Troubleshooting Abnormal Corn Ears and Related Disorders
Peter Thomison* and Allen Geyer
Horticulture and Crop Science
The Ohio State University
*614-292-2373 (thomison.1@osu.edu)
(Updated 5/20/08)
“Abnormal Corn Ears” Poster Now Available
Farmers frequently encounter abnormal corn ears in their fields when the crop has experienced a major stress, such as drought, temperature extremes, disease and insect injury, or misapplied chemicals. These abnormalities often affect yield and grain quality adversely. In this poster, ten abnormal corn ears with distinct symptoms and causes are highlighted. The purpose of the poster is to help corn growers and agricultural professionals diagnose various ear disorders.
A reduced 11 x 14 inch version of the poster is available for online at:
http://agcrops.osu.edu/corn/documents/AbnormalCornEarsPoster.pdf
Our Communications & Technology section (contact information below) has 26 x 33 inch copies of the poster available for distribution. The poster is printed on plasticized coated paper for durability. Poster cost is $10 plus shipping. Ask for “Abnormal Corn Ears” poster” ACE-1.
The Ohio State University
Communications and Technology
Media Distribution
216 Kottman Hall, 2021 Coffey Road
Columbus, OH 43210-1044
E-mail: pubs@ag.osu.edu
Phone 614-292-1607
Fax 614-292-1248
ABNORNMAL EAR DEVELOPMENT
Ear Deformities Associated with Low Temperatures
Drought Damage and Nubbin Ears
REDUCED KERNEL DEVELOPMENT AND NUMBERS
Incomplete Kernel Set - Whole Ear
EAR MOLDS AND DISEASE
Aspergillus Ear and Kernel Rot
FEEDING INJURY
MISC
(Also Referred to as “Beer Bottle” Ears)
Symptoms:
Kernel row number may decrease by half from bottom to top of ear (for example - from 16 to 7 to 8 kernel rows/ear). Ear length usually normal.
Causes:
Severe stress during the 7 to 10 leaf collar stages (V7-10) may result in reduced numbers of kernel rows. Late broadcast application of sulfonylurea herbicides can result in ear pinching.
Management:
Avoid postemergence broadcast applications of sulfonylurea herbicides (e.g. Accent, Accent Gold, Basis Gold, Clelebrity Plus, and Steadfast) after corn has reached the six-leaf collar stage (V6).
Blunt Ear Syndrome (Also Referred to as “Beer Can” Ears or Ear Stunting) & Other Types of Arrested Ear Development
Symptoms:
Characterized by ears with markedly reduced ear size and kernel numbers per row. Husk length and kernel row number may be normal. Sometimes associated with multiple ears at a node. Occurrence is usually rare and sporadic within a field. During late grain fill, leaf midribs, leaf blades, and leaf sheaths of plants with severely stunted ear development redden and purple (anthocyanin pigments).
Causes:
Unknown. Associated with temperature stress (brief cold shock?) during early ear formation stages (V8-12). Recently associated with pre-tassel foliar applications of certain foliar fungicides. Differs in severity among hybrids.
Management:
No known treatment. Avoid planting hybrids that are more likely to develop stunted ears in fields where ear stunt problems have occurred previously. Apply foliar fungicides, especially strobulurin fungicides no earlier than the tassel (VT) stage.
For more information consult the following:
Nafziger, Emerson. 2007. Unexpected Problems of Corn Ear Development. The Bulletin, Univ. of Illinois IPM. [On-Line]. Available at http://www.ipm.uiuc.edu/bulletin/article.php?id=836 (URL accessed 8/21/07).
Nielsen, R.L. (Bob). 2007. Symptomology of Arrested Ear Development in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/articles.04/GrainFillStress-0705.html. (URL verified 9/12/07).
Thomison, P. 2007. “Beer Can" Ears Appearing in Corn Fields Ohio State University C.O.R.N Newsletter 2007-26 (August 13-21, 2007).
Nielsen, RL (Bob). 2003. Blunt Ear Syndrome in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/articles.03/BeerCanEars-0812.html
(Also Referred to as “Bouquet Ears”)
Symptoms:
Characterized by multiple ears on the same ear shank. In some cases as many as 5 or 6 “side” ears may develop forming a “bouquet”. Side ears may be well developed or may resemble “beer can” ears or mere remnant ears; many probably failed to form kernels due to late silk emergence and lack of pollen.
Causes:
Unknown. Similar to those noted under “Blunt Ear Syndrome”.
Management:
Same as those noted under "Blunt Ear Syndrome"
For more information consult the following:
Elmore, R.W. and L. J. Abendroth. 2006 Multiple ears per node: Iowa 2006 situation & hypothesis
http://www.agronext.iastate.edu/corn/production/management/hybrid/multiple.html [URL verified 12 Sep 2007].
Nielsen, R.L. 2006. A problem with “Bouquets”. Purdue Univ. Online at
http://www.kingcorn.org/news/articles.06/Bouquets-0912.html [URL verified 12 Sep 2007].
Nielsen, R.L.. 1999. What A MESS! Corny News Network, Purdue Univ. Online at http://www.agry.purdue.edu/ext/corn/news/articles.99/990823b.html [URL verified 12 Sep 2007].
Ear Deformities Associated with Low Temperatures
Cold weather injury to sweet corn includes “bar-bell” ears (left and right ears).
Source: Pat Lipps (OSU-Plant Pathology)
Symptoms:
Tip of ear branches on otherwise normal ear; associated with certain sweet corn genetics.
Causes:
Problem associated with certain environmental conditions (cold weather) and certain sweet corn genetic background.
Drought Damage and "Nubbin Ears"
Ear from a corn plant produced under favorable growing conditions (far left) compared with four abnormal ears from plants subjected to protracted drought stress (late vegetative stages through grain fill)
Symptoms:
Small misshapened ears with poor kernel set, especially at ear tip. Reduced kernel numbers associated with reduced kernel row and kernels per row.
Cause:
Severe drought from mid vegetative growth through early to mid grain fill. Other stresses, including nitrogen deficiency and high plant population, can result in nubbin ears, twisted ears, irregular kernel rows, imperfectly developed ear tips also associate with phosphorous deficiencies.
Management:
Follow recommended guidelines for minimizing crop stress, including maintaining appropriate soil fertility, adjusting planting depth with varying soil conditions, and selecting adapted hybrids and seeding rates consistent for soil yield potential and date of planting. Avoid planting too early in wet soils and minimize weed competition with effective preemergence and postemergence herbicide application and/or timely cultivation.
Symptoms:
Combination tassel and ear in the same structure - a "tassel ear". The ear portion of this tassel ear structure usually contains only a limited number of kernels. Tassel ears often appear on tillers (suckers) arising from plants with normal ears and tassels. These tassel ears are produced at a terminal position on the tiller where a tassel would normally appear.
Causes:
Tassel ears often produced by tillers (suckers) when growing point is destroyed or injured by hail, frost, flooding, herbicides, and mechanical injury before V6. Some hybrids may also be more prone to tiller under certain environmental conditions and these tillers may give rise to tassel ears. Tassel ears are frequently observed along the edges of fields where early season soil compaction and saturated soil conditions may have contributed to this abnormal development.
Management:
For more information on tillering, check out fact sheet AGF-121-95, "Corn Growth and Development - Does Tillering Affect Hybrid Performance?" It’s available online at:http://ohioline.osu.edu/agf-fact/0121.html.
Dr. Bob Nielsen, extension corn specialist at Purdue University, has an article with excellent pictures of plants with tassel ears – “Tassel-Ears in Corn” available online at: http://www.agry.purdue.edu/ext/corn/news/articles.04/TasselEars-0713.html.
For more information consult the following:
Thomison, P. 2007. "Tassel Ears" in Corn. Ohio State University C.O.R.N. Newsletter 2007-27 (August 20, 2007-August 28, 2007). Available at http://corn.osu.edu/story.php?setissueID=199&storyID=1221
Nielson, RL (Bob). 2004. Tassel-Ears in Corn. Corny News Network, Purdue University. [On-Line]. Available at http://www.agry.purdue.edu/ext/corn/news/articles.04/TasselEars-0713.html
Stinkbug Injury to corn ears in Kansas, 2007. (Source: Kraig Roozeboom,Kansas State University)
Symptoms:
Developing ear exhibits a banana-shaped appearance. The shuck will also stop developing exposing the grain to everything. Injury also includes shrunken and/or missing kernels.
Cause:
In the South, stink bugs are frequently found in large numbers feeding on developing ears of corn.
Stink Bug on Corn Husk (Credit: University of Flordia)
The nymphs (immature stage) as well as the adults pierce the shuck and feed on the developing kernels. Activity is most concentrated from the time kernels begin to form through the milk stage of development. Feeding can occur through the hard dough stage. Where they sting into the ear during early ear development, the cob will not develop on that side and it will continue growing on the back side giving the ear a characteristic banana shaped appearance. The shuck will also stop developing exposing the grain to everything. Injury also includes shrunken and/or missing kernels. Heavy populations can reduce not only yields but also the quality of the grain.
Management:
For corn in the early silk through milk stage, treatment may be justified when there is 1 stink bug per 5 plants. From the end of milk through the hard dough stages treatment may be justified when there is an average of one stink bug per plant. Only stink bugs 1/4 inch or longer should be considered when determining thresholds.
For more information consult the following:
Sprenkel, R. 1993. Insect Management in Field Corn. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Available at http://edis.ifas.ufl.edu/IG060 [URL verified 9/14/07].
Symptoms:
Poor, reduced kernel set; only a limited number of kernels (ovules) pollinated. When severe, ears show mostly cob tissue with just scattered kernels or no distinct kernel rows
Causes:
Poor pollination of ear due to asynchronous pollen shed and silking (poor “nick”) due to severe drought and high temperatures; inadequate pollen supply due to uneven crop development, herbicides, insect feeding and silk clipping. Phosphorus shortages also interfere with pollination. Late applications of Lightning on Clearfield corn.
Management:
Follow recommended guidelines for minimizing crop stress, including maintaining appropriate soil fertility, adjusting planting depth with varying soil conditions, herbicide application dates, and selecting adapted hybrids and seeding rates consistent for soil yield potential and date of planting. Avoid planting too early in wet soils and minimize weed competition with effective preemergence and postemergence herbicide application and/or timely cultivation.
For more information consult the following:
Thomison, P. 2007. Key Steps In Corn Pollination. The Ohio State University C.O.R.N Newsletter 2007-21 (July 9, 2007 - July 17, 2007)
Available onlilne at http://corn.osu.edu/story.php?setissueID=192&storyID=1164
Symptoms:
Cob tissue without kernels on the last one or more inches of the ear tip. Ovules not fertilized at ear tip.
Causes:
Poor fertilization of ear tip ovules at silking; poor pollination of ear due to asynchronous pollen shed and silking (poor “nick”) due to severe drought and high temperatures; inadequate pollen supply due to uneven crop development, herbicides, insect feeding and silk clipping. Phosphorus shortages also interfere with pollination.
Management:
Follow recommended guidelines for minimizing crop stress, including maintaining appropriate soil fertility, adjusting planting depth with varying soil conditions, and selecting adapted hybrids and seeding rates consistent for soil yield potential and date of planting. Avoid planting too early in wet soils and minimize weed competition with effective preemergence and postemergence herbicide application and/or timely cultivation.
For more information consult the following:
Thomison, P. 2007. Drought and Heat Stress Affecting Corn Yield Potential. C.O.R.N Newsletter 2007-21(July 9, 2007 - July 17, 2007) Available online at http://corn.osu.edu/story.php?setissueID=192&storyID=1163
Symptoms:
Poor tip fill or unfilled ear tips; little or no kernel development on the last one or more inches of the ear tip. Kernel abortion at tip end of ear at the blister and milk stages; usually associated with poor ovule fertilization at tip. Ovules not fertilized and aborted kernels may both appear dried up and shrunken, but aborted kernels often have a slight yellowish color.
Causes:
Stress conditions during early kernel development, including severe drought and high temperatures; nitrogen deficiencies, foliar diseases, cloudy weather.
Management:
For more information consult the following:
Abendroth, L. 2005. Examine corn ears now for clues to earlier stresses. Univ. of Nebraska Extension Crop Watch (September 16, 2005). Available om-line at: http://cropwatch.unl.edu/archives/2005/crop05-21.htm#corn_stress
Thomison, p. 2007. Tip Dieback and Zipper Ears in Corn. The Ohio State University C.O.R.N Newsletter 2007-30 (September 11, 2007 - September 17, 2007). Available at http://corn.osu.edu/index.php?setissueID=202#C
“Zipper” Ears or “Banana” Ears
Symptoms:
Missing entire or parts of kernel rows on the outside or underside of the ear primarily due to kernel abortion. Ears often misshapen and bend (like banana) due to differential kernel formation along ear.
Causes:
Unknown. Often associated with severe drought stress or defoliation injury following pollination.
Management:
Thomison, p. 2007. 2007 Tip Dieback and Zipper Ears in Corn - Peter Thomison. The Ohio State University C.O.R.N Newsletter 2007-30 (September 11, 2007 - September 17, 2007). Available at http://corn.osu.edu/story.php?setissueID=202&storyID=1243
Symptoms:
Light weight ears with poorly filled, shrunken kernels. Spaces between kernels indicating incomplete kernel fill.
Multiple Causes:
Severe stress (photosynthetic stress) at dough (R4) through early dent (R5) stages, including frost damage, premature plant death due to drought, high plant population, foliar diseases, severe potassium deficiency and hail.
Management:
Symptoms:
Part or the entire ear is rotted by a white mold growing between the kernels. Infections generally start at base of ear and progress to the tip. Later the white mold changes to a grayish-brown growth over the husks and kernels. The entire ear may be shrunken, and infected kernels appear glued to the husks.
Cause:
Diplodia ear rot is caused by the fungus Stenocarpella maydis. Infection may occur from late vegetative stages to three 3 weeks after midsilk. It is more common in southern half of Ohio and appears to be associated with continuous corn and reduced tillage. Warm dry weather prior to silking followed by wet conditions following silking favors ear rot.
Management:
Planting resistant hybrids is the most effective way to control Diplodia ear rot. Crop rotation and fall tillage can reduce the occurrence of the disease by reducing fungal levels in the field. Dry harvested grain to 15% and below to prevent further mold growth in storage. Dilute moldy grain with clean grain prior to using it as feed to prevent problems with livestock. Evaluate the nutritional value of the feed to make sure animals are receiving adequate nutrition for rapid gains.
References:
Patrick Lipps, Peter Thomison, Bill Weiss. 2004. Diplodia Damaged Corn Grain: Assessing Feed Value. The Ohio State University C.O.R.N. Newsletter 2004-38. Available at http://agcrops.osu.edu/story.php?setissueID=62&storyID=337
P.E. Lipps & D.R. Mills. 2001. Diplodia Ear Rot of Corn. Ohio State University Plant Pathology Fact Sheet AC-0046-01. Available at http://ohioline.osu.edu/ac-fact/0046.html
P. Paul, P. Thomison, and D. Mills. 2005. Corn ear rot problems. The Ohio State University C.O.R.N Newsletter 2005-34 (October 10, 2005 – October 18, 2005) available online at http://corn.osu.edu/story.php?setissueID=109&storyID=630.
Symptoms:
Pinkish to reddish mold that starts on or near ear tip and progresses toward the base of the ear
Cause:
Corn is infected by wind-borne spores of the fungus Gibberella zeae (same fungus causes Gibberella stalk rot). The fungus survives in soil on crop residues. Cool temperatures (average daily temperatures below 72 degrees F) and 7 or more days of rain during the 3-week period after silking favors Gibberella ear rot. This ear rot is associated with several mycotoxins that are lethal to livestock.
Management:
Corn hybrids differ in susceptibility to Gibberella ear rot. Select hybrids with ears that dry in declined position and those well covered with husks. Hybrids with extremely tight husks may be more vulnerable to damage than hybrids with loose husks. Hybrids with Bt resistance to European corn borer may limit ear rot by preventing feeding by borers that may create entry points for fungal infection. Crop rotation and fall tillage can limit the occurrence of the disease by reducing fungal levels in the field.
For more information consult the following:
MOLDY GRAINS, MYCOTOXINS AND FEEDING PROBLEMS
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm [URL verified 5/20/08].
P. E. Lipps, A. E. Dorrance, L. H. Rhodes. 1998. Corn Diseases in Field Crop Disease Management. Extension Plant Pathology Bulletin 631-98. The Ohio State University. Available online at http://ohioline.osu.edu/b631/b631_3.html [URL verified 9/16/07].
Symptoms:
Pinkish or grayish discoloration of the caps of individual kernels or groups of kernels scattered over the ear; sometimes characterized by a pinkish mold growth.
Cause:
Fusarium ear rot is caused by Fusarium fungi that survive in soil on crop residues. Infection may occur from late vegetative stages to three 3 weeks after midsilk. It is more common in southern half of Ohio and appears to be associated with continuous corn and reduced tillage. Wet, warm weather following 2 to 3 weeks after silking and damage to kernels by insects, hail, and other mechanical means favors Fusarium kernel rot. Infection from wind-borne spores usually follows injury to ear from corn borer, ear worm, birds, etc. This kernel rot is associated with the mycotoxin, Fumonisin.
Management:
Planting resistant hybrids is the most effective way to control Fusarium kernel rot. Select hybrids with ears that dry in declined position and those well covered with husks. Control of insects that damage kernels reduces severity of the disease. Bt hybrids may limit injury by preventing injury of corn borer that create entry points for fungal infection. Crop rotation and fall tillage can reduce the occurrence of the disease by reducing fungal levels in the field.
For more information consult the following:
MOLDY GRAINS, MYCOTOXINS AND FEEDING PROBLEMS
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm [URL verified 5/20/08].
P. E. Lipps, A. E. Dorrance, L. H. Rhodes. 1998. Corn Diseases in Field Crop Disease Management. Extension Plant Pathology Bulletin 631-98. The Ohio State University. Available online at http://ohioline.osu.edu/b631/b631_3.html [URL verified 9/16/07].
“Blue Eye”Mold - Penicilllium and Aspergillus Kernel Rots
Symptoms:
Fungi may enter kernels through uninjured pericarps even at moisture content as low as 14%. The fungi grow grow in the germ and sporulate beneath the pericarp covering the germ area and giving this area a blue – green color. These fungi invade individual or groups of kernels; affected kernels may be at tip or scattered over the ear.
Cause:
Kernel infection by certain species of Aspergillus and Penicillin, cause damage to corn under poor storage conditions;
Management:
The rots may develop on either ear or shelled corn in storage, causing major losses in feed and market value. These kernel rots ordinariy of minor importance in a field before harvest. Kernel rot fungi are more likely to invade kernels damaged by insects and birds than sound
Grain with evidence of Aspergillus or Penicillium kernel rot should be dried to 14 percent moisture before storage and maintained at this level until used.
For more information consult the following:
MOLDY GRAINS, MYCOTOXINS AND FEEDING PROBLEMS
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm [URL verified 5/20/08].
P. E. Lipps, A. E. Dorrance, L. H. Rhodes. 1998. Corn Diseases in Field Crop Disease Management. Extension Plant Pathology Bulletin 631-98. The Ohio State University. Available online at http://ohioline.osu.edu/b631/b631_3.html [URL verified 9/16/07].
Aspergillus Ear and Kernel Rot
Symptoms:
Gray-green, powdery mold that starts at the tip of the ear or follows insect tracks. Primarily considered a storage mold.
Causes:
Several species of Aspergilllus fungi. much more common in hot, dry years.. Can produce mycotoxins (aflatoxin) . It can grow at temperatures higher than 90° F, and grain moisture content as low as 15 percent. The fungus can be detected in corn because it produces compounds that are fluorescent under black light, but this does not directly detect the presence of aflatoxins.
Management:
Plant a hybrid with ear rot resistance; avoid planting corn on corn, especially under conservation tillage, and reduce stress on the plants with adequate fertilization and good insect pest management.
For more information consult the following:
MOLDY GRAINS, MYCOTOXINS AND FEEDING PROBLEMS
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm [URL verified 5/20/08].
P. E. Lipps, A. E. Dorrance, L. H. Rhodes. 1998. Corn Diseases in Field Crop Disease Management. Extension Plant Pathology Bulletin 631-98. The Ohio State University. Available online at http://ohioline.osu.edu/b631/b631_3.html [URL verified 9/16/07].
Robertson,A. 2004. Corn Ear Rots.Iowa State University IPM.IC-492(21) [October 4, 2004] Available at http://www.ipm.iastate.edu/ipm/icm/2004/10-4-2004/earrot.html
Symptoms:
The corn plant may be infected at any time in the early stages of growth, but becomes less susceptible after the formation of the ear. Above-ground parts may be infected, but it is more common to see the smut galls on the ears, tassels, and nodes than on the leaves, internodes, and brace roots. The smut gall is composed of a great mass of black, greasy or powdery spores enclosed by a smooth white covering of corn tissue. The gall may be 4-5 inches in diameter. After the spores mature, the covering becomes dry and brittle, breaks open, and the spores sift out. Greatest yield losses occur when the ear becomes infected or if the smut gall forms on the stalk immediately above the ear.
Cause:
Corn smut is caused by the fungus, Ustilago zeae, that survives as a resistant spore over winter, and possibly for 2 to 3 years in the soil. These spores can be blown long distances with soil particles or carried into a new area on unshelled corn and in manure from animals that fed on infected corn stalks. Spores germinate in rainwater that has collected in the leaf sheaths. This leads to infections that are visible in 10 days or more. Wounds from various injuries (including hail, wind, and insects) provide points for the fungus to enter the plant.
The smut fungus is sensitive to temperature and moisture changes. In a warm season, the amount of smut is related closely to the amount of moisture in the soil especially during June. When temperatures are lower than normal, there may be little smut even though soil moisture may be high.
Management:
Seed treatment is of no value for smut control because few spores are on the corn seed.
Spraying for corn borer control helps in cases when insect populations are high. Avoid injury of roots, stalks, and leaves during cultivation. Tillage to bury diseased corn stalks in the fall will help give some control.
For more on information consult the following:
Rowe, R.C., P. E. Lipps, and D. R. Mills. 2001. Corn Smut. Ohio State University Extension Plant Pathology Fact Sheet AC-16-0001 Available online at http://ohioline.osu.edu/ac-fact/0034.html [URL verified 9/14/07].
Symptoms:
The most characteristic symptom is the proliferation of leafy structures from the ears and/or tassels, In many cases, leafy protrusions occur in only the ears resulting in a mass of strap-like leaves protruding from the ear zone. Affected plants may also have profuse tiller development.
Cause:
Crazy top is caused by the soil borne fungus, Sclerophthora macrospora. Crazy top can be found throughout Ohio but rarely causes substantial losses. The disease develops where soils have been saturated for 24 to 48 hours soon after planting. The fungus infects the growing point of the young corn plants usually before the second or third leaf stage, then grows systemically within the plant and develops in the rapidly growing tissues. The systemic growth causes a hormonal imbalance, which initiates the proliferation of leafy tissue in the ears and tassels.
Management:
No highly effective control measures can be recommended for crazy top. Very little is known about the level of resistance in corn hybrids to this disease. Proper soil drainage will reduce the risk of flooding and subsequent infection. Avoid planting corn in low wet spots where the disease is known to occur. Seed applied fungicides will not control crazy top.
For more on information consult the following:
P. E. Lipps and D. R. Mills. 2001. Crazy Top of Corn. Ohio State University Extension Plant Pathology Fact Sheet AC-0034-01 Available online at http://ohioline.osu.edu/ac-fact/0034.html [URL verified 9/13/07].
Western Bean Cutworm Ear Injury
Symptoms:
Scattered patches of partial and/or complete kernel destruction. Injury often associated with mold growth on affected kernels. Larvae of the western bean cutworm are not cannibalistic, and several larvae may infest one ear. Entry to ears is gained through silk channels or by chewing through husks, injuring the tip, base, and sides of the ear. Larvae feed on kernels until about mid-September, when they exit through husks.
Causes:
Kernel feeding by western bean cutworm (Striacosta albicosta). Tends to be restricted to limited parts of the ear. Western bean cutworm often enters ear through the husk in the sides of the ear. Partially consumed kernels may be further attacked by ear molds or secondary insect feeders that enter the ear through the cutworm’s feeding channel.
Management:
A variety of foliar fungicides are effective in controlling WBC. Insecticides may be necessary if 8% of the plants have eggs or newly hatched larvae and 90-95% of the plants have tasseled. Once larvae enter ear tips foliar insecticide not feasible. Bt corn hybrids containing the Herculex 1 (HX1) trait Bt resistance also provide protection against WBC.
Symptoms:
Earworm Larvae enter the ear primarily through the silk channel, unlike European corn borer and fall armyworm, which enter through the husks or cob. As silks dry, corn earworm begin chewing on individual and/or groups of kernels. Larvae feed at the tip and along the sides of the ear near the tip, continuing to feed until they mature. At that time, the larvae drop to the ground to pupate. When leaving the ear, corn earworm may drop from the ear tip or create exit holes by chewing through the husk. These exit holes can be mistaken for entrance holes caused by other larvae.
Cause:
Corn earworm (Heliothis zea) - Two full generations of earworm development can occur each year after the spring/summer migration into the state. Second generation larvae and moths occur during pollination. Population densities usually peak in late summer. Moths lay eggs on the silks of cornplants. Even though moths may lay more than one egg per ear, there is generally only one larva per ear because they are cannibalistic. Larvaewill migrate down the silks to the ear tips within 1 hour of hatching. Larvae feed on the developing kernels under the protective husk for the entire larval stage. When larval development is complete, the larva chews through the husk and exits the ear. It then drops to the ground, burrows into the soil, and pupates. The corn earworm, also known as the tomato fruitworm and the cotton bollworm, feeds on a number of crops including corn, tomato, cotton, green beans, clover, vetch, lettuce, peppers, soybeans, and sorghum. The most severe infestations of corn earworm generally occur in the southern United States. Losses due to the corn earworm in field corn has been estimated at 2.5% annually, with losses in the southern United States ranging from 1.5-16.7%. Losses in sweet corn may be as high as 50%.
Management:
Management of this pest in corn often lies with planting resistant hybrids and altering planting dates to avoid high densities of corn earworms. Resistant hybrids limit the amount of injury to both the leaf and the ear. A combination of silks that are antibiotic to larvae and husks that are tight around the ear to alter larval behavior offer the most effective type of resistance. Because of the tightness of the husk around the ear, feeding is limited to the ear tip, resulting in small larvae or larvae that leave the ear before completing development. Some Bthybrids suppress corn earworm populations and reduce the amount of injury to the ear. Neither crop rotation nor tillage significantly influences corn earworm survival. However, early-planted crops are most likely to escape peak populations of egg laying moths.Chemical control of the corn earworm can be expensive; most spraying occurs in sweet corn fields where a majority of the market value is in the quality of the ears.
For more on information consult the following:
Kelly A. Cook and Rick Weinzier 2004 Corn Earworm University of Illinois Integrated Pest Management Insect Fact Sheet
http://www.ipm.uiuc.edu/fieldcrops/insects/corn_earworm/index.html
Cook, K. 2005. Corn Earworm, European Corn Borer, Fall Armyworm, or Western Bean Cutworm: Which One Is Causing the Injury I'm Finding on My Corn Ears? The University of Illinois IPM The Bulletin No. 23 Article 4/October 7, 2005
http://ipm.uiuc.edu/bulletin/article.php?id=415
European Corn Borer Injury to Corn Ears
Symptoms:
Ear feeding by corn borer larvae is not focused on any one area. Kerenl chewing injury can be found at both ends and along all sides of the ear.
Cause:
European corn borer (Ostrina nubilus). Two to three generations of European corn borer occur in Ohio each year. Injury to corn ears is caused by the second and third generations. Loss of grain to larvae's direct feeding on kernels is usually not important in field corn, but in sweet corn and seed corn, losses can be significant. Larvae feed on pollen and silks before entering the ear. Entry to the ear is also gained by tunneling through the shank and cob.
Management:
Planting of ECB resistant or transgenic Bt-Corn is considered the most effective preventive option. If significant ECB infestations are detected prior to stalk boring, chemical treatment may be applied. Economic Threshold: First Brood: Detection of ECB larvae in 75% or more of stand may warrant treatment if an average of 1 larvae per stalk can be prevented from completing development. Second Brood: Treatment may be warranted if 50% or more of the plants have eggs or early larva. Fields having severe 2nd brood ECB infestations should be harvested early to minimize stalk lodging and ear drop.
Credit: USDA
Symptoms:
Unlike the corn earworm, the fall armyworm feeds by burrowing through the husk on the side of the ear. Larvae also enter at the base of the ear, feeding along the sides and even tunneling into the cob. They usually emerge at the base of the ear, leaving round holes in the husks.
Cause:
Like the corn earworm, fall armyworm moths migrate north into Illinois each year. Fall armyworms are a concern for cornfields from mid- to late summer. They cause serious leaf-feeding damage and feed directly on corn ears. Late-planted or later-maturing hybrids are more susceptible to fall armyworm injury. Most common is pretasseled corn. Larvae consume large amounts of leaf tissue, but as corn plants develop, larvae move to the ear.
Management:
For more on information consult the following:
Cook, K. 2005 The University of Illinois The Bulletin Corn Earworm, European Corn Borer, Fall Armyworm, or Western Bean Cutworm: Which One Is Causing the Injury I'm Finding on My Corn Ears? No. 23 Article 4/October 7, 2005. Available at http://ipm.uiuc.edu/bulletin/article.php?id=415
Bessin, R. 2004. Fall Army worm in corn. University of Kentucky Entomology Factsheet ENTFACT-110. Available at http://www.ca.uky.edu/entomology/entfacts/ef110.asp
Symptoms:
Lightweight, weathered ears with damaged, discolored moldy kernels that have been subjected to bird and insect feeding; often associated with kernel sprouting.
Causes:
Poor husk coverage at maturity combined with upright ear orientation allows bird feeding of tip kernels that may lead to secondary insect feeders injury. Moisture accumulation at base of ear promotes molds and may result in germination of scattered kernels.
Management:
Avoid hybrids with erect, upright ear orientation at maturity with loose husks and ear tips that may extend beyond the husk leaves.
Symptoms:
Red streaks form on sides of kernels and extend over the crown. Streaked kernels are more common at ear tips, especially if the husks are loose and kernels exposed.
Causes:
Caused by toxin secreted during feeding by the wheat curl mite Eriophyes tulipae, the vector of the wheat streak mosaic virus.
Management:
Severity of symptom expression varies among hybrids. Kernel red streak is most common on yellow dent and least common on white corn. The streaking develops in the pericarp but does not affect the feed or nutritional value of corn. The reddish discoloration may affect certain uses of food grade corn, and may thereby reduce premiums.
Symptoms:
.
Causes:
Management:
