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Gray beetle with long antennae that are alternating white and black pattern on green leaf petiole.

Dectes Stem Borer Adults Active in Sunflower

In South Dakota, one of the insects that is commonly observed in sunflower is the Dectes stem borer larva. At this point in the season, adults are beginning to become active with females laying eggs in sunflower plants.

Dark green and tan curled caterpillars with an orange stripe along their sides.

Watch for True Armyworms in Wheat

This week we observed some true armyworm caterpillars in winter wheat fields. The caterpillars were still relatively small, which means they will continue feeding for some time. So far, the true armyworm caterpillars were still feeding on the leaves of the nearly mature wheat, but they have the potential to also clip heads off of the plants.

Soybean leaves with several bright green lesions progressing into tears with brown crusting along the edges.

Bacterial Blight Common in Soybean Fields

Several soybean fields scouted the week of July 15, 2019 were found with bacterial blight developing. The frequent rains experienced in most soybean growing counties have led to the development of this disease. Bacterial blight affected leaves are most evident on younger leaves in the upper canopy.

Corn plants with noticable rotting near the bottom stem.

Fusarium Root and Crown Rot Developing in Corn

A few corn fields scouted in Brookings County were found with Fusarium root rot at low levels. Infected plants were wilting and upon splitting of the lower nodes revealed brown discoloration of the pith. Root and crown rots developing in corn after the seedling stage are usually caused by Fusarium spp. and can be enhanced by injury to the roots or crown, mainly by insect feeding.

Small, green soybean aphids on a green, soybean stem with pink flower.

Small Populations of Soybean Aphids Observed in South Dakota

While scouting fields last week, we observed small populations of soybean aphids near Volga, South Dakota. Although no sustained populations were observed, it is a good reminder that soybean aphid scouting should occur throughout the growing season to prevent population outbreaks.

Symptoms of three common corn diseases. From left: anthracnose leaf blight, common rust and eyespot.

Is a Fungicide Needed for Developing Corn Diseases?

Corn is starting to tassel in several locations across the state. This is also the growth stage when a fungicide may be applied to control fungal leaf diseases. Diseases currently starting to develop are: anthracnose leaf blight, common rust and eyespot.

Two flies side-by-side. The left fly is a Western horse fly. The right fly is a deer fly.

Horse Flies and Deer Flies Becoming Abundant

The above-average precipitation this year has led to increased numbers of horse flies and deer flies across South Dakota. Widespread flooding and an overall abundance of available water has made conditions perfect for these flies.

Two corn diseases displayed side-by-side. The left corn plant has holcus spot lesions on its leaves. The right has paraquat drift injury.

Holcus Spot or Plant Injury?

Is your corn developing spots? Corn fields have been found with what appears to be Holcus spot, a bacterial disease. Upon further investigations, the leaves were found to be negative for any plant pathogens.

A sprayer applying pre-emergent pesticide to a bare field.

Herbicide Rotation Restrictions

This is a quick reference guide to common herbicides and their rotation restrictions for selected crops.

Close-up of several black caterpillars feeding on a green sunflower leaf.

Checkerspot Caterpillars in Sunflower

While scouting sunflower near Sturgis this week, we came across outbreak levels of checkerspot caterpillars that were defoliating the plants. Similar sightings have been reported throughout Western and Central South Dakota in recent weeks.