Major Insect Pests of Red Clover in Pennsylvania
Red clover, a highly important forage crop, is grown on approximately 750,000 acres in Pennsylvania. It is relatively easy to establish and will usually produce respectable yields under a wide variety of field conditions. Unfortunately, red clover stands do not persist well and usually "fade out" before or during the second full year of production. Two insect pests, the clover root curculio and the clover root borer, are partially responsible for the reduction or elimination of red clover stands.
Feeding by the nymphal stages of meadow spittlebugs can cause reduced yields by stunting plant growth. This insect causes most damage to clover fields that were seeded into small grain stubble.
Clover Root Curculio (Sitona)
Very small, (less than 1/4 inch long) grayish brown weevils are active in late summer and in spring. Eggs are deposited on the ground in clover and alfalfa fields during both periods. During winter, they survive as adult weevils, eggs, and also larvae. The newly hatched, plump white larvae work their way to the roots of the plants where they seek out and feed upon the nodules. Larger larvae feed on lateral roots and main tap roots. This feeding weakens the lants and also permits easy enter sites for disease organisms. Infested plants are subject to late winter soil heaving and are likely to die under stress conditions. Adult weevils cause minor damage by notching the edges of clover leaflets.
Larvae reach maturity during June. A new brood of weevils appears in late June, seeks shelter, and remains inactive until September.
There is no effective way to control this pest. To date, minimal research effort has been given to studies on clover root curculio control.
Clover Root Borer
This insect belongs to the bark beetle family but attacks roots of clover plants instead of trees. The insects winter as tiny, brown beetles in root cavities of clover plants. The beetles emerge in the spring and fly to nearby clover fields to deposit their eggs. The tiny white grubs bore into the clover roots, causing extensive damage. Infested plants may not recover following harvest and many will die out by mid-summer. There is one generation of this beetle per year.
There is no practical method known to prevent or control this pest.
Overwintering takes place as eggs stick to plant residue within a few inches of the ground. A likely site for spittlebug eggs is on small grain stubble. The elongated eggs are deposited between a dried leaf sheath and the main stem side by side in rows of 10 to 15 eggs per cluster. Egg laying takes place during August and September. Tiny yellowish green nymphs move to almost any nearby plant and start feeding by sucking sap and enclosing themselves in a bubble of spittle. One spittlebug nymph per stem can stunt the plant, resulting in high yield losses.
The nymphs mature into brown, jumping bugs in mid-June. These adult insects are approximately the size and shape of a grain of wheat. Seasonal damage is completed by the time the adults appear, since they do not injure field crops.
Conventional seeding methods, where crop residues are turned under, will reduce spittlebug populations. When high populations (more than one nymph per stem) are present in early to mid-May, a rescue spray can be applied to help prevent yield losses. However, this spray may not be profitable unless there is an average of one or more nymphs per stem.
Proven control measures are not known for all pests, but means are available to help reduce most populations. Information on pest control is available in the current issue of The Penn State Agronomy Guide , from your local county Extension agent or from a farm supply dealer.
Authored by: Stanley Gesell, Extension Entomologist
Dennis Calvin, Professor
Last updated 1983
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