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GGreen Bean Syndrome Caused by Threecornered Alfalfa Hopper

Threecornered Alfalfa Hopper Threshold in Louisiana

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Over the past week, I have received a number of phone calls pertaining to what economic threshold should be used for Threecornered Alfalfa Hoppers (TCAH) in soybean.  Based on previous work conducted by Sparks and Newsom (1984), Sparks and Boethel (1987) and subsequent experiments conducted by the LSU AgCenter in the last five years, the LSU AgCenter recommended threshold is “starting at pod set, 3 nymphs per row foot or one adult per sweep”. This recommendation is based on published data and experiments conducted in Louisiana at LSU AgCenter Research Stations and Louisiana field locations.  Independent of yield loss, TCAH can also cause an increase in the “green bean/stem syndrome” that often is present in soybean fields. Green bean syndrome’s exact cause is not known but we do know that stress plays a large part in the malady. Environmental stress compounded by insect or disease related stress is often the culprit. The picture below is from a TCAH experiment conducted at the Macon Ridge Research Station to investigate the effects of TCAH on dryland soybeans.  The experiment was terminated at the onset of stink bugs and all non-target insects were controlled for the duration of the experiment. The green bean syndrome pictured below is directly related to TCAH feeding. The beans on the left were non-treated throughout the duration of the experiment, the beans on the right were keep free of hoppers. We also observed significant increases in green bean syndrome in both irrigated and dryland soybeans and observed significant differences in yield in dryland soybeans but not irrigated. The take home message is TCAH are economically important insects that have a documented, data backed economic threshold of 1 adult per sweep at pod set. If you have any questions or concerns feel free to contact your county agent or me for more information.

GGreen Bean Syndrome Caused by Threecornered Alfalfa Hopper
Green Bean Syndrome Caused by Threecornered Alfalfa Hopper

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.

Top leaf death in irrigated corn at the Dean Leaf Research and Extension Center, Alexandria, Louisiana, three quarter milk stage. July 17, 2018. Primarily due to high temperatures.

Top Leaf Death or Dieback in Corn

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Please see this post on top death in field corn by Dr. Dan Fromme: LSU AgCenter Corn, Cotton and Grain Sorghum Specialist.

We all know that as a corn crop progresses toward physiological maturity, the leaves naturally begin to senesce (die).  The timing and pattern of leaf senescence are genetically regulated but are also influenced by environmental triggers, including sever photosynthetic stress.  This year, where much of the grain fill period has experienced severe drought and/or heat stress, the onset of leaf senescence can occur earlier than expected prior to kernel black layer.  This means leaves begin to die sooner than expected, and the leaf pattern of leaf senescence sometimes changes.

Top leaf death in irrigated corn at the Dean Leaf Research and Extension Center, Alexandria, Louisiana, three quarter milk stage. July 17, 2018.  Primarily due to high temperatures.
Top leaf death in irrigated corn at the Dean Leaf Research and Extension Center, Alexandria, Louisiana, three quarter milk stage. July 17, 2018. Primarily due to high temperatures.

Most often the leaf pattern of senescence that we see in most years is one where leaf death begins at the bottom of the plant and slowly moves up toward the upper leaves.  However this year, due the late season stress, leaf senescence is progressing from both the bottom and the top of the plant with green leaves remaining in the middle of the plant for some time until complete leaf senescence occurs.  Also, these fields appear to cause an unusual golden glow in the upper canopy against the morning or evening sun.  The impact or effect on grain yield will depend on how early in the grain filling period the death of the upper leaves occurs.  This year, we might see some test weights on the low side.

Citations:  Nielson, R.L., Top leaf death or dieback in corn .2011.  Purdue University Department of Agronomy.

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.

Estimating Yield Potential of Corn

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This article covers how to estimate the yield potential of field corn.  Please contact Drs. Dan Fromme, cellphone: (318)-880-8079 office: (318) 427-4424 or Josh Copes, cellphone (318) 334-0401, office (318) 766-3769 for more information.

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.

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