Author Archives: Ames Herbert

Corn earworm soybean update.

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In both 2014 and 2015 we experienced very light corn earworm (CEW) infestations in our soybean crop. This summer we are back to a more normal situation with spotty light to moderate level infestations. Some fields have hit thresholds for sure, but not all. And, as is the case in most years, worms are in some fields that are only in the flowering stage—which has been proven many times over the years NOT to be a problem, that is, does NOT result in any yield loss. CEW do their damage when they feed on developing seed during the R5-R6 growth stages. If needed, a single application (if the right insecticide is used) during this stage should be all that is needed for season-long CEW control.

As always, in a year with spotty infestations, it pays to scout fields carefully to find those at threshold so they can be protected. We have recently proven that pyrethoid insecticides have a devastating effect on the thousands of beneficial insects and spiders in a soybean field. If left alone, they have then potential to control CEW infestations by eating the eggs and small worms and therefore prevent the need for an insecticide spray. So, be careful with pyrethroid applications and use them only if thresholds are met. You will very likely save money in the long run.

What are the thresholds for CEW in soybean? There is not a one-size-fits-all answer. This fact sheet Soybean_insect_mgmt_2016 has a CEW Calculator that can provide a good answer based on some of the factors that must be considered—like the estimated application cost and bushel value. Use this as a starting point.

What to treat with? We have been monitoring CEW for pyrethroid insecticide resistance for several years by collecting and testing adults (moths). This year is no exception. Individual moths are exposed to a pyrethroid and we document the percent that survive (=resistant). This year we are seeing high levels of survivorship averaging about 40% over all sample dates and locations.  This means that to achieve good CEW control, non-pyrethoids insecticides should be considered. For CEW, I would focus on those that ‘specialize’ in worm control (like Prevathon, Besiege, or Spinosad).  Lannate is another option but has essentially zero residual activity, whereas the others should provide several days of protection, depending on rainfall amounts and frequency. If stink bugs are also present in the field, the worm products will not be effective. A pyrethroid will need to be tank mixed with the worm product (example, Prevathon plus bifenthren)—or a product like Besiege can be used that contains both a worm product and a pyrethroid. Below is a list of insecticides labeled for use in soybean.

Soybean_insecticides_2016

Sorghum insect pest update: headworms and aphids

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Headworms: Corn earworm (CEW) is the primary headworm pest of Virginia sorghum and this summer CEW populations are higher than in the past two years. Sorghum heads are very attractive to worms—but not until the seed begins to form.  I suggest that sorghum is so attractive to this pest that every field will be infested at some point.  If you are not scouting your sorghum fields for CEW and not treating, it is very likely that heads are being damaged.  And, not only do worms do direct damage to the developing seed, damaged seed are more likely to be infested by the fungi that produce mycotoxins which can further degrade seed quality.

So bottom line, scout fields and sample heads for worms by shaking heads into a white or light colored 5-gal bucket. In our experience, this is the ONLY way to get an accurate count. The standard headworm threshold across the U.S. is an average of 1 to 2 worms per head during seed formation.

What to treat with? We have been monitoring CEW for pyrethroid insecticide resistance for several years by collecting and testing adults (moths). This year is no exception. Individual moths are exposed to a pyrethroid and we document the percent that survive (=resistant). This year we are seeing high levels of survivorship averaging about 40% over all sample dates and locations.  This means that to achieve good CEW control, non-pyrethoids insecticides should be considered. Posted below is a link to a list of insecticides labeled for use in sorghum. For CEW, I would focus on those that ‘specialize’ in worm control (like Prevathon, Besiege, or Spinosad).  Lannate is another option but has essentially zero residual activity, whereas the others should provide several days of protection, depending on rainfall amounts and frequency.

Aphids: We have posted several advisories about the sugarcane aphid (SCA) infestation in our sorghum. Bottom line, fields need to be scouted following the procedures and thresholds provided in the linked fact sheet. Only Sivanto or Transform insecticides are known to be really effective against this aphid species.

Fields with CEW and SCA: If thresholds of both pests are found, insecticide tank mixes are the only option—to include a CEW product as mentioned above, and either Sivanto or Transform for SCA. Of course this adds a lot to the cost of producing sorghum.  More details on both headworms and aphids can be found at this link. Midseason sorghum insect pests

Sorghum_insecticides_2016

Cotton insect pest update—bollworms are here.

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At this point in the season, many cotton fields have been treated once for mid-season plant bug/stink bug. The next decision will be focused on bollworm control—whether it is needed, and if so, what insecticides to use. We are seeing a general increase in bollworm moth activity at TAREC and have gotten recent reports of some pretty large worm infestations in a couple of peanut fields in the cotton area, and outbreaks in a couple of soybean fields in the Suffolk area. Caution: if the earlier applied mid-season plant bug/stink bug spray included a pyrethroid (e.g., bifenthrin), the beneficial populations in those fields will have been depleted—which makes them more susceptible to bollworm.

We have plenty of data that shows that cotton varieties with bollworm protection traits can be damaged by worms. Some escape the toxin, survive, and feed on bolls. We have seen as much as 9% or more boll damage in some varieties which is 3 times our working threshold of 3% live worms/fresh boll damage.  But, that was in years when bollworm pressure was high.  In years like 2014 and 2015 when bollworm populations were very light, we saw essentially no boll damage in any of the varieties.  So what is the 2016 situation?  So far it looks like we may be looking at heavier pressure than last year, light to moderate depending on the field—but—we won’t know for sure for another few weeks—as the main flight out of field corn has not kicked in yet. The corn crop is generally a little behind and a little less mature than normal for this time of year because of later planting and good rainfall.

The best approach for managing bollworm in cotton is to scout fields for worms by inspecting small bolls, the terminals, and under flowers (boll tags) for live worms or damage. As mentioned, our current threshold is 3% of the fruit or positions inspected with either live worms or damage.

We have a history of bollworm resistance to pyrethroids in Virginia and this year is no exception. Of the 650 or so moths tested so far, we are seeing about 40+% survival. This is high. So for the best control results we suggest using a non-pyrethroid (e.g., Prevathon, Belt, Blackhawk, or Intrepid Edge). Note that Belt is not widely available this season due to the registration being canceled by EPA. Distributors and growers can use existing stocks according to label, but when that is gone, that will be it—at least as far as we know.

We also recommend adding a pyrethroid to the worm product to clean up any plant bugs/stink bugs that may be in the cotton. There are several pyrethroid options, and I would use the highest labelled rate for stink bugs—for better kill and longer residual. Besiege is the only product that contains both the non-pyrethroid (= Prevathon) with a pyrethroid (= Karate). With all the other non-pyrethroids, you will have to do the tank mixing on the farm. And, it is past time to include any of the insecticides in the neonicotinoid class as they do not provide good control of either bollworms or stink bugs.

Sugarcane aphid sorghum update

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Brent Bean, Director of Agronomy, United Sorghum Checkoff Program, forwarded the following information on sugarcane aphid (SCA):

As many of you know, the sugarcane aphid has moved north faster than last year.  We now have confirmed reports of SCA in three southern counties of Kansas.  In addition, SCA is present as far north as Kentucky and Virginia.  In these northern sites SCA populations for the most part are low but have approached threshold levels in Virginia.  It is likely that at least low populations will be discovered in many counties within the Sorghum Belt in the coming weeks.

It is important to note that just because a few SCA are present in a field does not mean an insecticide application is or will be justified.  Those who planted hybrids with some tolerance to SCA can expect the populations to build more slowly.  In addition, beneficials in many areas are reported to be in high numbers, this will also help keep SCA populations in check.  Although SCA was present in South Texas this year, only a portion of the fields reached threshold levels.

Something we have clearly learned the last two years is that once SCA is present in an area, scouting of fields becomes critical.  Scouting should occur at least once a week once SCA has been discovered in a region, and in fields where SCA has already been detected, scouting should take place at least twice a week.  Insecticide application should begin as soon as the SCA population is at threshold levels.  Research has shown yields can be drastically reduced if insecticide application is delayed for several days once threshold levels are reached.  States and regions vary slightly in their recommended threshold levels, but in general, an insecticide application is justified when 50 aphids per leaf are present on 25 percent of the plants. Consult your state or regional extension service for specific threshold information.  We are entering a critical time in the Sorghum Belt, and SCA can potentially reach threshold levels very quickly.  Diligence in scouting is an absolute must!

There are two products that should be considered if an insecticide application is warranted.  These are Sivanto prime from Bayer, and Transform WG from Dow AgroSciences.  Both are effective, but good coverage is critical.  Most entomologists recommend 4 – 5 ounces of Sivanto Prime and 1 – 1.5 ounces of Transform WG.  The lower rates are usually recommended to control SCA at or close to threshold levels.  If SCA populations are way above threshold levels, then the higher rates may be justified.

If other insects such as midge or headworms are present with SCA, avoid using pyrethroids for their control.  Pyrethroids can lower beneficial populations significantly and cause a rapid increase in SCA populations.  In the South Plains region of Texas the ‘yellow’ sugarcane aphid is showing up in a few fields, often in the same fields with sugarcane aphid.  Care should be taken in distinguishing between these two aphids.

Although sweet sorghum is a minor U.S. crop, sugarcane aphids can greatly impact yield.  Sivanto prime has received a section 18 Crisis Exemption label in Mississippi, Arkansas, Tennessee and North Carolina for use on sweet sorghum in 2016.

NOTE from Ames Herbert, VT: Note that the ‘yellow’ sugar cane aphid mentioned above is a different species than SCA. Yellow sugarcane aphids are covered with small hairs and the two cornicles (pair of small upright backward-pointing tubes found on the top side of the last segment of the bodies) are small and pale (see attached image).  The SCA is also called ‘white’ sugarcane aphid. It does not have hairs on the body and the two cornicles are dark (see attached image).  Yellow sugarcane aphid is a known pest in Virginia of forage grasses like orchardgrass. Like Texas, we are also finding yellow sugar cane aphid mixed with SCA, and in a few fields also mixed with corn leaf aphid, another known pest of corn and sorghum. Corn leaf aphid is easy to distinguish from the other sorghum aphid species as they have a dark head and legs, a dark green body color, and dark cornicles (see attached image).

This sorghum aphid problem is new for us so we are having to make some ‘educated guesses’ about what constitutes a threat, and what the best control options might be. For now, we suggest that SCA numbers should guide control decisions, that is, abide by SCA thresholds—and stick with the products that are recommended for SCA. Avoid the use of pyrethroids since they will not be effective against SCA, and could flare secondary pests by disrupting natural enemy populations.  Natural enemies including tiny aphid parasitic wasps and a variety of lady beetles can be very effective in helping reduce aphid and other pest populations, so we need to conserve them whenever possible.

white sugarcane aphid yellow sugarcane aphid grantham osu corn leaf aphid

Stink bugs already in small grain and field corn

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Our overall mild winter and wet spring are the kinds of conditions that favor survivorship and early development of stink bug populations. Because of these conditions, this could be a summer when we see higher than normal stink bug infestations in a lot of crops including field corn, cotton and soybean. Brown stink bugs are already being found in small grain fields and areas of North Carolina are reporting pretty heavy stink bug pressure on seedling field corn.  See this article by Dr. Dominic Reisig at the NCSU station on Plymouth for details https://entomology.ces.ncsu.edu/2016/05/how-to-avoid-a-stink-bug-disaster-in-corn-2/

We need to be thinking ‘stink bugs’ this summer and aligning our field scouting, sampling and threshold efforts in that direction as the summer progresses—and that applies to cotton and soybean fields as they mature.

True armyworm infestation reported in small grain on Eastern Shore

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It’s been many years since we’ve seen a true armyworm (see the attached image) infestation in our small grain crop, but one is reported to be ongoing in the barley and wheat fields on the Eastern Shore. These caterpillars can do two types of damage—leaf feeding and head cutting.  Leaf feeding is rarely extensive enough to warrant control, especially if fields are within a couple of weeks of harvest.  Head cutting is less tolerable.  For some reason no one has been able to explain, caterpillars will sometimes eat through the stem below the heads casing them to drop to the ground.  Finding otherwise healthy looking heads-short stems on the ground is a good indicator that true armyworms are present and still active.  It is often hard to find them on plants during the day as they typically feed more at night and seek cover under plant residue during the day.  When we have worked with this pest, we found that fields with the most plant residue on the soil surface tended to have the heaviest infestations.

We do have thresholds for true armyworm for those motivated to scout for them. As a general rule, barley should be treated if the number of armyworms exceeds one per linear foot between rows and most of the worms are greater than 0.75-inch long. In wheat, armyworms tend to nibble on the tips of kernels rather than clip heads; thus, populations of two to three worms per linear foot between rows are required to justify control. In high management wheat fields with 4-inch rows, treatment is recommended when armyworm levels exceed 3 to 5 per square foot of surface area, or per linear foot of row.

If a treatment is warranted, there are a few good choices but the PHI (Pre Harvest Interval) may be a challenge. Some work we did many years ago showed that pyrethroids were generally effective but have a PHI of 14 days (example, Mustang Max) to 30 days (example, Baythroid), which could be a problem for barley, wheat not so much. Lannate has a PHI of 7 days but did only an OK job in our trial and not as good as the pyrethroids. We chalked that up to the fact that although Lannate has great efficacy against most caterpillar species, it has almost zero residual activity. So a day-time spray may not have had as much horsepower by the evening when caterpillars become active. Since our work was done, several new products have been introduced to the market that we have not tested, like Prevathon (PHI 14 days), and Besiege (PHI 30 days). These should work well. See the Pest Management Guide Field Crops 2016, 4-49, p. 53 for more product listings (http://www.pubs.ext.vt.edu/456/456-016/Section04-Insects-1.pdf).

With any treatment, coverage will be essential so deliver the highest volume you can live with and direct it to go as deep into the canopy as possible.

TAW_larvae

Section 18 granted for use of Transform to control sugarcane aphid on sorghum

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EPA just granted a Section 18 for use of Transform™ WG in Virginia against sugarcane aphid in sorghum. Transform (50% a.i. sulfoxaflor), manufactured by Dow AgroSciences, may be applied through April 8, 2017 on a maximum of 16,591 acres of sorghum fields (grain and forage) in the following counties: Accomack, Albemarle, Alleghany, Amelia, Appomattox, Augusta, Bedford , Botetourt, Brunswick , Campbell, Caroline, Carroll, Charlotte, Charles City, Culpeper, Cumberland, Dinwiddie , Essex, Fauquier, Floyd, Fluvanna , Franklin, Frederick, Gloucester, Goochland, Greensville, Halifax, Hanover , Henrico, Isle of Wright, George , King William, King and queen , Loudon, Louisa, Luneburg, Madison , Mathews, Mecklenburg, New Kent, George , Prince William, Rockbridge , Rockingham , Russell, Southampton, Spotsylvania, Suffolk, Surry, Sussex, Virginia Beach, Washington, Westmoreland, and Wythe. 

The following directions, restrictions, and precautions must be observed. Foliar applications may be made by ground or air at a rate of 0.75-1.5 oz of product (0.023-0.047 lb a.i.) per acre. A maximum of 2 applications may be made per year, at least 14 days apart, resulting in a seasonal maximum application rate of 3.0 oz of product (0.09 lb a.i.) per acre per year. Do not apply product 3 days pre-bloom or until after seed set. 

To minimize spray drift and potential exposure of bees when foraging on plants adjacent to treated fields: applications are prohibited above wind speeds of 10 miles per hour (mph) and must be made with medium to course spray nozzles (i.e., with median droplet size of 341 µm or greater). A restricted entry interval (REI) of 24 hours applies to all applications. Do not apply within 14 days of grain or straw harvest or within 7 days of grazing, or forage, fodder, or hay harvest. 

Environmental Hazards Statement: “This product is highly toxic to bees exposed through contact during spraying and while spray droplets are still wet. This product may be toxic to bees exposed to treated foliage for up to 3 hours following application. Toxicity is reduced when spray droplets are dry. Risks to pollinators from contact with pesticide spray or residues can be minimized when applications are made before 7:00 am or after 7:00 pm local time or when the temperature is below 55 degrees Fahrenheit (°F) at the site of application.” 

We will provide updates on the presence and spread of sugarcane aphid as the season progresses.

 

Adjust your cotton and peanut thrips control programs

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Due to the frequent rains in May, only and estimated 50% or so of our cotton is planted and maybe even less of the peanut crop. A later planted crop may require some changes in how we manage pests and thrips are a good example.  Thrips are a major challenge for both crops and for this pest at least, later planting has advantages.  Although the crops are delayed, the thrips population seems to be on a pretty normal schedule, that is, we are seeing a lot of adults active on volunteer peanut plants and feeding injury symptoms.  We typically see one major peak of thrips activity when adults move from spring weeds into crops, so later planted fields may escape this peak—which means less thrips pressure compared to years when we plant on time.  Also with the moisture we have in our fields, once the weather warms up (expecting that next week) we will see quick emergence and rapid seedling growth. This combination of rapid growth and reduced thrips pressure means less need for protective insecticide treatments.

My recommendations are that any cotton planted from today (May 17) forward should only need a standard insecticide seed treatment. And importantly, I would NOT automatically follow with a foliar application to the seedlings.  Plant the seed-treated cotton and wait to see if anything more is needed.  This could be year when the seed treatment will provide enough protection—a standalone.

For any peanuts planted from today forward, I would not put any insecticide into the seed furrow, or at least only a low rate. Scout fields after plants emerge and clean up any visible thrips injury with a broadcast application of either acephate or spinetoram.

Bt-Corn Refuge Requirements for Virginia Counties With and Without Cotton Acreage

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Field corn hybrids—what are you buying? The dizzying array of Bt trait combinations available in field corn hybrids makes it important to understand what you are buying in a corn hybrid. Because of the different Bt toxins expressed in the plants, different hybrids protect, or not, against different insect pests.  So you should choose your hybrids at least in part based on the history of insect pest pressure in your fields. Good summaries of which hybrids protect against which insect pests are provided in the fact sheets, below (developed by Dr. Chris Difonzo at Michigan State University).

What are Bt-corn refuges and why do we need them? Bt-corn refuges are areas within or near Bt-hybrid planted fields where non-Bt hybrids are planted. They can be either structured (planted as a block or series of rows), or as refuge-in-a-bag (RIB) where the seed is pre-mixed to the correct ratio of Bt and non-Bt hybrids. In Virginia, the refuge requirement is primarily because of the corn earworm. Having the non-Bt corn refuge available in the near vicinity of the Bt hybrids allows at least some corn earworms to not be exposed to the toxins—which should prevent or slow the resistance development process.

Refuge requirements for counties with no cotton! Non-Bt corn refuges are required for corn fields planted to Bt hybrids. These requirements (% of field that must be planted to a non-Bt hybrid or RIB) are different for the different Bt-corn hybrids—and these details are presented in the fact sheet, below, ‘Handy Bt Trait Table’.

Refuge requirements for counties with cotton! Bt-corn refuge requirements are different for areas where cotton is grown because the risk of corn earworm (also called cotton bollworm) developing resistance to the Bt toxins in these areas is greater. Corn earworm attacks both corn and cotton and some of the Bt traits in corn hybrids are also in cotton varieties.  Feeding on the same Bt products in both crops exposes corn earworm to the same toxin in successive generations in the same growing season (corn first, then cotton).  This increases the risk of the insects developing resistance to the toxins. For Virginia, EPA has designated Dinwiddie, Franklin City, Greensville, Isle of Wight, Northampton, Southampton, Suffolk City, Surry, and Sussex as cotton growing regions.  Refuge requirements for the different Bt-corn hybrids are presented in the fact sheet, below, ‘Handy Bt Trait Table for the Southern Cotton-growing Region’.

Abiding by Bt-corn refuge requirements is good stewardship and important for helping sustain the efficacy of Bt-corn hybrids against insect pests. So, to determine your Bt-corn refuge requirement, you need to know if you are planting in a cotton-growing county, and what varieties you plan to plant. Read the attached fact sheets carefully for details to help you select the right corn hybrids for your farm, and what your refuge requirements are.

HandyBtTraitTable2016 CottonRegionBtCornTraitTable2015

CottonRegionBtCornTraitTable2015

Sugarcane aphid update

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Sugarcane aphid (SCA) infestations have been documented in sorghum fields in 5 Virginia counties (Suffolk, Southampton, Surry, Sussex, and Isle of Wight—see infestation map, below). The area of the infestation likely includes more counties, but this is just a guess. Fortunately we are late into the season and many fields have either been harvested or desiccated in preparation for harvest. We maintain that there are fields still at some risk—those that will not be harvested for several weeks, especially any late planted fields. We are not concerned about loss caused by direct feeding, but the build-up of honey dew and sooty mold on leaves and heads. SCA infestations begin on lower leaves and these are not as important at this point in the season and pose less risk if they get covered with sooty mold. But if infestations move up the plant to upper leaves and heads, problems with combining could occur.

If you have been keeping up with pervious advisories you know that the insecticides most commonly recommended for control of SCA are Sivanto (Bayer CropScience) and Transform (Dow). But only Sivanto is currently labeled. We attempted to secure a Section 18 Emergence Exemption for the use of Transform but hit a snag. Following are the recent comments from the EPA reviewer regarding the status of our request. “Due to the federal court’s recent (September 10th) decision vacating EPA’s unconditional registration of sulfoxaflor the authorization of our request is on hold and remains pending.  The EPA is reviewing the court’s opinion to determine their next steps”. So, right now it does not sound promising for the Section 18 use of Transform in Virginia before the end of the use season.  It definitely means we don’t have use of the product for the recently found infestations. So Sivanto would be the best alternative, but hopefully, fields will not have to be treated.

SCA_map_24_Sep_2015