C.O.R.N. Newsletter 2012-21

Dates Covered: 
July 9, 2012 - July 15, 2012
Editor: 
Amanda Douridas

Symptoms and Effects of Water Stress on Soybean Production

With most of the state experiencing at least moderate drought conditions and high temperatures, soybeans are exhibiting symptoms of water stress.  A visual indication of soybean water stress includes flipped leaves (see photo).  The flipped leaves expose a silver-green underside which reflects light.  In more severe cases, the outer leaves of the trifoliate will close together to reduce the leaf area exposed to sunlight and reduce water loss.  Water-stressed soybeans will grow slower and have smaller leaves compared to soybeans growing with adequate soil moisture. 

Soybean yield potential is influenced by total number of pods per plant, number of beans per pod, and seed size.  Stress conditions during soybean reproduction can reduce yield by affecting one or more of these yield components.  Vegetative growth, flowering, pod development, and seed filling stages overlap allowing the plant to compensate for short periods of stress.  Currently in Ohio, many soybeans are beginning to flower.  In a normal year, 60 to 75% of soybean flowers will abort, but this number can increase in a stressful year.  However, flowering can occur through the beginning of the R5 growth stage (beginning seed).  If water stress is alleviated prior to the R5 growth stage, some flowers and pods can still be produced compensating for the flowers that were aborted earlier.  If water stress persists, soybean yield will be reduced, especially as plants enter the R4 growth stage (full pod).  Yield reductions at this time result mainly from reductions in total pod number per plant.  At the R6 growth stage, water stress will cause a reduction in seed size.    

References: 

Casteel, Shaun.  2012.  Signs of Drought Stress in Soybean.  Soybean Station, Purdue University.  http://www.agry.purdue.edu/ext/soybean/news/2012/2012_0627SOYDroughtSigns.pdf [URL verified July 2012]

Pedersen, Palle.  2004.  Soybean Growth and Development.  Iowa State University Extension.  http://extension.agron.iastate.edu/soybean/production_growthstages.html [URL verified July 2012] 

Midseason soybean diseases

Across the state we have just about every condition possible in soybean this year.  With the cooler temperatures this week here are some things to scout for.

1. Soybean cyst nematode – Unfortunately, this pathogen is not affected by the dry weather and will still be active in the soils.  Where there are high populations, soybeans will be stunted and may have symptoms similar to those of nutrient deficiencies.  If the soybeans within an area of the field are shorter than they are in another part of the field, dig up the soybeans, shake the soil off of the roots, and look for the ‘pearls’ on the roots.  Many, many times I have found SCN in these fields.

2. Phytophthora stem rot – this is caused by the water mold, Phytophthora sojae and is present in fields that tend to be poorly drained.  The best time to look for this disease is 1 week after a heavy rain.  The key symptom of this disease is a brown chocolate canker that goes from the soil line up the stem, plants will wilt and eventually turn yellow and die.  A few places in the state have gotten some dumpers and this provides the perfect conditions for Phytophthora to develop.  The Rps genes are not providing 100% protection and we are relying on the “field resistance”, partial resistance, part of the resistance package.  Searching for the stem rot phase is a good key to know if that resistance is working for your field.

3. Frogeye leaf spot – this is caused by the fungus, Cercospora sojina.  Now is the time to check fields for the presence for this fungal disease.  I also have a favor to ask if you find it.  Could you please send me a few leaves with spots (from Ohio only please).  A colleague at Univ. of Illinois is evaluating the population for resistance to the strobilurin class of fungicides (Headline, Quadris).  There are still a few highly susceptible varieties out there, and we have also had some early morning fogs in a few places.  Fields that are in continuous soybean and planted to susceptible varieties are the most likely candidates for this disease.

4.  White mold – Sclerotinia stem rot.  This disease hits some areas of the state, northeast Ohio and north central on an annual basis.  Again, variety resistance plays a key role in this, as well as thick stands, and canopy closure during flowering.  Despite the heat of last week, we have had some cool nights and fog – but the soil has been dry.  I’ve found sclerotia in some fields that are soft and healthy, but no apothecia.  Last year, apothecia formed late in some fields during a period when night time temperatures were down in the ‘60s.  Once these apothecia form, they shoot their spores onto the flowers of plants.  This gives them a great carbon source as they germinate and grow and form the white fluffy growth on the stems of the plants.

5. Soybean rust.  No, it is not here in Ohio.  This disease we monitor in the southern states.  To date it has been identified in Texas, Alabama, and Florida in counties where it is hugging the Gulf as well as a few counties in Southern Georgia.  The heat will slow the development down, thus making it hard to build up inoculum that may affect this region.  (http://sbr.ipmpipe.org/cgi-bin/sbr/public.cgi).  Once again, many thanks to our colleagues in the south who scout the kudzu patches to monitor for this disease.

Soybeans, Insecticide/Miticide Applications, and Bees

With the potential to have to spray insecticide/miticides on soybeans in the coming weeks during the flowering stages (R1-R2), we would remind growers of the concern with foraging bees.  With drought conditions, the likelihood of bees coming to soybeans to forage is higher than usual.  Because many of these pests are occurring while flowering is predominant because of 1) their earlier arrival this spring due to the warm winter and spring, or else because of 2) the need to spray now for the twospotted spider mite, growers should be aware of requirements and actions they should take before applying anything to soybeans in flower.  According to Ohio law, if a pesticide is toxic to bees, it is the applicator’s responsibility to contact the beekeepers with registered apiaries (beehives) within ½ mile of the target area if it is more than ½ acre in size and the crop is in flower.  Contact the Ohio Department of Agriculture for more information on apiaries in your area.  If at all possible, applications should be made early or late in the day when bees are less likely to be out foraging. 

Drought, Insects, and Field Crops

Twospotted spider mites on soybeans are now a concern in the state.   Numerous areas in the drier areas of Ohio are already seeing them, and some fields are being sprayed.  Mites are showing up not only on field edges but also within the field.  See http://corn.osu.edu/newsletters/2012/2012-18/twospotted-spider-mites-on-soybeans for information on treatment decisions and materials to use.  Currently, materials of choice are chlorpyrifos (Lorsban and generics), dimethoate, and various bifenthrin formulations (including those that are in combination with other materials).  Although we do not have much experience with the bifenthrin materials, they do have many mite species on their labels.  If you use materials containing bifenthrin, we would like to hear how efficacious they are.  Other pyrethroids, while having mites on their label, are listed only for “suppression”; we do not recommend those materials.  A question we often get is if it is worth spraying during such a dry year.  Past experience shows us that when soybeans are protected from mites, later rains in August will allow the soybeans to recover somewhat and give acceptable yields compared to fields where mites are not controlled.  Also, remember if the hot and dry weather continues, none of these materials will give long term control; all might need a second treatment later on, even within a few weeks.  Thus, continued scouting is a requirement.  And if a second treatment is required, we strongly recommend switching to a different material to help reduce the chances of miticide resistance from developing in the mite.  Insecticides/miticides should be rotated just like crops!

Silking on corn is occurring, and growers should be aware that the insects of concern are in the fields already.  The two most important pests concerning silk feeding are the adult Japanese beetle and adult western corn rootworm (WCR).  For the rootworm, the question is how heavy they will be this year knowing that, in general, populations have been low the past few years.  However, we have heard of fields with higher than expected numbers feeding on the silks.  What growers should examine is whether these higher insect populations are in fields where the corn is silking evenly across the area, or if the corn is showing uneven growth, with silking occurring only in pockets.  Corn rootworm adults will tend to occur only in the areas that are silking.  As other parts of the field begin to silk, the beetles will move to them. Treatment is warranted when an average of 5 or more WCR adults or 2 or more Japanese beetles are found on silks, silks have not been pollinated, or silk clipping to 0.25 inches or less is observed.  If silks are wilting and turning brown, pollination is complete.

We are now seeing soybeans entering their flowering stages.  Because of the early arrival of many insects this year, we are seeing more defoliation during these early flowering stages than usual.  Adult Japanese beetles and the first generation of adult bean leaf beetles are occurring at least 2 weeks earlier than normal.  And because of the dry weather in much of the state, soybeans are not growing well and are much smaller in size with low levels of leaf area.  This lack of growth results in low LAI levels (leaf area index, a measure of the amount of leaf area present in a field) and thus lower light interception by the plant canopy.  When scouting for insect feeding, the 15-20% defoliation threshold on small soybeans with low LAIs will be reached more quickly and have a greater yield-reducing impact than if those soybeans were larger in size with large amounts of leaf area present.  Although we still believe it best to keep the defoliation thresholds at the current levels, growers might want to be conservative with these thresholds and make a decision to treat sooner than they would in a “normal” year with adequate moisture and crop growth.

Finally, potato leafhoppers remain active in alfalfa, and with the crop not regrowing as well as expected because of the dry weather, perhaps the leafhopper demands greater attention.  If you read our fact sheet on this pest, you will see that when alfalfa is under stress, we suggest that leafhopper thresholds be lowered from the normal ones (http://ohioline.osu.edu/ent-fact/pdf/0033.pdf ); the threshold when under stress is about half of the normal threshold.  This is one time period that leafhoppers should be treated sooner than later if populations are in the field. 

Foliar Fungicide Application in Field Corn: Q and A

It has been hot and dry for most of the corn growing season so far. These conditions are highly unfavorable for foliar diseases to develop in field corn, yet several producers have expressed interest in applying foliar fungicides. Gray leaf spot (GLS), the number one foliar disease of corn in the state, develops best at temperatures between 70 and 90 F, especially when conditions are consistently wet and humid. For GLS infection to occur the leaf surface needs to be wet for 11 to 13 hours and relative humidity in the canopy needs to be at or above 90% for an uninterrupted period of 12 to 13 hours. Similarly, northern corn leaf blight (NCLB), a disease that has been increasingly prevalent in the state over the last few years, requires even cooler, wetter conditions. NCLB infection occurs when free water is present on the leaf surface for 6-18 hours and temperatures are between 66 and 80°F. Therefore, temperatures this year, mostly in the upper 80s and upper 90s, and moisture in particular, have not been favorable for either GLS or NCLB to develop. With the year’s crop already between late vegetative and early reproductive stages, it is highly unlikely that either GLS or NCLB will reach levels high enough to impact grain yield.            

Questions and Answers:

Question 1. Do foliar fungicides increase yield in field corn?

Answer 1. Fungicides MAY indeed lead to an increase in yield in field corn, but the yield response is HIGHLY variable. The greatest and most consistent increases in yield are usually seen when foliar diseases are present and at high levels.  

Question 2. What about yield increase in stressed corn?

Answer 2. I know of no research data showing conclusively that fungicides lead to higher yields in corn under stress conditions, other than when the stress is caused by diseases. Comparisons made between fields, between hybrids, or even between years are not valid to drawing conclusions about fungicide effects on yield. For instance, you should not base your assessment and conclusion on a comparison between the field next to your house that was treated with a fungicide and the field five miles down the road that was not treated. To conclusively say whether or not a given fungicide increases yield in stressed corn, you will need to compare treated and non-treated, stressed and non-stressed corn in the same field, planted with the same hybrid, all exposed to the same set of weather, soil, and crop production conditions. In addition, such a comparison will need to be made over multiple years and locations.

Question 3. Will the fungicide pay for itself?

Answer 3. It depends mainly on grain price, fungicide cost, application cost, hybrid susceptibility to disease, and the level of disease in the field. You are most likely to see a return on your fungicide investment when grain prices are high, fungicide and application costs are low, the hybrid is susceptible, and disease levels are high.                

Question 4. Do fungicides affect respiration, photosynthesis and other physiological processes?

Answer 4. Yes, some fungicides do indeed affect crop physiology. However, most of these effects have been observed in the greenhouse, under controlled conditions. In the field where conditions are highly variable, a greening effect is sometimes seen when strobilurin fungicides are used, however, the association between this greening effect and grain yield is not clear or consistent. Remember, the biggest drivers of yield are hybrid genetics, weather conditions, and crop nutrition, not fungicide application in the absence of disease.

Summary results from 8 years of fungicide research - up to 172 trials

Fungicides tested: Headline, Stratego, Quilt and Quadris. All fungicides were applied at VT (tasseling) or at R1 (silking).

Average yield range: 164 to 197 bushels/acre.

Yield difference between fungicide-treated and untreated plots: In 28 to 48% of the trials, yield was higher in the untreated plots than in the fungicide-treated plots. Remember the piano graphs you see at meetings? These clearly show how highly variable yield responses are to fungicides.   

Average yield difference between fungicide-treated and untreated plots: 3.6 to 6.2 bushels/acre.

Average yield difference between fungicide-treated and untreated plots when foliar disease levels are low (<5%): 1 to 5 bushels/acre.  

Average yield difference between fungicide-treated and untreated plots when foliar disease levels are higher (> 5%): 7 to 10 bushels/acre.

Much Needed Rain Comes at a Cost – Root Lodging and “Green Snap” in Corn

Scattered thunderstorms brought much needed relief to Ohio corn fields enduring blistering temperatures and drought conditions. However, the rains in some cases came at a cost. Strong winds associated with the storms caused localized crop injury - root lodging and “green snap”. The magnitude of the damage was influenced by other factors including crop stage of development and hybrid genetics.

Root lodging occurs when strong winds pull corn roots part way out of the soil. The problem is more pronounced when soil are saturated by heavy rains accompanying winds. If root lodging occurs before grain fill, plants usually recover at least partly by "kneeing up." This response results in the characteristic gooseneck bend in the lower stalk with brace roots providing above ground support. If this stalk bending takes place before pollination, there may be little effect on yield. When lodging occurs later in the season, some yield decrease due to partial loss of root activity and reduced light interception may occur. If root lodging occurs shortly before or during pollen shed and pollination, it may interfere with effective fertilization thereby reducing kernel set. In a University of Wisconsin study, wind damage was simulated at various vegetative stages through silking (V10 to R1). Compared to hand harvested grain yields of control plants, grain yield decreased by 2 to 6%, 5 to 15% and 13 to 31% when the lodging occurred at early (V10-V12), mid (V13-V15) and late (V17-R1) stages, respectively.

Green snap or "brittle snap" are terms used to characterize pre-tassel stalk brakeage caused by wind . Corn plants are more prone to green snap during the rapid elongation stage of growth between V8 and tasseling, especially during the two week period prior to tasseling. Breaks in the stalk usually occur at nodes (along nodal plates) below the ear. When soil moisture and temperature conditions are favorable for growth during this stage of plant development, plants elongate rapidly but stalks are unusually brittle. Stalk brittleness is greatest in rapidly growing corn under high temperature, high soil moisture conditions. There is speculation that rapidly growing plants are more susceptible to snapping-off for several days during the few weeks before tasseling because there has been little time for plants to develop lignified tissues at the nodes.

Although we encounter green snap problems periodically in Ohio, it's usually a more serious problem in the western Corn Belt. Vulnerability to green snap damage varies among hybrids. However, all hybrids are at risk from such wind injury when they are growing rapidly prior to tasseling. Once the crop tassels green snap problems generally disappear. Back in the 1990’s, Nebraska researchers observed that it was often the most productive fields with the highest yield potential that experienced the greatest green snap injury. They concluded that factors promoting rapid growth early in the growing season also predisposed corn to greater green snap injury.

According to Dr. Emerson Nafziger at the University of Illinois  “Yield effects of green snap depend on the number of plants snapped and where the breakage takes place. Stalks that break above the ear will usually produce an ear, but if nearby plants are intact, they will shade the broken-off plants and reduce ear size. When plants break at the node below the top ear, dormancy will break and allow the next ear down to develop, but it may not receive enough pollen to produce a lot of kernels. Plants that break near the ground won't produce yield, of course, but will allow more light to reach intact plants, which in turn will produce more grain. Loss of plants thus typically reduces overall yield less than the percentage of broken plants might suggest.”

Pricing Drought-Stressed Corn for Corn Silage

With a “normal” corn crop, pricing a standing crop for silage can be “interesting”.  Pricing a drought-stressed corn crop is even more interesting.  What is the actual nutrient content of the crop?  How well will the crop ferment?   Will nitrate levels put the potential silage crop at risk?  There are many unknowns, with the biggest challenge being how to determine the dollar value to assign to that risk.

The value of drought-stressed corn silage can be estimated using expected nutrient composition and the cost of the nutrients.  The average composition of drought-stressed corn silage in Table 1 is reasonable, but the composition of silage for a specific situation (e.g., hybrid, growing conditions, etc.) could be substantially different. The nutrient values were calculated based on numerous feed prices in central Ohio.   

Table 1.  Average composition of drought-stressed corn silage and current (Jan-July 2012) value of nutrients in Ohio.

Nutrient                     Concentration                   Units/T of DM              Nutrient cost       Economic value
_________________________________________________________________________________

NEL                             0.60 Mcal/lb                       1200 Mcal                    $0.15/Mcal             $180

Metabolizable protein    6.6%                               132 lbs                        $0.35/lb                 $46

Non-effective NDF          12.5%                              250 lbs                      -$0.05/lb                -$13

Effective NDF                  37.5%                              750 lbs                       $0.0/lb                   $0

Total value                                                                                                                      $213/T of DM

__________________________________________________________________________________

1 DM = dry matter, Mcal = megacalories, eNDF and neNDF = effective and non-effective neutral detergent fiber, NEL = net energy for lactation.

The $213/ton of DM (±$20) or $75/ton (± $7) assuming 35% dry matter is the value for the corn silage when fed to the cow and includes harvest and storage costs and shrink.  It assumes the fermented feed is excellent quality and will allow for high dry matter intakes and good production when fed in a balanced diet.  When corn is standing in the field you do not know whether the resulting silage will turn out good or bad.   Making silage from drought- stressed corn has some additional risks that must be considered when pricing.  It could be high in nitrates, which in the worst situation will make the silage totally unacceptable as a feed (for additional information on nitrates see: http://ohioline.osu.edu/as-fact/0003.html). The silage may have much higher fiber and lower energy than anticipated.  We are using the composition of ‘average’ immature corn silage for these calculations.  Drought stress can greatly affect the composition of the corn plant and therefor it’s value. 

If you are purchasing standing corn, the purchase price must be adjusted to account for these costs and risks.  When you purchase standing corn, in contrast to buying fermented corn silage, the user of the silage (e.g., the dairy farmer) assumes those risks and the price of standing corn should be discounted to account for the risk. We cannot give you a value for risk; each buyer must determine that value for themselves based on the conditions of the crop they are purchasing and negotiate the final price with the seller.   

In addition, for more than 6 years, good corn silage (made from normally developed corn plants) has almost always been a ‘bargain’ feed in that its market price is 15 to 25% less than the value of its nutrients.  Based on this historic relationship, corn silage with a nutrient value of $213/T of dry matter (see Table 1.) would sell for about $170/ton of dry matter ($60/ton at 35% dry matter) – remember that this value is for good quality corn silage in front of the cow.  This normal relationship between corn silage selling price and corn silage value should also be considered in the negotiations.

 

Example:  Price of Standing Corn (assumed 35% dry matter)

___________________________________________________________________________________

Nutrient value of corn silage when fed to cow: $75/ton of 35% DM silage

Harvest costs     - $ 6 to 11/ton depending on yield1

Storage costs     - $ 9/ton

Shrink (13%)      - $ 10/ton

Risk?                   - $???  (this could be substantial)

 = Price of standing corn $48/ton at 35% dry matter (± $5) minus the value of risk. 

If you apply the typical selling price vs. nutrient value discount of ~20%, this becomes $38/ton at 35% DM. 

__________________________________________________________________________

1Lower cost for “normal” corn silage yields, higher cost for lower, drought-stressed corn silage yields.

For many people both the price of corn silage as fed to the cow ($60-75/ton) and the price of standing corn ($38 to 48/ton ± $5) seems high (and they are). However, you have to consider replacement costs, i.e., what will it cost if you have to purchase other feeds to replace the nutrients provided by corn silage. These are the maximum prices a farmer should pay for purchasing corn silage or standing corn.

Calculating the Floor Price

The lowest price (on a per acre basis) a seller (the grower) should be willing to sell standing corn as corn silage is equal to the estimated dollar return per acre if the crop was sold as grain.  The seller should first estimate the potential grain yield and multiply that by the estimated market price he thinks he will receive when it is sold. The seller should then estimate potential silage yield (see slides 4-7 in ‘Pricing Corn Silage in 2007” at http://dairy.osu.edu/resource/OSU%20Dairy%20Pubs.htmlThe estimated dollar return per acre for the crop sold as grain divided by the estimated silage yield per acre would be the floor price per ton of corn silage for these negotiations.  At a price below this floor, the grower would be better off harvesting and selling the crop as grain.  For “normal” corn, the cost of harvesting the crop as grain approximately offsets the value of nutrients that are removed with the corn plant that would be left in the field if the crop were not harvested as silage.

Additional articles on pricing corn silage are available at http://dairy.osu.edu.

The 2012 Wheat Season in Review

More than 95% of the 2012 wheat crop has been harvested, with yields ranging from a low of 40 bu/acre to a high of about 85 bu/acre, and test weights from 45 to 60 lb/bu. Warmer-than-usual late-winter and early-spring conditions caused the crop to green-up early and its growth and development remained about two weeks earlier than usual throughout the season. For instance, the crop reached anthesis between late-April to mid-May, which is quite unusual for wheat in Ohio. An early start to the wheat crop usually means an extended grain fill period, and consequently, excellent yields and test weighs, if disease levels remain low.       

Conditions were warm and dry throughout most of the spring, which kept disease levels very low. With the exception of a few isolated locations, powdery mildew remained restricted to the lower leaves, and only trace amounts of Septoria and Stagonospora were seen. Scab and vomitoxin levels were also very low this year, being the lowest in the last 5 or more years. As usual, leaf rust came in late, but the biggest surprise this season from a disease standpoint was stripe rust. Stripe rust reached fairly high levels on susceptible varieties at multiple locations in the state and may have impacted yield in field where most of the flag leaf was damaged well before grain fill was complete. For instance, in one of my research trials in Wooster, untreated stripe rust-infected plots had 16% lower grain yield than plots treated with Prosaro at flowering. As you plan for the next wheat crop, it would be important to remember the varieties that were affected by stripe rust so as to avoid planting them in 2013 or to plan in advance to protect them with a timely fungicide application.

While the warm, dry conditions did indeed kept disease levels very low, they also shorten the grain-fill period, leading to lower yields than expected. Temperatures reached 90+ F for several days during grain development, and couple with the dry conditions, prevented most varieties from reaching their full yield potential.                  

Western ARS Agronomy Field Day Reminder

The OARDC’s Western Agricultural Research Station (ARS) will be hosting the 2012 Agronomy Field Day on July 18th from 9 a.m. to 3 p.m.

The field day begins with a wagon tour of the Agronomic Crops research at the Western ARS.  During the tour, speakers will share information on a variety of topics including seedling germination, utilization of manure resources, weed management issues, variable emergence, and maximizing soybean yield. Each speaker will address drought concerns, as well.

After lunch, speakers will lead four in-depth discussion sessions on disease management, weed management, insect problems, or corn management.  Each discussion will be 50 minutes, so attendees will be able to participate in two sessions.

Pre-registration is required.  The registration fee is $20 per person, and includes a barbeque box lunch, payable on-site.  To register, contact Harold Watters, OSU Extension, at watters.35@osu.edu or 937-292-4159 or Joe Davlin, Western ARS Manager, at davlin.1@osu.edu or 937-462-8016.

Weather Update

Nothing has changed. The overall pattern remains in place with above normal temperatures and below normal rainfall but there is some hope for increased rainfall chances and near normal rainfall in places.

The good news is there will be some rain chances by this weekend into next week. The favored area for best rains will be southeast of Interstate 71. There is a 70-80 percent chance of normal rainfall of 2 inches the next two weeks there. To the northwest of that line, there is still a 40-50% chance of 2 inches. The main message is most places will at least get some rain the next 2 weeks which is better than what we have had and there is at least a chance of some areas getting some decent rainfall. However, it will not end the drought at this time and the worst hit areas of northwest Ohio may get the least rainfall where it is needed most.

Temperatures will average about 5 degrees above normal over the next 2-3 weeks. This means lots of 80s and at times 90s for highs but the heat will not be the extreme heat we saw earlier in the month of July.

 

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About the C.O.R.N. Newsletter

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.