Pest & Crop


Purdue Cooperative Extension Service


Issue 18, July 28, 2017 • USDA-NIFA Extension IPM Grant

Insects, Mites, and Nematodes

Plant Diseases

Weather Update


Identification of Worms in Silks and Ears (John Obermeyer and Christian Krupke) -

This year’s Western Bean Cutworm (WBC) flight in northern Indiana counties has been quite impressive. Though it is not over, by looking at the moth captures the past couple weeks (see report) we are past peak flight. Most eggs have been laid by this point, and there were many. We are aware that many fields have been scouted, found over the 5% threshold, and subsequently treated with insecticide. In the next weeks, folks will be out to determine the extent of damaged ears, if any, are present in fields. The distinguishing characteristics between mature western bean cutworm and corn earworm (CEW) larvae are found below. It is a little trickier to determine species when the larvae are small, i.e., early instars. For small caterpillars, you must use skin texture: WBC being smooth and CEW being bumpy. This requires a 10X magnifying lens. Not to add to the confusion, but there are a couple other caterpillars, fall armyworm and European corn borer, that also may be found in the ear. For now though, we will keep it to the two most likely suspects. As we enter later summer, caterpillars will be larger, more obvious and easier to tell apart. We will check back in at that time with another report. Happy scouting!

Western bean cutworm identifiers.

Western bean cutworm identifiers.

Corn earworm identifiers.

Corn earworm identifiers.

Early to late instars of the western bean cutworm. Notice that the distinctive “black rectangles” are lacking on the young larvae.

Early to late instars of the western bean cutworm. Notice that the distinctive “black rectangles” are lacking on the young larvae.

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Japanese Beetle Treatment Guidelines (Christian Krupke and John Obermeyer) -

• Beetle damage usually looks far worse than it is.
• Corn and soybean damage and treatment guidelines are given.

Japanese beetles have been seen throughout the state for several weeks, some are reporting very high numbers. Though adult emergence is past peak, there is still concern to field crop producers and (especially) homeowners. The one important thing to remember when it comes to Japanese beetles – their presence and damage almost always looks worse than it is.

Field Corn: Japanese beetle feed on corn leaves, tassels, and silks. Generally, leaf and tassel feeding can be ignored. If beetles are present and feeding on corn silks, an insecticide should be applied only if on average the silks are being cut off to less than 1/2 inch before 50% pollination has taken place. This rarely happens on a field-wide basis. Edges are typically at much higher levels than the rest of the field, so don’t let that dictate treatments. Also, don’t be overly excited by this pest’s tendency to clump on a few ears within an area and eat the silks down to the husks. With sufficient soil moisture (not a problem in most of the state this year), silks will grow from 1/2 to 1 inch per day during the one to two weeks of pollen shed. Silks only need to be peeking out of the husk to receive pollen. Besides, beetles are often attracted to silks that have already completed the fertilization process even though they are still somewhat yellow. Check for pollen shed and silk feeding in several areas of the field. Don’t be overly influenced by what you think you may see from windshield surveys! Get out into fields to determine beetle activity.

Soybean: Soybean plants have the amazing ability to withstand considerable leaf damage (defoliation) before yield is impacted. The impact of defoliation is greatest during pod fill because of the importance of leaf area to photosynthesis, and ultimately to yield. Therefore, greater than 15% defoliation during pod fill can be tolerated before yields are economically affected. This defoliation must occur across the whole plant, not just the upper canopy. The beetles often congregate in areas of a field where they are first attracted to weeds such as smartweed and velvetleaf. As in the case of corn, don’t be overly alarmed by these bright, iridescent beetles feeding on soybean plants near field edges. Consider that as they feed their defoliation allows for better sunlight penetration into the lower plant canopy!

However, should controls be needed, refer to publications:
Corn Insect Control Recommendations

Soybean Insect Control Recommendations

Japanese beetle attracted to wild grape on a fence line next to soybean.

Japanese beetle attracted to wild grape on a fence line next to soybean.

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2017 Western Bean Cutworm Pheromone Trap Report(John Obermeyer) -

County Cooperator WBC Trapped
Week 1
6/22/17 - 6/28/17
Week 2
6/29/17 - 7/5/17
Week 3
7/6/17 - 7/12/17
Week 4
7/13/17 - 7/19/17
Week 5
7/20/17 - 7/26/17
Adams Kaminsky/New Era Ag 0 6 4 0 5
Adams Roe/Mercer Landmark 0 8 6 1 0
Allen Anderson/Syngenta Seed 0 4 26 34 14
Allen Gynn/Southwind Farms 0 8 13 15 19
Allen Kneubuhler/G&K Concepts/Harlan 0 4 13 4  
Allen Kneubuhler/G&K Concepts/Koch 0 10 0 4  
Bartholomew Bush/Pioneer Hybrids 0 0 0 0 0
Clay Bower/Ceres Solutions/Clay City   0 0 0  
Clay Bower/Ceres Solutions/Brazil   0 0 0  
Clinton Emanuel/Boone Co. CES 1 1 1 0 1
Clinton Foster/Purdue Entomology 0 0 2 1  
DeKalb Hoffman/ATA Solutions     87 174 167
Dubois Eck/Purdue CES 0 1 0 0 1
Elkhart Kauffman/Crop Tech Inc.   35 156 150 95
Fayette Schelle/Falmouth Farm Supply Inc. 1 1 0 0 0
Fountain Mroczkiewicz/Syngenta 41 31 14 4 0
Fulton Jenkins/N. Central Coop/Talma 379 385 167 76 5
Fulton Ranstead/N. Central Coop/Rochester     309 46  
Gibson Schmitz/Gibson Co. CES 0 0 2    
Hamilton Campbell/Beck's Hybrids 3 2 2 2  
Hendricks Nicholson/Nicholson Consulting 0 1 1 1 2
Jasper Overstreet/Purdue CES 438 410 304 237 103
Jasper Ritter/Brodbeck Seeds 302 171 124 97 14
Jay Boyer/Davis PAC 5 1 0 3  
Jay Shrack/Ran Del Agri Services 0 0 0 1  
Jay Temple/Jay County CES/Pennville 0 1 3 2 0
Jay Temple/Jay County CES/Redkey 3 4 7 2 0
Jennings Bauerle/SEPAC 0 0 0 1  
Knox Bower/Ceres Solutions/Vincennes   0 0 0  
Knox Bower/Ceres Solutions/Freelandville   0 0    
Kosciusko Klotz/Etna Green 75 112 92 46  
Lake Kleine/Kleine Farms 0 4 41 11 0
Lake Moyer/Dekalb Hybrids, Shelby 157 108 63 16 20
Lake Moyer/Dekalb Hybrids, Schneider 246 151 101 93 63
LaPorte Rocke/Agri-Mgmt Solutions, Wanatah 120 122 321 138 10
LaPorte Smith/Co-Alliance/LaPorte 0 11 29 22 7
LaPorte Smith/Co-Alliance/Fish Lake 6 20 109 107 115
LaPorte Smith/Co-Alliance/Union Mills 15 19 122 100 40
LaPorte Smith/Co-Alliance/LaCrosse 35 149 337 112 17
Marshall Harrell/Harrell Ag Services   4 118 149 6
Marshall Klotz/SR 10 & SR 331 29 81 130 90 13
Marshall Miller/North Central Coop     48 43 10
Miami Early/Pioneer Hybrids 189 216 140 154 9
Newton Moyer/Dekalb Hybrids, Lake Village 16 139 262 193 32
Porter Leuck/PPAC 11 17 335 287 68
Pulaski Capouch/M&R Ag Services 42 49 94 50 20
Pulaski Leman/North Central Coop 4 22 34    
Putnam Nicholson/Nicholson Consulting 0 2 0    
Randolph Boyer/DPAC 2 2 3 0  
Rush Schelle/Falmouth Farm Supply Inc.   0 0 0 0
Shelby Fisher/Shelby Co. Co-Op 0 0 0 0 0
Shelby Simpson/Simpson Farms 4 5 2 0 0
Starke Capouch/M&R Ag Services 0 184 246 10 7
Starke David Wickert/Wickert Consulting 5 28 21 10 4
Starke Larry Wickert/Wickert Consulting 136 292 185 16 4
St. Joseph Barry/Helena 3 28 108 56 26
St. Joseph Gary Battles 1 12 16 16 10
St. Joseph Carbiener/Union Twp. 0 11 50 19 7
St. Joseph Smith/Co-Alliance/Granger 7 46 87 69 95
St. Joseph Smith/Co-Alliance/New Carlisle 0 3 69 93 109
Sullivan Bower/Ceres Solutions/Farmersburg   0 0 0  
Tippecanoe Bower/Ceres Solutions/Sullivan   0 8 0  
Tippecanoe Bower/Ceres Solutions/Lafayette   15 25 24  
Tippecanoe Nagel/Ceres Solutions 1 1 6    
Tippecanoe Obermeyer/Purdue Entomology 0 0 0 0 0
Tippecanoe Westerfeld/Monsanto 2 3 0    
Tipton Campbell/Beck's Hybrids 0 2 0 0  
Vermillion Bower/Ceres Solutions/Clinton   0 0 0  
Wabash Enyeart/North Central Coop 1 10 15   4
Whitley Richards/NEPAC 23 70 39 13 5
Whitley Richards/NEPAC     182 101 23

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2017 Corn Earworm Pheromone Trap Report (John Obermeyer) -

Corn Earworm Trap Report

Corn Earworm Trap Report

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Update on Southern Rust in Indiana (Kiersten Wise, University of Kentucky Plant Pathologist and Tom Creswell, Director of Purdue’s Plant and Pest Diagnostic Lab) -

Southern rust of corn, caused by the fungus Puccinia polysora, has been detected in several Indiana counties (Figure 1). The detection of southern rust is earlier than normal, and has caused concern because there are many acres of late planted or re-planted corn in the state in 2017 that have the potential to be impacted by the disease.  However, whether or not southern rust will develop into a disease of concern will largely depend on the weather.

Southern rust can be a damaging disease, and foliar fungicide applications between tassel (VT) and milk (R3) can help protect plants from infection and disease development. However, it is important to consider corn growth stage AND weather conditions before deciding on a fungicide application. If the weather is hot, (mid-80s and above), humid, and there are heavy dews and rainfall, then southern rust may develop and spread more quickly.  Cooler, less humid weather will cause the disease to develop and spread slowly.  

Yield potential should also be a consideration, and high-yield potential fields should be prioritized when making management decisions. Farmers trying to decide if a fungicide application is warranted can scout fields carefully and frequently and watch the weather to determine if and when a fungicide application is needed.

There are several fungicides available that provide very good control of southern rust. Fungicide efficacy of specific fungicide products for corn diseases are described in the updated fungicide efficacy table for management of corn diseases, which is developed by the national Corn Disease Working Group:

Just remember that common rust, caused by Puccinia sorghi, and southern rust are easy diseases to confuse, and any suspected samples should be sent to the Purdue Plant and Pest Diagnostic Laboratory (PPDL) for confirmation before deciding on a management tactic. Weather conditions have favored continued development of common rust, but fungicide applications for common rust in hybrid corn are unlikely to be economically beneficial.

The Purdue Extension publication "Diseases of Corn: Common and Southern Rust" has more information on distinguishing between common and southern rust, and additional details on both diseases.

Confirmed findings of southern rust, July 28, source P&PDL <>.

Figure 1. Confirmed findings of counties with southern rust, July 28, source P&PDL .

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total precipitation

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average temperature

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Contact Information

Purdue Extension Entomology
901 W. State Street
West Lafayette, IN, 47907
(765) 494-8761



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