In This Issue:
- Wheat Grain Quality and Vomitoxin Issues
- Natural Gas Prices and Nitrogen Fertilizer
- Bean Leaf Beetles and other Soybean Defoliators
- Soybean Aphid Update
- Precautions on Late Season Application of Soybean Herbicides
- Leaf Cupping and Wrinkling in Soybeans
- Timing of Herbicide Applications in Double Crop Soybeans
- Controlling Weeds in Wheat Stubble and Preventative Planted Acres
- Kernel Development Starting in Early Corn
Authors: Patrick Lipps
As wheat harvest continues in Ohio more grain quality issues become apparent. The main area of high head scab risk this year was north central Ohio due to the excessive wet conditions recorded in this area, however other areas of Ohio were at risk as well. As expected, head scab continues to be the main culprit of poor grain quality and the primary cause of potential problems from vomitoxin, a metabolic by-product of the head scab fungus Fusarium graminearum. Fusarium produces the toxin as it grows on wheat head tissue, on grain, and into wheat grain. The fungus is a very fast colonizer of wheat tissues including the grain, and whenever the moisture content of the grain is high enough the fungus will continue to produce the toxin. This is why it is a good idea to harvest wheat fields as soon as possible and to dry the grain to about 14% to limit the growth of the fungus and the time it can produce the toxin. Nothing can be done to reduce the amount of toxin in grain once it is there.
The level of vomitoxin (or DON) in Ohio's wheat crop is quite variable, with some loads below or slightly above 1 ppm and some as high as 5 ppm. Most reports have indicated averages around 2 to 3 ppm. Loads of wheat with higher levels of vomitoxin are being rejected. Variability in the level of vomitoxin is due to many different factors impacting the level of head scab in the field and the growth of the fungus once it is present in the grain. With the level of head scab being higher this year than last year, we expected the vomitoxin levels to be higher this year as well. The relationship between the level of head scab in the field and the vomitoxin content of the grain is not well established. In general, grain from fields with a lot of head scab generally have significant levels of vomitoxin. However under some circumstances, fields with moderate to low levels of head scab can still have critical levels of vomitoxin. Also just because test weights are high (58-60 lb/bu) does not mean that vomitoxin levels are low. Growth of the fungus on non-shriveled seed occurs and vomitoxin can be present in high test weight grain. Unfortunately we do not understand all the factors that affect production and accumulation of vomitoxin in the grain and therefore we can not accurately predict the occurrence or level of vomitoxin in the crop.
Vomitoxin is a problem for the wheat grower, the miller, the baker and the consumer. Wheat growers are concerned with yield and test weight since these factors greatly impact the money they receive for their crop. However, anytime vomitoxin levels in the grain are above 1 part per million (ppm), or above the advisory level for human consumption, it is a problem for the entire wheat industry. The grower can do some things to help reduce the problem, mostly by combining early, removing as many shriveled seed as possible during combining and drying the crop to prevent accumulation of additional vomitoxin while the grain is in storage. The milling industry can do a few things during the milling process to reduce the amount of toxin present. These include additional cleaning of the seed before milling and adjusting the machinery not to mill as close to the bran. However, if the grain contains levels of vomitoxin above 2 ppm these process are only so effective in reducing levels in the flour. Additionally, if vomitoxin is present internally in the grain and not just in the bran, little can be done to reduce levels in the flour. All these steps cost the milling industry money and some of the cost is passed onto the grower as dockage for the grain with elevated levels of vomitoxin. The miller must also satisfy his customers, the baking industry. The baking industry imposes very strict requirements on flour quality because vomitoxin levels in their products must be below the action level to meet consumer standards. Obviously, each group involved in wheat from the crop producer to the consumer has a stake in providing a safe and healthy product. Scab costs everyone money.
Authors: Robert Mullen, Edwin Lentz
As you all know, nitrogen fertilizer prices have risen considerably over the last few years as the price of natural gas production has increased. So what is the relationship between nitrogen fertilizer and natural gas, and how long are these prices going to stay high?
The primary nitrogen source for fertilizer is ammonia. To produce ammonia, atmospheric N is combined with hydrogen gas to produce NH3 in a reaction known as the Haber-Bosch reaction. To produce the hydrogen necessary, steam is added to methane (natural gas) at high temperature. It takes over 32,000 cubic feet of natural gas to produce one ton of ammonia. This is the link that ties natural gas cost and fertilizer price. Since natural gas is consumed directly by ammonia production, as the cost of natural gas increases so too does the price of ammonia. At the current cost of natural gas, $6.28 per MMBtu (same as Mcf or 1,000 cubic feet), it costs approximately $235 to produce a ton of ammonia. Over 75% of the production cost is attributed to the cost of natural gas. Production of ammonia accounts for approximately 3% of the natural gas produced by the U.S.
Economic analysts project the price of natural gas will remain high for at least the next four years. Like most predictions no one can accurately foresee what will occur in the future, but the prospects for increased natural gas prices are there. Increased demand from the energy sector is placing a high demand on natural gas, and the wells are barely producing enough to keep up. So, unfortunately, the prospects for declining N fertilizer prices are not there. Increased natural gas prices will also increase our reliance on imported sources of N.
Authors: Ron Hammond, Bruce Eisley
First generation bean leaf beetles are beginning to occur in soybean fields throughout Ohio. For those growers who chose to take action against possible vectoring of bean pod mottle virus by this insect by applying an early season application of an insecticide after soybean emergence, the suggested practice for best protection against transmission of the virus is to apply a second application at the beginning of this first generation. This is now occurring and growers are so advised.
In terms of defoliation by all insects, most early-planted soybeans are now in the R1-2 flowering growth stages. Early reproductive growth stages are when soybeans become most sensitive to defoliation, and when thresholds needed for treatment drop to 15-20%. Growers will be seeing most of the common defoliators appearing over the next month. Defoliators expected to make their annual appearance include the already mentioned bean leaf beetle adults, Mexican bean beetle adults and larvae, Japanese beetles, green cloverworm larvae, and grasshoppers. Although it would be unusual for any of these single insects to cause significant defoliation alone, a complex of two or more might cause defoliation levels to rise above threshold levels. Growers are advised to initiate scouting procedures to prevent defoliation from reaching the 15-20% defoliation threshold during the early reproductive growth stages, R1-R5, later rising to 20-25% during growth stage R6. A list of labeled insecticides for control of all these soybean pests is available at http://corn.osu.edu/library/articles/03insectupdate.html.
There is a special reason to scout specifically for bean leaf beetle populations. Evidence suggests that the population size of the second generation of bean leaf beetle that causes pod injury in late August and early September is relative to the size of this upcoming first generation. We recommend growers monitor this first bean leaf beetle generation to give them an insight as to the potential size of the second generation and possible pod injury. If the first generation is large, evident either through sampling large numbers of bean leaf beetles or presence of significant leaf feeding, it will be imperative that the second generation and subsequent pod injury be watched more closely later this summer. If the first generation is relative low or non-existent, the probability of later problems is lower (although we will still recommend scouting all fields through the entire summer). Determining the relative size of the first generation will offer better insight as to potential problems later in the growing season.
Authors: Ron Hammond, Bruce Eisley
Ohio has officially joined the other northern states as having the soybean aphid this summer. Extremely low numbers of the aphids were found in numerous fields in Wayne County. Of importance is not having found them, but having discovered them only in extremely low numbers after looking for hours. The difficulty in finding them and the lack of reports of aphids by extension agents, consultants, and other field workers suggest that the soybean aphid is in extremely low, if almost non-existent, densities throughout Ohio.
Reports from other states and Ontario last week confirm the continued lack of soybean aphid populations. Although all states have now reported finding aphids, none of them are reporting moderate or high numbers; all are reporting very low densities. Some of the reports of fields having been sprayed earlier in states to the west of us suggest that populations were in fact nowhere near threshold. Also, misidentification continues to be a problem, mistaking both thrips http://entomology.osu.edu/ag/thrips.htm and small potato leafhopper nymphs http://ohioline.osu.edu/icm-fact/images/113.html for aphids http://entomology.osu.edu/ag/saclose.htm.
As suggested in earlier C.O.R.N. newsletters, when only single or a few individuals are found, it is essential that correct identification be made. Thus, carrying a small hand lens into the field will assist with the correct I.D.
At the present time, insecticide treatments would not be warranted. Not only will money be wasted, but also a larger aphid problem could be initiated. Killing off beneficial insects at this time, which are very active in helping keep aphid populations in check, might allow the few aphids that are present to escape natural control and rise to higher numbers. Treatments should ONLY be applied at a threshold of 250-300 aphids per plant and a rising population.
This current lack of soybean aphids does NOT mean that they should be forgotten. We are still only in mid-summer, and the situation could change quickly. Therefore, we strongly recommend that growers continue to visit their soybean fields and sample for aphid populations, and to read this weekly C.O.R.N. newsletter for updates. Samples should be taken randomly throughout the field by visiting at least 20 locations and checking a number of plants at each spot for aphids. Although aphids will usually be found on the top, young leaves of the plant, the entire plant should also be checked. If and when aphids begin to appear, the 250-300 aphids per plant threshold and a rising population density should be used to dictate the need for treatment.
Authors: Mark Loux
A number of late-planted soybean fields in the state will yet require a postemergence herbicide application, but some precautions are in order when selecting herbicides. Some things to consider:
1.Soybeans planted early that grow at a fairly “normal” rate can usually outgrow minor injury from postemergence herbicides with little risk of yield loss. Based on OSU research, the greatest risk of yield loss in soybeans seems to occur when soybeans are planted late in the season and are still fairly small at the time of postemergence herbicide application. In this situation, we have occasionally observed yield loss, probably because soybeans lack sufficient time to recover from herbicide injury before pod development and fill. So, in those soybean fields that will still be treated, try to avoid herbicide mixtures that can cause excessive injury.
2. We are well past the time of peak emergence of summer annual weeds, and weeds that emerge after a postemergence application at this time of the year should be few in number. Therefore, we recommend application of herbicides in late-planted fields as soon as possible when weeds are still small, which will allow the use of fewer and less injurious herbicides in tank mixtures.
3. Postemergence soybean herbicides generally present little risk of carryover to major crops, as long as recrop intervals and other precautions on the label are followed. The risk of carryover can increase with late-season application, especially if dry conditions prevail for the rest of the summer and fall. Herbicides that may present more of a carryover risk when applied late include Flexstar/Reflex, Pursuit, Raptor, FirstRate, Classic, and Synchrony STS. Be sure to consult labels and Table 21, page 171, of the current Ohio/Indiana Weed Control Guide (ohioline.osu.edu/b789/index.html) to address carryover concerns when selecting herbicides for late-season applications.
4. The preharvest restrictions on herbicide labels, which indicate how much time should elapse between application and soybean harvest, are also a concern with late-season herbicide applications. Preharvest intervals range from 7 to 90 days before soybean harvest depending upon the product. Consult Table 15, page 125, in the OSU/Indiana Weed Control Guide http://ohioline.osu.edu/b789/index.html and herbicide labels for more information on preharvest restrictions.
Authors: Mark Loux
We have received a number of calls about cupping or wrinkling of soybean leaves, and it seems that this has become an annual issue in much of the corn belt. Some of the symptoms are undoubtedly due to drift or volatility of herbicides due to the many windy days this year, but some are undoubtedly due to other problems as well. A number of factors can cause these symptoms, and it can be difficult to pinpoint the exact cause. Some additional information on this issue follows. There is also a new fact sheet with color photos available from the University of Wisconsin, “Dicamba Injury to Soybeans”, which can be downloaded from http://ipcm.wisc.edu/pubs/pest/Dicamba2004.htm
One of the first herbicides to get blamed in many fields is dicamba, which may have been applied in a nearby corn field. Products containing dicamba include Banvel, Clarity, Marksman, Celebrity Plus, Distinct, Northstar, Yukon, and numerous generic products. Exposure of soybeans to low concentrations of dicamba through drift or volatility, or even dicamba residues in spray tanks may be the culprit in some fields. The potential for volatility varies among these products, but all can drift if applied during windy conditions. However, many of the affected fields seem to be far enough away from treated corn fields, or dicamba was not used in the area, and this possibility can be ruled out. The most typical symptoms from exposure of soybeans to dicamba are puckering of the new leaves that are emerging 7 to 10 days after exposure. This may be accompanied by stunting of the plant. Soybeans may show these symptoms on several trifoliates, and then recover completely. Spray particle drift from Distinct application often causes more severe symptoms than dicamba alone, due to the diflufenzopyr component of Distinct. However, there is little risk of volatilization of diflufenzopyr, while dicamba can volatilize readily depending upon formulation and temperature.
Research indicates that soybean yield is not generally reduced when minor symptoms occur, and yield loss is more likely if soybeans are in the reproductive stage at the time of exposure (although still unlikely unless symptoms are severe). Our research with postemergence soybean herbicides indicates that soybeans can tolerate considerable early-season injury with little or no impact on yield, when rainfall and other environmental conditions are generally favorable for crop growth after the injury has occurred. Yield loss seems to be most likely when herbicides are applied after about the beginning of July, and soybeans are small at the time of application (which might occur from late planting or poor early-season growing conditions). Where this has occurred, soybeans may not recover well enough to attain the size needed for maximum yield potential.
Over the past decade, we have heard reports of and observed fields where leaf puckering or cupping was uniform over the entire field. Other fields have shown symptoms only in some areas. In OSU research plots, we have occasionally observed puckering in Roundup Ready soybeans following application of glyphosate. Spider mites and leafhopper have been known to cause cupping and wrinkling of soybean leaves. Many of the fields with puckering were previously treated with a postemergence herbicide other than glyphosate. ALS-inhibiting herbicides seem to be most often used in fields with the symptoms, but other herbicides have also been used. One working theory about these symptoms - when the postemergence herbicide causes injury to the terminal buds on soybeans, apical dominance is altered, and plant hormones are redistributed within the plant. The result is the appearance of injury that is similar to that from plant growth regulator herbicides (dicamba, 2,4-D). New shoots may occur at nodes below the injured zone, the plant may take on more of a bushy appearance, and leaves may be wrinkled and cupped. However, most of the fields have not exhibited the increased "bushiness" that might occur if apical dominance was lost.
While herbicides may be responsible for some of the puckering, cupping, and wrinkling that has been observed, we suspect that environmental conditions and soybean variety may have a significant role. This is based on the observation of uniform cupping in fields where no postemergence herbicide was used. Some varieties may be more likely to show symptoms than others. We have not been able to come up with a good explanation for this phenomenon. However, the good news is that leaf cupping and wrinkling should not affect yields, and soybeans generally compensate well from other herbicide-related problems given enough time and moisture.
Authors: Mark Loux
With the extra early wheat harvest this year there were more double-crop soybeans planted than normally. For no-tillage double-crop soybeans, allow weeds to regrow 3-6 inches after wheat harvest before applying herbicides. That means some fields are ready to be sprayed in southern Ohio. If Roundup Ready soybeans were planted, use a minimum of 1.125 pound acid equivalent per acre (# ae/A) of glyphosate (33 oz/A of Roundup WeatherMax or 48 oz/A of a 3.0 # ae/gallon product) but preferably 1.5 # ae/A of glyphosate. These higher rates are needed due to the larger than normal size of weeds, especially for marestail/horseweed and giant ragweed. Due to this early postemergence application, fields will need to be scouted for emergence of volunteer wheat later in the season. Do not postpone this early application to allow all of the volunteer wheat to emerge, because it will continuously germinate for the rest of the season when adequate moisture is available.
When controlling weeds in wheat stubble, you must first determine your main target. The three main targets are summer annual weeds, warm-season perennials, or cool-season perennials. The main goal for summer annual weeds is to not let them go to seed. If they are allowed to go to seed, then weeds will be more difficult to control in future growing seasons. There are three ways to reduce or eliminate summer annual weed seed production, mowing the field, tilling the field, or applying an herbicide. Due to the earlier than normal wheat harvest, these fields may need one or two additional mowings compared to normal. The application of an herbicide is more likely to eliminate summer annual weed seed production than mowing or tilling. Undisturbed summer annual grasses are already producing seeds, so the herbicide application should be made quickly in order to have the greatest effect at reducing weed seed production, however wait for the weeds to have 3-6 inches of new regrowth to allow for maximum herbicide uptake. The preferred herbicide recommendation is a minimum of 1.125 pounds acid equivalent per acre (# ae/A) of glyphosate plus 2,4-D ester at 1.0 to 1.5 pt/A. These rates are needed because the weeds are usually greater than 15 inches tall.
If warm-season perennials (johnsongrass, wirestem muhly, hemp dogbane, common pokeweed, and common milkweed for examples) are your target, then mow the field soon (before end of July) and allow the perennial weeds to regrow and apply glyphosate plus or minus 2,4-D ester in mid-September.
If cool-season perennials (quackgrass, Canada thistle, and dandelion for examples) are your target, then mow the fields now and again at the beginning of August or apply glyphosate at 0.38 to 0.56 # ae/A now to control or reduce summer annual weeds from producing seeds. Then in mid-October apply glyphosate plus or minus 2,4-D ester to control the perennial weeds. We are still a little unsure about the use of an herbicide application now that may severely injure the perennial species and not allow them to recover in enough time to properly be controlled in the fall, but this will reduce more summer annual weed seed production than just mowing.
For preventative-planting acres where nothing has been done, mow the fields as soon as possible. Then determine your target as with wheat stubble and treat similarly. The only differences are to allow the summer annual weeds to regrow 6-8 inches before spraying and summer annual weeds should be the main target for most fields. The key is to not allow summer annual weeds to produce seeds because weed control to be more difficult in future growing seasons. After the regrowth apply a mixture of glyphosate and 2,4-D ester. The minimum glyphosate rate should be 0.75 # ae/A and more certainly would be better.
Authors: Peter Thomison
Kernel development has started in many corn fields that were planted in April. Following pollination, kernel development (or grain fill) is the most critical period in the development of the corn plant for the determination of grain yield. Kernel development proceeds through a number of stages which have been characterized by such terms as blister, milk, roasting ear, soft dough, dent, etc. Since these descriptive terms can sometimes be difficult to interpret, alternative systems have been proposed. A staging system widely used by agronomists and crop consultants divides kernel development into 6 stages, designated numerically as R1, R2, through R6. The table below lists kernel developmental stages in sequence and provides a brief description of each phase.
Kernal Development Stages in Corn
|STAGE (see note below)
|APPROXIMATE DAYS FROM SILKING
|Fresh silks (no blisters)
|Silks brown, no or few kernal pimples and little clear fluid
|Visible kernel blisters with fluid
|Mostly white kernels w/milky-white fluid, some yellow kernals
|Mostly yellow kernels w/milky-white fluid, no solids yet
|Late milk-early dough
|Solids beginning to form, kernal pasty texture (barely edible)
|Soft dough (R4)
|Pasty or semi-solid (not edible), no visible denting
|Late dough-early dent
|Few kernals beginning to dent, especially near butt
|Majority of kernals dented or denting
|Essentially all kernals dented, milk line may just be visible
|Black layer (R6)
|Maximum kernal dry weight, kernal moisture 27-32%
Note: R-stages 1 through 6; specific number of days associated with each stage may vary from season to season, from location to location, and from hybrid to hybrid.
Keep in mind that the values for average number of days per stage and approximate days from silking in the table above are based on timely corn planting (e.g. early May). When corn is planted late, as was the case in many fields this year, it generally requires fewer heat units to achieve R6, physiological maturity or “black layer”, and this may affect the number of days per stage and days from silking.
Stress conditions such as drought, high temperatures, nutrient deficiency, disease or insect injury, excessive shade, hail damage, and overpopulation during grain fill may cause complete abortion of kernels toward the ear tip (“tip dieback”). Ear tip kernel abortion occurs when the youngest kernels resulting from the most recent pollination are cut off from nutrient flow because the supply is insufficient to fill all the kernels that have been set. Such kernel abortion is most likely to occur during the first two weeks after pollination (during R2, the blister stage). These same stress factors may also reduce kernel size and weight. Premature plant death resulting from diseases (such as stalk rots) or frost cuts off starch accumulation and results in small, light-weight (low test weight) kernels.
State Specialists: Pat Lipps, Dennis Mills & Anne Dorrance, (Plant Pathology), Robert Mullen (Soil Fertility), Ron Hammond and Bruce Eisley (Entomolgy), Peter Thomison (Corn Production), Mark Loux and Jeff Stachler (Weed Science); Extension Agents and Associates: Roger Bender (Shelby), Ed Lentz (Seneca), Mark Keonig (Sandusky), Harold Watters (Miami), Dusty Sonneberg (Henry), Steve Foster (Darke), and Steve Prochaska (Crawford).