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Bt Cotton Situation

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Over the past two weeks Louisiana has experienced a slow but steady corn earworm moth flight in cotton, which  has lead to a slow but steady egg lay.  Fortunately, this type of worm activity has not put the selection pressure on our  Bt technology we experienced last year.  This has also drastically reduced our insecticide oversprays as well. As of this week, Louisiana has more cotton that has not been sprayed for bollworms than cotton that has been sprayed.

Based on small plot research and Bt sentinel plot work from the Louisiana cotton growing areas, all of the technologies are performing better this year than last year. Results from our Bt technology tests indicate Bollgard 2 varieties are experiencing an average of 2.5% fruit injury, Bollgard 3 varieties are experiencing an average 3.0% fruit injury, both Widestrike and Widestrike 3 varieties are experiencing 4.0% fruit injury. TwinLink and TwinLink Plus are experiencing 5.0% and 3.0% fruit injury respectively.  These numbers are also reflected in reports I am receiving from the field with only a few instances of rescue sprays needed for bollworm escapes in Bt cotton.  Remember, the fruit injury threshold for Louisiana cotton is 6% with the presence of live worms.

Overall, this is good news for Louisiana cotton producers and signals that our Bt technology may still have some life left in it. Beware, this situation can change quickly and bollworm escapes can and will happen in all technologies. Scouting is key and under light pressure our Bt technology is appearing to hold but if pressure intensifies a rescue spray may be warranted.   Keep in mind that bollworms are cryptic feeders, and worms that have established in squares and bolls may not be controlled by insecticides including the diamides. If you have any questions or comments, please feel free to contact your county agent or me.

Successful soybean production demands proper early-season decisions

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Todd Spivey, Sebe Brown, Trey Price, and Daniel Stephenson

 

Soybean Planting Decisions

In Louisiana, soybean planting practices vary across the state, due in large part to varying environments and cropping systems.  Planting date, seeding rate, and seeding depth decisions should all be based on local conditions and factors affecting your farm such as soil moisture and temperature, soil type, and cropping rotation.

Planting Date

Regardless of location and cropping system, our optimal planting window will typically fall between April 10 and May 10.  Although it is possible to produce high yields outside of this window, research from the LSU AgCenter has shown yields are most consistent when planted timely.  Due to recent mild winters observed across Louisiana, it is not uncommon for soybeans to be planted as early as late March, though additional considerations should be taken to account for potential cool, wet conditions that are often observed.  If growers intend to plant early, soil temperatures should be monitored so that soils reach at least 55 to 60°F by 10AM.  The forecast for up to seven days after planting should also be considered for early planted soybean as emergence will also be affected by cool soil temperatures after planting.

Planting date of soybean, being a photoperiod sensitive crop, also directly influences the number of days to flowering.  Timely planted soybean has more time and a greater potential to develop adequate vegetative infrastructure to support maximum yields than do late plantings.  The goal of vegetative growth, as it concerns planting date decisions, is to close the canopy before R1 (first flower).

Seeding Rate

Because seed size can vary by variety and even by seed lot within a variety, pounds of seed per acre should never be used in determining seeding rates.  Growers should calibrate seeding rates based on seed per foot (Table 1).  Seeding rates that are too low do not allow for adequate vegetative infrastructure for optimal yields.  On the other hand, seeding rates that are too dense can reduce yields, encourage disease proliferation and lodging, and increase seed cost.  Research conducted by the LSU AgCenter has shown that soybean yields are not reduced with populations as low as 70,000 plants per acre as long as plants are uniformly distributed through the field (Figure 1).  These same studies show that yields are not increased by increasing seeding rates as high as 175,000 seed per acre.

The LSU AgCenter recommendation for soybean seeding rates on sugarcane beds is 140,000 seed per acre.  In most other systems, seeding rates should range from 115,000 to 130,000 seed per acre in optimal planting conditions down to 30 inch rows.  Seeding rates should be increased to a range of 125,000 to 140,000 on 20 inch rows or less.  Regardless of row spacing, these values should be adjusted up to a maximum of 150,000 seed when environmental conditions before or after seeding are not conducive to seedling development.  These environmental conditions are often encountered with early plantings and include current or forecasted cool soil temperatures or excessive soil moisture.  Late planted soybean seeding rates should also be adjusted up to account for the lack of time available for vegetative growth before flowering, as discussed previously.  With few exceptions, soybean seeding rates in Louisiana should not exceed 150,000.

 

Table 1. Seeding rates expressed as seed per foot of row.
Row Spacing 6 ft Sugarcane Bed 38” 36” 20” 15” 7”
  3 drills 2 drills
  —————————————- seed / foot —————————————-
150,000 seed 6.9 10.3 10.9 10.3 5.7 4.3 2.0
140,000 seed 6.4 9.6 10.2 9.6 5.4 4.0 1.9
130,000 seed 6.0 9.0 9.5 9.0 5.0 3.7 1.7
120,000 seed 5.5 8.3 8.7 8.3 4.6 3.4 1.6
115,000 seed 5.3 7.9 8.4 7.9 4.4 3.3 1.5

Figure 1. LSU AgCenter studies have shown seeding rates as low as 75,000 seed per acre are able to maintain optimal yield.

Seeding Depth

Plant only deep enough to place the seed in moist soil.  Dependent on soil moisture, seed should be planted from 0.75 to 1.5 inches on sandy or silt loam soils and 1 to 2 inches on clay soils.  Good seed to soil contact is imperative and must be a strong focus, especially when planting into residue from the previous crop or cover crop.  Although planting deeper often results in reduced vigor, many of our varieties can emerge from depths below what is recommended and growers can err on the deep side if soil coverage is a concern.

 

Seedling Disease and Fungicide Considerations

Early season soybean disease concerns can include Pythium or Phytophthora species causing seed rot, damping off, or root rot in areas that are not well-drained.  Group 4 seed treatment fungicides will provide some protection against these species.  If soils are well-drained and planting conditions are optimal, disease caused by these pathogens is unlikely.

Pre-emergence seedling disease or post-emergence damping-off caused by Rhizoctonia solani is the most-commonly observed seedling disease in soybean in Louisiana (Figures 2 & 3).  Plants surviving the seedling stage may develop a root rot resulting in delayed development and stunting.  Stresses such as cold weather, nematode/insect infestation, or herbicide damage may exacerbate Rhizoctonia damping off.  In recent years, significant stand losses have been observed in Louisiana due to less-than-ideal planting conditions.  Seed treatments containing a strobilurin (Group 11) or SDHI (Group 7) compound are very effective at reducing incidence and severity of Rhizoctonia damping off.  The pathogen population, which is soilborne, may be reduced during long periods of flooding, high soil temperatures, or fallowing fields.  Potential for disease is greater in lighter soils, and optimal conditions for disease development are 75 to 90°F with 30 to 60% soil moisture, although the pathogen is capable of causing disease at lower temperatures and in any soil type.

Figure 2. Thin soybean stand as a result of Rhizoctonia solani.

Figure 3. Soybean seedling infected by Rhizoctonia solani.

In recent years, “base” fungicide seed treatments (usually consisting of metalaxyl/mefenoxam + at least one broad spectrum fungicide) are more-commonly found on soybean than in previous years.  In most cases “base” fungicide seed treatments are adequate at protecting seedlings under adverse growing conditions that are often encountered early during the planting window.  Results from many years of field research trials at multiple research stations in the state indicate that fungicide seed treatments will result in increased stand under moderate to severe disease pressure; however, realizing significant yield preservation and economic benefit in soybeans is the exception rather than the rule.  If your seed company does not offer a choice of seed treatments, the “base” offering likely will be sufficient for establishing a stand under tough conditions.  It is not necessary to over-treat base fungicides with additional fungicides in soybeans unless you are targeting a specific problem on your farm.  Also, it is important to specifically know which fungicides come on the seed as it is redundant to over treat with a fungicide having the same mode-of-action.  If seed companies offer “naked” seed, soybeans may be planted without fungicide seed treatment as long as you have no history of seedling disease issues, plant during the recommended window, achieve appropriate soil temperature and soil moisture, and schedule planting when the long term weather forecast is ideal for soybean development.  If you prefer to plant fungicide-treated seed, significant cost savings may be attainable by allowing distributors to over-treat or treating naked soybean seed yourself with a product of choice.

 

Early-Season Insect Pests and Insecticide Seed Treatment Decisions

One of the most important decisions producers must make when planting soybeans in Louisiana is planting date. Soybeans have the utility to be planted in early March to late June. This wide variation in planting dates exposes seedling soybeans to a multitude of insect pests that affect both above and below ground plant structures.

 

Optimal Seeding Dates in Louisiana by Maturity Group
Group III April 15 – May 10
Group IV April 15 – May 10
Group V March 25 – May 5
Group VI March 25 – April 30

 

Soybean seedlings possess an exceptional amount of vigor and can tolerate a substantial amount of insect injury during the seedling stage. However, early planted soybeans may also encounter greater amounts of environmental fluctuations that affect air and soil temperature. Cool conditions can negatively affect vigor and under the right conditions stall plant growth and development. The addition of insect injury, to the aforementioned mentioned environmental conditions, increases stress the plant encounters resulting in loss of stand and yield potential. Therefore, the inclusion of an insecticide seed treatment (IST) provides growers a risk management tool when soybeans are planted early.  The primary insect pests of early planted soybeans are bean leaf beetles, wireworms and grape colaspis.

On the opposite end of the spectrum are soybeans planted late, i.e. behind wheat or are late due to unforeseen circumstances such as inadequate or excessive soil moisture. These beans are more at risk for insect injury due to the potential for large insect populations to build in neighboring fields and generally more insects present in the environment. As a general rule with all agronomic crops, the later the crop the more insect pressure that will be encountered throughout the season.  This is particularly evident when soybeans are planted into wheat stubble. Wheat stubble is favorable for the development of threecornered alfalfa hoppers and thrips. Thus, an IST is a sound investment when soybeans are planted late.

However, soybeans planted in a timely manner, that being within the recommended planting window, under optimal soil conditions, and low pest densities will often not benefit from the addition of an IST.  Insecticide seed treatments typically produce the most benefits when environmental conditions are sub optimal as outlined in the prior paragraphs. With the current economic climate and many ag-professionals looking at areas to cut inputs, justifying the use of IST on soybeans when planted under optimal conditions becomes harder to support. Saving the cost of an IST can go to making a stink bug application later season that may provide a greater economic return.

In addition to early or late-plantings, there are other situations in which ISTs are justifiable. These include weedy fields with incomplete burn down applications, reduced tillage field arrangements, fields with historically problematic early insect pests (wireworms and/or threecornered alfalfa hoppers) and continuous plantings of one crop.  Each field is unique and the use of ISTs as a blanket treatment over every acre may not be justifiable with $8 soybeans.

 

Early-Season Soybean Weed Control Decisions

Data has shown that maintaining soybean weed-free for the first 5 weeks after emergence is required to maximize yield.  The best program to maintain soybean weed-free for 5 weeks is

 

  1. Apply a residual herbicide to the soil after planting before soybean emergence. This application is commonly called a preemergence or PRE application.  The choice of PRE herbicide depends upon the weed spectrum in the field, so call your LSU AgCenter parish agent or a weed scientist for help.  If small weeds are present at planting, tank-mix paraquat at 0.5 lb ai/A (32 oz/A of a 2 lb/gallon formulation or 21.3 oz/A of a 3 lb/gallon formulation) with the PRE residual herbicide to provide control.

 

  1. Apply a residual herbicide, such as Dual Magnum, Zidua, Zidua SC, Warrant, Prefix, or Warrant Ultra, at labeled rates tank-mixed with glyphosate or Liberty postemergence (POST) 2 to 3 ½ weeks after PRE application.

 

Farmers, consultants, and pesticide dealers often worry about injury to seedling soybean by a PRE herbicide and don’t want to use them.  I have evaluated PRE herbicides in soybean for the past 8 years and rarely have I observed a reduction soybean yield due to early-season herbicide injury.  Did some of these herbicides reduce soybean growth?  Yes, but when growing conditions are proper, yield most likely won’t be reduced.

Glyphosate-resistant Palmer amaranth and waterhemp, both pigweed species, can be found in virtually all Louisiana parishes where soybean is grown.  To manage resistant pigweeds, a herbicide program must contain residual herbicides.  Also, a herbicide program for resistance management must contain multiple modes of actions, meaning every herbicide applied is killing the weed in a different way.  If a weed isn’t killed by a herbicide application, the first thing to do is remove it from the field by pulling it up, then call us to help you figure out why the herbicide application didn’t work.

 

 

Use of Harvest Aids in Louisiana Soybeans

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Todd Spivey, Sebe Brown, Josh Copes, Donnie Miller, Boyd Padgett

Over the last several weeks, we have received numerous calls about soybean harvest aid timing, products, and general recommendations.  The use of harvest aids in Louisiana soybeans is a common practice, with timely applications improving seed quality and harvest efficiency while potentially resulting in a soybean harvest 10 to 14 days earlier when compared to non-treated beans.

Timing

If the goal of harvest aid use in soybeans is to promote early harvest and improved harvest efficiency, harvest aids must be applied as timely as possible.  Once seed have separated from the white membrane inside the pod, they have reached physiological maturity and will no longer increase in size.  Any use of a harvest aid prior to the majority of seed reaching physiological maturity will result in a loss in yield.  Table 1 gives the paraquat label requirements for harvest aid application timing in soybean. Research conducted in Louisiana by Dr. Jim Griffin and Joey Boudreaux established that a harvest aid application could be made to soybean without yield penalty as long as soybeans are at reproductive growth stage R6.5 (physiological maturity). They provided a list of procedures to help determine when harvest aids can be safely applied to soybeans:

  1. Begin to scout fields for harvest aid timing when leaves begin to yellow
  2. Collect pods from the top four nodes of the plant at multiple, random locations within a field
  3. Open soybeans from pod, they should shell easily, and look for soybean separation from the white membrane
  4. If soybean separation from the white membrane has occurred for all pods collected, the seed has reached maximum dry weight and harvest aid application can be made without yield penalty

Plant appearance at growth stage R6.5 will vary by variety so close attention should be made to pods collected from the field and if seed have separated from the white membrane (Griffin and Boudreaux 2011 Louisiana Agriculture magazine Vol. 54, No. 2, Spring 2011).

Table 1. Proper application timing of harvest aid in indeterminate and determinate soybean varieties.
Indeterminate Varieties 65% of pods have reached a mature brown color or seed moisture is less than 30%
Determinate Varieties Plants are mature; beans are fully developed, 50% of leaves have dropped and remaining leaves are yellowing.

Products

Producers have several harvest aid options, though the typical harvest aid application consists of paraquat with an additional nonionic surfactant.  With excessive morningglory pressure, growers might consider including carfentrazone (Aim) or saflufenacil (Sharpen) with paraquat to improve desiccation of vines and in situations with high grass pressure, a tank-mix of paraquat with sodium chlorate may be warranted to improve the desiccation of grassy weeds prior to harvest.  Questions have also been received in regards to the use of sodium chlorate to aid in drift reduction of paraquat applications made by air.  The LSU AgCenter has no data to support this claim and only recommends the use of these products together for improved desiccation of weeds and soybeans present in the field.

It is also imperative that producers consider the required preharvest interval (PHI) associated with each product label.  When using multiple products, the longest PHI must be adhered to.  Labeled rates and comments are presented below in the excerpt from the 2017 Louisiana Suggested Weed Management Guide.

Labeled rates and comments of soybean harvest aid products from the 2017 Louisiana Suggested Weed Management Guide

Redbanded Stink Bug Considerations

Producers should also continue monitoring redbanded stink bug (RBSB) populations and should not rule out the inclusion of an insecticide with the application of a harvest aid.  LSU AgCenter entomologists recommend the control of threshold populations of RBSB until the soybeans are out of the field.  This means that many producers could, and should, include an insecticide for the control of RBSB with their harvest aid application (sodium chlorate cannot be tank-mixed with any insecticide).  It is important to keep in mind the restrictions placed upon many of the products at this point in the season.  These restrictions may include total active ingredient restrictions and PHIs.  Acephate, a common recommendation for RBSB control, can only be applied up to 2 lb ai A-1 year-1 in Louisiana.  Other insecticides also have increased PHI such as the pre-mix product Endigo, with a PHI of 30 days.  It is important to read and adhere to the label of all labeled materials prior to use.  When label restrictions prevent the inclusion of an insecticide with the harvest aid, producers should not delay the harvest of soybean so that the seed can be removed from the field as quick as the label allows.

Redbanded Stink Bug Numbers Increasing in Soybeans

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Reports from the field indicate redbanded stink bug (RBSB) numbers are beginning to build in soybeans at the R5 development stage and beyond. Once RBSB colonize a field, native stink bugs often are forced out or are outcompeted, leaving only RBSB behind. The Louisiana threshold for RBSB is four insects per 25 sweeps. RBSB are strong fliers, and routine scouting is essential to detecting an influx of these insects. Furthermore, the presence of immatures signals that RBSBs are reproducing, meaning previously applied insecticidal controls may no longer be active. Recommended insecticides include pyrethroids, neonicotonoids and organophosphates.

The use of premix insecticides, including Endigo ZC and Leverage 360, may offer a degree of repellency not observed with other insecticides. Insecticide efficacy tests conducted at the Macon Ridge Research Station in Winnsboro demonstrated satisfactory control of RBSB while also having a possible added benefit of repellency. However, these insecticides perform best when populations of RBSB have not exceeded threshold. Once RBSB populations have exceeded threshold, the use of tank mixes of either acephate (0.75 to 1.0 pounds per acre) plus bifenthrin (6.4 ounces per acre) or Belay (4.0 ounces per acre) plus bifenthrin (4.0 ounces per acre) may be required to get them under control.

As with most insects, staying ahead of RBSB populations will make season-long control much easier while also reducing injury. Please contact your county agent or me for more information.

Bt Cotton Situation

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For the past two weeks, most of Louisiana has been in the midst of a very large bollworm moth flight. Our moth trap catches were averaging about 10 moths per day and moved to more than 100 late last week. I have received numerous phone calls on how the technology is holding up and what insecticide should be used to over-spray. Another issue to consider is how much these worms were pre-selected in Bt corn. My colleagues around the Midsouth and Texas have seen a very large number of worms coming through Bt corn and Louisiana is no exception. Further, LSU AgCenter entomologists discovered a change in susceptibility of bollworm to Cry1Ac and Cry2Ab. The resistance does not appear to be complete and some fitness costs may be associated. If these results are any indication of Louisiana’s bollworm population this year, we may experience more escapes in Bt cotton.

Results from our Bt technology tests and reports from the field indicate that Widestrike cottons (including 499, 312 and 333) are experiencing large amounts of injury. Our small plot work at the Macon Ridge Research Station in Winnsboro is averaging 10 percent fruit injury in Widestrike (WS) and 6 percent in Widestrike 3 (WS3). Based on our work we conducted with the mid-South entomology group last year, we validated a 6 percent fruit injury threshold in Bt cotton. Therefore, WS3 is better than WS, but both technologies would need to be over-sprayed to preserve yield in this situation.

Furthermore, Bollgard 2 (BG2) and Twinlink (TL) have a more robust Bt package than WS. However, I have seen these technologies fail under severe pressure. As of this week, reports from the field and results from our trial work indicate BG2 is still performing well — but this can change quickly. TwinLink’s performance has been inconsistent, with a number escapes being reported. This seems to be dependent on the environment and insect pressure. Keep in mind that stress can negatively affect Bt expression in cotton. Stressed plants may not express a high enough level of toxin to control bollworms.

Independent of environmental factors, if bollworm escapes are detected, a rescue spray may be warranted. The use of pyrethroids is strongly discouraged. Louisiana bollworm populations have the highest level of pyrethroid resistance in the United States, and pyrethroid applications may not provide adequate control. They may even flare secondary pests such as spider mites. The LSU AgCenter recommends the diamide chemistry (Prevathon, Besiege) for control of bollworms in cotton. Beware that Besiege contains a pyrethroid and use may inadvertently flare secondary pests. Keep in mind that bollworms are cryptic feeders, and worms that have established in squares and bolls may not be controlled by diamides. If you have any questions or comments, please feel free to contact your county agent or me.

Louisiana Rice Notes #6

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(click to view)

This edition covers current crop progress and issues, recommended fungicide rates and timings, shortage of Sercadis, and stink bug BMP’s.

Thrips Management in Cotton

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With the abnormally warm winter and spring, cotton planting in Louisiana has gotten off to an early start. In Louisiana, and across most of cotton states, thrips are considered the number one early season insect pest. The species we encounter greater than 85% of the time is tobacco thrips with western flower thrips typically comprising the other 15%.

Thrips control options are limited to seed treatments, in-furrow applications and foliar sprays. Over the past few years, control of tobacco thrips with thiamethoxam (Avicta, Cruiser, etc) has been declining and resistance has been confirmed through bioassays. As a result, we have switched almost exclusively to imidacloprid products (Aeris, Gaucho, Acceleron F1) and no longer recommend thiamethoxam (alone) as a seed treatment in cotton. Aeris treated seed contains imidacloprid + thiodicarb and performs very well in our thrips trials and in the field. The use of imidacloprid alone is another option; however, it may not perform as well as Aeris or imidacloprid + an acephate overtreatment. Overtreatment with acephate is an economical option that has demonstrated increased thrips control when applied on top of imidacloprid. Acephate alone controls thrips but the residual is significantly shorter than currently used products and increases the likelihood of foliar follow up applications.

The use of in-furrow applications of imidacloprid and AgLogic 15G are also options that work well for controlling thrips and other early season insects in cotton. AgLogic 15G is an aldicarb based replacement for Temik that is available in either gypsum or corn cob grit formulations with performance very similar to Temik when used at the appropriate rate.

Finally, foliar rescue treatments are utilized when seed treatments have played out. Foliar treatments should be made when immature thrips are present and/or when large numbers of adults are present and damage is occurring. The presence of immature thrips often signifies that the insecticide seed treatment has lost its efficacy. Avoid spraying solely based on plant injury since the damage has already occurred. Below are some considerations when deciding what foliar insecticide to use.

Dimethoate:

Positives: Relatively inexpensive, good efficacy at high rates, less likely to flare spider mites and aphids than acephate

Negatives: Ineffective towards western flower thrips, less effective than acephate or bidrin when applied at lower rates

Acephate

Positives: Relatively inexpensive, effective towards western flower thrips

Negatives: May flare spider mites and aphids if present, may be weaker against tobacco thrips in certain circumstances

Bidrin

Positives: Effective, less likely to flare spider mites and aphids than acephate

Negatives: Less flexibility with applications early season

Radiant

Positives: Effective, least likely to flare spider mites and aphids

Negatives:  More expensive, requires adjuvant

Insecticide choice depends on a number of factors such as cost, impact on secondary pests and spectrum of thrips species present. If a foliar thrips treatment is justified, do not wait for a herbicide application and only spray when necessary to avoid flaring spider mites and aphids.

Transform (Sulfoxaflor) Granted Section 18 for Use in Louisiana Cotton

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The EPA has granted a section 18 request for the use of Transform (sulfoxaflor) for 2016 Louisiana cotton production season. Please see the link below for information on conditions and restrictions outlined by the section 18 label.

Section 18 Authorization Letter for Transform in Louisiana Cotton

Soybean Insecticide Seed Treatment Decisions

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One of the most important decisions producers must make when planting soybeans in Louisiana is planting date. Soybeans have the utility to be planted in early March to late June. This wide variation in planting dates exposes seedling soybeans to a multitude of insect pests that affect both above and below ground plant structures.

Optimal seeding dates for each maturity group planted in Louisiana are:

  • Group III – April 15–May 10
  • Group IV – April 15–May 10
  • Group V – March 25–May 5
  • Group VI – March 25–April 30

Soybean seedlings possess an exceptional amount of vigor and can tolerate a substantial amount of insect injury during the seedling stage. However, early planted soybeans may also encounter greater amounts of environmental fluctuations that affect air and soil temperature. Cool conditions can negatively affect vigor and under the right conditions stall plant growth and development. The addition of insect injury, to the aforementioned  environmental conditions, increases stress the plant encounters resulting in loss of stand and yield potential. Therefore, the inclusion of an insecticide seed treatment (IST) provides growers a risk management tool when soybeans are planted early.  The primary insect pests of early planted soybeans are bean leaf beetles, wireworms and grape colaspis.

On the opposite end of the spectrum are soybeans planted late i.e. behind wheat or are late due to unforeseen circumstances such as inadequate or excessive soil moisture. These beans are more at risk for insect injury due to the potential for large insect populations to build in neighboring fields and generally more insects present in the environment. As a general rule with all agronomic crops, the later the crop the more insect pressure that will be encountered throughout the season.  This is particularly evident when soybeans are planted into wheat stubble. Wheat stubble is favorable for the development of threecornered alfalfa hoppers and thrips. Thus, an IST is a sound investment when soybeans are planted late.

However, soybeans planted in a timely manner that being within the recommended planting window, under optimal soil conditions and low pest densities will often not benefit from the addition of an IST.  Insecticide seed treatments typically produce the most benefits when environmental conditions are sub optimal as outlined in the prior paragraphs. With the current economic climate and many ag professionals looking at areas to cut inputs, justifying the use of an IST on soybeans when planted under optimal conditions becomes harder to support. Saving the cost of an IST can go to making a stink bug application later season that may provide a greater economic return.

Outside of early or late planted soybeans are situations where ISTs are justifiable. These include weedy fields with incomplete burn down applications, reduced tillage field arrangements, fields with historically problematic early insect pests (wireworms and/or threecornered alfalfa hoppers) and continuous plantings of one crop.  Each field is unique and the use of ISTs as a blanket treatment over every acre may not be justifiable with $8 soybeans.

The Value of Insecticide Seed Treatments in Corn Following Cover Crops

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Cover crops can provide producers a variety of benefits from nutrient cycling and soil cover to nitrogen fixation and pollinator food sources. Cover crops come in many varieties including grasses, legumes and brassicas, however; cover crops maintain a “green bridge” throughout the fall and early spring that may facilitate the movement of pest insects into above and below ground plant structures.

Seedling corn, in Louisiana, is often adversely affected by many factors including excess moisture, cold temperatures and a complex of above/below ground insect pests. The complex of underground insects includes southern corn rootworm, wireworms and white grubs, while the above ground complex includes sugarcane beetles, chinch bugs and cutworms. Most of these insects require a food source that is present in fields for them to successfully overwinter and subsequently begin reproduction when temperatures begin to warm in the spring. The inherent benefits of cover crops often include the presence of large volumes of biomass and an abundant root structure that anchors soil or penetrates a hard pan. Yet, these attributes make cover crops an ideal source for the buildup of yield limiting insects.

Insecticide seed treatments (ISTs) are neonicotinoid based insecticides that coat the outer layer of the seed offering protection from below and above ground early season insect pests. The systemic nature of ISTs make these compounds water soluble and facilitate the vascular movement of the insecticide into the plant tissue. The value of ISTs in Louisiana varies among crops and environmental conditions, most agricultural commodities will usually not benefit from ISTs when planted under optimal environmental conditions (adequate soil temperature, optimal soil moisture and low pest pressure). However, insecticide seed treatments will typically produce an economic benefit when conditions are sub-optimal including very late or early planting, reduced tillage field arrangements, double cropping systems (soybeans behind wheat), pests that are present every year and consecutive plantings (i.e., corn behind corn). In addition to the above mentioned situations, data from the LSU AgCenter’s Macon Ridge Research Station confirmed the need of an IST when corn is planted behind cover crops (Figure 1). A statistically significant increase in yield was observed in corn treated with Poncho 500 IST in Berseen Clover, Crimson Clover and Hairy Vetch while a significantly lower yield was measured in corn planted behind Tillage Radishes treated with the IST (Figure 1). No fungicide seed treatment was used in this study. The measurable difference in yield may be due to the presence of below ground insects that also produced a notable decrease in vigor (Figure 2). Unfortunately for producers, there are no rescue treatments available for below ground insect injury in corn or any other agriculturally managed crop in Louisiana. Therefore, the use of an IST can help safely and effectively control below above and below ground insect pests in corn planted behind cover crops.

Figure 1. Yield of corn treated with Poncho 500 IST vs non-treated following cover crops.
Figure 1. Yield of corn treated with Poncho 500 IST vs non-treated following cover crops.

Aside from the use of ISTs, there are other management practices that can be done to minimize the effects of pest insects, from cover crops, on corn. Burning down cover crops in a timely fashion (6 weeks before planting) will provide enough time for available biomass above the soil to dessicate and force any harbored insects off of the plants. Yet, this timing may not allow enough time for below ground insects to cycle out or succumb to a lack of forage. Earlier burn down timings and the use of minimum tillage may allow enough time for insects to cycle out or be physically removed or destroyed with implements. If you elect to destroy your cover crops earlier than intended, check with your local NRCS representative or LSU AgCenter county agent to ensure enough time has passed that your preplant intentions are met (ie. Nitrogen fixation, nutrient cycling, etc.).

Figure 2. Vigor of corn treated with Poncho 500 IST vs non-treated following cover crops.
Figure 2. Vigor of corn treated with Poncho 500 IST vs non-treated following cover crops.

The use of ISTs is a best management practice recommended by the LSU AgCenter and will help ensure your crop is protected from yield limiting insects. The use of ISTs is highly recommended if you choose to plant corn behind cover crops particularly Berseen Clover, Crimson Clover and Hairy Vetch. If you have any questions or concerns please contact your local LSU AgCenter extension service.

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