C.O.R.N. Newsletter: 2016-28
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Some Tips for Evaluating Corn Hybrid Demonstration Plots
This is the time of year when many farmers visit and evaluate hybrid demonstration plots planted by seed companies and county Extension personnel, among others. When we experience a year like 2016 in which drought and heat impacted corn performance in many fields, it’s likely we will see some striking differences among hybrids in demonstration plots. When evaluating these plots, it’s important to keep in mind their relative value and limitations. Demonstration plots can be useful in providing information on certain hybrid traits that are usually not reported in state corn performance summaries. The following are some traits to consider when examining hybrid demonstration plots.
PLANT/EAR HEIGHT. Corn reaches it maximum plant height soon after tasseling occurs. Remember that although a taller hybrid may have a lot of "eye appeal," it may also be more prone to stalk lodging in the fall. Unless your interest is primarily silage production, increasing plant height should not be a major concern. Generally later maturity hybrids are taller than earlier maturity hybrids. Big ears placed head high on a plant translate to a high center of gravity, predisposing a plant to potential lodging. The negative effects of stalk rot on stalk lodging in the fall may be greater with high ear placement. Plots that have been subjected to early season (V7 or earlier) defoliation caused by hail or frost often have lower than normal ear height.
STALK SIZE. Generally speaking, a thicker stalk is preferable to a thinner one in terms of overall stalk strength and resistance to stalk lodging. As you inspect a test plot, you will see distinct differences among hybrids for stalk diameter. However, also check that the hybrids are planted at similar populations. As population increases, stalk diameter generally decreases. Also keep in mind that uneven emergence and development may make such comparisons difficult because late emerging plants are “spindlier”.
DISEASES. During the grain fill period, leaf diseases can cause serious yield reductions and predispose corn to stalk rot and lodging problems at maturity. Ear rots can also impact yield and grain quality. The onset of leaf death shortly after pollination can be devastating to potential yield, since maximum photosynthetic leaf surface is needed to optimize grain yield. Hybrids can vary considerably in their ability to resist infection by these diseases. Demonstration plots provide an excellent opportunity to compare differences among hybrids to disease problems that have only occurred on a localized basis. Look for differences in resistance to northern corn leaf blight, gray leaf spot, and diplodia ear rot. Check to see if foliar fungicides have been applied and what crop rotation has been followed. Typically you’ll encounter more severe foliar disease problems in no-till, continuous corn.
STALK ROTS. Hybrids will likely differ widely when faced with strong stalk rot pressure. Begin checking plants about 6 weeks after pollination (at about black layer) by pinching lower stalk internodes with your thumb and forefinger. Stalks that collapse easily are a sure indicator of stalk rot. Remember that hybrids with thicker stalks may be in plots having thin stands.
LODGING. Perhaps as important as stalk rot resistance is the stalk strength characteristics of a hybrid. Sometimes, superior stalk strength will limit the adverse effects of stalk rot. If your demonstration plot is affected by stalk rot in late August and early September, evaluate stalk lodging of the different hybrids. The best time to make this assessment is shortly before plot harvest. Most agronomists characterize plants with stalks broken below the ear as ‘stalk lodged’ plants. In contrast, corn stalks leaning 30 degrees or more from the center are generally described as ‘root lodged’ plants; broken stalks are usually not involved. Root lodging can occur as early as the mid-to- late vegetative stages and as late as harvest maturity. Both stalk and root lodging can be affected by hybrid susceptibility, environmental stress (drought), and insect and disease injury. Root lodging may be associated with western corn rootworm injury. However, much root lodging in Ohio occurs as the result of other factors, i.e. when a hybrid susceptible to root lodging is hit by a severe windstorm. A hybrid may be particularly sensitive to root lodging yet very resistant to stalk lodging. A corn field may exhibit extensive root lodging in July but show little or no evidence of root lodging at harvest maturity in September (except for a slight “goose necking” at the base of the plant). In recent OSU tests evaluating hybrid by plant population interactions, we observed less recovery in certain hybrids when plant populations exceeded 34-35,000 plants/A.
GREEN SNAP (aka "brittle snap") is pre-tassel stalk brakeage caused by wind. The problem has become more common in Ohio in recent years because of the greater frequency of severe wind storms in late June and mid-July. Vulnerability to green snap damage varies among hybrids. Breaks in the stalk usually occur at nodes (along nodal plates) below the ear.
TRANSGENIC TRAITS: Because damage from European corn borer (ECB), western corn rootworm (RW), and western bean cutworm can be very localized, strip plot demonstrations may be one of the best ways to assess the advantages of ECB Bt, RW Bt and WBC Bt corns. The potential benefit of the ECB Bt trait is likely to be most evident in plots planted very early or very late; the potential benefit of the RW Bt trait is likely to be most evident in plots planted following corn or in a field where the western corn rootworm variant is present.
HUSK COVERAGE/EAR ANGLE. Hybrids will vary for completeness of husk coverage on the ear as well as tightness of the husk leaves around the ear. Ears protruding from the husk leaves are susceptible to insect and bird feeding This year there have been reports of hybrids exhibiting short husks in states to the west of Ohio (http://cropwatch.unl.edu/2016/corn-ear-formation-issues-likely-correlated-loss-primary-ear-node). Husks that remain tight around the ear delay field drydown of the grain. Hybrids with upright ears are often associated with short shanks that may be more prone to ear and kernel rots than those ears that point down after maturity. This relationship received considerable attention in 2009 when Gibberella ear rot problems were widespread across the Eastern Corn Belt. However, we’ve observed that differences in ear “orientation” among hybrids can be strongly influenced by growing season and plant density. Also, under certain environmental conditions, some hybrids are more prone to drop ears, a major problem if harvesting is delayed.
The following are some additional points to consider during your plot evaluations:
1. Field variability alone can easily account for differences of 10 to 50 bushels per acre. Be extremely wary of strip plots that are not replicated, or only have "check" or "tester" hybrids inserted between every 5 to 10 hybrids. The best test plots are replicated (with all hybrids replicated at least three times).
2. Don't put much stock in yield results from ONE LOCATION AND ONE YEAR, even if the trial is well run and reliable. Don't overemphasize results from ONE TYPE OF TRIAL. Use data and observations from multiple university trials, local demonstration plots, and then your own on-farm trials to look for consistent trends.
3. Initial appearances can be deceiving, especially visual assessments! Use field days to make careful observations and ask questions, but reserve decisions concerning hybrid selection until you've seen performance results.
4. Walk into plots and check plant populations. Hybrids with large ears or two ears/plant may have thin stands.
5. Break ears in two to check relative kernel development of different hybrids. Use kernel milk line development to compare relative maturity of hybrids if hybrids have not yet reached black layer. Hybrids that look most healthy and green may be more immature than others. Don't confuse good late season plant health ("stay green") with late maturity.
6. Differences in standability will not show up until later in the season and/or until after a windstorm. Pinch or split the lower stalk to see whether the stalk pith is beginning to rot.
7. Visual observations of kernel set, ear-tip fill, ear length, number of kernel rows and kernel depth, etc. may provide some approximate basis for comparisons among hybrids but may not indicate much about actual yield potential. This year we’ve seen differences in tip kernel abortion (“tip dieback” or “tip-back”) among hybrids and heard reports of “zipper ears” (missing kernel rows). Even if corn ear tips are not filled completely, due to poor pollination or kernel abortion, yield potential may not be affected significantly, if at all, because the numbers of kernels per row may still be above normal.
8. Find out if the seed treatments (seed applied fungicides and insecticides) applied varied among hybrids planted, e.g. were the hybrids treated with the same seed applied insecticide at the same rate? Differences in treatments may affect final stand and injury caused by insects and diseases.
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Western Bean Cutworm Infestation and Disease Issues
Reports of ear feeding by western bean cutworm (WBC) have come in at a steady pace over the last few weeks. This is the 3rd consecutive year that we have seen a fair amount of feeding, some of it likely has led to an economic loss. The heaviest feeding has occurred in the Northwest and Northeast corners of Ohio. While it is too late to spray or control at this point (since most larvae are protected in the ear and are getting ready to pupate anyway), growers may need to watch for the development of ear rots. WBC can leave entry or exit holes in the corn husk, which can then provide a nice wound for pathogens like Fusarium and Gibberella. Some of these organisms can then be a further source for mycotoxins, including Fumonisins and deoxynivalenol, AKA vomitoxin.
In some cases, damaged kernels will likely be colonized by opportunistic molds, meaning that the mold-causing fungi are just there because they gain easy access to the grain. However, in other cases, damaged ears may be colonized by fungi such as Fusarium, Gibberella and Aspergillus that produce harmful mycotoxins. Some molds that are associated with mycotoxins are easy to detect based on the color of the damaged areas. For instance reddish or pinkish molds are often cause by Gibberella zeae, a fungus know to be associated with several toxins, including vomitoxin. On the other hand, greenish molds may be caused by Aspergillus, which is known to be associated with aflatoxins, but not all green molds are caused by Aspergillus. The same can be said for whitish mold growth, some, but not all are caused by mycotoxin-producing fungi.
So, since it is not always easy to tell which mold is associated with which fungus or which fungus produces mycotoxins, the safe thing to do is to avoid feeding moldy grain to livestock. Mycotoxins are harmful to animals – some animals are more sensitive to vomitoxin while others are more sensitive to Fumonisins, but it is quite possible for multiple toxins to be present in those damaged ears. If you have damaged ears and moldy grain, get it tested for mycotoxins before feeding to livestock, and if you absolutely have to use moldy grain, make sure it does not make up more than the recommended limit for the toxin detected and the animal being fed. This link provides more information on ear molds and mycotoxin contamination:
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Important Wheat Management Decisions
Among the questions that we have had to answer thus far this season as we get ready to plant wheat are:
1- What are the real dangers of planting wheat after wheat?
2- Now that we have an excellent group of fungicides, can we get away with planting wheat after wheat?
Response: We never recommend planting wheat after wheat or ever wheat after corn simply because these are very bad disease management practices. Several important diseases of wheat (powdery mildew, Septoria, Stagonospora, head scab, and root diseases) survive in wheat stubble and some of the same pathogens that affect wheat also affect corn, therefore, planting wheat after wheat or wheat after corn drastically increases the risk of losses due to diseases. How big of a problem you have will depend on the growing conditions, as well as your disease management program. For mildew, Septoria and Stagonospora, planting a resistant variety and applying a good fungicide should prevent major problems. For head scab, planting the best resistant variety and applying Prosaro or Caramba will help, but will not give you the best results if you plant wheat after wheat or corn and the weather becomes very wet and humid at flowering time. However, the biggest problems with wheat-on-wheat, with fewer solutions, are root diseases such as take-all. Fungicides will not help, and although varieties are known to vary in their susceptibility to take-all, this type of information is not readily available. Old-fashion deep tillage with a moldboard plow will help to control all of the aforementioned diseases, including take-all, but we all know of the detriment of this type of tillage.
Recommendation:
- Just avoid planting wheat after wheat or after corn, soybean should be off early, just wait;
- If you absolutely have to or want to plant wheat after wheat, make sure you plant a resistant variety, but remember, no variety is resistant to all of the diseases you are likely to see in a wheat-on-wheat system;
- Be prepared to apply a fungicide, but this will not help with root diseases;
- If you can, plow under crop residue to remove them from the surface and speed up decomposition.
3- Do we have good, high-yielding scab resistant varieties?
Response: When selecting varieties give priority to head scab resistance. We now have several moderate-to-high-yielding varieties with very good resistance to scab, so you no longer need to choose between yield and scab resistance. In the table below (modified from the wheat performance trial http://www.oardc.ohio-state.edu/wheattrials/), any variety with a scab score similar to or lower than that of Truman, one of the most scab resistant varieties, is considered “resistant (R)” to scab. But remember, “R” for scab is not the same as R for Septoria or powdery mildew. In other words “R” for scab does not mean you will not get scab or have problems with vomitoxin if the weather becomes wet and humid at flowering, it simply means that if you plant a R or MR variety you will get less scab and less vomitoxin than if you plant an S or MS variety, but you will still need to apply Prosaro or Caramba at anthesis (at flowering) if conditions become favorable for scab.
Recommendation: User the table below to identify R and MR varieties and then go to the performance trial results (http://www.oardc.ohio-state.edu/wheattrials/) to check yield and other agronomic traits. Select high-yielding varieties with high test weight, good straw strength, and adequate disease resistance.
R = resistance equal to or better than Truman
MR = not as resistant as Truman but similar to Freedom
S = just as susceptible as Pioneer2545
MS = better than Pioneer2545, but not as resistant as Freedom or Truman.
Other Management Recommendations:
Optimum seeding rates are between 1.2 and 1.6 million seeds per acre. For drills with 7.5-inch row spacing this is about 18 to 24 seeds per foot of row with normal sized seed. When wheat is planted on time, actual seeding rate has little effect on yield, but high seeding rates (above 30 seeds per foot of row) increase lodging and the risk of severe powdery mildew development next spring. During the 2014-2015 with funding from the Ohio Small Grains Marketing Program, we conducted a wheat seeding rate study at three locations in Ohio (Crawford, Pickaway, and Wood Counties). We seeded wheat at 0.25, 0.50, 1.0, 1.5, and 2.0 million seeds/acre. On average, there was a 9 bu/acre yield reduction when seeding rate was reduced from 2.0 to 0.25 million seeds/acre. Economic return tended to be greatest when wheat was seeded between 1.0 to 1.5 million seeds/acre. There is no evidence that more seed is better, it only costs more money.
Plant after the Hessian Fly Safe Date for your county. This date varies depending on state location – starting as early as September 22 for northern counties and as late as October 5 for southern counties. Planting before the Fly Safe Date increases the risk of insect and diseases problems including Hessian fly and aphids carrying Barley Yellow Dwarf Virus. The best time to plant is within 10 days after the Fly Safe Date. Delayed planting may result in reduced winter hardiness from inadequate fall growth. The Hessian Fly Safe Date for each county can be found at:
Ohio fly safe planting date map.
Plant seed 1.5 inches deep and make sure planting depth is uniform across the field. Planting depth is critical for tiller development and winter survival. No-till wheat into soybean stubble is ideal, but make sure the soybean residue is uniformly spread over the surface of the ground. Shallow planting is the main cause of low tiller numbers and poor over-winter survival caused by heaving and freezing injury. Remember, you cannot compensate for a poor planting job by planting more seeds; it just costs more money.
Apply 20 to 30 lb of actual nitrogen per acre at planting to promote fall tiller development. A soil test should be completed to determine phosphorus and potassium needs. Wheat requires more phosphorus than corn or soybean, and soil test levels should be maintained between 25-40 ppm for optimum production. If the soil test indicates less than 25 ppm, then apply 80 to 100 pounds of P2O5 at planting, depending on yield potential. Do not add any phosphorus if soil test levels are higher than 50 ppm. Soil potassium should be maintained at levels of 100, 120, and 140 ppm for soils with cation exchange capacities of 10, 20, or 30 meq, respectively. If potassium levels are low, apply 100-200 pounds of K2O at planting, depending on soil CEC and yield potential. In Ohio, limed soils usually have adequate calcium and magnesium. Soil pH should be between 6.3 and 7.0. Wheat generally does not respond to sulfur on most Ohio soils unless fields are sandy, low organic matter, low CEC, and/or have a history of sulfur response. Sulfur should be applied on responsive soils in the spring unless applying elemental sulfur. The key to a successful wheat crop is adequate and timely management.
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Bacterial Leaf Streak: Another New Corn Disease out West, but not yet in Ohio
Bacterial leaf streak (BLS), a foliar disease of corn caused by the bacterium Xanthomonas vasicola pv. vasculorum, was reported in the US for the first time in Nebraska and has since been found in several other states out west, including Kansas, Colorado, Iowa, Illinois, Minnesota, South Dakota, Texas and Oklahoma. It has not yet been found in Ohio and neighboring states.
BLS has a very close resemblance to other common foliar diseases of corn such as gray leaf spot (GLS). Like GLS, it is characterized by the presence of rectangular-looking lesions on the leaf that are tan, brown, or orange in color. However, lesions of BLS have less well-defined margins and may be narrower and longer than those of GLS. But one of the biggest differences between lesions of BLS and those of GLS is that BLS lesions have wavy margins with a yellow halo that is easily seen when leaves are held up against the light – there is a “windowpane” (translucent) aspect to BLS lesions. Although very early GLS lesions are also translucent when observed against the light, mature lesions are not. BLS lesions first appear on the lower leaves, later moving up the plant, and may occur singly or in clusters, eventually expanding and damaging huge sections of the leaf.
Being a new disease, there are still lots of unanswered questions about BLS, such as how and when it infects the corn plant, how it spreads within and between fields, whether or not it is seedborne, hybrid resistance/susceptibility, its survival from one growing season to another, its impact on grain yield, and the efficacy of tillage and crop rotation as possible management strategies.
Send suspect samples the Cereal Disease Epidemiology and Pathology Lab. @ 1680 Madison Ave, Wooster, Ohio for analysis and diagnosis.
Sources:
http://broderslab.agsci.colostate.edu/corn-bacterial-leaf-streak/
http://cropwatch.unl.edu/2016-CW-News/Images/Corn-Diseases/BLS-GLS-Other-Flyer.pdf
http://cropwatch.unl.edu/bacterial-leaf-streak
http://www.agriculture.com/crops/bacterial-leaf-streak-is-a-new-corn-disease
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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