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5/13/2013 - 5/19/2013

2013 Black Cutworm Scouting Advisory

By Adam Sisson, Integrated Pest Management; Laura Jesse, Plant and Insect Diagnostic Clinic; and Erin Hodgson, Department of Entomology

We asked black cutworm monitoring participants to start watching traps at the beginning of April. The first moth was recorded in Ringgold County on April 3 this year. Our predictions of cutting dates (the date when black cutworm larvae are likely to be damaging corn) are based on peak flights that took place beginning April 8 in the southwestern corner of the state. Estimated peak flights for other climate divisions occurred towards the end of April and beginning of May. The map (Fig. 1) shows the predicted cutting dates for the nine Iowa climate divisions. Predictions are based on actual and historical degree day data accumulated from the dates of peak flights.

Figure 1. Estimated black cutworm cutting dates for each Iowa climate division based on peak flights of moths occurring in 2013. *The first peak flight in this climate division took place about three weeks before other parts of Iowa, and several other peak flights occurred here throughout April.

 

Scouting

Black cutworms are light grey to black with granular-appearing skin and four pairs of fleshy prolegs on the hind end (Fig. 2). They can be confused with another insect that may be found in fields during spring, the dingy cutworm. However, there are some characteristics that can help to set species apart, which are outlined further in this article on cutworm identification.


Figure 2. Black cutworms are best identified by the dark tubercles found along the middle of the back. On each body segment, the pair of tubercles closest to the head is about one-third to one-half the size of the pair nearest to the abdomen.

 

Certain fields may be at a higher risk for black cutworm damage than others. These fields include those that are poorly drained and low lying, those next to areas of natural vegetation and those that are weedy or have reduced tillage. Black cutworm may be more troublesome in fields in which corn is planted late, as plants are smaller and more vulnerable to damage. Also, if high numbers of larvae exist in a cornfield, they may cause problems despite the use of Bt hybrids.

Scouts are encouraged to start looking several days before the estimated cutting dates as local development may be sped up (or slowed down) by localized weather. Larvae from later or yet to occur peak flights can continue to damage corn so it is important to continue scouting, especially with the later planted corn in 2013. Fields should be scouted for larvae weekly until the corn reaches V5 by examining 50 corn plants in five areas in each field. Look for plants with wilting, leaf discoloration and damage, or those that are missing or cut (Fig. 3). Note areas with suspected damage (with a flag) and return later to assess further damage. Larvae can be found by carefully excavating the soil around a damaged plant.

Figure 3. Black cutworm larval damage usually starts above the soil surface. Leaf feeding (left) can occur. As larvae mature, they can cut plants (right). Photos copyright Marlin Rice.

 

There is evidence to suggest that black cutworm eggs are able to survive for at least one night of sub-freezing temperatures. So it may be that eggs laid before frost will still produce cutting larvae; however, scouting a field is the only way to tell if an economic infestation is occurring in an emerged crop.

 

Thresholds

With corn price and input fluctuations, a dynamic threshold may be useful. An Excel spreadsheet with the calculations built in can be downloaded here and can be used to help management decisions regarding black cutworm.

Preventive black cutworm insecticide treatments applied as a tank-mix with herbicides are of questionable worth. Black cutworm is a sporadic pest; therefore, every field should be scouted to determine the presence of the insect prior to spraying insecticides.

 

Biology

Adult moths migrate on the wind from southern states near the start of spring, then mate and lay eggs. Around 1,300 eggs are laid by a single mated adult female. Eggs are laid in crop stubble, low spots in the field and in weedy areas. Younger larvae injure corn plants by feeding on leaf tissue and older larvae can cut seedlings.

 

Trap catches in Iowa

In 2013, traps have been established in 43 Iowa counties, with several counties having multiple traps. The moths trapped in Iowa so far can be viewed by going to www.ncipmpipe.org , selecting “View all maps” and clicking on “Iowa Black Cutworm Monitoring 2013.” Please consider that adult moth trap captures do not necessarily mean there will be economically significant black cutworm infestations in a particular location. Field scouting is essential to determine if an economically damaging infestation exists.

If you see any damage from black cutworm larvae while scouting, please let us know by sending a message to bcutworm@iastate.edu. This information could help us to refine our prediction efforts in coming years.

 

Adam Sisson is an extension specialist for the Integrated Pest Management. He can be contacted by email at ajsisson@iastate.edu or by calling 515-294-5899. Laura Jesse is an entomologist with the Iowa State University Extension Plant and Insect Diagnostic Clinic; contact at ljesse@iastate.edu or by phone 515-294-0581. Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at ewh@iastate.edu or phone 515-294-2847.

Sign Up Now for the Early Season Crop Disease Workshop

By Alison Robertson, Department of Plant Pathology and Microbiology

This year, Iowa State University (ISU) Extension and Outreach is offering an Early Season Crop Disease Workshop at the ISU Field Extension and Education Laboratory (FEEL) near Boone.  This full day workshop will be held on Thursday, June 6 and will cover diagnosis of early corn and soybean diseases, the biology of seedling pathogens and their management.

The goals of the workshop are to improve disease diagnostic skills and enhance participants’ knowledge of the biology of pathogens that cause early season diseases. The workshop includes hands-on activities in both the classroom and field and interactive presentations. Speakers include Alison Robertson, Daren Mueller, Greg Tylka and Margaret Ellis form the Department of Plant Pathology and Microbiology.

A full agenda is available at www.aep.iastate.edu/feel/esd.  Pre-registration is required by Monday, June 3 at midnight.  Class enrollment is limited to 25. A total of 6.0 pest management credits for certified crop advisors are available.

Registration can be completed online with a credit card (Discover, MasterCard or VISA only) at www.aep.iastate.edu/feel/esd. For more information, call 515-294-6429 or email anr@iastate.edu.

 

Alison Robertson is an associate professor in the Department of Plant Pathology and Microbiology with extension and research responsibilities; contact her at alisonr@iastate.edu or phone 515-294-6708.

Analog Years for Weather Forecasting and Correlating Corn Planting Dates with Yield in Iowa

By Roger Elmore and Elwynn Taylor, Department of Agronomy

As of May 12, 15 percent of Iowa’s corn was planted (USDA-NASS).  This is a slower pace than what Iowan’s experienced even in the flood year, 1993, when 20 percent was planted at this time in May. The 8 percent planted before May 5 was subjected to dramatic soil temperature changes as well as up to a foot of snow in parts of Iowa. Many Integrated  Crop Management News articles, blogs, Twitter posts, and other media document  spring 2013 conditions and concerns. 

To the surprise of many, soil moisture profiles across the state are filled or closely filled as we write. The U.S. Drought Monitor receded to the west and northwest every progressive week. Based on what has already happened, what does the 2013 cropping season look like from this mid-May perspective?

 

Analog: A person or thing seen as comparable to another

When faced with different weather patterns like those we’ve experienced so far this year, we often turn to analog years. These are years considered as having similar trends in temperature and/or precipitation as those we are currently experiencing.  Whether we agree or not, people use analog years to compare data like planting progress as well. It is often tempting to speculate that if we’ve had similar trends in weather or planting dates historically, we can use that as an analog year to forecast conditions – and thus corn yields - the rest of the current growing season.  Even if the analog year is not a totally reliable for the yield outlook it does at least provide an idea of the risks and potentials that could be experienced during the growing season.

 

Spring weather analog year for 2013: 1947

Figure 1 displays Iowa state average Growing Degree Day (GDD)accumulations, Precipitation, and Stress Degree Days (SDD) for April 1 through May 8 for 1947, 1995 and 2013. 1947 is suggested as a spring-weather analog year for 2013. This is probably based on certain similarities of April weather in both years. April through June 1947 was cold and wet. Corn stands were reduced by ‘water damage’ across the state. The cold-wet weather transitioned to drought in July (Figure 2).  By July 20th, 1947, heat stress set in and GDD exceeded normal (Figure 2). 

Figure 1.  Iowa Average Accumulated Growing Degree Days (GDD), Precipitation, and Stress Degree Days (SDD) for Spring 1947, 1995  and 2013. Graphs from Mesonet. Full-size image

Figure 2. Iowa Average Accumulated Growing Degree Days (GDD), Precipitation, and Stress Degree Days (SDD) for the 1947, 1995 and 2012 Growing Seasons. Graphs from Mesonet. Full-size image

 

Planting dates in 1947 ranged from May 5 to May 21 (Elmore unpublished data). About half of the 1947 corn crop was planted by May 15. This may seem late to us now, but this range of planting dates and the 50 percent planted date were normal for that era.  However, early rains probably resulted in shallow rooting. This coupled with stress later in the 1947 growing season probably reduced corn yield (Figure 2). Mid-season heat coupled with limited rain reduced Iowa average corn yields to 31 bushels per acre, 39 percent below the 1937-2012 trendline yield (Figure 3).

 

Figure 3.  Corn yield United States. and Iowa, 1866-2012. Data from USDA-NASS. Full-size image

 

Corn planting date analog years for 2013: 1984, 1993 and 1995

Another way to think about analog years is planting progress. As mentioned in our introduction, as of Sunday, May 12, only 15 percent of Iowa’s corn was planted. That was an increase from 8 percent the week before. Little corn planting occurred May 6–10 because of mid-week rains that unfortunately re-saturated fields just when they were nearly dry enough for planting following the early May snow; this delayed planting once more.  

Since 1980, planting progress in early May of three years - 1984, 1993 and 1995 - was similar to what we’ve experienced this year.  Because flooding resulted in delayed planting in 1993, let’s focus on the other two as possible analog years for planting date. 

1984: Six percent of Iowa’s corn was planted by May 6; however, one week later, by May 13, Iowa farmers planted another 29 percent (Figure 4). Planting in 1984 began by April 29 and ended by June 10. Half the crop was planted by May 15, 1o days behind the 1978-1987 average of May 5 (Elmore, 2013, in press). By May 12 of this year, 2013, we only had 15 percent of our corn planted for the reasons we mentioned above.  Corn yields in 1984 were 3 percent above trend line (see Pierson & Elmore) (Figure 3).  The delayed planting in early May was correlated with increased yields. Although 1984 SDD were slightly greater than normal, there were fewer SDD in that year compared to either 1947 or 1995.

Figure 4.  Percent of Iowa's corn planted at different dates and years.  2004 and 2009 yields were well-above trend line. Record breaking planting progress occurred in  2010. Adapted from USDA-NASS data. Full-size image

 

1995: Only 10 percent of Iowa’s corn was planted by May 7, 1995 (Figure 4). Another 20 percent was added the next week and 62 pecent of the crop was in by May 21.  Although planting progress was similar to that of 1984, yields in 1995 were 9 percent below trend line (see Pierson & Elmore) (Figure 3). Planting delays in 1995 were correlated with reduced yields; please note this doesn’t mean delays that year actually reduced yields. The primary impact in 1995 was high heat stress following silking relative to normal (Figure 2).

 

Cautions

Although analog years for weather and corn planting dates are interesting and help us understand potential hazards as well as opportunities, they may or not be accurate predictors of what will happen in 2013. Weather patterns the rest of the growing season will dictate that.

 

Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at relmore@iastate.edu or (515) 294-6655. Elwynn Taylor is extension climatologist and can be reached at setaylor@iastate.edu or by calling (515) 294-1923.

UAN and Herbicides on Emerged Corn

By Bob Hartzler and John Sawyer, Department of Agronomy

Prolonged wet periods often disrupt the normal sequence of field operations. Some fields may be planted before nitrogen and/or pre-emergence herbicides are applied. While UAN (urea-ammonium nitrate) and many pre-emergence products can be applied to emerged corn, using UAN as a herbicide carrier enhances the foliar activity of products and may result in foliar damage. Check herbicide labels for restrictions on use of UAN as a carrier.

UAN alone can be applied to emerged corn, and the risk of injury to the corn is dependent upon UAN rate, corn stage and weather conditions. Conservative suggestions are to limit postemergence applications of UAN to 90 lb N/acre when corn is at the V3 to V4 stage and to 60 lb N/acre at the V7 stage. Applications beyond the V7 stage are not recommended, and the risk of injury increases during hot, dry conditions.

The combination of herbicides with UAN greatly enhances the foliar activity of these products and poses a real threat of killing all emerged tissue contacted by the spray.  

Some might try to rationalize this combination if the corn is at the VE-V1 stage since the growing point is still underground. While corn often can recover quickly from loss of the shoot at this growth stage, the herbicide may influence the plant's ability to recover and therefore result in uneven plant size and yield loss. 

 

Bob Hartzler is a professor of agronomy with extension, teaching and research responsibilities. John Sawyer is professor with research and extension responsibilities in soil fertility and nutrient management.

2013 Weed Science Field Day

The 2013 Weed Science Field Day is scheduled for June 27 and will be held at the Iowa State University Curtiss Farm on South State Street.  Registration will begin at 8 a.m. and a $20 fee will cover a field book and refreshments. A brief program will occur at 8:30 a.m. The field day is open to all who are interested in attending including growers, agchem dealers and agchem industry representatives. The field day will include no tillage, conservation tillage and conventional tillage experiments. New herbicides and application techniques will be demonstrated. If you have questions, please contact Micheal D.K. Owen at (515) 294-5936 or mdowen@iastate.edu.



This article was published originally on 5/20/2013 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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