Order: Hemiptera (Homoptera)
“Something is going on with our purple hull peas. We had a little rain and wind last night, and this morning some of the plants were broken and laying on their sides. These are young plants, about 10 to 12 inches tall. It looks like something cut around the stem a few inches above the ground and this is where the breaks occurred. My cousin says the same thing happens in his soybeans.”
As the photo shows, threecornered alfalfa hoppers are well-named. These robust little treehoppers are about ¼ inch long as adults and quickly jump and fly away when disturbed. Adults use their piercing-sucking mouthparts to feed on plant sap, but it is the immature stage, or nymphs, that cause the damage described above. Although they occasionally feed on other plants, alfalfa hoppers prefer legumes such as peas, green beans, and soybeans.
Nymphs are generally shaped like adults but are soft-bodied and have a row of spine-covered spikes along the center of their back. My wife, who did her master’s degree work on this insect and spent a lot of time rearing them, often describes them as “cute.”
Nymphs feed on plant stems by circling the stem while feeding with their piercing-sucking mouthparts to create a ring of dead and damaged tissue around the stem. They have a plan; they are making a dam. This girdled ring blocks transport of phloem from the upper part of the plant to the roots, causing nutrients to accumulate just above the girdled ring where the nymphs can feed on this extra nutritious sap.
As nutrients accumulate above the girdled area, this portion of the stem usually continues to grow in diameter while stem growth below the girdle is reduced, resulting in plants that are top-heavy. Sometimes plants respond by producing adventitious roots above the girdle in an attempt to re-establish contact with the ground. Sometimes this injury is fatal, especially when serious plant diseases are introduced, but more often the girdled ring heals, and plants survive to maturity. Still, this girdled ring is a point of weakness, and physical stress, such as heavy winds, can cause plants to break.
Control: Control is usually not practical to protect peas and beans in home gardens. Damage is sporadic and by the time you see broken plants it is usually too late to spray. Sprays of pyrethroid insecticides, such as zeta-cypermethrin applied to control bean leaf beetles on young plants may also help reduce early alfalfa hopper injury, but it is usually not necessary to spray for bean leaf beetles either. Cowpea curculios and stink bugs are the most important pests of southern peas. These two pests often do require treatment.
Thanks to Maureen Layton and Dr. Fred Musser for their input on this article.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
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