Watch for worms in grain sorghum heads

Doug Johnson, Extension Entomologist

Fig. 1. Corn earworm on Corn

Fig. 2. Sorghum webworm
 on sorghum

It is about the time of year for problems with corn earworm (Fig.1.) to begin in grain sorghum. Though I have not seen or heard of any local problems my colleague in VA, Dr. Ames Herbert, is beginning to see some problems. In Kentucky we generally see these problems in the area west of the Pennyrile Parkway and more importantly in LATE planted fields. You are also likely to see a mixture of worm species including the sorghum webworm (Fig. 2.)

Refuge Requirements for Transgenic Insect Control Traits in Field Corn.

Doug Johnson, Extension Entomologist

2013 is one of those transitional years for changes in refuge requirements for transgenic control traits in field corn. Several changes have been made over the last several years and one can expect for changes to continue as we (likely) move away from large structural refuges and toward refuge in a bag. Generally the % of refuge seed (those seed without transgenic insect control traits) has dropped from 20% to 10% or even 5% depending upon the traits included and the company. In addition those products that  require separate structural refuges (usually as blocks or a series of rows) is giving way to the inclusion of not traited seed within the bag of traited seed; the so called refuge in a bag (RIB). The result is a somewhat confusing situation where products are available that contain different refuge requirements. Obtaining the desired corn genetics which contains the correct transgenic traits to control the likely pests and planting this with the correct refuge in the proper location can be very confusing.

If you follow the link:    http://pest.ca.uky.edu/EXT/Recs/ENT16-Field%20corn.pdf ,    it will take you to ENT-16, the 2013 Insecticide Recommendations for Corn. On pages 6 and 7 of this publication you will find a Bt Trait Table that list the various packages of transgenic insect control traits by trade name, insect toxins, and the event used to include the toxins in the corn plant. This table also includes relative ratings for how well these toxin packages works against the most common and important insect pests of field corn in Kentucky. Additionally, the type (block vs RIB) of refuge and the percent of non-traited seed required to be in the refuge.

In Kentucky producers can expect their greatest and most consistent return on investment from protection against European corn borer (ECB) and southwestern corn borer (SWCB). Traits for control of western corn rootworm (WCRW) are not needed nor recommended in corn fields that are rotated with non-corn crops. Corn that is not rotated (continuous corn) should be planted with products that contain more than one or “stacked” western corn rootworm (WCRW) traits. In any case products containing only the Cry3Bb1 corn rootworm toxin should not be planted in non-rotated corn. Though not yet noted in Kentucky, this is the trait for which resistance has been show in several states to our north. So far this has only occurred in corn planted in the same field for three successive years and using only the Cry3Bb1 trait for protection against western corn rootworm. Black cutworm (BCW), corn earworm (CEW) and fall armyworm (FAW) infestations are very much dependent on the growing year. Very early planting may benefit from BCW traits while very late plantings will likely benefit from control of corn earworm and fall armyworm.

Capture of corn earworm moths in IPM pheromone baited traps at UK-REC, Princeton (Caldwell Co.) Ky in 2012.

Doug Johnson, Extension Entomologist

CEW caterpillar and damge on soybean.

Corn ear worm (CEW), also known as soybean podworm, are currently active in soybeans. This is a direct damage pest as it feeds on pods, seeds, & petioles. You are unlikely to detect this pest by checking for defoliation because it does not feed much on leaves. There is no sure way to detect this pest in your soybean crop except to scout for it. This means sweeping or direct visual examination of the pods.

CEW may occur in many color phases. It sometimes appears very dark, almost black, to brown to red and green. The green color phase is most often seen when feeding in soybeans. When fully grown, the larvae are about 1 ½“ long. They are marked by alternating light and dark stripes running the entire length of the body. These stripes are not always the same from one caterpillar to another. Usually a double dark stripe will run down the middle of the back.

You can certainly look for direct damage feeding on the pods to see if they are causing damage. In rows narrower than 30”, sweeping with a 15” sweep net is about the only way to measure this pest. The threshold is 9 worms per 25 sweeps.

Capture of CEW moths at UKREC 2012

We do know that corn earworm moth flight has been increasing and populations are greater than we normally see. Moth capture in our IPM pheromone baited traps at the UK-REC in Princeton is shown in Figure 2. Remember, these are moth counts and moths are NOT the damaging stage. Caterpillars will appear about a week after the moth flight. In 2012, moth numbers (green line) are greater than the rolling five- year average (blue line) so we are at an elevated risk of damage from this pest compared to most years. However, trap captures will NOT tell you what will happen in an individual field. Only field sampling will help you establish whether or not a threshold has been met. Moth flight numbers will give you a week or two heads up on what might happen.

If insecticide control is warranted, you may find products listed for control of CEW in soybeans online at: http://pest.ca.uky.edu/EXT/Recs/welcomerecs.html or from your County Extension Office. Be wary of spraying too early, you may kill the predatory insects that are providing some natural control and miss the actual pest.

Corn Earworm Moth Counts Increasing Significantly.

Author: Doug Johnson, Extension Entomologist

Capture of corn earworm moths in IPM pheromone-baited traps in Princeton, (Caldwell Co.) KY and in Fulton Co. KY have taken a significant increase over the past two to three weeks. This follows on the heels of warnings of corn earworm problems in states south of KY.

The counts in Cam Kenimer’s Fulton Co. traps are by far the largest, with a capture of 547 moths on 8/5/12 and 486 on 8/12/12. Numbers are increasing in Princeton, too, with 200 captured during the trap week ending 8/2/12 and 206 for the week ending 8/9/12. This is a substantial increase compared to the rest of the year. The increase also came earlier in the year by several weeks and is much larger when compared to the rolling five year average. ( See:

http://www.uky.edu/Ag/IPMPrinceton/counts/cew/cewgraph.htm)

These insects are likely coming out of corn that is maturing and will be looking for another host, probably soybean on which to lay their eggs. The moths are not the damaging stage, but in a couple of weeks, their offspring will appear in the form of caterpillars.

The first really big jump in capture was in Fulton Co. on July 22, but that capture is only about 1/3 of the most recent capture. Using July 22 as a starting date, small larvae to medium larvae could already be present. Larvae from moths caught over the last couple of weeks should come in a steady stream.

With corn maturing and being harvested in most western KY areas, soybeans are the most likely field crop target for this pest. Of course these counts cannot predict what will happen in a particular field. Conversely, the captures are certainly above the rolling five year average so represent an increased level of risk. Areas in the south and west will be impacted sooner and areas in the north and east somewhat later. You should be scouting your soybeans NOW!

Newly hatched CEW larvae are translucent yellowish-white, but larger larvae have considerable color variation. When feeding on soybeans they tend to be light reddish- brown and large larvae are often green, yellowish or black with distinct cream colored bands running their length and their heads are usually orange.

CEW can consume foliage, flowers and pods of both full-season and double-crop soybeans. Economic threshold in wide row (30”) beans sampled using the 3’ shake-cloth method would be two worms per row foot. If sweeping (15” sweep net) narrow row beans the threshold would be an average of 9 caterpillars per 25 sweeps.

If insecticidal control is warranted, suggested insecticides may be found in ENT- 13 which you may obtain from your county extension office or on line at: http://pest.ca.uky.edu/EXT/Recs/welcomerecs.html

Relative Efficacy of Single and Stacked Corn Traits Against Insect Pests in Kentucky

Ric Bessin, Extension Entomology, University of Kentucky
Latest update: May 2011

Corn Types	Insect toxins		Dual modes of Action	ECB	SWCB	BCW	CEW	FAW	WCRW	Min. Refuge Requirement
YieldGard CB	Cry1Ab			++++	++++		++	++		20% block
Herculex 1	Cry1F			++++	++++	++	+	+++		20% block
Agrisure CB	Cry1Ab			++++	++++		++	++		20% block
YieldGard RW	Cry3Bb1								++	20% block
Herculex RW	Cry34Ab1, Cry35Ab1								++	20% block
Agrisure RW	mCry3A								++	20% block
YieldGard Plus	Cry1Ab, Cry3Bb1			++++	++++		++	++	++	20% block
Herculex Xtra	Cry1F, Cry34Ab1, Cry35Ab1			++++	++++	++	+	+++	++	20% block
Agrisure 3000GT	Cry1Ab, mCry3A			++++	++++		++	++	++	20% block
YieldGard VT3	Cry1Ab, Cry3Bb1			++++	++++		++	++	+++	20% block
YieldGard VT2 Pro	Cry1A.105, Cry2Ab2		yes	++++	++++	++	+++	++++		5% block
YieldGard VT3 Pro	Cry1A.105, Cry2Ab2, Cry3Bb1			++++	++++	++	+++	++++	+++	20% block
SmartStax	Cry1A.105, Cry2Ab2, Cry3Bb1, Cry1F, Cry34Ab1, Cry35Ab1		yes	++++	++++	+++	+++	++++	+++	5% block
Optimum Intrasect	Cry1Ab, Cry1F		yes	++++	++++	++				5% block
Agrisure Viptera 3110	Vip3Aa, Cry1Ab			++++	++++	+++	++++	++++		20% block
Agrisure Viptera 3111	Vip3Aa, Cry1Ab, mCry3A			++++	++++	+++	++++	++++	++	20% block
AcreMax 1	90% Cry1F, Cry34Ab1, Cry35Ab1 + 10% Cry1F			++++	++++	++	+	+++	++	RIB + 20% block
AcreMax RW	90% Cry34Ab1, Cry35Ab1								++	RIB
SmartStax Refuge Advanced/Complete	Cry1A.105, Cry2Ab2, Cry3Bb1, Cry1F, Cry34Ab1, Cry35Ab1 + 5% refuge seed		yes	++++	++++	+++	+++	++++	+++	RIB

ECB = European corn borer
SWCB = Southwestern corn borer
BCW = Black cutworm
CEW = Corn earworm
FAW = Fall armyworm
WCRW = Western corn rootworm


‘ + ‘ = Poor to fair control
‘++’ = Good control
‘+++’ = Very good control
‘++++’ = Excellent control
May 2011