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Extension Entomology

Category: Corn

CORN LEAF APHIDS

Posted on by Sharon Schroll

–Dr. Jeff Whitworth

 

Corn leaf aphids feed on corn and/or sorghum and are usually most evident during the whorl stage of sorghum. This year seems to be a very good year for corn leaf aphids as we have received many inquiries relative to possible damage caused by corn leaf aphids. Corn leaf aphids can be found every year. However, I could find no data to show that corn leaf aphids ever occur in field-wide populations that would justify an insecticide application and as farther indication of this, there is no treatment threshold. Corn leaf aphids are usually just considered as a great host for beneficials to utilize to sustain their populations. Figure 2 is a corn leaf aphid being fed upon by a lady beetle larva. Sorghum, and soybeans, have been relatively pest free compared to past years, at least so far this year.

Figure 2. Lady beetle larva feeding on aphids (picture by Cody Wyckoff)

 

Corn – adult western corn rootworm, corn earworm and fall armyworm

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

Corn – adult western corn rootworm, corn earworm and fall armyworm

The first adult western corn rootworms (WCRW) (fig. 1) were detected on 5 July, 2020, in north central Kansas.  Since this first emergence there has been considerably more emergence, to the point that there are several areas of north central Kansas that are now concerned about silk clippings by these adults.  WCRW adults spend much of their time in the early morning, and then again toward evening, feeding on silks (fig. 2)—thus, shown here in a position that they are commonly found in while feeding on silks.  They may spend much of the middle, warmer, part of the day in more shaded areas, i.e., behind leaf collars, etc.  Figure 3 shows typical “goosenecking”, from the previous root feeding, which is now completed, by the larval stage of the WCRW.

 

Figure 1: Adult Western Corn Rootworm (WCRW)  ( Cody Wyckoff)

Figure 2: WCRW in position that they are commonly found while feeding on silk (Cody Wyckoff)

Figure 3: Goosenecked corn  (Cody Wyckoff)

There is also much corn earworm and fall armyworm activity in corn fields that are just now, and have just recently, started silking.  The larvae (fig. 4) observed around north central Kansas will probably feed for about another 2 weeks, then, pupate in the soil, emerge as adults which mate, and start depositing eggs.  These eggs will most likely be deposited in late planted corn, or sorghum (between flowering and soft dough) and/ or soybeans.

Figure 4: Larva feeding on corn (Cody Wyckoff)

 

Western Corn Rootworms

Posted on by Sharon Schroll

–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)

 

CORN ROOTWORMS

Posted on by Sharon Schroll

–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

Posted on by Sharon Schroll

–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)

Corn—corn rootworm larva

Posted on by Sharon Schroll

–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

 

Sorghum “Ragworms”

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Davis

Much of the sorghum around north central Kansas is at, or just coming into, the whorl stage.  As the leaves unfurl and grow out of the whorls, a pretty high number of plants are showing large holes that have been chewed in leaves.  These holes are from smaller larvae (most that we have sampled are corn earworms) that feed on the leaves while they are still furled. When leaves grow out of the whorl they have showy, ragged looking feeding that may cause concern.

Larvae sampled this week still have about one additional week of feeding within these whorls, then they will exit and crawl down the plant to pupate in the soil.  Larvae in the whorl are rarely worth spraying for four reasons: 1) by the time the leaves unfurl making feeding damage visible, most larvae have already accomplished most of their development and thus feeding, 2) insecticides usually can’t penetrate far enough down into the whorl to actually impact the larvae, 3) a general insecticide will kill most beneficial insects, and 4) ragged looking leaves during this stage have little to no effect on yield, and no, you cannot eliminate the next generation by spraying this generation.

 

Corn Update – Corn Rootworms and “Ragworms”

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Davis

Corn rootworm larvae continue to be very active in fields of continuous corn that have been planted to susceptible varieties.

Corn earworms have been feeding in north central Kansas corn for about a week now and signs of this feeding are now becoming visible as the leave start growing out of the whorl.  The small larvae may consist of corn earworms, fall armyworms, and/or armyworms, but all may cause the same type of ragged looking leaves, earning them the name “ragworms”.

 

 

This type of leaf feeding can be highly visible, and many plants can be impacted, but the data has always indicated there is little to no effect on yield.  In addition, the larvae are well sheltered within the whorl and thus insecticides only impact them when they exit the whorls to pupate in the soil.  And, by that time, all the feeding is completed anyway.

Corn Rootworms

Posted on by Sharon Schroll

— by Dr. Jeff Whitworth and Dr. Holly Davis

Western corn rootworm larvae have been detected for the 1st time this year in north central Kansas.  All were 1st instar larvae and most were still very small (recently hatched).  Thus, if you have any fields of three-plus year continuous corn planted with corn rootworm susceptible varieties, the rootworm feeding may become more and more evident over about the next three weeks.

For more information on corn rootworm management, please see Corn Rootworm Management in Kansas Field Corn: https://www.bookstore.ksre.ksu.edu/pubs/MF845.pdf

For more information relative to all corn pests, please see the KSU Corn Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF810.pdf