants. They can cause the leaves of the plant to turn yellow due to their continuous feeding on the plant.
You can get rid of potato leafhoppers by using insecticidal soap. You may need to treat the plant several times to make sure that all of the insects have been killed.
Leaf spot disease
In the springtime, the alfalfa plant can fall prey to a host of different leaf spot diseases. The most common leaf spot diseases in alfalfa plants are the summer black stem and leaf spot, and the Lepto leaf spot.
These diseases happen more often during rainy weather in the spring and summer. Wet, humid weather in the summer favors leaf spotting and blighting diseases.
These diseases weaken the alfalfa plant but there are some plants that are able to outgrow the damage from the disease.
Use a fungicide to treat your plants.
Tips on Growing Alfalfa
Alfalfa plants only need partial sunlight and like to be in afternoon shade. Ideally, they should get three to four hours of sunlight in the morning and then be in the shade in the afternoon.
The sprouts of the alfalfa can be grown indoors in a matter of days. You can keep them in a small tray or in a glass jar. When the sprouts are around three to five inches, they can be transferred to the outdoor garden beds if you wish.
Water the alfalfa regularly if you notice that the top soil is dry. Alfalfa plants like their soil moist but not at all soggy. This helps to keep possible root rot and fungal diseases at bay.
Sow seeds in the spring or summer. Plant them in a firm seedbed in order to improve seed contact with the soil. The seedbed should have no weeds and should be moist. This helps keep the seeds moist and helps keep the new roots from drying out.
Alfalfa plants should be kept free from weeds, which compete with the plants for the nutrients and minerals in the soil. You can use a herbicide to get rid of the weeds or you can simply pull them out.
Apply fertilizer if you find that the soil is missing any key nutrients. The most important nutrients that need to be present in your alfalfa’s soil are potassium, phosphorus and lime.
Harvesting alfalfa is best done during the late budding and early bloom stage of the plant. This specific time yields high-quality feed. You can harvest alfalfa twice without any detrimental effect to the plant’s winter survival.
Conclusion
Alfalfa leaves turn yellow when there is an environmental factor causing the plant stress. In order to properly treat the plant, you need to be able to correctly diagnose the cause of the leaf discoloration.
The most common causes of alfalfa leaf yellowing are overwatering, crown rot disease, poor nodulation, root rot, potassium deficiency, soil compaction and leaf spot disease.
Image: istockphoto.com / Olga Seifutdinova