It’s a Yellow Sweet Clover Year

Throughout the area, in roadways and fields, there is a heavy growth of a yellow flowering plant. Yellow sweet clover is plentiful this summer. The smell is pleasing to some, while the flowers do cause allergy problems for others.  

This plant is drought tolerant and successful in a wide range of soils. It is very winter hardy and is found in all types of communities including agricultural lands, roadsides, river banks and waste areas. 

It is an aggressive species which is often the first plant to appear on disturbed sites. 

Sweet clover is a biennial plant, meaning it has a two-year life cycle, with the second year producing flowers. 

Yellow sweet clover is a legume in the pea family, similar to alfalfa. It flowers in June and July, with plants continuing to flower until freezing weather. 

Yellow sweet clover can produce more than 100,000 seeds per plant and remain viable in the soil for more than 20 years. 

With proper growing conditions, sweet clover can provide a nutritious forage if managed properly. It is high in protein and easily digested by livestock. It also provides food for wildlife, nesting habitat for birds and is a pollinator for honeybees. 

Associated issues

However, there are problems associated with yellow sweet clover. 

If used as a grazing resource, there is potential for bloat. Livestock should be acclimated to the clover before being turned out fully on pasture with abundant clover. Turning out livestock that are not particularly hungry and less likely to rapidly eat clover will help prevent bloat. Limiting sweet clover intake until a tolerance is developed is also good practice. 

Additionally, if clover is turned into hay and not allowed to dry properly – causing moldy hay – there is a concern for sweet clover poisoning. 

Moldy sweet clover produces a fungus which reacts with substances within the clover causing cattle to hemorrhage. To prevent this phenomenon, make sure hay is cured well before baling. However this can be hard if bales are large and dense. 

Detecting the poisoning can also be hard, as the bleeding is internal. 

Grazing sweet clover cannot cause the conversion of substances that cause sweet clover disease. 

Harvesting sweet clover into silage can also help prevent the formation of the fungus which causes hemorrhaging as long as the ensiling fermentation process is rapid and complete so the silage is stable and does not allow mold growth.

Control and prevention  

Controlling yellow sweet clover can be a ficult task. 

Preventing or reducing seed production and dispersal is effective but is season dependent.

Hand pulling is effective in small areas and should be done in late summer or in early fall. 

Cutting can also be effective if done before flowers emerge and close to the ground below the lowest branch axils. However, this is not an eradication method. 

Mowing will not eradicate, just help manage. 

According to an article by the North Dakota Department of Agriculture, burning sweet clover can actually be counterproductive as it stimulates germination and production of first-year plants if done in March and April or in the fall. 

Burning during the dormant season in late fall or early spring, followed by a second burn in late spring, may be more effective in plant reduction, but the second burn must be done prior to seed set and when the plants are elongating so the buds of the plants don’t escape injury by being too close to the ground. 

Chemicals can also be used. Imazapyr, picloram, dicamba, clopyralid and 2,4-D may control the plant. 

Biological control such as heavy grazing by livestock in early spring may reduce plant numbers. A sweet clover weevil may also severely damage the plant but will also attack alfalfa or other legumes in the area.

Overall, sweet clover will be prolific on optimum growing years. Finding the value in this forage plant will be an easier solution than trying to eradicate it, and those who find sweet clover obnoxious for their allergies might want to find a good allergy medicine and enjoy some sweet clover honey. 

Sara Fleenor is the University of Wyoming Extension agriculture and natural resources educator serving Crook County. She can be reached at sfleenor@uwyo.edu or 307-283-1192.