C.O.R.N. Newsletter: 2021-37
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Low Vomitoxin Levels in Corn but Rain and Delayed Harvest Could Change this Picture
After walking more than 40 corn fields and sampling more than 3,500 ears, we believe that Gibberella ear rot (GER), and consequently, vomitoxin levels likely will be much lower this year than they were last fall. This is because conditions during the weeks after silking were considerably less favorable for the disease to develop and the toxin to contaminate grain this year than last year. However, as is often the case, there were a few exceptions. We found low levels of GER in (sentinel-type) plots and research fields deliberately planted with hybrids that are highly susceptible to the disease, and these plots/fields will likely yield grain with some level of vomitoxin contamination (we are still processing our samples). Averaged across 10 locations, the incidence of GER on a susceptible hybrid ranged from 10 to 20%, i.e., 1 to 2 out of every 10 ears had visual symptoms of GER, and on average, less than 5% of the surface area of affected ears showed symptoms of the disease.
GER tends to be most severe, and the crop is usually as greater risk for vomitoxin contamination, when infections occur early (during silking), before the ears mature and grain dries down, and conditions are warm and wet during the first three weeks after silking. However, it is not uncommon for grain to become contaminated with vomitoxin as a result of infections occurring late in the season. This is particularly true when harvest is delayed by frequent rainfall, hybrids are susceptible, and ears dry-down in an upright position. Water collects at the base of upright ears, creating conditions suitable for the fungus to enter and infect the ear from the base upwards.
It is not always possible to tell which fields were planted with GER susceptible hybrids, because this information is not readily available in all seed catalogs. However, it should be noted that no hybrid is 100% resistant or immune to GER. As a result, all fields that have not been harvested and have been exposed to rain over the last several days are at risk for Gibberella and other ear rots (including Trichoderma) and grain contamination with mycotoxins. Peel back the husk and examine about 10 ears in each of 8 to 10 sections (approximately 50-ft-long stretches of rows) spread out across the field for symptoms of GER either at the tip or at the base of the ear (see pictures). This will give you an idea of whether your field is affected by GER and vomitoxin will likely be a concern. Where possible, handle and store grain from severely affected fields separately from grain harvested from healthier fields (fields harvested before the rains with little or no GER).
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Still a Big Window for Fall Herbicide Treatments
Many growers know the benefits of fall herbicide treatments, and like how fields look the following spring. We know that it’s not always possible to complete harvest and then still find the time, weather, or field conditions to get herbicides applied. This is just a reminder that we have a lot of time yet to apply herbicide this fall. In OSU weed science plots, we have typically applied most of our fall herbicides in early to mid November, but have occasionally applied into December and maintained effectiveness on winter annuals and dandelion. When we get a period of very cold weather in later November, there is typically a decline in dandelion and thistle (change from green to purplish) so that control decreases, but we seem to still control the winter annuals. So we should still have up to 6 weeks yet to apply herbicides, although we may be up against increasingly wet field conditions.
Following our previous article on fall herbicides, where we discussed how to proceed without glyphosate, we were told that 2,4-D prices have increased considerably, and supply may be short. There are apparently some ongoing adaptations of fall herbicide programs to minimize use of 2,4-D and glyphosate both, and we are getting questions about using dicamba as the base for treatments instead of 2,4-D. Among all of the herbicides we have used in fall, dicamba seems to be affected by cold weather the most and require considerable help from another herbicide to obtain comprehensive control. Some considerations based on our research:
- Do not apply dicamba alone – it won’t be effective enough and misses some key weeds (same can be said for 2,4-D which misses chickweed)
- When using dicamba as a base to mix with lower rates of 2,4-D or glyphosate, use a dicamba rate of at least 0.5 lb ai/A. In the mixtures mentioned below, use a rate between 0.25 and 0.5 lb ai/A, depending upon how effective the mix partner is.
- Mixtures of dicamba and metribuzin can be “good enough”. Our most typical mix has been 0.25 lb ai dicamba plus 0.38 lbs ai metribuzin. We have not tested mixtures of dicamba with simazine.
- We have tested mixtures of dicamba with some ALS inhibitors (Harmony Xtra and Express) in the fall in wheat, and they have worked well. We have not tested these combinations in the fall in a fallow situation but our assumption is that they will provide adequate control there as well. This would include combinations of dicamba with products containing tribenuron and/or rimsulfuron, or chlorimuron.
- In our research, we do not use adjuvants with dicamba/2,4-D. If they are mixed with glyphosate, we add AMS. Treatments containing metribuzin, simazine, and the ALS inhibitors are usually applied with crop oil concentrate.
Different topic – the shortage or anticipated shortage of various products has caused some growers to buy and take possession of herbicide this fall, including filled shuttles, for use next spring (maybe this is a common practice for some growers – we don’t follow how herbicide moves around). Be sure to know the storage requirements for situations like this – minimum temperature, etc. Also be aware that changes in the product – separation or settling out of certain components – can occur over time, and there may be recommended procedures to prevent this or restore the integrity of product at the end of long storage. Check with manufacturer and distributor representatives for the appropriate information.
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Take the Test to Beat the Pest
One of the main reasons soybean cyst nematode (SCN) remains the most economically important pathogen of soybean is that it can cause yield loss between 15 and 30% with absolutely no visible symptoms. Resistance to SCN remains the most effective management strategy when rotating to a non-host crop is not an option. The predominant source of resistance in most commercially available soybean cultivars comes from Plant Introduction (PI) 88788, which confers resistance to SCN Type 0 (formerly race 3). Soybean varieties labeled ‘SCN-resistant’ most likely have resistance from PI 88788. The use of the same source of resistance over the past 20 years has placed selection pressure on
SCN populations resulting in a shift in virulence, leading to adaption to now infect PI 88788-derived resistant soybean cultivars. In other words, nematodes reproduce at higher levels than before on soybeans developed with PI 88788 resistance.‘What’s your number,’ Ohio? Since 2018, with funding from the soybean check-off through the Ohio Soybean Council and The SCN Coalition, and in collaboration with OSU Extension Educators and growers, we extensively sampled soybean fields in Ohio. To date, a total of 741 soil samples from 57 counties in Ohio were submitted for SCN testing (Fig.1). For most samples, SCN was either not detected (38% of samples) or present in very low numbers (23% of samples with less than 200 eggs/100 cc soil), however, 38% had SCN above 200 eggs/100 cc soil. Some fields (8%) had levels above 5,000 eggs/100 cc soil, which we know can significantly reduce soybean yield (Fig. 2). The number of SCN found in the soil sample will determine the best management plan for that field (Table 1).
Can SCN populations reproduce on the most commonly used sources of resistance (i.e., Peking [PI 548402], PI 88788, and Hartwig [PI 437654])? Samples with high SCN numbers were used to determine which source of resistance was still effective in limiting SCN reproduction in a greenhouse assay (i.e., SCN Type test). A resistant cultivar will allow less than 10% SCN reproduction compared to a susceptible cultivar. A total of 61 SCN Type tests have been completed so far, each from an SCN population from a single field. Only 10% of these samples were SCN Type 0, for which soybean cultivars with any source of resistance will be effective. More than 85% of these SCN populations in Ohio can reproduce on PI 88788 (SCN Type 2) at levels from 30 to 60% of a susceptible soybean. There are few SCN populations that can reproduce on Peking (SCN Type 1) at very low levels (10 to 30% of susceptible). Hartwig remains highly resistance to our SCN populations, but it is not easy to find soybean cultivars with this source of resistance. And now what? Soybean cyst nematode is silently gaining territory in Ohio as SCN numbers are rising. The ability to reproduce on soybean cultivars with ‘SCN-resistance’ will lead to an imminent loss in our battle to protect Ohio soybean production. To take action, we need to know our numbers. Managing SCN begins with an adequate and correct soil sample. The SCN Coalition has launched its next phase of raising awareness of SCN distribution and its virulence profile in the U.S. We are excited to continue sampling soybean fields in Ohio to test for SCN with funding from the Ohio Soybean Council and The SCN Coalition. Our goal is to sample more soybean fields, targeting those that have consistently been yielding low, under continuous soybean or double crop, and with weed issues. Fall is a great time to sample for SCN and we are excited to help with this task by processing up to TWO soil samples, per grower, to be tested for SCN, free of charge. For more information on how to sample for SCN and where to send these samples, please visit our sampling article in this issue ‘Collect Fall Soil Samples for SCN.’
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Collect Fall Soil Samples for SCN
Soybean cyst nematode (SCN) is a major soybean pathogen that continues to spread throughout Ohio. Yield reduction commonly occurs with no visible above-ground symptoms. To know if this nematode is present in a field, soil samples must be properly collected and handled. The presence of SCN in a field, but more importantly, the SCN numbers will determine the best management strategy.
When should you sample for SCN? Fall is the best time to sample for SCN. After soybean plants are harvested, a soil test will reveal if SCN is present and at what levels. Knowing your SCN numbers in fall will give enough time to plan for next year and to identify the best management practices([more on SCN management here). Furthermore, if you are planning to collect samples for soil fertility, a subsample can be used for SCN testing. Please see Dr. Lindsey’s article on fall soil fertility sampling.
How should you collect soil samples for SCN? Different sampling strategies can be used to collect soil sample for SCN testing, including those used for soil fertility sampling. We strongly recommend using a 1-inch-diameter cylindrical probe to collect 15 to 20 (more is better) soil cores, 8 inches deep, for every 20 acres. Collect these soil cores in a zig-zag pattern across an area similar in soil texture and cropping history. Thoroughly mix the composite sample by gently breaking the soil cores. At this point we advise splitting the composite sample in two: one for soil fertility and one for SCN testing. Place 1 pint (approx. 2 cups) of soil in a labeled plastic bag and ship it to the lab as soon as possible. For more information on how to collect soil sample for SCN testing visit here.
How should you handle your SCN soil sample? Your soil sample is alive, therefore you must handle it carefully. To keep the nematodes alive, store your SCN samples in a cool, dark place out of direct exposure to sunlight and ship them to the lab as quickly as possible.
Where should you send your soil sample for analysis? There are several SCN testing labs in the North Central Region, however, with funding from the Ohio Soybean Council and The SCN Coalition, growers may submit up to two soil samples to my lab, and we will test them for SCN free of charge. We suggest collecting one composite sample from a low- and another from a high-yielding area, as this will allow us to determine whether SCN is the reason for low yield. Download and complete this Soil Sample Submission Form and mail your samples to:
OSU Nematology and Soybean Pathology Lab
Attn: Horacio Lopez-Nicora, Ph.D.
110 Kottman Hall
2021 Coffey Rd.
Columbus, Ohio 43210
lopez-nicora.1@osu.eduFor more information on SCN sampling and management visit our factsheet here.
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Fall Soil Fertility Sampling
The fall is a great time to collect soil samples to identify any needs for lime, P, and K. Soil sampling either this fall or spring 2022 will be particularly important with the high costs of agricultural inputs. If soil test P and soil test K levels are within the maintenance range it is extremely unlikely that there will be a yield response with additional fertilizer application. For more information on the state soil fertility guidelines, see the newly revised ‘Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa available here: https://agcrops.osu.edu/FertilityResources/tri-state_info
Keep in mind, when you collect a soil sample for fertility analysis, you can also collect soil for soybean cyst nematode (SCN) analysis. Please see Dr. Lopez-Nicora’s article on collecting soil samples for SCN in the fall.
When should you soil sample? Consistency is important. Sampling at the same time of the year the field was last sampled is ideal to help track trends. The fall after harvest or the spring before planting is generally the easiest time to sample. Fall sampling is preferred if lime applications are anticipated.
How frequently should you soil sample? Most fields should be sampled every three to four years.
What kind of sampling strategy should you use? The three primary soil sampling strategies include: 1) whole field sampling (one representative sample per field), 2) zone sampling (field sub-divided into geo-referenced zones based on soil texture, landscape position, yield potential, or some other factor), 3) grid sampling (field sub-divided systematically in a grid pattern). Each sampling strategy has limitations and strengths (Figure 1). Zone and grid soil sampling will provide the highest level of information from soil test results as fields can have a great deal of variability of soil test P, K, and pH (Figure 2). However, these two methods are also the costliest and require a greater sampling effort. With the current high fertilizer prices, this extra effort in soil sampling will typically pay off in fertilizer and lime savings.
How deep should you sample? Sampling depth consistency is extremely important. The guidelines in the Tri-State Fertilizer Recommendations are based on a 0 to 8-inch soil sample. Samples collected shallower or deeper than 8 inches will not align with the guidelines due to nutrient stratification, which depends on multiple factors (tillage, soil texture, fertilizer placement, etc). How should I handle my soil samples? Soil samples should be sent to a laboratory as soon as possible. Excessive heat or prolonged storage in a bag can compromise the soil test results. Soil samples can also be air-dried.
Where should I send my soil for analysis? There are many commercial soil testing laboratories located within Ohio and surrounding states. The North Central Regional Research Committee (NCR-13) has developed methods that work best on soils in the north central region. Laboratories that test Ohio soils should use these procedures. You may also want to choose a laboratory that provides lime and fertilizer recommendations based on the Tri-State Fertilizer Recommendations bulletin.
For more information on soil sampling techniques, including the importance of soil sampling and scheme (starting at minute 1:11), how to use Google tools to create grid soil sampling points (starting at minute 11:19), and how to begin sampling your fields (starting at minute 20:35), please see: https://www.youtube.com/watch?v=6bKW6GRO6Cg
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2021 Ohio Soybean Performance Trial: Sandusky County, Union County, and Preble County Yield Results Available
Three out of six of the 2021 Ohio Soybean Performance Trial locations have been harvested, including Sandusky County, Union County, and Preble County. Results can be found here: https://stepupsoy.osu.edu/sites/hcs-soy/files/2021_OSPT_3%20location%20yield.pdf
We will continue to update this website with additional locations as harvest progresses (hopefully, soon with some dry weather.)
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Ohio Certified Crop Adviser Pre-Exam Preparation
The Certified Crop Adviser (CCA) Exam Training program, delivered by OSU Agronomic Crops Team members, will be available online
and in-person to help you prepare for the 2022 CCA exams. An in-person two-day training class will be held on January 12 & 13 from 9 AM to 5 PM each day at the Shelby County Ag Building, 810-820 Fair Rd, Sidney, Ohio 45365. The content is a great basic agronomy course covering information to prepare for the local CCA exam. The cost for this program is $250/person. Registration includes the publications below, lunch both days, and other program materials. Class size is limited to 25, and registration closes on December 20, 2021. Publications provided with the in-person option:
- Ohio Agronomy Guide
- Ohio, Indiana & Illinois Weed Control Guide
- The Ohio Corn, Soybean, Wheat and Forages Field Guide
- 2020 Tri-State Fertilizer Recommendations
- Modern Corn & Soybean Production
Course contact:
Lee Beers, CCA
Ohio State University Extension
Beers.66@osu.edu
330-638-6783New this year is an online option. The self-paced recorded sessions offer a convenient option for those unable to attend the in-person session. Both the in-person and online options will help participants study for the performance objectives for the international and state CCA exams. Registration for the online course closes on November 15, 2021. Once registered, participants will have access to the course until February 15, 2022. The cost for the online course is $155/person. Publications are not included but can be purchased separately through your local Extension office or at https://extensionpubs.osu.edu.
Secure online registration for both the in-person and online options via credit card, debit card, or check is available on the Ohio AgriBusiness Association website: https://go.osu.edu/CCA2022.
The Local and International Exams are proctored online tests. You must pass both exams to obtain Certified Crop Adviser status. The international exam is available on-demand, but the local exam is only available during the exam week of February 2 through February 9, 2022. Registration for the February local CCA exam closes on January 5, 2022. You can register for both exams here: https://www.certifiedcropadviser.org/exams/registration.
For more information about the CCA program, visit https://www.certifiedcropadviser.org/about-program
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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Disclaimer
The information presented here, along with any trade names used, is supplied with the understanding that no discrimination is intended and no endorsement is made by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
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