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Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

Western Corn Rootworms

–by Dr. Jeff Whitworth

Western corn rootworm larval feeding seems to be almost finished around the north central part of Kansas, anyway. Root monitoring yielded mostly mature larvae– but also one that had just recently pupated (see fig 2). No western corn rootworm adults have been observed yet.

Figure 2 Two WCRW larvae plus new pupa  (by Cody Wyckoff)

 

DECTES (soybean) Stem Borer

–Dr. Jeff Whitworth

The 1st adult Dectes (soybean) stem borers were observed on 29 June in north central Kansas (see fig. 1). This adult emergence seems to be right on schedule with past years, as we have found adults emerging right around the 4th of July since 1997. These adults usually feed a little while on pollen, then mate for about 7-14 days before disbursing to soybean (or sunflower) fields to deposit their eggs in the stems right at the petiole.

Figure 1 Adult Dectes Stem Borer (BY Cody Wyckoff)

 

ID to last week’s bug

–by Frannie Miller

 

Squash bug – Squash bugs use their piercing-sucking mouthparts to suck the sap out of plants leaves. This feeding can lead to the plants to wilt. These pests prefer to feed on zucchini, winter squash, and pumpkins, but will also attack members of the cucurbit family, such as cucumbers, cantaloupe and watermelon. It is important to detect the presence of these pests early, in order to try to control their population.

BEAN LEAF BEETLES

–by Dr. Jeff Whitworth

Adult bean leaf beetles are very active throughout north central Kansas at the present time. They typically chew round/oblong holes in leaves (note fig. 4 with bean leaf beetle at the tip of the arrow) and deposit eggs in the soil around the base of soybean plants. There are two color phases of adult bean leaf beetles (fig 5), a tan phase and a reddish phase, but both have six black spots surrounded by a black border on their backs. Both color types can be seen in fig 5.

Figure 4 Soybean leaf damage from beetles (Cody Wyckoff)

Figure 5 Bean leaf beetles (Cody Wyckoff)

CLICK BEETLES

–by Dr. Jeff Whitworth

Just FYI: This photo (fig. 3) is of a click beetle. Wireworms are the larval stage- and after they pupate in the soil, they emerge as an adult, which looks nothing like the wireworm. There are several species of wireworms (click beetles) in Kansas, and the one pictured is one of the more common species, all of which are usually well controlled by insecticide seed treatments. However, these seed treatments generally do not offer seed/seedling protection 21-28 days after the seeds were planted.

Figure 3 Click beetle (Cody Wyckoff)

 

CORN ROOTWORMS

–by Dr. Jeff Whitworth

Western corn rootworm (WCR) larvae are voraciously feeding on corn roots (see fig 1) and thus continuing to grow and develop as seen in fig 2.  The WCR larva on the right, in this photo, was collected on 3 June 2020, while the ones on the left were collected from the same field on 17 June 2020.

Figure 1: WCR emerging from root (Cody Wyckoff)

Figure 2: WCR larvae (Cody Wyckoff)

 

CORN—Herbicide Roundup

–by Dr. Jeff Whitworth

Just FYI: Many weed species have become resistant to the herbicide Roundup. However, as can be seen in this photo (fig 1.), non-Roundup Ready corn is still highly susceptible to Roundup while the Roundup Ready corn, which was sprayed at the same time, is still highly resistant!

Figure 1  Non-Roundup Ready corn in the foreground, Roundup Ready corn in the background (picture by Cody Wyckoff)

Alfalfa—pea aphids, adult green lacewings, lady beetles, potato leaf hopper

–by Dr. Jeff Whitworth

Many alfalfa fields were sampled throughout north central Kansas over the last few days. Very few pea aphids were detected (fig 2.) – but those that remain are providing nutrition for many beneficials in alfalfa fields i.e., adult green lacewings and lady beetles (many) and lady beetle larvae (fig 3.). No alfalfa weevils were observed.

 

Figure 2 Pea aphids

 

Figure 3a Adult green lacewing

Figure 3b Adult ladybug

Figure 3c Lady beetle larva

However, potato leafhoppers, all adults, were collected in every field sampled (fig 4.). This indicates potato leafhoppers are immigrating into the state and will soon, if not already, be depositing eggs in stems, which soon hatch and thus increase populations. Potato leafhoppers remove plant juice and while so doing may inject a toxin into the plant. This feeding alone, may stress plants, especially in the often hot/dry conditions in July/August in Kansas. However, the introduction of a toxin may also negatively affect the plants. One characteristic symptom of potato leafhopper feeding starts out with yellowing from the tip of the leaves and travels through the leaf to the stem. This is often called “hopper burn” and can then negatively impact alfalfa production, both in quantity and quality by lowering the nutritional value.

 

Figure 4 Potato leafhopper

 

Corn—corn rootworm larva

–by Dr. Jeff Whitworth

Corn root sampling yielded the first western corn rootworm larva from north central Kansas on 3 June (fig 1). Many areas of continuous susceptible corn were sampled from fields that had significant corn rootworm adults in 2019. This was the only larva found but rootworm larvae will probably be hatching and start root feeding over the next 7-10 days.

 

Figure 1 Corn rootworm larva

 

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