Winter Brassica-small grains mixture at the OSU cover crop garden.
One of the more common “newer” mixing ideas is to add a brassica or non-legume broadleaf to the cover crop mix, either in place or with legumes. While adding legumes provided the potential of N directly to the production system, the benefit of legumes is often nutrient scavenging and bio-tillage. Most brassica species have deep tap roots that can grow throughout the soil system, and they have the potential to use these expansive and deeper rooting systems to find and take up nutrients (N, P, K, and other micronutrients) from deeper in the soil profile. These are redistributed onto the soil surface and can be more accessible to future cash crops upon decomposition. In doing so, growers can potentially limit nutrients entering groundwater from overfertilization or under-recovery of previous crops. The other benefits of these rooting systems are biotilling. This results from more extensive rooting systems, creating an increased number of macro and mesopores in the soil system. This can increase water infiltration in future cash crop systems. For both benefits, adequate growth must be achieved.
While these crops can scavenge to find nutrients, if a major deficiency is present, limited root growth will limit the ability of the crop to reach these lower depths. The other major issue is the time needed for adequate growth. Additional discussion is below on the potential for winter kill in these brassica species, but if too much or too little fall growth is achieved before a major killing frost/freeze, significant winter kill can be observed. Winter kill could limit the benefits of these crops.
Planting date is a significant factor for covers that integrate brassica. Some brassica species (such as Daikon Radish) have some winter survivability but typically much less than other species. However, others like canola can have as good winter survival as the winter small grains. This can be good as this will typically maintain solid soil coverage throughout the winter and spring months. However, canola can be challenging to terminate once the crop has transitioned from vegetative to reproductive growth. Therefore, winter killing this cover crop may be the desired outcome. Growers will then have to tend to maintain soil coverage. Therefore, mixing these crops with a small grain is always a good option. Brassica has also been documented to provide other benefits, such as aiding in nematode control. This occurs when the glucosinolates from the plants go through the breakdown process. An intermediate step of this breakdown is a volatile compound that can act as a fumigant. This means these cover crops could provide a biodegradable fumigant to help in insect and nematode control.
Winter legume-small grain mixture at the OSU cover crop garden.
Mixing in winter legumes to a winter small grains mixture is prevalent in other parts of the county and world. The benefits of the small grains mixes are still present in these systems. However, as the small grain total percentage and planted volume are typically lower than when planted without legumes, benefits like canopy coverage and total C may be slightly lower. While some of the limitations from a small grain only mixture, high C causing immobilization of N in the successive cropping system, are often not as critical if even present following these mixes due to the N contributed from the legume.
One of the primary challenges with this mixture is getting early cover. Most legumes have a prolonged early growing period. These mixed components can be very valuable from numerous avenues later in the season but are known for slower early growth. Therefore, enough small grains should be in the mixture to provide adequate early season cover, especially if it is intended for grazing. Another challenge is cost. Legumes will often be one of the direct costs of a cover crop mixture. To negate these costs, many growers will plant lower rates of legumes. However, growers need to ensure enough percentage of volume of the mixture is present as legumes to capture the benefits of that component of the mix. The final part is to ensure the mix ratio allows for the growth of both crops. Optimum early-season conditions can result in the small grain growing rapidly and inhibiting significant growth of the legume crop, especially if planted with a high enough rate. However, lower small grain percentage and higher legumes can increase cost and result in thinner or spotty stands earlier in the growing period. Spotty stands can be a greater challenge in winter cover crops systems compared to summer system as there is often a prolonged period of limited to no growth during the winter months.
The most significant benefit of adding legumes into a mixture is potentially supplying the successive cash crop with some N without adding it as fertilizer. The amount or N rate that growers can expect for their successive crop varies. With good breakdown conditions early in the season, it would not be unexpected to see 20-50 lbs N/ac being supplied to the subsequent crop. However, numerous factors will influence this. Factors like the amount of legume biomass produced, stage of the crop, termination timing and method, and C:N ratio of the cover as a whole will greatly impact the amount that should be expected. Most legumes reach peak N fixation around flowering. Shortly after this (depending on the legume) the plant will dedicate more of the sugars produced in photosynthesis toward growing the developing seed than fixing N. This increases the amount of C in the plant and widen the C:N ratio. Therefore, the highest N contributions will be when a crop is terminated after flowering but before pod set.
Image of small grains mix cover crops at OSU cover crop garden
This mix would be considered a traditional Oklahoma cover crop mix, as the state and most growers are well versed and familiar with growing small grains. This mix can and, in most years, will provide a fairly rapid canopy development. It will also have a strong canopy throughout the winter and spring months, as most small grains have strong cold hardiness. For those interested in grazing their cover crop mix, the inclusion of wheat, rye, and barley will typically provide enough tonnage and quality in the fall, winter, and spring. If the crop is not over-grazed, this mix should have good forage recovery. The ability to recover will benefit both forage production and conservation.
Another benefit of this cover crop mixture is the amount of C (Carbon) it can contribute to the system. Small grains are a good source for growers looking to build carbon reserves. However, if grown in rotation with traditional row-crops, growers should know they may need to manage their N inputs more heavily as high C can result in limited biomass availability (N immobilization). There is a balance between letting these cover crops grow longer in the system to develop more C reserves and terminating the cover crop too early to not have lasting residue.
One of the most significant benefits of cover crops many traditional row-crop producers value is aiding in weed control prior to planting and during the early-season. Because these small grains produce a rapid canopy and can maintain this canopy through grazing, these small grain mixes are good options to help in weed management.
This cover crop system can be planted in late-summer to early fall and still achieve most of the system’s benefits (biomass, cover, grazing potential, carbon). A winter grass mix can still be planted later in the fall into early winter, but the early-season benefits will not be as evident. Enough biomass to provide C to the system or do some light grazing while still maintaining a canopy to help cover the soil in the spring, but this will not be as good as with earlier planting. Growers should consider planting these systems simultaneously as fall winter wheat pastures but before grain-only wheat systems to get the most benefit from the system.
Over the next couple of weeks, we will be looking through several crops grown in Oklahoma, discussing their benefits within a rotation and some management issues/considerations growers may be interested. This will by no means be an extensive list, but an introduction to the discussion.
Over the last several years, Oklahoma producers have begun integrating several crops into their production systems. There are several reasons to adopted new crops into production systems, including commodity price, new crops being introduced into the region, adoption of new technology (i.e. herbicide resistance, adoption of irrigation), or changes of practices. Beyond these, integrating a crop rotation has been shown to increase crop yields, decrease insect and disease pressure, improve weed management, improve nutrient cycling, and provide better water and nutrient use efficiency. It has also been noted that there is no perfect or right crop rotation but to use crop rotation to improve the flexibility, intensity, and diversity of their production system.
Grain sorghum:
Grain sorghum has been heavily integrated into the western portion of the state. This is because sorghum is considered one of the most drought tolerant crops grown in Oklahoma. Grain sorghum only needs 6.5 inches of water for the plant to make grain. Once this level is met, the plant will gain 350 to 425 pounds of grain for each additional inch of water received. This not only includes received water but also stored water prior to planting.
The yield benefits of crops following sorghum have been well-documented. Two of the best documented benefits of grain sorghum have been with cotton and corn. This is primarily due to sorghum commonly being grown in regions that sustain a large number of corn and cotton acres. The most beneficial crop rotations frequently involve both a grass and broadleaf crop, due to the lack of insect, diseases, and weedy plants that will commonly affect both crop types. However, data from Kansas State University had demonstrated an 8.4 percent increase in corn yields following sorghum compared to continuous corn. These results have also been seen in Oklahoma. A study at the OPREC station in Goodwell, Oklahoma showed that a corn-sorghum rotation yielded similarly to a corn-soybean rotation, with both yielding nearly 20% more, compared to a continuous corn rotation. Part of these documented benefits could be attributed to pest cycles, such as Goss’ wilt, root worms, and corn borers.
Cotton and sorghum is a common rotation throughout more traditional cotton production regions in Oklahoma as well as throughout Texas. This is primarily due to both crops being considered low water use and providing a number of rotational benefits to one another. Data from Texas A&M has shown that cotton following sorghum produced 22% higher yields than continuous cotton (Table 1). One of the greatest values that grain sorghum can provide for cotton systems is residue. As very little residue is left following cotton harvest, most continuous cotton growers have to integrate cover crops or other high residue crops to decrease wind erosion, increase moisture storage, and minimize the negative impacts of wind on cotton seedlings.
Credit: Trostle 2000, Texas A&M
While there are several agronomic benefits between cotton and sorghum, growers have to be mindful of herbicide restrictions. For sorghum, several cotton herbicides pyrithiobac sodium (Staple LX/Pyrimax) and Trifloxysulfuron-Sodium (Envoke) possess long rotation restrictions and typically will require a minimum of a season between planting cotton and sorghum. Therefore, growers should understand what herbicides they have used in their cotton system and how these might influence the next sorghum crop.
Less is known regarding the rotational effects of grain sorghum on soybean. This is partly because these two crops are typically grown in very different regions of the state. However, with an increase in soybean acres in the western portions of the state, there is an increased potential for more sorghum acres to be rotated with soybean. Previous studies have suggested that growing soybean following sorghum resulted in similar yield benefits compared to corn (up to 17% yield increase). Sorghum can provide several benefits to soybean, including improved fertility and soil physical properties. However, similar to cotton, sorghum residue can greatly improve the soil moisture storage and retention, which is critical for soybean grown in western Oklahoma.
Managing a grain sorghum crop:
With all of the benefits of sorghum discussed above, optimum management is critical to ensure growers are optimizing productivity and profitability of the sorghum portion of crop rotations. Several production challenges have arisen in recent years that should be addressed.
How late is too late for planting (outside of the panhandle):
As with most production issues like this, the realistic answer is “it depends”. There is no firm calendar date that will always tell producers when the optimum time for planting will occur. This is because growers should delay planting until soil temperatures are adequate and enough soil moisture is present to allow for rapid germination and emergence. In most years, this will result in planting beginning in early to mid-April for southern regions and mid- to late-April for northern regions. Planting can continue past these points as long as adequate conditions persist. However, planting too late into May (typically past May 10th to 15th) could risk the sorghum plant reaching critical growth stages, i.e. flowering and grain fill, during what is typically the hottest and driest portions of the year. In years that these conditions are pronounced, significant yield loss can occur with sorghum planted in the 2nd and 3rd weeks of May. However, years with more mild and wetter July and August, these later plantings could yield equivalent to or higher than earlier plantings. For 2019, with cooler and wet conditions persisting through early May, sorghum may need to be planted later. Only time will tell the impacts that these later planting dates will have on yields.
Managing weeds in grain sorghum production:
Grassy weeds are one of the most difficult production challenges for sorghum production. There are virtually no methods for controlling grasses in-season. Therefore, growers must successfully manage these weeds prior to or at planting. Most growers integrate some form of S-Metolachlor in order to help control these grasses. Unfortunately, this product only has “partial control” rating for johnsongrass (one of the more challenging grassy weeds in Oklahoma). This requires growers to manage these weeds outside the sorghum crop within their rotation. Prior to planting grain sorghum, growers need to ensure that grassy weeds have been previously managed and pressure is low.
N management in sorghum
Based on recent studies across Oklahoma, N still seems to be one of the most limiting yield factors in sorghum production. Sorghum needs between 1.1-1.2 pounds of N per bushel of sorghum grain. Therefore, if growers are applying 75 pounds N per acre, the top end yield potential will be approximately 68 bushels per acre. As grain sorghum is considered a “low-input” crop, N is typically one of the first inputs growers reduce in order to cut costs. However, it has to be understood that decreasing N applications will directly lower yields.
Sugarcane aphids:
Since originally finding sugarcane aphids (SCA) in Oklahoma in 2015, they have been a major pest in sorghum production. As SCA were very difficult to manage, they have been a major concern for growers since their arrival. As such, they have been a reason for decreasing sorghum acres in recent years. Over the last several years, research programs throughout the southern Great Plains have learned a great deal about managing SCA. This research has provided information, which has allowed for easier management through agronomic practices, host-plant resistance, and insecticide applications.
Grain sorghum will continue to be a valuable crop for Oklahoma production systems, as it can be very efficient and productive in a wide variety of production systems across the state. Several production challenges have to be addressed in order to maintain the productivity and profitability of the system. It is because of some of these production challenges (namely, grassy weeds) sorghum cannot be grown continuously. Fortunately, grain sorghum serves as a very valuable rotation crop with many other crops grown in the state. Sorghum not only has the ability to improve yields in corn, soybean, and cotton production systems when grown in rotation, but sorghum rotations can also help manage against several weed, insect, and disease pests.
Questions have been arising about the impact some of the cooler temperatures experienced over the last couple of days and those to come will influence soybean still in the field across the state. Similar to other crops, it will greatly depend on numerous factors, including: temperatures, duration, stage of the crop, and conditions surrounding the event.
Temperature:
As with most wintery weather, temperature is the overarching issue. Temperature is an important and somewhat dynamic aspect for soybean production. Cool temperatures, especially paired with excessive moisture, are not favorable conditions for soybean production. However, temperatures above 40F will rarely result in detrimental impacts on soybean production, especially if paired with more optimum conditions before and following. These cooler temperatures will slow or even halt soybean growth for a period but should not result in large amounts of permanent damage.
Below 40F, more permanent damage would be expected. A yield decrease would be expected with prolong periods below this critical threshold, mainly from decreased seed size due to premature seed shrinkage. Colder temperatures will continue to be detrimental to the crop. The next critical threshold for soybean plants is 28F. Prolong periods with these cooler temperatures will result in whole plant death.
The impact of these temperatures and what this will actually mean for crop yield will depend on the stage of growth.
Growth Stage:
Growth stage is one of the largest determining factors in determining the extent of damage that could occur during cool or near freezing conditions. The first thing that needs to be determined is if the soybean plant has reached maturity. At maturity, the individual seeds have separated from the plant itself and anything that will negatively impact the plant will not little to no impact on the seed itself. Maturity begins at growth stage R7 (one mature colored pod anywhere on the plant). At this stage, plant and seed dry weight have been fully accumulated and seed moisture is around 60-70%. Past this stage, seed and plant dry-down are the primary activities. However, it should be noted that in soybean plants, especially in indeterminate soybean varieties, a plant will not reach maturity at the same stage throughout the entire plant. Therefore, this will not be universal throughout a plant let alone an entire field.
Soybean plants beyond maturity:
Once the soybean plants have reached maturity and plant/seed dry weight have been mostly accumulated, frost to freezing conditions will have only a minor impact on yield. Research has shown that a freeze around R7 growth stage has most often resulted in a <10% yield loss. In fact, a freeze event can help to defoliate some leaves still remaining on the plant. However, depending on the condition of the plant, a frost or light freeze can actually result in the plant remaining green for long or could result in high amounts of greenbean syndrome. Fields should be evaluated once conditions have warmed following the freeze event to determine potential harvest activities needed.
The freeze event around Oklahoma will require action much faster as it has been paired with widespread precipitation. If pods were at or near harvestable prior to recent rain or freeze events, they will need to be harvested quickly as wetting and dry of the pods will decrease the integrity of the pods potentially resulting in increased shattering. Therefore, growers should place priority on harvesting these soybean fields prior to any other activities.
Soybean plants not yet at maturity:
Some later-season double-crop soybean field might not have reached maturity. Recent and potential freeze events will have a larger impact on yield of these plants. If soybean have reached full seed (R6; where the seeds have begun to touch in a fully seeded pod), yield declines associated with a major freeze could reach as high as 30%. This will be primarily due to early and rapid seed shrinkage without accumulating total seed weight. Plants less mature will suffer increased damage. Frost or freezes on plants that have only reached beginning seed filling (R5) could result in as high as 60% yield decline.
Other factors that could influence freezes on the soybean crop:
While this may sound ominous for late-planted double-crop soybean fields, especially the crop planted following late wheat harvest, some positive effects may help. First, the temperatures do not appear to be getting cold enough to do substantial damage to the crop. Initial forecasts suggested that temperatures may get close to the below freezing mark. Additionally, the statewide rainfall received in the last several days can help stabilize the temperatures at or near the soybean canopy.
Any freeze event on a soybean crop prior to harvest is not ideal, as soybean are sensitive to late-season environmental stress. However, the positive thing for most soybean fields throughout the state is they have reached, at minimum, the R6 growth stages with, even a majority of our double-crop fields, having reached R6.5 to R7. As mentioned previously, beyond this stage minimal yield effects would be expected. However, on these less mature soybean crops, growers need to evaluate how they will harvest their soybean crop following these frost to freeze events, as some form of desiccation may be needed.
Soybean production throughout Oklahoma is very diverse. This is because of the wide array of production systems, ranging from early, full-season production through double-crop soybean production, with soybean being planted following wheat harvest. These diverse systems came with unique challenges that growers had to overcome in order to improve the success of these systems. One challenge that is present universally across all production systems is harvest. Harvest efficiency can be reduced by a number of factors, these can include late-season weeds present in the field, green leaves and petioles even with mature pods, and immature stems and stalks. In these cases, a harvest aid or desiccant may not only help improve the efficiency of harvest in the current season but also improve the fields for future years.
Application timing:
Determining the timing for harvest aids in soybean production systems is one of the most challenges aspects. Applying harvest aids too early could result in significant yield loss due to termination of the plant while the crop is still filling the seed and producing seed weight. Too late of application could result in delayed harvest, due to labeled restrictions (Table 1), resulting in higher amounts of seed loss due to shattering prior to or during harvest.
Determining an exact growth stage of a soybean field is the challenging aspect of harvest aid management. This is because the highly variable nature of the crop, especially with indeterminate soybean varieties. In many soybean fields, parts of the field or, even, parts of an individual plant could be in the early stages of maturity while other parts are still progressing through reproductive growth. Growth stage determination should be done on a whole field basis.
Harvest aids should be applied when the soybean plant has begun to mature. Maturity begins when the crop reaches R7 growth stage, or when one normal pod (non-damaged) on the main stem has reached its mature color. During this stage, most of the green color of the plant will begin to disappear and the crop will have a paler or yellow appearance. At the beginning of this stage seed moisture will typically vary around 60% moisture. This is still too early to apply harvest aids. Growers should allow the plant to reach 30-40% seed moisture prior to desiccating the crop. This will allow for rapid dry down of the vegetative material and allow for smoother dry down of the seed. It should be noted that the application of desiccants will not directly influence seed moisture and this practice should only be used to manage the green material in the field. Increased wind flow and higher light penetration associated with the use of desiccants can help to begin to dry down the seeds but the chemicals applied will have no impact.
Products available:
Several products are available that can be successfully used as a harvest aid in soybean production. Care should be taken on two different standpoints: 1) label restrictions of the individual materials, and 2) what value these products actually provide. Table 1 highlights products that are available and can be used as a harvest aid as well as products, harvest restrictions, and any potential additive required/suggested.
Paraquat:
The industry standard for soybean desiccation is paraquat. Paraquat does a very good job desiccating the soybean crop and weeds within a field given proper application and high enough carrier water. The primary flaw with paraquat is the long pre-harvest interval that is required, 15 days from application to harvest. Especially in Oklahoma conditions, soybean applied with paraquat should dry very quickly. This requires that producers should be ready to harvest following the harvest interval requirement to ensure minimal shatter loss.
Saflufenacil:
One of the newest soybean desiccants is saflufenacil, going by the tradename Sharpen®. Original harvest interval required was 7 days; however, supplemental labels have allowed for the crop to be harvested 3 days following application. While quicker harvest is allowed, it will typically require 7 days to allow for the crop to desiccate if the harvest aid was applied at around 30-40% moisture. One of the largest benefits of this harvest aid is the ability to apply it later within the maturation window and allow for quicker harvest. If used correctly, growers can use this harvest aid to help manage harvest around adverse environmental conditions or labor restrictions. Work done by Dr. Jim Griffin at LSU AgCenter showed that, 7 days following application, the desiccation potential was similar between saflufenacil and paraquat.
Carfentrazone-ethyl:
Under the tradename of Aim® can also be used as soybean desiccant. Carfentrazone is actually a soybean herbicide that can be used in-season to control many weeds, specifically viney weeds. Unfortunately, it being an herbicide that can be applied in-season, it has limited ability to desiccate the soybean crop. It should be noted that if viney weeds (specifically Morningglories) are a problem late-season, Carfentrazone can be very effective at desiccating weeds that could be an issue.
Sodium Chlorate:
As opposed to the other chemicals that have been highlighted above, sodium chlorate is an actual desiccant. As a true desiccant, not a harvest aid, sodium chlorate works to draw the moisture out of not only the crop but also any weeds that are present within the fields. This means, especially when paired with typical Oklahoma drying conditions, that the soybean crop will dry rapidly. The preharvest interval for sodium chlorate is 7-10 days depending on the formulation (Table 1). Similar to paraquat, following the preharvest interval, growers should be ready to harvest the crop immediately.
Management of late-season weeds:
One of the largest benefits of harvest aids in Oklahoma soybean production systems is late-season weed management. Several conventional herbicides are allowed to be applied later into reproductive growth (Lactofen, etc.); however, most common herbicides used in Oklahoma soybean production (glyphosate and dicamba) can only be utilized until early flower. This allows a long time between final herbicide applications until harvest. Harvest aids can be utilized as a means to help not only efficient harvest in the current season but also better weed management in future years. All chemicals that can be utilized as a harvest aid in soybean production can be successful at restricting late-season weed growth. Harvest aids, however, cannot be the last weed management strategy in the field during the season. As most weed plants are at or close to maturity and fully developed by the time they are treated with a harvest aid, complete termination of the plant is unlikely. Follow-up application before a fallow period or a successive winter crop will typically be required.
Harvest aid use in Oklahoma soybean production can be a very valuable tool. Increased harvest efficiency, aid in weed management, and evening out field maturity are all benefits that can be gained from this practice. However, growers have to know the limitations of the practice. Increased seed dry down and complete termination of adult weed stands cannot be consistently done with harvest aids. The success of using harvest aids as an in-season management tool for soybeans has been done in part with good early-season control and adequate fallow season management.
For further information, please contact your local county educator.
There has been a recent uptick in the amount of calls and reports we have been getting on the increasing presence of sugarcane aphids in the western grain sorghum production regions of Oklahoma, Kansas, and Texas. This is particularly in the panhandle region where sorghum is just now reaching the reproductive stages of growth. This has not only resulted in concern for these pests presence early in reproductive growth but has also increased the number of fields that have been sprayed or intend to be sprayed in the coming week. This has been meet some indication that applications are being made premature or when sugarcane aphids are not even present in the fields.
Proper identification:
Probably the most challenging thing for consultants and producers working to manage grain sorghum in sorghum production is proper identification of sugarcane aphids in the field. This is due to the fact that in small populations or with immature nymphs, many of the distinguishing features are difficult to see with the naked eye. A hand-lens or magnifying glass should be used to allow for proper identification. These can typically be purchased at a local store or purchased online at a reasonable price.
Many in-field indicators can aid growers in the identification of sugarcane aphids in the field. Honeydew on the top side of the leaves is one of the most telling signs of a sugarcane aphid infestation. However, two issues typically exist with using honeydew for identification or make recommendations on chemical control. Firstly, when noticeable honeydew is present in the field, especially enough that can be seen during quick field checks, often the population has grown large enough to create serious losses to the sorghum crop. Furthermore, several other insects in sorghum can create honeydew. One of these in-particular is corn-leaf aphids. These aphids are typically found in the whorl during vegetative growth or in the collar region of sorghum during reproductive growth stages. While these can create a large amount of honeydew, they typically cause little to no yield reduction of the sorghum plant and application is rarely ever recommended. These corn-leaf aphids also aid in the sustenance of predators that can be helpful in controlling sugarcane aphids if communities establish. Therefore, making an application to control these pests are frequently cost adverse and can negatively impact natural predator populations.
Corn leaf aphid at flowering in sorghum (Photo courtesy of Jason Warren).
There has also been increased reports of sugarcane aphids in the sorghum head during early flowering. While this is always within the realm of possibilities, these aphid pests do not like sunlight and will typically not be in the head at these early stages due to the high amount of sunlight that is present. We can see sugarcane aphids in the heads but often much later in the season during grain fill or ripening when there is much less exposure to sun. Sugarcane aphids, for the bulk majority of the season, will be found on the underside of the sorghum leaf. Aphids can be present on the upper side of the leaf, but these will typically be yellow sugarcane aphids not the white sugarcane aphids we are concerned with.
While honeydew and location are good indicators that sugarcane aphids could be present, physical identification needs to be done prior to making an application. This is the only true way to positively identify these pests as well as know the magnitude of populations growers will have to manage around.
When to make an application:
When to pull the trigger on a chemical application is very challenging and several factors (including population, stage of the crop, and environment) come into play in this decision. Furthermore, based on the potential growth patterns of these pests, the line between under threshold and exceeding threshold is very narrow. Growers do not want to become overwhelmed with aphids prior to making an application. Not only could this drastically effect yields but incomplete coverage applications could allow for lower efficacy of applications resulting in not achieving a complete kill. However, growers do not want to apply before the economic threshold. These applications can be costly, especially when applying high gallons. Early application do not use the potential predators in the field to help control these pests and may result in an application that was unwarranted.
Growers should make an application when a minimum of 50% of plants have between 50-100 aphids per leaf. To visualize, 50-100 aphids will result of being able to be completely covered by a quarter. Higher populations would be considered over threshold.
Should I treat aphids in forage sorghum/BRM sorghum/Sorghum-Sudan:
This is a difficult question to answer. While there has been some indication that aphids do impact these forage-type sorghums in-season, whether or not to spend money on an application is more difficult. The challenge with application is two-fold, both return on investment and application efficacy. Determining the return on investment is difficult as we do not fully understand or know the amount of impact sugarcane aphids can have on tonnage or quality. Initial indication from Texas A&M has indicated that quality did decrease in forage-type sorghums that were infested by sugarcane aphids but not to the level that was expected. The second challenge come with application. As the current chemistries used to manage sugarcane aphids do not have true systemic nature, coverage is critical. On forage-type sorghums, this can be very challenging, especially later as the crop nears cuttings. Therefore, control of the upper canopy may be achieved but mid- to lower canopy would only be marginal.
So what should I do?
One of the best management for sugarcane aphids in more maturity forage-sorghums is to harvest. Cutting and baling will remove or minimize the impact these pests can have on the crop. However, there has been reports that aphids on the cut and windrowed hay have caused issues in the baling process. There current is not solid answer for what to do if aphids persist on the cut hay. Both chemicals have harvest and grazing restrictions that growers will have to adhere. However, the return on investment and efficacy still come into question and unfortunately there is no solid answer to this currently.
Managing aphids late-season:
Outside of the far west regions, sorghum producers have begun to finish up the growing season, with several fields being harvested prior to recent rains. However, with increased aphid pressure, questions arise on how to manage a crop that is infested with aphids at or near harvest. Discussions were had last year that growers could use desiccants to management sugarcane aphids at harvest. The results on the success of this practice have been highly variable. A rapid dry-down of the plant may dissuade the pests from those plants and active populations could deplete food stores and die out, resulting in success of this practice. However, it has been shown that more gradual dry-down of sorghum can result in the aphids moving into the head of the sorghum plant and causing greater harvest issues there. It should be noted that sugarcane aphids present after black-layer will no longer effect grain yield but may decrease the harvest efficiency and lead to lower yields realized on a per acre basis through increased honeydew. This should be evaluated on a case-by-case basis. Low populations down within the canopy of the plant should result in little to not issue at planting and a desiccant may be sufficient to control these pest at harvest. However, if populations are high, particularly higher in the plant canopy or in the head of the plant, the application of a desiccant and insecticide (Transform® or Sivanto®) may be warranted. Be cautious as there are harvest restrictions on both of these chemicals.
Overall, this is a good crop in front of much of Oklahoma. Grower should make sure to take steps to ensure that yields and profits are optimized on each field individually because with insect management, fields can change across the road. Sugarcane aphids have been a minimal pest up until now throughout the region. However, now is the time to get out into sorghum fields to be scouting for sugarcane aphids. For further questions please visit your local Oklahoma County Extension office for additional information and management details.
Throughout the state, the crop could be considered average to above-average. However, similar to wheat, canola, corn, soybean, and cotton crops this year, it is highly variable. Certain areas that have received moisture have taken advantage of the warmer temperatures and look quite well. The areas that have not receive rains or only portions of the overall rainfall have more evident stressed plants.
Above average sorghum crop planted early near Chickasha. This area has received numerous rains since planting.
What will happen to these stressed plants?
This will depend on what happens in the next several days to weeks. Areas of the state that have failed to receive many of the recent rains, the crop is starting to struggle. This has resulted in a majority of leaves beginning to roll earlier in the day. Even under these stressful conditions, many earlier maturity sorghum hybrids are beginning to push reproductive growth. Moisture stress during booting and early flowering stage quickly reduces yield be decreasing the total number of seeds set for each head and decreasing overall seed size. If water stress continues, it will decrease seed weight in addition to the other factors. This will result in many of these hybrids yield potential, that could be achieve later in the year, decreasing. However, we cannot forget that the tillering nature of sorghum can allow the plant to recover from these conditions a lot better than most other crops, as long as adequate conditions return shortly.
Can these recover?
Yes, the crop can still recover, especially if the crop was planted into decent moisture and had any degree of moisture within the soil profile. Yield have begun to become to be limiting. However, this is only after moisture stress. Grain sorghum leaves will inherently begin to roll when humidity is low and temperatures are high. Growers should evaluate moisture stress between 9-10am. If leaves are already rolled or have started to roll, the plant are under moisture stress. If leaves do not begin to roll until later in the afternoon, this is a natural reaction to the environment around the plant. If hot, dry conditions persist, moisture stress will get more severe and the physiological response will occur earlier in the day.
Moisture stressed sorghum. Leaves were rolled by 10am
What about sugarcane aphids?
There has been increasing reports of sugarcane aphids being found throughout the state. The best place to keep up to date with sugarcane aphid activity is the MyFields website (https://www.myfields.info/pests/sugarcane-aphid). This will keep you up to date with where sugarcane aphids have been identified by sorghum specialists from around the state and nation. It must be noted that this is done on a county by county basis and your county being on this list solely means sugarcane aphids have been found in your county on sorghum. Furthermore, this does not indicate that sugarcane aphids have even been found at a treatable level in the county but they have just been found. Seeing your county on this list should solely be an indication that extra care and scouting should be done and not that action is warranted. This should be used as another tool at producer’s disposal to help with management of sugarcane aphids.
What will the temperature do with sugarcane aphid populations?
Overall, general thought is that hot and dry conditions cause an increase in population to sugarcane aphids. The mechanism for this is a little less known. Some have indicated that sugarcane aphids thrive in these environments and can quickly overwhelm the grain sorghum plants due to not only population increases but the added stress on the plants from the environmental conditions. Other indicate that sugarcane aphid population growth is not directly influenced by hot and dry weather but rather beneficial insects that would typically help keep aphid populations in check and negative impacted by these conditions. Decrease in beneficial populations allows the aphids to grow unchecked and result in a drastic increase in population. Indifferent of the mechanism, under hot, dry conditions, aphid populations will likely continue to increase and extra scouting should be done in order to catch populations low prior to any needed application.
When should I make an application for aphids?
Target threshold for aphid applications is the same as it has been the last several years. We are looking for 100 aphids per leaf. However, the way we distinguish this threshold has changed from previous years. This season, when scouting for aphids, we will need to evaluate a minimum of 20 plants. It is better if 40-50 plants are evaluated but 20 gives a decent indication. Once a plant has been identified, growers will need look at two leaves. This will make a total of 40-100 leaves being evaluated depending on how many plants are selected. If over 50% of these leaves surpass the 100 aphid per leaf threshold an application is warranted. We have shifted to this newer evaluation method to ensure applications are being made when aphids are present throughout the field and not just in isolated hotspots. If hotspots are identified, there may be a validity in spot spraying these areas, especially if they are areas of the field prone to aphid movement and buildup (i.e. edges of fields near ditches with Johnsongrass or tree lines).
Overall, similar to other crops in the state, this year’s crop will be plagued by spottiness, where some areas of the state will have a great to average crop while other portions will be meet with challenges. However, most of this is due to challenges with Mother Nature. As far as aphids are concerned with this year, we have had several reports of aphids; however, number have been low. This does not mean the applications are imminent or that populations will crash, solely that growers in these regions should be more proactive in their scouting patterns and visit the site an addition time or two during a week to scout.
With recent freezes across the region, there will probably be several questions over the next couple of days and weeks regarding the status of the canola crop. It has been said and it could not be any truer, no two freeze events are the same. This is definitely true for the freeze event that was experienced nearly statewide over the weekend. Many factors play into the severity of a freeze event, these will include: how cold were the temperatures, length of the freeze event, and stage of the crop. For the most part, this last freeze did not play nicely with any of these factors. Quite a bit of the crop was nearly flowering or at beginning flower. Most folks experienced with canola will tell you that the bottom third of the canola raceme hold a fair amount of total yield (in a typical season). For those with fields flowering, the temperatures were cold enough for a prolonged period of time that we could see some decent loss of flowers on these primary stems. This is because all the flower exposed to this freeze event will typically go sterile and not produce a viable pod. Those producers that were at bolting or at late rosette, the canola should be in a much better place. Most of the canola that I found today presented with crooked stems that did not bend beyond half-way down the plant. Plants should have adequate time to correct this and produce and adequate main stem. Furthermore, most buds that were not quite at the flowering stage looked good and should have been protected against the cold weather and still should produce flowers.
Canola plant with stem bending typically associated with freeze damage, 2014 freeze (Josh Bushong, Oklahoma State University).
As with most crops following a freeze event, the conditions over the next several days and weeks will determine how much yield was lost. If the weather cooperates over this period, even the most severely damaged canola should put on further axillary buds and be able to put on additional flowers. This indeterminate nature is a value of canola during these later freeze events. As opposed to wheat, where if the head of a tiller is killed that tiller is no longer productive, canola can still produce yields from that primary stem. If good growing conditions present, the canola plant may still produce but will likely be delayed. The fear from the delayed maturity of the plant will be the plant maturing into less favorable conditions. This is especially true regarding flowering during months that typically have much higher average temperatures. This could result in poor pollination which in turn will result in poor pod set.
Several other questions have arisen, particularly regarding the impact the drought conditions will have on the canola plant heading into a major freeze. This should have little to maybe a slightly positive effect. A more stressed plant will produce physiological features to handle this stress, this could result in less impact on the plant due to the freeze. The primary concern regarding the dry conditions prior to this freeze will be on the limited vegetative growth following green-up that much of the state has experienced. This lack of vegetation could leave more limited reserves for the plant to catch up and the plant will be more reliant on cool, moisture conditions over the next several days to weeks.
To evaluate the damage of the canola, most will have to wait for adequate growing conditions to return. Based on the 10-day forecast, this could be the end of next week or the week following. If the reproductive structures continue to progress, whether that be continue to grow or to produce flowers, the plant should be able to adequately yield. If sub-optimal conditions come over the next several days, the yield potential could be damaged. With a freeze of this magnitude, growers should expect to see some gaps in the flowering structure and potential stem splitting when they return to the fields next week. This stem splits have less an impact on yield but a higher potential impact on stalk strength and standability later in the season. Higher amounts of split stems will result in higher amount of lodging and potential decreased harvest efficiency.
Split stem following a major freeze event. This may cause issues with stem strength and potentially increased lodging (Photo used with permission from Dr. Mike Stamm, Kansas State University).
With growers assessing the damage over the next several days for both wheat and canola, growers can take solace in that canola has very good resilience and can rebound from these events. As of now, we must take time to let both plants try to rebound and produce adequate yields for these two critical winter crops.
Everything but Wheat 