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From The Extension Desk

Recently, there have been reports of increased false chinch bug activity across Montana. This activity has been reported in canola and mustard fields, and includes areas bordering Roosevelt County.

The false chinch bug is a native insect to the prairies, that generally feeds on weeds and range plants. During dry springs, however, they can become problematic in crops, especially members of the mustard family. They will feed on several other crops and garden plants, including wheat, sunflowers, soybeans and potatoes.

The adult false chinch bug is gray or light brown and 1/8 to 1/6 inches long. Adult false chinch bugs also have transparent/white wings that form an X when the wings are folded. They are similar in appearance to bigeyed bugs and chinch bugs.

The adult false chinch bug overwinters under plant debris (generally in weedy borders and rangeland), emerging when spring temperatures begin to warm. They will lay eggs soon after emerging. False chinch bugs lay their eggs in cracks in the soil. Eggs incubate around four days before the nymphs hatch. The nymphs are lighter colored than the adults, with occasional orange spots on their abdomen. The nymphs are generally found around the base of plants. Over the next 21 days, nymphs will undergo around five molts before reaching adult size. Multiple generations are possible through the summer. The false chinch bugs feed by piercing the plants and sucking out the juices. Adults are capable of flying and feed on all parts of the plant.

During most years, false chinch bugs are not considered a problem. During dry years, however, they can cause stunting or more severe damage. Damage may occur at any stage of growth and tends to be scattered throughout the field. Assessing damage is often difficult, as it is often in isolated pockets. Signs of damage may include dry plants, leaf curling and stunted growth.

During most years, treatment is not needed but when large numbers gather, treatment may become necessary. In severe outbreaks you may notice hundreds to thousands of bugs on a single plant or what is sometimes described as “clouds of false chinch bugs” flying over the field.

Quantifying the number on each plant may be difficult as they fly easily. This behavior, as well as the generally scattered, isolated nature of the damage in a field, makes setting economic thresholds difficult. Economic thresholds in canola in one resource differ from at 5-10 adult insects per head (of the plant) at blooming and 10-20 per head at pod fill to 20-30 per plant at flowering, and 40-50 per plant at pod fill. Scouting is especially important because damage is often scattered and isolated throughout the field.

Spot treatments are often more effective than total field treatments. Pyrethroids, mixed in large volumes of water are often recommended. Aim for full plant coverage when spraying.

Heavy rains may wash the insects off of the plants and drown them. Irrigation, when available, helps support the plant to recover from insect injury.

For more information, contact MSU Extension – Roosevelt County Agent Jeffrey Chilson at 787-5312 or Jeffrey. [email protected]

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