C.O.R.N. Newsletter: 2014-08
Bt Options for Corn Insect Control and “Know Before you Grow”
Since the mid 1990’s and the first Bt corn product to control European corn borer was released, there are now numerous options available for corn insect management. At times, this information can be confusing, and thankfully our colleagues Dr. Eileen Cullen at the University of Wisconsin and Dr. Chris DiFonzo at Michigan State university have developed a handy Bt-Trait table, which lists all currently available options (a copy can be found at our webpage:http://www.oardc.ohio-state.edu/ag/images/Handy_Bt_Trait_Table_a.pdf).
Of note this year is a new product from Syngenta called Duracade™, which is targeted mainly for western corn rootworms. This is an important trait for rootworm control, especially since Dr. Aaron Gassmann and his team at Iowa State University have found rootworms resistant to Cry3Bb1 and mCry3A (seehttp://www.pnas.org/content/early/2014/03/12/1317179111).
However, not all markets have approved Duracade™, including China and the European Union, restricting where this seed can be sold. Furthermore, certain elevators and ethanol plants will not take Duracade™ grain. Growers that use Duracade™ are recommended to be cautious about how their grain is planted, harvested and sold to limit mixing with other traits.
Restrictions also apply to a few other corn traits, and the National Corn Growers Association has a list of traits not currently approved for certain export markets (seehttp://www.ncga.com/for-farmers/know-before-you-grow), as part of their Know Before You Grow program.
Getting Your Corn Crop Off to a Good Start in 2014Author(s): Peter Thomison
Mistakes made during crop establishment are usually irreversible, and can put a "ceiling" on a crop's yield potential before the plants have even emerged. The following are some proven practices that will help get a corn crop off to a good start.
Perform Tillage Operations Only When Necessary and Under the Proper Soil Conditions.
Avoid working wet soil and reduce secondary tillage passes. Perform secondary tillage operations only when necessary to prepare an adequate seedbed. Shallow compaction created by excessive secondary tillage can reduce crop yields. Deep tillage should only be used when a compacted zone has been identified and soil is relatively dry. Late summer and fall are the best times of year for deep tillage.
Complete Planting by Early May
The recommended time for planting corn in northern Ohio is April 15 to May 10 and in southern Ohio, April 10 to May 10. However if soil conditions are dry and soil temperatures are rising fast, start planting before the optimum date. During the two to three weeks of optimal corn planting time, there is, on average, only one out of three days when field work can occur. Avoid early planting on poorly drained soils or those prone to ponding. Yield reductions resulting from "mudding the seed in" are often much greater than those resulting from a slight planting delay. If the rainy conditions we are currently experiencing persist, remember that good yields are still possible with later planting dates. In 2011 and 2012, many Ohio growers observed that their later planted corn yielded better than early corn due to unusually favorable rainfall and temperature conditions in late July and August.
Adjust Seeding Depth According to Soil Conditions
Plant between 1-1/2 to 2 inches deep to provide for frost protection and adequate root development. Seeding depth should be monitored regularly during the planting operation and adjusted for varying weather and soil conditions. Irregular, especially shallow planting depths contribute to uneven plant emergence, which can reduce yields.
Adjust Seeding Rates on a Field-by-Field Basis
Adjust planting rates using the yield potential of a site as a major criterion for determining the appropriate plant populations. Lower seeding rates are usually preferable when droughty or marginal soils limit yield potential. On soils that average 120 bu/acre or less, final stands of 20,000 to 22,000 plants/acre are adequate for optimal yields. Plant population studies conducted by OSU from 2006 to the present suggest that on more highly productive soils, with greater yield potential, final stands of 30,000 plants/acre or higher were required to maximize yields. Seeding rates can be cut to lower seed costs but on most highly productive Ohio soils, this approach typically costs more than it saves.
Most research suggests that planting a hybrid at suboptimal seeding rates is more likely to cause yield loss than planting above recommended rates (unless lodging becomes more severe at higher population levels) and harvest delays occur. When early planting is likely to create stressful conditions for corn during emergence, e.g. no-till in corn residues in early to mid April, consider seeding rates 10 to15% higher than the desired harvest population. Follow seed company recommendations with regard to optimal seeding rates for different hybrids.
Plant a Mix of Hybrid Maturities
Planting a mix of hybrids with different maturities reduces damage from diseases and environmental stress at different growth stages (improving the odds of successful pollination) and spreads out harvest time and workload. Consider spreading hybrid maturity selections between early‑, mid‑, and full‑season hybrids‑for example, a 25‑50‑25 maturity planting, with 25 percent in early‑ to mid‑season, 50 percent in mid‑ to full‑season, and 25 percent in full‑season. Planting a range of hybrid maturities is probably the simplest and most effective way to diversify and broaden hybrid genetic backgrounds.
Plant full‑season hybrids first
Planting a full‑season hybrid first, then alternately planting early‑season and mid‑season hybrids, allows the grower to take full advantage of maturity ranges and gives the late‑season hybrids the benefit of maximum heat unit accumulation. Full‑season hybrids generally show greater yield reduction when planting is delayed compared with short ‑to mid‑season hybrids.
Weed Identification ResourcesAuthor(s): Mark Loux
We frequently receive questions about how to identify weeds and what the best resources are to help with identification. There are many resources available for plant identification, but these are some of the ones we use the most, divided into four categories – books, online pdf’s, websites, and apps (internet access not necessarily required except to download initially). We still often start the identification process with several books, because this can be faster and more comprehensive than using the web.
We have shelves of ID books and all of them serve a purpose. They are full of amazing descriptions, sketches, and pictures. Our top picks, in order of preference are: Weeds Of the Northeast, Weeds of the Midwestern United States and Central Canada, and Weeds of the North Central States. These are all available for purchase on the web.
2. Online pdf’s
Weed seedling ID - http://fieldcrop.msu.edu/uploads/documents/Ncr607.pdf
Early spring no-till weed IDhttp://weeds.cropsci.illinois.edu/extension/Other/NCR614.pdf
Many solid weed ID websites are available, and the best one is really a matter of personal preference. Weed science programs at Virginia Tech and the Universities of Illinois and Wisconsin have good ID sites. A favorite for just looking at photos of weeds is http://images.bugwood.org. The “images” tool in Google is very helpful for confirming an ID.
- good arrangement and labeling
- written descriptions better than some pics
- database with search options
“ID Weeds” from University of Missouri Extension. A little technical; however, a solid weed list with a good vocabulary to get you headed in the right direction.
Weed ID” by BASF. This one has a “take a picture” option that can be very helpful. It also has general ID pictures instead of just terms when choosing characteristics.
Ag Weed ID by Penton Media Inc.. Has a Compare Image option that is nice, or browse option with unique narrowing search option
AG-PHD by FM - multiple tools, has a pest detection section with list of weeds and photos
Invasive Plants in Southern Forest: Identification Management - specialized list of species
Federal Noxious Weeds Key by USDA - seed and fruit for the hardcore ID
The first and normally easiest step in identification is determining if the weed is a monocot (grass) of dicot (broadleaf). If you go with grass the main characteristics to look at are the leaf shape, presence or absence of hair, auricle, ligule, flower shape, and overall plant structure. If you go with broadleaf the main characteristics are cotyledons (if still present), hair (present or absent), leaf arrangement, leaf type, leaf shape, leaf margin, petioles, ochrea, and flower shape/color. With all of these characteristics a lot of variation occurs, and not just between species but within as well. Feel free to email us for help with weed identification. We can often identify a weed with a few good digital photos.
Evaluate Alfalfa Stands For Winter Injury
As alfalfa stands break dormancy and begin growth, growers should make plans to take some time to evaluate the health of those stands and determine if there was winter injury. Some early bud growth was observed the last full week of March in the southern half of Ohio. This evaluation is especially important in those areas of the state where we had periods of near zero to below zero temperatures this winter combined with little to no snow cover during some of those cold temperatures.
After doing a quick literature review, it appears that there is general agreement that temperatures in the 5 to 15 degree F range as measured at the alfalfa crown can begin to damage the plant and prolonged exposure to these and lower temperatures can kill the plant. Generally, the soil temperature at a 2 inch depth is associated with the temperature of the alfalfa crown. Snow cover is an important component of protecting an alfalfa plant from sub-zero temperatures since even a cover of 4 inches of snow can provide 10 to 15 degrees of protection. Once again, the concern is for those areas that experienced periods of zero and subzero temperatures without a 4 inch or greater snow cover. For many areas of the state, however, soil temperatures at the 2-inch depth remained at or above 26F even through the coldest days this winter.
An alfalfa stand health evaluation and winter injury assessment needs to be done by getting out into the field and doing a combination of stand counts and digging up some plant roots. Generally that evaluation should be done when there is 3 to 4 inches of growth from the plant. Evaluation involves selecting random sites throughout the field and counting the plants in a one foot square area. Check at least one site for every 5-10 acres, and like soil sampling, more random sampling is better. In addition to counting the plants per square foot, a count of the total stems per square foot is also useful because healthy plants can often produce more stems per plant thereby compensating for potential yield loss from fewer plants per square foot. After counting the plants, dig up all the plants in a one foot square area for every 5 to 10 acres and examine the crown and roots of the plants.
The winter survival rating determined by the plants per square foot is based upon the age of the stand. The following table is from a 2012 article on the Iowa State University (ISU) Integrated Crop Management web site by Stephen K. Barnhart, ISU Extension forage specialist.
Plants Per square foot
Year after seeding
Less than 8
Less than 5
Less than 4
4 years and older
Less than 3
As mentioned previously, counting the total stem number in a square foot is another method of evaluating winter survival and yield potential of a stand and has been promoted by Dan Undersander, Extension forage specialist at the University of Wisconsin. Here is a summary of that system:
Stem number/square foot
Expected result or action
Stem density not limiting yield
Some yield reduction expected
Less than 39
Consider stand replacement
Source: Undersander et al 2011, University of WI Extension publication A3620
While plant and stem counts are useful, to get a true determination of stand health, plants must be dug up so that crown and root tissue can be evaluated. To do this you must split the crowns/roots. The inside should be a creamy white color. If it is yellowish brown to chocolate brown color the tissue is damaged or dying. If more than 50% of the roots show these symptoms, reduce your stand counts and yield potential.
One other weather condition that can have a detrimental impact on alfalfa stands is freeze/thaw cycles. These cycles that typically occur in February through March often present the greatest danger of winter injury in Ohio. There is the potential during these cycles to physically lift or heave alfalfa plants out of the soil. This heaving exposes the crown of the alfalfa plant making it more susceptible to temperature and physical injury. In some cases, heaving breaks the root system, effectively killing the plant. Heaving tends to be more of a problem in wet, saturated soils and clay soils.
Although winter temperatures and snow cover amount are primary driving factors affecting alfalfa winter survival, there are also management factors that growers can control to decrease the chance of winter injury. Those factors include:
- Selecting varieties with good winter hardiness and disease resistance.
- Maintaining soil fertility levels. Potassium in particular is associated with enhancing alfalfa tolerance to winter injury.
- Improving soil drainage.
- Harvest management: more cuts is generally associated with a higher risk of winter injury, particularly if the last fall cut falls in that mid-September to mid-October time frame.
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.
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