Scout alfalfa now

John E. Woodmansee, Purdue University Extension, Whitley County

Heaving of alfalfa taproots has been found in southern Indiana

Heaving of alfalfa taproots has been found in southern Indiana, and a Purdue expert feels that this damage could be more widespread. It’s time to scout alfalfa fields now for heaving damage, and to begin scouting shortly for alfalfa weevil.

Keith Johnson, Purdue forage specialist, recently sent an alert to be on the lookout for alfalfa heaving. “With the extreme temperature swings this winter and moist soils, I would expect that this damage could be more widespread than most years,” said Johnson. “I would encourage growers of alfalfa to scout fields for winter injury and heaving.”

 

 

Heaving is a condition that periodically occurs over winter when freezing and thawing eventually push plant crowns and upper taproots up and out of the soil a few inches. Johnson said, “Soil heaving is a condition that predisposes many forage crops to disease.”

If heaving is found, Johnson recommended adjusting cutting height so crowns are not severed from the taproot when mowing occurs. “Heaving can cause wounds to the taproot which results in the possible movement of pathogens into the alfalfa,” said Johnson. “In severe cases alternative forages may need to be seeded to meet the forage inventory needs of livestock owned by producers.”

“As temperatures warm in April, scouting for the presence of alfalfa weevil should be a routine task, too,” Johnson said. Larvae are small and pale green with black heads. Each has a distinct white stripe on the back that runs the length of the body. When fully grown, it will reach 3/8 inch (9 mm) in length.

 

 

Before first cutting, walk a representative sample area in the field in an “M” pattern. Examine 5 plant stems at each corner and middle of the “M” and note feeding injury, size of larvae, diseased, larvae, plant maturity and stem length.

Early attacks by alfalfa weevil larvae are pinholes in leaves, particularly near the stem growing point. Later, larger larvae instars (larvae that have undergone molts to grow) shred or skeletonize leaves. Fields with severe leaf damage will appear gray.

Alfalfa weevil adults are brown and have a darker brown stripe on the back that runs the length of the body. Adults also have a prominent “snout.”

Scouting and management guidelines may be found in Purdue Extension’s Forage Field Guide, available for purchase at Purdue Extension offices, or online through the Education Store, www.edustore.purdue.edu. Additionally, search for a free downloadable publication at the Education Store titled, “Alfalfa Insect Control Recommendations.”

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