C.O.R.N. Newsletter 2009-22

Dates Covered: 
July 14, 2009 - July 21, 2009
Editor: 
Howard J. Siegrist

Western Bean Cutworm Catches Increasing

Authors: Bruce Eisley, Ron Hammond, Andy Michel

After 2 full weeks of sampling, adult catch numbers of western bean cutworm (WBCW) have increased. As of July 13, we have caught a total of 31 moths, with multiple catches in several counties. An updated count by county can be found at our new website http://entomology.osu.edu/ag/ under the corn menu. At this point last year we had caught only 10 adults. While peak flight probably will occur this week or even next week, we still recommend scouting for eggs or larvae in corn. To scout for eggs or larvae, inspect 20 consecutive plants in 5 random locations, making sure to include corn of differing growth stages if fields are uneven. Eggs can be found in random clusters of 20-100, and will first appear white, then tan, and then a deep purple color. Larvae will emerge within 48 hours once eggs turn purple. As most corn is in the pre-tassel stage at this point, larvae will most likely be found feeding within the whorl. In earlier planted corn, larvae will be found feeding on the emerging silk.

A suggested threshold is 5% of plants infested with either eggs or larvae. However, control is not effective if tassels have not emerged, as the WBCW will be protected from insecticides inside the whorl. Many insecticides are labeled for WBCW-see our 545 bulletin at our new website. If your field is transgenic, only corn with Cry1F (Herculex) offers some protection from WBCW (but still check the refuge). As the summer progresses, we will continue to check these traps throughout the state and provide updates, especially if counts increase significantly. As you check your fields, please let us know of any suspected eggs or larval infestations.

Check for Corn Rootworm Injury

Authors: Bruce Eisley, Andy Michel, Ron Hammond

This is the time when growers should begin checking their corn fields for corn rootworm larval injury. The coming weeks will be the time to root sample because the maximum larval feeding injury will have been completed. After larval feeding has ended, the roots on some hybrids will begin to regenerate and when this happens, rootworm larval injury is more difficult to detect. Sampling should be done in corn fields following corn fields, or in corn fields following soybean fields in areas where the western corn rootworm variant is known to occur or is a growing concern. Any first year corn showing root lodging should be checked to determine if the lodging is from rootworm feeding or environmental factors.

We suggest the following method to check for rootworm injury:

1. Carefully dig plants, don’t pull them, from the field taking as much soil as possible with the plant.

2. Carefully remove as much soil as possible from the plant without damaging the roots and also look for any larvae that might still be in the soil or on the roots. Rootworm larvae are white, about 1/2 inch in length when full grown with a brown head and brown plate on the tail.

3. If there is still soil on the roots you can either soak the root system in a bucket to loosen this remaining soil or you can spray the root system with a hose to remove the remaining soil.

4. After the soil has been removed, check the roots for feeding injury, either roots chewed back to the stalk or tunneling in the roots.

Root systems can be rated using the 0 to 3 scale. The scale indicates the amount of damage to the root system and can be used to determine if economic injury has occurred.

Modified Node-Injury Scale.

Rating Visible Damage to Roots
0 no visible damage to roots
0.05 slight scarring
0.08 moderate to severe scarring with no roots chewed to 1.5 inches of stalk
0.1 one root chewed to 1.5 inches of stalk
0.5 half node of roots chewed to 1.5 inches of stalk
1 one node of roots destroyed
2 two nodes of roots destroyed
3 three nodes of roots destroyed

Soybean Aphid Update

Authors: Bruce Eisley, Andy Michel, Ron Hammond

Although we have not received any reports of economic problems in Ohio, we continue to find additional fields that have low populations of soybean aphids. Additionally, locations to our north where we expect the big aphid flight to come from within the next month are beginning to have their aphid populations build. Of interest in Ohio is finding a low aphid population in a field on the Farm Science Review site in Madison County along I-70 west of Columbus. This is a very southern location to be finding aphids at this time. Growers should begin sampling their fields in anticipation of the (potential) coming flight of winged aphids and be ready to follow (possible) rising populations of soybean aphids. Remember that treatment should not be done until the economic threshold, or action level, of an average of 250 soybean aphids per plant is reached.

Understanding Corn Crop Water Needs: Available Soil Moisture

Authors: Robert Mullen, Peter Thomison

Significant rainfall (0.5 to one inch or more) over the past weekend should ease concerns of growers regarding potential water stress in corn fields that are just starting to pollinate However, the rainfall was not uniform across the state and some areas, especially parts of NE Ohio, received only trace amounts of rain. Given the likelihood that rain for the next week is not great, how much can we rely on soil moisture to meet crop needs. Average water use by a corn crop during pollination and early grain fill is about 1/3 inch per day. Evapotranspiration rates in corn depend on temperature, humidity, wind, solar radiation and total leaf area of the crop. (Evaporation from the soil surface combined with transpiration from plants is evapotranspiration). When temperature is relatively low and humidity is high as on a calm, cloudy day, the evapotranspiration rate will be low. If temperature is high and humidity low as on a sunny, windy day, the rate will be high.

In areas that have received negligible rainfall during the past 3 to 4 weeks, how much of the corn crop’s water needs can be met by subsoil moisture?

The following is information from the National Corn Handbook - Chapter NCH-20 “Irrigation Scheduling for Corn-Why and How” https://engineering.purdue.edu/~abe325/RESOURCES/Irrigation%20Scheduling%20for%20Corn%20Why%20and%20How.pdf to help address these questions.

Soil textural characteristics dictate the water holding capacity, intake rate and drainage rate. Soils may have available water capacity of as little as 4 inches or may exceed 8 inches in 4 feet of soil. Table 1 gives the available-water holding capacities of ten different soil types. Soils also differ as to depth adequate for active root development; some have underlying layers of gravel or hard pan that would restrict root growth.

Information in this table might be used to estimate the number of days that moisture stored in the soil could “carry” a corn crop. For example, with a storage capacity of 1.8 in./ft, a fully charged silty clay loam soil might carry corn with a 3 foot rooting depth up to 18 days during silking and early grain fill stages (1.8 in/ft times 3 foot depth= 5.4 inches available water; 5.4 in. divided by 0.3 inch/A/day water requirement = 18 days). Although corn roots can grow as deep as 8 feet, when actively growing, corn obtains 90% of its water requirements from the top 3 feet of the soil profile.

A major factor determining the ability of corn to extract available soil water is soil compaction. In some Ohio corn fields, surface compaction, combined with excessive soil moisture early in the season, late plantings, etc. have resulted in corn root systems restricted to the top few inches of the soil profile. Shallow root systems make the crop especially vulnerable to drought. In addition to soil compaction, when relating the information from Table 1 to various Ohio soil types, keep in mind that other factors may influence water availability. Differences in soil organic matter and texture often occur at different rooting depths, for example the top foot of soil may be a silty clay loam but underlying layers may be clay, sand, or gravel.

Table 1. Available-Water Holding Capacity of Ten Soil Types.*

Soil type Textural characteristics Storage capacity
in./ft.
0 Sandy clay corn 2.0
1 Silty clay loam 1.8
2 Clay loam 1.8
3 Loam
Low (2%) Very fine sandy loam 2.0
O.M. Silt loam
4 Loam
High (3%) Very fine sandy loams 2.5
O.M. Silt loam
5 Fine sandy loam 1.8
6 Sandy loam 1.4
7 Loamy sand 1.1
8 Fine sands 1.0
9 Silty clay
Clay 1.6

*Source: Chapter NCH-20 “Irrigation Scheduling for Corn - Why and How”

Weather Update

Authors: Jim Noel

No significant changes to the rest of July outlook from last week. Note: the computer models were wrong and we were right on thinking that it would be a lot drier than our computers models suggests which suggest wet conditions for the rest of July. This is likely the start of the drier than normal pattern that takes us into this winter. We will keep you posted on this though.

Overall, below normal temperatures and rainfall for the rest of July. Below to much below normal temperatures over the next week will relax to near normal after that for the rest of July. Rainfall will be below normal in most areas. There will be some scattered activity about Wednesday of this week and then not much until late next week. Unless you were in that nice band of heavy rain over the weekend from west-central and northwest through central and south-central Ohio, rainfall was limited over the last week. Extreme northeast Ohio also had some reasonable rainfall. It was the haves and have nots for rainfall. If you did not get it in the last week, it looks like limited chances for the next few weeks.

One last note: some real cool mornings lows are on tap tonight with 40s in the north and low to mid 50s in the south!

Mid-30s in central Michigan this AM and low 40s in the south!

Summer Field Day Events

Authors: Greg LaBarge

Summer Field Day activities are occurring at several locations across the state. The Agronomic Crop Team Calendar page https://agcrops.osu.edu/calendar/ has information and along with link details for the following events.

July 21 & July 23
Manure Science Review

Rowe Dairy 9877 Strasburg-Bolivar Rd. NW Strasburg, OH (July 21) and Brown Dairy 7535 State Route 364 New Bremen, OH (July 23).

July 22
Agronomy Field Day at OARDC Western Agriculture Research Station

From 9 am to 3 pm on display will be the latest research and information on agronomic issues with specialist from OSU. The Research station is located at 7721 S Charleston Pike, South Charleston OH.

July 30
Field Crops Day at OARDC Northwestern Agriculture Research Station

From 9 am to 11:30 am on display will be the latest research and information on agronomic issues with specialist fro OSU. The Research station is located at 4240 Range Line Rd, Custar, OH.

July 30
Central Ohio Agronomy Field Day

David Miller Farm, 10750 Millersport Road, Millersport, Ohio (Fairfield County), 5:30 p.m. to 9:00 p.m. Registration begins at 5:00 p.m.

August 12
Southwest Ohio Corn Growers Association/Fayette Agronomy Club Field Day

Field Day from 9:30 to 3:00 at the Fayette County Demonstration Farm, 2770 SR 38, Washington Court House, OH.

September 1
Ohio No-Till Field Day

From 9 am to 4 pm at the Jim Rodman Farm, 6822 SR 203, Radnor OH (Delaware County).

September 22-24
Farm Science Review

Machinery show and demonstrations plus a whole lot more on the latest in products for Ohio agriculture.

Archive Issue Contributors: 

State Specialists: Pierce Paul, and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel, and Bruce Eisley (Entomology), Peter Thomison (Horticulture and Crop Sciences), and Jim Noel (NOAA). Extension Educators and Associates: Glen Arnold (Putnam), Roger Bender (Shelby), Tim Fine (Miami), Mike Gastier (Huron), Jonah Johnson (Clark), Mark Koenig (Sandusky), Greg LaBarge (Fulton), Les Ober (Geauga), Howard Siegrist (Licking), and Harold Watters (Champaign).

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.