In This Issue:
- Questions and Answers on Moldy Grain and Mycotoxins Part 3: 2010 Hybrid Selection and Management
- Effects of liming on soil surface pH and herbicide carryover risk
- Nitrogen Fertilizer Considerations for Recently-Limed No-Till Fields
- Fertilizer Recommendations for Multiple Crops in Rotation
- Winter Application of P and K Considerations
- Agronomic Crops Insects Webpage
Q8. What hybrids are we seeing ear rot (and mycotoxin problems) in?
Q9. Which hybrids are not showing these problems? Why?
Q10. Do we plant these hybrids (affected by molds) next year?
Q11. Any way to run strip trials to determine hybrid tolerance?
Answers to Q8-11: Whenever we see major and widespread disease (and in this case, toxin) problems in agriculture it can always be linked to three main factors lining up perfectly: favorable weather conditions, a viable and active pathogen population, and widespread cultivation of a susceptible host. Although we do not know the exact level of Gibberella resistance of the hybrids that are out there, the fact that the problem was so widespread, affecting multiple hybrids over a fairly large area and in multiple states, suggest one of two things: either most of the hybrids are susceptible or a few susceptible hybrids occupied most of the acreage.
Hybrids vary in their susceptibility to Gibberella ear rot and contamination with vomitoxin. Growers have commented this year on differences in ear rots and mycotoxin levels among hybrids. These differences can be attributed to differences in a hybrid’s genetic response to infection by ear rot fungi. Differences among hybrids can also be attributed to what stage of development a hybrid was at when it was exposed to conditions favorable for infection and ear rot development. In addition, certain hybrid traits have been associated with greater ear rot problems including an upright ear position, tight husks, and kernel composition. However, these are secondary traits for disease response and will not solve a problem caused by poor genetic resistance, especially if weather conditions are favorable. Gibberella ear rot is generally most severe when rain and wet weather is prevalent during the 7 to 10 days after silking and temperatures are cooler than normal. In many areas this year, July, the month in which most flowering (silking) and early kernel development occurred, was cooler and wetter than normal.
In a “normal” year, even susceptible hybrids may escape severe ear rot problems by flowering when conditions are less favorable for fungal infection of the silks. However, in our corn testing program this year we observed that differences in the 50% silking date between the earliest and latest maturing hybrids was much smaller than in past years suggesting that weather conditions caused many full season and early-mid maturing hybrids to develop at approximately the same rate. Such synchronous development meant that most hybrids reached the susceptible growth stage (silking) under similar conditions, leading to widespread mold development across all hybrid maturities; even those that would have escaped the problem due to earlier or later maturity in a normal year.
In Ohio, identifying hybrids with good disease resistance is a key step in hybrid selection. However our focus is on the most common diseases, especially the foliar blights and stalks rots, which, year in and year out cause the greatest economic losses. By comparison, ear rots are more sporadic and widespread losses are rare relative to those caused by foliar diseases, but losses can reach 100% if infections are high and grain is rejected due to high toxin levels. Information concerning the ear rot and kernel rot susceptibility of hybrids is not readily available. Ratings of ear rot damage are typically not determined by university/extension hybrid testing programs. Most seed companies also do not have information on disease reactions in their literature and publically available hybrid profile information.
Your own observations from 2009 can be useful when selecting hybrids for 2010. However, corn growers seeking alternatives to 2009 hybrids because of ear molds and mycotoxin problems, need to be careful in assessing whether potential hybrid replacements are indeed less susceptible to ear molds. Low ear rot development and vomitoxin contamination in a single field may not be due to resistance, but to conditions in that field or at that location being unfavorable for disease and toxin contamination. However, if you had two hybrids with similar maturity planted under similar conditions and hybrid A ended up with more ear rot and vomitoxin than hybrid B, then you can safely say that hybrid A was more susceptible than B. In fact, if wet weather after silking was all it took for ear rot to develop in your field, then your hybrid was susceptible. This was certainly the case in many fields in 2009. Consult the seed companies you work with to determine if they have information on the levels of ear rot and mycotoxin problems associated with hybrids they are marketing. Some seed companies may have ratings of ear rot for their hybrids based on data collected from a number of different fields and this information will be more reliable [than observations from a single location strip test] because hybrid response across a wider range of environments is considered.
It‘s important to keep in mind that ear rots are relatively uncommon, and as a result should not be the only trait considered when selecting a hybrid. Other things to consider are: maturity, yield potential, standability and other diseases (gray leaf spot, northern corn leaf blight, stalk rots, in particular). Moreover, no hybrid is resistant and tolerant to all the diseases that may occur and it’s highly unlikely that all diseases will occur in the same year at the same level. Planting hybrids of different maturities will diversify and broaden hybrid genetic backgrounds, and may reduce damage from diseases and environmental stress at different growth stages. No one knows if conditions will be favorable for ear rots in 2010, however, here are a few scenarios to consider when selecting hybrids:
1- Relative to foliar diseases, ear rots are rare, but when they occur, losses may be high because of grain rejection and price discounts due to toxin contamination and poor overall grain quality. In addition, unlike ear rots, losses due to foliar disease can be minimized with a well timed fungicide application.
2- No hybrid is resistant to every pest and disease and has all the desired yield and agronomic traits. Sacrificing yield for disease resistance can affect your bottom-line. However, high yields are of no value if grain is entirely rejected due to high toxin levels (poor quality).
3- Because of our cropping system, spores of Gibberella zeae are always present, and you have no control over the weather, which may or may not be favorable for ear rots in 2010; however, you can control which hybrid you choose to plant.
4- If the hybrid you planted in 2009 was heavily infected and had high levels of vomitoxin contamination, it is susceptible and should be avoided in 2010. There are high-yielding hybrids with good disease resistance out there.
Q12. Besides planting a hybrid package with different maturities and genetic backgrounds, what else could help?
Avoid continuous corn or planting after wheat (the fungus that causes scab in wheat is responsible for Gibberella ear rot). Follow management practices that will promote decomposition and breakdown of corn residues.
Q13. Do you think it is possible to develop a "gibberella" risk model for corn like you have for wheat? A model or tests with Folicur type products in areas with lots of moisture following pollination might be interesting.
In terms of fungicides for ear rot management in corn, this is not something that is done on a regular basis; in fact we do not recall seeing a single recommendation for fungicide application for ear mold control. This is largely because the problem is not common enough to allow for adequate testing of fungicides and adequate application timing will likely be a big concern. Since this disease does not occur every year, a risk prediction model will be useful to help predict when we will likely have a problem like we did this year. However, no such tool is available for corn ear rots.
Q14. How far can Gibberella spores travel?
Q15. Will corn grown in close proximity to wheat fields be more vulnerable to ear rot problems? How will this problem in corn affect head scab and vomitoxin problems in wheat in 2010?
Answers to Q14-15: Staying away from wheat and corn stubble infected with the fungus (Gibberella zeae) will reduce the risk of having ear rot problems in some years. However, when conditions are favorable for several weeks over a wide area as was the case this year, even fields without infection stubble may still have ear rot problems. Here in the Corn Belt, Gibberella spore can be collected in traps in the air throughout the field season. The fungus survives the winter in winter-hardy spore-producing structures (perithecia… small black dots on corn stalk [especially near the node], wheat stubble, and scabby heads). These structures remain on the stubble and produce spores throughout the field season. Spores (ascospores) are released (ejected) and carried by wind for miles. Ejection is affected by humidity, temperature and light intensity; conditions that are almost always present in the Corn Belt. In the field, especially if it rains a lot, instead of being ejected, spores ooze out onto the surface of the stalk or stubble and are then splashed around by rain… hence, the relationship among high amounts of stubble in the field, rainfall, and head scab or ear mold. So, the risk increases greatly if the stubble is already in the field. However, even if spores do not come directly from within the field, they can move easily from one neighboring field to another by wind, causing scab and ear mold problems, especially if the weather is wet and humid for an extended period like it has been this year. When the weather is wet and humid for most of the season, it does not take a lot of spores to create a problem… the same rain that wash spores from the air, help them to germinate and penetrate, causing problems like we’ve seen this year.
The availability of spores has never been the limiting factor for disease development here in OH, our growing season and cropping systems ensure that spores are always available. What is limiting though is weather conditions that are favorable for EXTENDED periods… that’s why disease is so spotty. What the current ear rot epidemic means for scab next year?…. only time will tell. More spores mean higher risk for head scab, but if the late-spring and early-summer conditions are dry, we may not have a problem with head scab.
Q16. Is the widespread use of conservation tillage and no-tillage increasing disease problems, such ear rots, because there is more residue available that harbors disease inoculum?
Q17. Should corn growers affected by ear rots this year switch to conventional tillage to manage this problem?
Answers to Q16-17. As noted above, the crop residues associated with reduced tillage, especially no-till, can increase the potential for ear rots, as well as other corn diseases like gray leaf spot. However, for conventional tillage to be effective in consistently reducing disease, it would have to be practiced widely to ensure that fungal spores do not drift into a conventionally tilled field from a neighboring no-till corn field. Nevertheless management practices that enhance corn residue breakdown shredding stalks, shallow tillage) may promote decomposition of residues and thereby reduce disease inoculum.
Q18. Is the Bt trait in transgenic corn hybrids contributing to ear rot problems, especially in no-till systems, by slowing breakdown of residues that harbor disease inoculum?
In recent years, there have been questions about the persistence of corn stover and in particular whether Bt hybrids produced stover that breaks down more slowly. It seems we have more problems with stover when planting in high yielding corn on corn fields than before. Theoretically this could be due to a change in the corn stover composition in Bt lines, increased stalk strength or some impact on the soils microbial community that inhibited the breakdown.
During the past two years several papers have been published addressing the issue. One study, conducted by a team of USDA scientists in South Dakota evaluated the breakdown of Bt and non Bt corn stover from two pairs of hybrids from different companies. They did not detect any differences in the decomposition rates over 384 days due to the Bt genes (both cry1Ab and cry3Bb1 genes) and also did not detect any difference in the stalk strength measurements they conducted. They also did not find any consistent compositional differences that would impact stover decomposition. Also, they compared stover sample decomposition in the root zone of both Bt and conventional hybrids and found they actually decomposed faster in the root zone of the Bt hybrid. Another study conducted in Nebraska monitored the decomposition of Bt and non Bt residues from two hybrid pairs for 23 months. It concluded that there was no difference in decomposition rates due to the Bt genes. These results suggest that Bt genes are not the reason for the perceived slower breakdown of stover. This answer adapted from the following reference: Roth, G. 2009. Bt Corn Stover ...Does it Persist Longer. Penn State Field Crop News Online http://fcn.agronomy.psu.edu/2009/fcn0926.cfm#e
Other management practices may also increase crop residues e.g. higher seeding rates that lead to greater plant stands can result in more residue after harvest. However, higher seeding rates contribute to higher yields. It may be that improvements in stalk quality (thick stalk rinds, etc) that allow corn to tolerate higher plant populations by enhancing standability and reducing stalk lodging also slow stalk deterioration after harvest.
Moldy Grains, Mycotoxins and Feeding Problems http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm
Gibberella ear rot of corn http://www.agry.purdue.edu/ext/corn/news/others/2009/Gibberella-1002.pdf
Storage rots of corn:http://ipm.illinois.edu/diseases/series200/rpd206/index.html
Mold and mycotoxin feeding problems in livestock feeding: http://www.das.psu.edu/research-extension/dairy/nutrition/pdf/mold.pdf
Crop Maturity & Harvest Issues (see “Grain Drying and Storage”) http://www.agry.purdue.edu/ext/corn/cafe/harvest/
And the Purdue Grain Lab directly: http://extension.entm.purdue.edu/grainlab/index.php?page=home.php
Storage and handling recommendations for flood damaged corn: http://www.extension.org/pages/Storage_and_Handling_Recommendations_for_Flood_Damaged_Grain
2009 post harvest tips for later maturing corn:http://www.ag.ndsu.nodak.edu/abeng/Corn%20Presentation/Post%20Harvest%20Tips%20for%20Later%20Maturing%20Corn%20Oct2009.doc
Legal issues related to grain quality and contracts, from the AgLaw Blog (http://ohioaglaw.wordpress.com/) of Peggy Hall, OSU Extension: http://ohioaglaw.wordpress.com/2010/01/25/guest-blog-vomitoxin-in-corn-–-legal-ramifications-for-producers-and-buyers/
Applying large amounts of lime can result in fairly rapid and substantial increases in soil pH at shallow soil depths. Although the lime eventually moves deeper into the soil profile, and the pH at the soil surface equilibrates and decreases somewhat, the temporary increase in pH can have consequences for the persistence and activity of herbicides applied this spring. A number of herbicides can be more active as soil pH increases above 7, including atrazine, metribuzin, and chlorimuron. Increased activity can be a good thing relative to weed control, but can also increase the risk of crop injury where other factors are favorable for injury to occur.
The increased carryover risk at high pH is the more important issue here. Our main caution is to possibly avoid use of chlorimuron-containing herbicides (Canopy, Cloak, Valor XLT, Envive, Enlite) where lime was applied this winter and the pH at the soil surface is above 7. The first several months after herbicide application are important for herbicide degradation. Degradation of chlorimuron will be inhibited at the high pH that can result from liming, and lack of substantial degradation during these first few months increases the carryover risk.
Statements from herbicide labels regarding high soil pH include the following:
Isoxaflutole (Balance Flexx, Corvus, Prequel) – labels indicate the high soil pH is one of the conditions that can increase risk of crop injury
Hornet, Python, SureStart – do not apply where soil pH is greater than 7.8
Metribuzin (corn) – do not apply where soil pH is 7.0 or greater
Authority Assist – within a rate range for a given soil type, use the lower rates where soil pH is greater than 7
Authority MTZ – do not apply to soils with pH greater than 7.5
Metribuzin (soybeans) – injury risk increases where soil pH is more than 7.5
Lime is an important input for many Ohio fields, and for producers with no-tillage cropping systems, the surface application of lime brings up additional management considerations before the spring corn planting season.
Lime is not terribly soluble in water (think of the many piles of lime seen in fields over sometimes long periods of time, they do not shrink or dissolved much in precipitation events). Tillage is a good method for working lime into the soil, but a layer of high pH material may exist on the soil surface in no-till fields. High pH levels combine with ammonium/urea-based fertilizers in a chemical reaction converting NH4+ (ammonium) to NH3 (ammonia gas) which can escape to the air, and provide no nutritional benefit to crops. As air and soil temperatures increase in the spring and summer, this process runs faster and N losses increase accordingly. This volatilization process is most exacerbated with surface application of urea and 28% UAN on recently limed fields on a warm day. This process also occurs to a smaller extent in ammonium sulfate, much smaller in MAP and DAP, and significantly even less with ammonium nitrate.
To avoid surface volatilization losses with recently-limed no-tillage fields, avoiding surface urea and UAN is key. Instead, band starter materials if UAN or urea is used, and knife-in sidedress applications of UAN being sure that the application equipment is set to inject the material in the slot through the lime layer and into the soil where it does the most good for crops. This sort of application also has the benefit of reducing the possibility of surface losses or runoff in rainfall events.
A common question this time of year is how one would decide broadcast rates of phosphorus (P) and potassium (K) for multiple years and crops in rotation while still aware of the factors of high fertilizer prices, rented vs. owned land, and buildup vs. maintenance. Since the Tri-State Fertilizer recommendations for P and K are based upon a buildup-maintenance approach, a producer may make one application that is applicable for the next three to four cropping years in a corn, soybean and wheat system. This would allow a producer to purchase a three to four year’s P and K supply when prices are low to moderate or only for one year, if prices are unusually high and are anticipated to drop in the future. As for other nutrient management programs, a soil test needs to be taken to determine soil levels for P and K. (For information on taking and preparing soil samples, see our Factsheet here:http://ohioline.osu.edu/agf-fact/0206.html).After the soil test, think about your proposed agronomic crop rotation.
In a multiyear nutrient program, the P and K recommendations should first be determined for each crop separately and then add the recommendations for each cropping year to get the total P and K to be applied. For example, let’s consider a field with soil test P of 15 ppm (or 30 lbs/acre) with a corn-soybean-wheat rotation. From the Tri State Fertilizer Recommendations, we will use Tables 13, 15, and 16 for the P rates for a 160, 50, and 70 bu yield potential for corn, soybean and wheat, respectively. The separate recommendation for each crop would be 60, 40, and 95 lb P/acre, respectively. The sum of the three crops is 195 pounds per acre. Thus the producer may apply 195 pounds of P per acre to fulfill the requirements of the three crops for the next three years. Or if P prices are high or the producer may lose the rent ground after the corn year, only apply enough P for the coming corn crop and re-evaluate price and rent environments before applying the rest. In this situation the corn and soybeans were at crop removal but the wheat with a larger critical level than corn or soybeans was actually a buildup recommendation. Since the wheat was below the critical level, another soil test may be considered prior to its planting if the corn and soybean yields were unusually larger than normal. However, if the soil P levels were at 100 lb of P, recommendations would have been zero for the next three years. In summary, a nutrient program for multiple crops in a rotation may add flexibility to when P and K need to be applied using a buildup-maintenance approach.
More details and commentary about this topic may be found in the Tri State Fertilizer Recommendations online at:http://ohioline.osu.edu/e2567/index.html and the Ohio Agronomy Guide, found here: http://ohioline.osu.edu/b472/0004.html.
A lot of fertilizer has been going on fields in the last couple of weeks, and though it is certainly not an optimal time, there is one advantage to application now with the wet autumn in 2009: compaction is minimized on frozen soils compared to saturated ones. However, just like manure applications on frozen or snow-covered ground, the possibility of commercial fertilizers moving off-site in runoff increases greatly when P and K do not migrate into the soil profile (perhaps more so since commercial P and K sources are water soluble by design). Environmental concerns notwithstanding, fertilizer inputs are a significant part of a crop enterprise budget, and losses from the field equate to losses on a balance sheet.
Consider if an application of P and K to particular fields is even necessary by checking a recent soil test against the Tri State Fertilizer Recommendations for the planned crop and crop rotation. Also strongly consider an application setback from sensitive areas (ditches, waterways, streams, etc.) of at least 200 ft, especially on sloping land where surface movement is accelerated. For more information, there is an Extension Fact Sheet on phosphorus best management practices available online: http://ohioline.osu.edu/agf-fact/pdf/0509.pdf.
As we begin this New Year, we would like to remind growers about our new Agronomic Crops Insects webpage at http://entomology.osu.edu/ag/. Although we have previously mentioned this webpage in the C.O.R.N. newsletter, we have added much since that time and now consider it a more “finished” product. However, we will continue to add and update the information as needed and will inform you of major changes or additions. Currently, the webpage has information on the major insect pests of alfalfa, corn, soybean, and wheat, including biological information, insecticide recommendations including Bulletin 545, the Agronomic Field Guide Bulletin 827, and various insect photographs.
We have 14 newly revised insect fact sheets available on the site, and have recently added 15 video presentations ranging from 10 to 45 minutes on various insect pests and issues related to insect pest management. These video presentations are similar to those we present at meetings throughout the year, but these videos pertain more to a single topic or insect. Finally, we have various links to other information available both at Ohio State University and across the Midwest.
- Glen Arnold (Nutrient Management Field Specialist),
- Roger Bender, ret. (Shelby),
- Greg LaBarge (Agronomy Field Specialist),
- Les Ober (Geauga),
- Mike Gastier (Huron),
- Mark Koenig (Sandusky),
- Ed Lentz (Hancock),
- Jeff McCutcheon (Morrow),
- Wes Haun (Logan),
- Bruce Clevenger (Defiance),
- Harold Watters, CPAg/CCA (Agronomy Field Specialist),
- Suzanne Mills-Wasniak (Montgomery)