The adult threecornered alfalfa hopper is a green, wedge-shaped insect about 1/4 inch long. They are an occasional pest of soybean. The adults are very mobile and hop when disturbed. Adults and nymphs feed by inserting their piercing-sucking mouthparts and girdling the circumference of stems or leaf petioles. A callus (girdle) is created at the site of feeding. Plants may snap over while walking through the field or during a storm if threecornered alfalfa hoppers, typically the adults, have girdled the main stem of plants less than 10 – 12 inches tall. Lodging is often observed long after the girdle was made and when plants are no longer susceptible to damage. Leaves may be seen turning brown where petioles have been girdled. Feeding by threecornered alfalfa hopper does not cause yield loss unless lodging occurs, and especially when this lodging occurs during the mid or late reproductive stages (R4 and beyond).
Sampling for threecornered alfalfa hoppers in seedling soybeans is difficult. Fields should be scouted for this pest from emergence until plants are 10 – 12 inches tall. A sweep net can be used to detect the presence of adults. Adults may also be observed hopping as you walk through the field. A sweep net handle can be used to bend seedling plants over. Girdled plants often snap when this is done. Make sure sample points are scattered over the entire field as infestations are often highest along field margins.
There is no established sweep net threshold for threecornered alfalfa hopper, but treatment may be needed if you catch more than 10 hoppers per 25 sweeps and when plants are less than 10 inches tall, and especially in fields where plant stands are below optimal levels. Also consider treatment if 10% or more of seedling plants are infested with nymphs or adults or when 50% or more of plants are girdled. Treatment is not generally recommended for plants greater than 12 inches tall. Fields may be re-infested quickly after an insecticide application is made, but multiple applications for this pest are rarely justified.
Insecticide seed treatments such as Cruiser, Gaucho, and NipsIt Inside provide some protection during the seedling stage, but injury may still be observed, particularly in small fields or on the edges of larger fields.
|Insecticide (Trade Names) for THREECORNERED ALFALFA HOPPER||Lb Active Ingredient per Acre||Amount Formulation per Acre||Performance Rating|
|acephate 90 (Orthene 90S)||0.75 - 0.99||0.83 - 1.10 lb||8|
|bifenthrin (Brigade 2E, Discipline 2E, Fanfare 2E)||0.05 - 0.10||3.2 - 6.4 oz||9|
|esfenvalerate (Asana XL 0.66E)||0.03 - 0.05||5.8 - 9.6 oz||8|
|β-cyfluthrin (Baythroid XL 1)||0.025 - 0.044||1.6 - 2.8 oz||8|
|γ-cyhalothrin (Declare 1.25)||0.0075 - 0.0125||0.77 - 1.28 oz||8|
|λ-cyhalothrin (Karate 2.08, Warrior II)||0.015 - 0.025||0.96 - 1.6 oz||8|
|Z-cypermethrin (Mustang Max 0.8E)||0.0175 - 0.025||2.8 - 4 oz||8|
- Threecornered alfalfa hoppers are more problematic in reduced tillage systems. The highest populations are typically observed in late planted fields such as double-cropped soybeans.
- Lodging of plants tends to be worse in fields with low plant populations, and thus, achieving adequate plant stands can reduce the risk of economic injury.
- Maintaining a clean field border may help reduce population numbers.
- For more information see http://utcrops.com/soybean/soybean_insects/SoybeanTCAH.htm.