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Sweetclover Weevil
Sweetclover seedlings should be scouted frequently for damage caused by the sweetclover weevil. Adult weevils (1/4 inch in length and dark brown-gray in color) emerge in early spring and prefer feeding on sweetclover. However, if sweetclover is not available the insects will feed on alfalfa. The weevil is difficult to detect, however, its feeding is easily identified (crescent-shaped notches on leaves). Eggs are laid from late May to July. Larvae emerge and feed on the base of the stem and roots, eventually moving into the soil and attaching to plant roots. In July, the larvae move near the soil surface, pupate, and emerge as adults in August. Feeding will occur before the weevils overwinter in crop residue and soil.
Dry spring weather is conducive to high sweetclover weevil populations. Weevil feeding is intense in the spring and fall. Seedling sweetclover may be destroyed if weevil populations are high. Defoliated plants usually do not survive the winter. At the Carrington Research Extension Center, severe damage has occurred on newly-seeded sweetclover in research plots. For example, in 1991, entire sweetclover plots were destroyed by the weevil. In commercial fields, the sweetclover weevil may contribute to poor sweetclover stands. Second year stands normally tolerate defoliation, but plants may be stunted, especially under poor growing conditions.
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