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5/18/2009 - 5/24/2009

2009 Predicted Black Cutworm Cutting Dates in Corn

Erin Hodgson and Jon Tollefson, Department of Entomology and Rich Pope, Corn and Soybean Initiative


The black cutworm does not overwinter in Iowa, however adults migrate here on southwesterly winds in early spring. Potentially significant numbers of adults  were first documented on April 27 and 28 this year across most of the southern two-thirds of Iowa.  A second notable flight occurred on May 5 and 6; that flight was recorded throughout the state. 

Mated females will deposit about 1300 eggs singly or in masses in field low spots or overflow ground; areas overgrown with grasses and winter annual weeds are particularly attractive locations. Although the black cutworm is a cosmopolitan pest, females often lay eggs near soybean stubble. Newly-hatched larvae will feed on weeds until corn emerges. Larvae feed and pass through six instars in about 35 days, depending on temperatures. 

Based on trap capture, adult black cutworms flight and temperatures this spring, larvae could be cutting corn beginning around May 25 and 26 in the southern two thirds of Iowa, and the first week of June in the northern three tiers of counties. Black cutworm arrival varies each year, but 2009 is about a week later than in recent years.
Black cutworm scouting projection map

Appearance.  Black cutworm larvae vary from light grey to black with an overall greasy and shiny appearance. Fully-grown larvae are about 1 1/2" long and curl up when disturbed. Distinguishing black cutworm from dingy cutworm larvae in the field is important; both species will feed on corn but dingy cutworms rarely cut leaves. Find out how to separate the two species with a previous ICM News article. The adults are night-flying moths with thick, grey bodies. Black cutworm adults have a wing span of 1 1/2", and the forewings have a black dagger-shaped mark near the edge.

Damage.  Factors that favor black cutworm outbreaks include late/reduced tillage, late planting, the presence of weeds, and fields next to permanent vegetation. Larvae will move from weeds as they are destroyed/consumed and start feeding on emerging corn leaves. Young larvae make small, irregular holes and feed aboveground. Older larvae (fourth to sixth instars) can cut stems or clip leaves and usually feed underground at night. Black cutworm larvae can consume four to six leaves before pupating. If soils are dry or crusted, larvae can burrow down to moist soil and move to new plants. Black cutworms have difficulty cutting plants past the V5 (five true leaves) stage and therefore corn less than 15" is most susceptible.

Sampling.  Start looking for black cutworms as soon as corn emerges, paying special attention to late-planted or weedy fields. IPM recommendations would be to examine 250 plants (50 plants in five locations) weekly until corn gets to V5. Check for wilted, discolored or damaged leaves, and missing plants. Sometimes a cut plant may look like it's coming out of the ground at an odd angle. If damaged leaves are found, dig around the base of the plant for the presence of larvae. In addition, flag suspected "hot spots" and monitor larval feeding (or lack of) over a few days.


Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at ewh@iastate.edu or phone (515) 294-2847. Jon Tollefson is a professor of entomology with responsibilities in research and extension, and Rich Pope is an extension program specialist with responsibilities in integrated pest management.

Scouting Soybean Seedling Diseases

By XB Yang, Department of Plant Pathology

With soybean planting completed in some regions, seedlings are emerging in early planted soybean fields. Starting now and continuing for the next two weeks, producers should scout for soybean seedling diseases.

Soybean producers may think scouting for seedling diseases is no longer needed due to increased seed treatments. Actually, that is not the case. Different fields have different seedling diseases and no seed treatment is effective to all diseases. Scouting will help determine the necessity of seed treatment for a particular field and the efficacy of seed treatment used.  

Damping off by Pythium and Phytophthora. For seedlings infected by fungal pathogens, damping-off can occur either before or after soybean emergence. When the seed fails to emerge because of fungal attack, seed rot or pre-emergence damping-off can occur. Pythium and Phytophthora are two fungi causing pre-emergence damping-off in Iowa. When the fungi attack the seed before germination, seed rot occurs. Seed that is dead before germination will be soft and rotted with soil adhering to it. If infection occurs after germination, seed may fail to emerge and dead plants will have rotted cotyledons, which are seen more often in hard surface fields. (See Photo 1).

 

pre-emergence damping off

Pre-emergence damping-off

Seedling blight  occurs after seedlings emerge. Seedling blight by Pythium is very similar to that by Phytophthora in terms of symptoms. One normally cannot separate the two without further laboratory tests. When seedling blight occurs, dead seedlings are visible on the ground. Infected plants dead before true leaf stage will have a rotted appearance. If leaves are present, infected seedling leaves will have a gray-green color before turning brown. A few days later, the plants die and have a rotted appearance. Diseased plants are easily pulled from the soil because of rotted roots. Seedling blight by Phytophthora can be differentiated from Pythium after V2 growth stage or later. Plants infected by Phytophthora have a brown discoloration extending from root up the stem. The two fungi attack soybeans in different temperature regimes. Soybeans planted in cold, wet soil are most likely to be attacked by Pythium. If disease occurs in warm conditions (around 80F), it is more likely caused by Phytophthora.

Seedling blight by Rhizoctonia also can cause seedling diseases. Seedling disease by Rhizoctonia is different from those caused by Pythium and Phytophthora. Unlike Pythium and Phytophthora damping-off, stem discoloration by Rhizoctonia is usually limited to the cortical layer of the main root and hypocotyl. Infected stems remain firm and dry. Typical symptoms are localized brown to reddish brown lesions on the hypocotyl and lower stem that do not extend above the soil line. The reddish brown color is a key symptom in diagnosing the disease. Seedling blight by Rhizcotonia normally appears as the weather becomes warm (80F) and it is more often seen in late planted soybean fields. 

Cool early May temperatures have contributed to good stands in emerged soybean fields and no replanting has been reported, although seedling blight has been observed.

If stand reduction happens in a soybean field that needs replanting, producers should determine if a fungal disease is involved – before replanting. A fungicide seed treatment may be needed for damping-off caused by fungal pathogens. Identification of seedling disease is essential in fixing the problems as different fungicides are effective in controlling different seedling diseases. The information is also useful for seed treatment of next year’s soybean.

damping off

Damping-off by Phytophthora


 

damping off rhizoctonia

Damping-off by Rhizoctonia


 

seedling disease

Seedling disease by Rhizoctonia

 

XB Yang is a professor of plant pathology with responsibility in research and extension. Yang can be contacted by email at xbyang@iastate.edu or by phone at (515) 294-8826.

Field Guides Allow Quick, In-field Diagnosis of Soybean Problems

By Tamsyn Jones, Corn and Soybean Initiative

Corn and soybean planting is almost done. As young plants start to emerge, growers will increasingly want to watch for pest and disease issues that could affect yield. An Iowa State University Extension field guide series is available to help farmers, agronomists and crop advisors quickly diagnose plant problems.

The Iowa Soybean Association partnered with ISU Extension to produce the guides in 2008.Copies are available free from the ISU Extension online store.

field guides

The series currently includes three pocket-sized, weather-resistant guides covering management of general soybean pests and diseases, soybean cyst nematodes and soybean aphids. A companion tri-fold pamphlet on speed-scouting of soybean aphids, which includes step-by-step directions and a worksheet for individual field assessment, is also available. The series provides the latest research and information on managing yield-lowering soybean pests and diseases. Photos accompany descriptions of all pests and diseases.

The Soybean Disease & Pest Management Field Guide covers a variety of leaf, seed and root diseases; damage from environmental stresses; and the primary insect pests that target soybean plants. It also explains soybean growth stages, planting considerations in Iowa and integrated pest management.

The Soybean Aphid Management Field Guide focuses on the soybean aphid, a major pest first found in Iowa in 2000. Since its arrival, several major outbreaks occurring in alternating years have caused significant yield loss. The guide explains the soybean aphid life cycle, identification, virus transmission, injury symptoms, management considerations, natural aphid enemies and treatment options. It also gives background on the origin and history of soybean aphids in Iowa, thoughts on population variation and insecticide considerations.

The Soybean Cyst Nematode Management Field Guide covers the life cycle, biology and management of soybean cyst nematodes, the most destructive soybean pest in the United States. The guide explains how nematodes damage soybean plants, symptoms of damage, scouting and soil sampling techniques, long-term management options, nematode effects on other soybean diseases and when to consider a nematode type test.

Portability and ease of use in the field were key goals in designing the guides. The spiral-bound books are visual aids with succinct text and a sturdy build that can resist mud, rain and other realities growers face working their fields.

While some of the information in the guides is specific to Iowa growing conditions, people outside the state may still find it useful and relevant. Those outside Iowa who use the guides should check with their state Extension services for local recommendations.

To obtain the guides visit the online store at www.extension.iastate.edu/store/Default.aspx and search by category or reference number.The soybean pest and disease guide is CSI 0010; the aphid guide is CSI 0011; the cyst nematode guide is CSI 0012; and the aphid speed scouting companion pamphlet is CSI 0015.


 

Tamsyn Jones is a communications specialist with the Corn and Soybean Initiative. Jones can be reached at (515)294-7192 or email at tamsyn@iastate.edu.

Western Iowa No-tillers to Hold Field Day June 16

By Kyle Jensen, Extension Field Agronomist

The second Western Iowa No-tillers (WIN) Demonstration Field Day is planned for Tuesday, June 16 near Shelby, Iowa. Over 200 producers and agriculture professionals attended the daylong event in 2008 to learn more about implementing no-till practices. No-till farming practices provide a positive option for southwest Iowa producers who have highly erodible soils in their fields and are dealing with increasing input costs. To accommodate an anticipated larger audience, more equipment displays and increased parking, the 2009 event will be held at the Carstens 1880 Farmstead just south of Shelby, Iowa.

Field day speakers will include Iowa’s Secretary of Agriculture Bill Northey, DTN Ag Meteorologist Bryce Anderson and ISU Extension Ag Economist, Chad Hart.  A panel of area farmers with years of no-till practices experience will be on hand to answer questions.  Prominent no-till farmer Randy Rink of Pender, Nebraska will also be in attendance to discuss cover crop usage.

Topics at this year’s field day will also include corn on corn, fertilizer placement and cover crops. Field trials will feature planting in corn stubble and the use of the latest no-till equipment.  At least six different cover crops used in row-crop fields will be shown in a separate demonstration plot. Presentations will begin at 9 a.m. Lunch will be provided by the Harrison County Cattlemen.  The day will conclude by 2 p.m.

There is no charge for the day, but pre-registration is required by June 11 for the noon meal.  The program brochure and registration form are available online and at the Harrison County office.  Registration can be completed by e-mailing csgorham@iastate.edu.  Registrations may also be faxed to 712-644-2100 or be mailed to: ISU Extension Harrison County, 304 East 7 St., Logan, IA 51546. For more information contact the Harrison County Extension Office at 888-644-2105. 

This event is sponsored by NRCS, ISU Extension and the Soil and Water Conservation Districts (SWCD) in Harrison, Pottawattamie and Shelby Counties.  Sponsors for the day include the Farm Bureau, Iowa Corn Growers Association, Cargill Ag Horizons, Farmers & Merchants State Bank, Midstates Bank, Shelby County State Bank, Heller Implement, Brokaw Equipment, United Bank of Iowa, the Iowa Soybean Association, A&M Green Power, Titan Machinery, Heartland Technology Solutions, Sorensen Equipment Company and Arbor Bank. 

USDA is an equal opportunity employer and provider.  USDA, SWCD and Extension programs are available to all without regard to race, color, national origin, religion, sex, or disability.  Persons with disabilities who require accommodations to attend or participate in meetings/events/functions should contact Robert Lawson at (712) 755-2417 (Federal Relay Service at 1-800-877-8339), or Robert.Lawson@ia.usda.gov by June 12.

 

 

Kyle Jensen is an Extension field agronomist serving southwestern Iowa. Terry Torneten is the Shelby County Extension Education Director, Jensen can be reached at (712) 769-2600 or by emailing jensenkg@iastate.edu. Torneten can be reached at (712) 755-3104 or by emailing ttorn@iastate.edu.

May 18 Crop and Weather Report

Iowa State University Extension climatologist Elwynn Taylor, integrated pest management specialist Rich Pope, and soybean agronomist Palle Pedersen are interviewed during the weekly crop and weather report with Doug Cooper.

Taylor says La Niña will not be a factor during the 2009 growing season and there is a chance that an El Niño could develop. El Niño would take the threat of drought out of the picture, according to Taylor.

Rich Pope reports Extension field specialists are in agreement with the latest USDA Crops and Weather report – 90 percent of Iowa's corn has been planted and nearly half of the soybean crop is in the ground. He recommends farmers scout their fields for weeds and other pests regularly.

Pedersen says despite a few setbacks in planting soybeans - the situation is much improved over one year ago. Indiana, Illinois and Ohio are all well behind in planting both corn and soybean.

Check General Root and Mesocotyl Health when Assessing Corn Stands

By Alison Robertson and Gary Munkvold, Department of Plant Pathology

This growing season has started out cool with slow heat unit accumulation with frequent precipitation events across the state keeping soils wet. Although some are still out planting corn, there are some fields where corn is at growth stage V2.  Reports of seedling blights are beginning to filter in.

As you start to assess plant stands, remember also to check below ground growth, specifically general root and mesocotyl health. Wet and cool soil conditions ( less than 50-55 F) predispose seedlings to infection by a number of fungi which cause disease that may result in seedling death.  Remember too, that while uneven emergence and stunted seedlings may indicate seedling disease, insect feeding and herbicide damage may be factors. 

Survival of young corn seedlings depends on a healthy kernel and mesocotyl which should remain firm and white through at least growth stage V6.  Damage to the kernel or mesocotyl prior to establishment of the nodal root system can result in stunted, weak or dead seedlings. A developing corn seedling relies on the kernel endosperm for nourishment until the nodal root system has fully developed, usually around the 6-leaf stage. Thus the mesocotyl acts as the “pipeline” for translocation of nutrients from the kernel and seminal roots to the seedling stalk and leaf tissues. 

Seedling diseases of corn (seed rots, seedling blights and/or root rots) are caused by numerous fungi including Pythium, Fusarium, Rhizoctonia, Aspergillus, Penicillium, and Trichoderma, all of which are common inhabitants of soils. In addition, these fungi also can be seed-borne in corn, except Pythium. Seedling susceptibility to infection increases the longer the seed sits in the ground, and the more stress germinating corn undergoes.  Corn germinates well at soil temperatures above 68 F.  When soil temperatures are below 55 F, germination is greatly retarded. Thus seedling disease often is more severe in early planted or no-till/reduced tillage fields because of cool soil temperatures. 

Typical below ground symptoms associated with seedling disease include rotting seed and brown discoloration (rotting) of the mesocotyl and seminal roots (Figure 1).  It is sometimes possible to determine in the lab which fungus is the culprit, however this information is not crucial since management options are the same for all seedling disease:  plant high quality fungicide-treated seed, plant when soil temperatures are above 50 F, and ensure planting depth is not too deep. 

Although crop rotation can be helpful in reducing inoculum levels, some fungi are pathogenic on both corn and soybean. Thus good records of seedling disease problems can be a helpful management tool.  For example, fields with a history of seedling blight can be planted later in a planting schedule when soil temperatures are warmer.

seedling blight

Figure 1.  Brown, discolored (rotten) mesocotyls are a symptom of seedling blight.

 

Seed treatment fungicides have been standard practice in corn production since the 1930s, but many changes have occurred recently and other changes are on the way.  The fungicide combination on most commercial corn seed now includes Maxim XL® /Apron XL® (fludioxonil and mefenoxam) and Dynasty® (azoxystrobin) from Syngenta Crop Protection. Some seed also may be treated with Trilex® (trifloxystrobin, Bayer CropScience) instead of Dynasty, or with Allegiance (Metalaxyl) instead of Apron XL. Stamina® (pyraclostrobin) seed treatment fungicide (BASF Corp.) was approved for use in 2009, and is available on a limited scale this year.

In 2010, we will see the launch of Monsanto’s Acceleron® seed treatment brand on corn, which will include the fungicide ipconazole, in combination with other active ingredients. Many seed companies are routinely applying  insecticides such as Cruiser® (thiamethoxam, from Syngenta) and Poncho® (clothianidin, Bayer CropScience)) in combination with the fungicide seed treatments. 

Earlier this year, the nematicide Avicta® (abamectin) was registered for use on corn.  The product will be launched commercially in 2010 in combination with Cruiser® seed treatment insecticide and the seed treatment fungicide Apron XL®, Maxim® XL and Dynasty®.  Many other fungicides and insecticides are registered for use on corn, some for on-farm use (see 2009 Missouri Pest Management Guide).

The rapid developments in commercial seed treatment use are strengthening the spectrum and duration of protection, but no amount of seed treatment will eliminate seed and seedling disease under all conditions. It continues to be important to be aware of what’s on your seed and the performance that you experience with the products

 

 

Alison Robertson is an assistant professor of plant pathology with extension and research responsibilities field and forage crops. Robertson can be reached at (515) 294-6708 or alisonr@iastate.edu. Gary Munkvold is a seed pathologist and associate professor of plant pathology with research responsibilities in diseases affecting seed production and utilization.Munkvold can be reached at (515) 294-7560 or munkvold@iastate.edu.

Volunteer Corn Management

By Bob Hartzler - Department of Agronomy

Many fields in southern Iowa have significant infestations of volunteer corn.  Research at Iowa State University in 2007 found that one volunteer corn plant per 10-foot of row resulted in a 1.3 percent yield loss.  South Dakota State University researchers found that volunteer corn was much more competitive in soybean than corn, thus management is critical in both corn and soybean to protect yields.

The widespread adoption of Roundup Ready corn has complicated management of volunteer corn in corn.   Few options, other than cultivation, are available to control volunteer control once this year’s corn has emerged.  If this year’s hybrid carries an herbicide resistant trait not found in last year’s hybrid, then the appropriate herbicide can be used (e.g. use of Ignite/Liberty on LL corn in 2009 when RR corn was planted in 2008). Ignite often does not provide complete kill of corn since it is a contact herbicide, but it will greatly reduce the plant’s competiveness by killing emerged leaves.

For no-till fields infested with volunteer corn that are not yet planted, knowing the herbicide traits in the prior year’s corn is critical. If resistant traits rule out glyphosate, either paraquat or SelectMax can be used.  A six day interval is required between SelectMax application and planting to avoid injury from the herbicide residues. Other herbicides in the ACC-ase family (Poast, Fusilade, Select, Assure, etc.) are not registered for this use.  Like Ignite, paraquat is a contact herbicide and may not provide complete control of corn.

Management of volunteer corn in soybean is much easier than in corn due to the availability of the ACC-ase herbicides.  Poast Plus is not as active on volunteer corn as the other ACC-ase herbicides.   Raptor also provides good control of volunteer corn.

Volunteer corn is highly competitive with both corn and soybean.  Timely management is critical in order to protect crop yields infested with this plant.

 

 

Bob Hartzler is a professor of weed science with extension, teaching and research responsibilities. He can be contacted by email at hartzler@iastate.edu or phone (515) 294-1164.

Early-Season Weed Competition

By Bob Hartzler, Department of Agronomy

The pressure to plant fields in a timely fashion frequently results in delayed application of preemergence herbicides due to rain or windy conditions.  This situation isn’t as troublesome as it would have been in the past due to the availability of effective postemergence herbicides; however, establishment of weeds with the crop can result in yield loss early in the season if not managed properly. 

Research in northern Iowa in 2008 documented a 10 percent yield loss as early as the V2 corn stage due to weed competition.  Allowing weeds to grow too long with corn also can increase economic optimum nitrogen rates due to N immobilization by the weeds.

Several factors determine when weeds begin to impact yields, including emergence time, weed species and density, cultural practices and environmental conditions.  Due to our inability to predict accurately when weeds begin to impact yields, it is best to act conservatively to minimize risks, particularly in fields with high weed populations. 

If a field is heavily infested with weeds (10 weeds or more per square foot), weeds should be controlled before they exceed 2 inches in height. Lighter infestations provide greater flexibility in application timing, but early control will minimize risks and provide more consistent control.


 

Bob Hartzler is a professor of weed science with extension, teaching and research responsibilities. He can be contacted by email at hartzler@iastate.edu or phone (515) 294-1164.

Degree Days - Brisk, but Basically OK

by Rich Pope, Corn and Soybean Initiative

The week of May 10 was seasonally cold; all areas of Iowa fell behind long term average degree-day accumulations. Departures from normal were equivalent to 2.5 days of May growth in northwest Iowa to 3.5 days in southeast Iowa.

Map of accumulated degree days from May 1 through May 17, 2009.

But there is a silver lining! Iowa farmers have planted over 80 percent of corn acres and around one-third of soybean acres statewide, numbers that are not only near normal, but clearly lead the rest of the Corn Belt states.  

The cooler than normal weather has slowed corn development, but also has delayed the growth of black cutworm larvae. Later this week, an article will be posted here with projected scouting dates across Iowa.

 

Rich Pope is a program specialist with responsibilities with Integrated Pest Management. Pope can be contacted by email at ropope@iastate.edu or by calling 515-294-5899.



This article was published originally on 5/25/2009 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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