C.O.R.N. Newsletter: 2017-19
-
1st Generation European Corn Borer Management in non-Bt Corn
European corn borer (ECB) was once our most important corn insect, but its population has decreased over the past 20 years, likely due to Bt-corn that provides excellent protection. For this and other various reasons, many farms have switched to corn that does not contain Bt proteins to control ECB and other caterpillar pests. Keep in mind that ECB is not an extinct species—we can find ECB still flying around. This year, we have seen ECB feeding in conventional corn.
ECB has 2 generations per year. Currently, we are seeing larval feeding on the leaves and in the whorl. Soon, and if not already, these larvae will tunnel through the stalk where they will usually continue to feed and pupate. Adults will emerge in late July-early August.
Growers of conventional corn should inspect their fields for the characteristic shot hole damage (see figure). If found, you may see larvae feeding in the whorl—you may need to pull the whorl out of a couple of damaged plants to check. Although challenging, larvae in the whorl that are in the 3rd instar or less (usually no bigger than 1/2 of an inch) are still vulnerable to insecticide application.
If the larvae are not in the whorl, they may have died, or worse, tunneled in the stalk. Look for the appearance of sawdust like frass, which ECB larvae leave on the outside while tunneling. Once they bore into the stalk, then control is difficult, if not impossible.
As a guide, we recommend treatment for 1st generation ECB when 75% -80% of the corn shows shot hole damage, and that larvae can be seen in the whorl (i.e. have not bored into the stalk). There are many chemicals that can control ECB (see our bulletin: https://agcrops.osu.edu/publications/control-insect-pests-field-crops-bulletin-545), although granular forms tend to be more effective than liquid.
-
Hay and Straw Barn Fires a Real Danger.
We’ve heard of one barn fire here in Ohio this morning and a lot of hay was put up last Thursday ahead of the rain. Much of the hay was wetter than it should have been for safe dry hay storage. Watch those moist bales very carefully for the next two to three weeks! Use a hay temperature probe and monitor the internal temperature of the hay during these first three weeks after baling.
Usually, we think of water and moisture as a way to put a fire out, but the opposite is true with hay and straw, which when too wet can heat and spontaneously combust. This is more common with hay than straw because there is more plant cell respiration in hay. When baled at moistures over 20% mesophilic bacteria release heat-causing temperatures to rise between 130⁰F and 140⁰F. If bacteria die and bales cool, you are in the clear but if thermophilic bacteria take over temperatures can raise to over 175⁰F.
The moist bales should be kept outside or in a well-ventilated area. Don’t stack the moist bales, because that prevents the heat and moisture left in the hay from escaping. It is normal for hay to go through a “sweat” in the first few days after baling. Internal temperatures of 110° F in the first five days after baling are quite common in our region and are not a big concern.
Assessing the Fire Risk
- Most hay fires occur within the first six weeks after baling
- Was the field evenly dry or did it have wet spots
- Were moistures levels kept at 20% or less
- If over 20% was hay preservative used
Monitoring at-risk Hay
If you are concerned that your hay or straw may be a fire risk, you should monitor it twice a day for the first six weeks or until low temperatures stabilize. Ideally, temperatures are taken from the center of the stack or down about 8 feet in large stacks.
If you have a long probe thermometer it can be used but some homemade options are available. A ¾ inch pipe with the ends closed into a point and 3/16 inch holes drilled in the bottom 4 inches can work well, lower a thermometer on a string or the sensor wire of a thermometer into the pipe. The sensor on a long wire can work very well once in place you can read temperatures without removing it. Leave the thermometer in the stack for 15 minutes to get an accurate reading.
Another cruder option is to stick a 3/8 pipe into the stack and pull out twice a day if the pipe is too hot to hold in your hand, you are at risk for a fire. Be very cautious when taking hay temperatures if the hay gets hot and a cavity burns out underneath you can fall in. Use planks to spread out your weight and have someone nearby in case you fall in a burned out pocket. Using a harness and tying yourself off would be even better as a safety measure when checking bales.
Hay bale temperatures of 120° to 130° F will likely result in mold growth and will make the protein in the hay less available to animals. While those temperatures are not high enough to cause hay fires, the concern is if the mold growth continues and pushes temperatures upward into the danger zone.
If the temperature in the hay continues to rise, reaching temperatures of 160° to 170° F, then there is cause for alarm. At those elevated temperatures, other chemical reactions begin to occur that elevate the temperature much higher, resulting in spontaneous combustion of the hay in a relatively short period of time. If the hay temperature is 175° F or higher, call the fire department immediately, because fire is imminent or present in the stack.
Critical Temperatures and Actions to Take
Temperatures (⁰F)
Condition and Action
125°
No Action Needed
150°
Hay is entering the danger zone. Check twice daily. Disassemble stacked hay bales to promote air circulation to cool the hay outside.
160°
Hay has reached the danger zone. Check hay temperature every couple of hours. Disassemble stacked hay to promote air circulation to cool hay have fire department present while unstacking from here on.
175°
Hot pockets are likely. Alert fire service to possible hay fire incident. Close barns tightly to eliminate oxygen
190°
With the assistance of the fire service, remove hot hay. Be aware the bales may burst into flames keep tractors wet
200° +
With the assistance of the fire service, remove hot hay. Most likely, a fire will occur. Keep tractors wet and fire hose lines charged in the barn and along the route of where bales are to be stacked.
If you are in the risk zone and there is machinery or livestock also in the barn, remove them before removing the hay for safety. Also call the fire department when you are in the risk range. They would much rather be present and not have to put a fire out them have to call mutual aid when your entire barn is on fire. For more information on Preventing Fires in Baled have and straw visit- http://articles.extension.org/pages/66577/preventing-fires-in-baled-hay-and-straw
Extreme caution needs to be taken when monitoring hot hay. Please read the article below for additional safety guidelines and procedures for monitoring hot bales and for preventing and controlling hay fires:
Hay Fire Prevention and Control, Virginia Cooperative Extension http://www.pubs.ext.vt.edu/442/442-105/442-105.html
References:
Preventing fires in baled hay and straw. (2012). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from http://www.extension.org/pages/66577/preventing-fires-in-baled-hay-and-straw.
Hay Fire Prevention and Control, Virginia Cooperative Extension http://www.pubs.ext.vt.edu/442/442-105/442-105.html
-
Determination of ear size in corn well underway
During the past two weeks, corn has “exploded” in growth in many Ohio fields. Under favorable growing conditions corn plants can grow nearly three inches per day between V8 (i.e., the eight leaf collar stage) and V15. However, there is considerable variability in corn development across the state, between neighboring fields, and within fields. Most of this variation can be attributed to planting date differences. Corn planted in mid to late April is at or beyond V13 whereas corn planted in early to mid-June is usually at stages no later than V3-4. Variation in growth and development is also related to differences in rainfall accumulation. Within fields, corn subject to ponding and prolonged anaerobic conditions often appears chlorotic and stunted and may be one to three leaf collar stages behind corn growing nearby under more favorable drainage conditions. Keep in mind that canopy and plant height can be quite variable at any given collar stage (Table 1).
What impact will these varying environmental conditions have on kernel numbers and ultimately grain yield? As early as the V5 or V6 stage, the tassel and the uppermost (harvestable) ear are initiated (Nielsen, 2007 and Abendroth et al., 2011). Kernel row numbers per ear may be established as early as V8. Kernel row numbers are usually affected less by environmental conditions than by genetic background. Corn hybrids characterized by "girthy" ears exhibit more kernel rows (about 18 or 20 rows) than hybrids with long tapering ears (about 14 or 16 rows). Determination of kernels per row (ear length) is usually complete by V15 stage and maybe as early as V12 (Nielsen, 2007).
Unlike kernel rows per ear, kernels per row can be strongly influenced by environmental conditions. Kernels per row (ear length) can be adversely impacted by stress (often drought) in the two weeks prior to pollination. Many of our late planted corn fields experiencing excess soil moisture have not yet reached these critical stages. For most of these fields, loss of kernels per row on developing ears may be minimal and impact on potential yield limited. However, if N losses associated with ponding are substantial they may result in N deficiencies that can lead to kernel abortion during early grainfill stages and premature plant senescence.
Canopy height and extended leaf height at different V-stages, S. Charleston, OH, 2007-2009.
V-Stage
Canopy Height
Extended Leaf Height
----------------------inches----------------------
V5
14-20
20-28
V8
33-37
41-49
V11
53-63
61-78
V15
70-81
78-93
References
Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marlay. 2011. Corn growth and development. Iowa State Univ. Ext. PMR 1009.
Nielsen, R.L. 2007. Ear Size Determination in Corn. Corny News Network, Purdue Univ. [online] http://www.kingcorn.org/news/timeless/EarSize.html. [URL accessed 6/26/17].
-
Is yield jeopardized when replants result in excessive stands?
When widespread replanting occurs as it did this year, situations arise in which the original corn planting is not entirely killed and competes with the replanted corn. To make room for a replant, several herbicide treatments are recommended and these were described in an earlier C.O.R.N. Newsletter (https://agcrops.osu.edu/newsletter/corn-newsletter/2017-14/more-killing-corn-replant-situation). However, these treatments are sometimes not applied. Following severe frosts and protracted periods of freezing, it may appear that the initial planting or stand is dead when, in fact, some portion of it survived. In extreme situations, fields may end up with final stands nearly double what was normally targeted. There is a perception that the greater competition for nutrients, soil moisture and light associated with these excessive stands will result in barren plants and/or small ears (too small to harvest effectively) and will cause major yield losses.
Seed company and university research across the Corn Belt indicates that corn can tolerate plant stands of 50,000 plants per acre and higher without major yield loss. However, in the replant situation that results in excessive stands, plants from the original stand and the replant may only be a few inches apart (sometimes resembling “twin rows”) and at different stages of development, often with those of the replant at more advanced stages. So, does mean the later developing plants will be weeds adversely affecting the yield potential of the replant? We participated in a study in 2009 and 2010 (Terry et al., 2012) that gave us an opportunity to compare the yield potential of a replant in which original stand was eliminated and a replant in which most of the original stand was present.
The goal of this study was to identify effective herbicide treatments for killing an original stand of corn when replanting herbicide resistant corn. A seeding rate of 32,000 plants per acre was used for the original planting and the replant. One of the treatments (Select Max + Roundup) effectively eliminated the initial stand and the final stand of the replant was approx. 29,000 to 32000 plants per acre in 2009 and 2010 (Table 1). Another treatment (Gramoxone) killed much of the vegetative growth of the initial stand (simulating frost/low temperature damage) but failed to kill most of the plants, and when replanted, the final stand was approximately 53,000 to 61,000 plants per acres. Yields for the Gramoxone treatment were about 5 to 14% less than the Select Max + Roundup treatment but the magnitude of the losses would probably be acceptable to most growers dealing with a replant situation. The results suggest that the likelihood of major yield reductions resulting from competition between plants of a replant and an original stand are small.
Table 1. Herbicide treatment effects on yield, grain moisture and final stand, S. Charleston, OH 2009-2010.
Year
Treatment
Yield
Grain Moisture
Final Stand
-- Bu/A--
%
-- plants/A--
2009
Gramoxonea
213
15.7
60766
Select Max plus Roundupb
247
17.4
32180
2010
Gramoxonea
231
12.9
53143
Select Max plus Roundupb
242
15.7
28804
aGramoxone Inteon (2 LBA/GAL)
bSelect Max (1 LBA/GAL) and Roundup PowerMax (4.5 LBAE/GAL)
References
Loux, Mark. 2017. More on killing corn in a replant situation. Ohio State University C.O.R.N. Newsletter. 2017-14. https://agcrops.osu.edu/newsletter/corn-newsletter/2017-14/more-killing-corn-replant-situation
Terry, R.M., Tony Dobbels, Mark M. Loux, Peter R. Thomison, and William B. Johnson. 2012. Corn Replant Situations: Herbicide Options and the Effect of Replanting into Partial Corn Stands. Weed Technology 26: 432-437.
-
Interested in becoming a Certified Crop Adviser?
CCA Exam Registration Closes This Friday – for specialty exams and the basics
This is the last few days to register for the August Certified Crop Adviser exams. The exams include International, Local Board (Ohio, Indiana and Illinois for us), Manure Management, 4R NMS, Sustainability Specialty, and Resistance Management Specialty. Resistance Management and Sustainability exams will be held at all locations listed in August. Performance Objectives, study materials, and other registration information are listed on the exam pages: https://www.certifiedcropadviser.org/exams.
5 Year Exam Limit – This is a change
The ICCA Program has added a new requirement to their exam process, which was decided at the last North American Board meeting in September 2016. Starting this year in 2017, a candidate will have up to five years to pass both the International and Local Board CCA exams as part of the certification requirements to become a CCA. The five year timeline begins with the first passing exam score being reported. All exam websites and policy manuals have been updated with this verbiage.
The Ohio State University Agronomic Crops Team will not offer the exam preparation class this summer, but will provide the program next January on the 10th and 11th for the February exam. Watch the C.O.R.N. newsletter for more details this fall. Many of our summer field day programs offer continuing education credits to current CCAs – watch our calendar: https://agcrops.osu.edu/events/calendar/.
-
Hail injury to corn varies depending on development stage
The impact of hail damage is largely dependent on corn’s stage of development. Hail affects yield primarily by reducing stands and defoliating plants. Most of the hail damage results from defoliation. Generally, the corn plant is little affected by hail prior to the 6-leaf collar stage because the growing point is at or below the soil surface and in the leaf whorl. However, once the growing point is elevated above the soil surface due to internode elongation, the plant grows rapidly and becomes increasingly vulnerable to hail damage with the tassel stage/pollen shedding stage (VT) being the most critical period.
Severe hail damage prior to the 6 to 7-leaf stage can also result in “twisted” or “tied” leaf whorls as injured plants recover and new leaves try to unroll; however, most plants will grow out of this problem and tied whorls seldom cause major yield loss.
Leaf damage by hail usually looks much worse than it really is, especially during the early stages of vegetative growth. Shredded leaves and plants with broken midribs still have some capacity to contribute to plant growth. Plants not killed outright by hail usually show new growth within 3 to 5 days after injury occurs (i.e. if damage occurs prior to tasseling). For this reason, estimates of hail damage should be delayed several days to allow for this period of re-growth.
The hail insurance adjustor's growth staging system counts leaves beyond the last visible collar to the uppermost leaf that is 40-50% exposed whose tip points downward - usually this results in a leaf stage that is numerically 2 leaves greater than the "leaf collar method" (e.g. a V11 plant according to the leaf collar method would probably correspond to a 13-leaf plant according to the hail adjustor's method).
How do we estimate the potential yield loss from recent hail storms? This year stages of development will vary considerably depending on location, planting date, etc. Within some corn fields, it’s not unusual to see corn differ by three or more growth stages because of differences in soil color, drainage, and previous crop residues. Most corn has not progressed much beyond the V13 stage in many areas. Based on estimates of the National Crop Insurance Association (see table below), at the 15-leaf stage (or about V13) if 50% of the leaf tissue is destroyed by hail, a corn plant loses 15% of its grain yield potential; if 100% defoliation occurs, a corn plant loses 51% of its yield potential.
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.
Contributors
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.
CFAES provides research and related educational programs to clientele on a nondiscriminatory basis. For an accessible format of this publication, visit cfaes.osu.edu/accessibility.