Author Archives: Ames Herbert

Soybean aphid being found at threshold levels in soybean fields

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For reasons I cannot explain, our soybean field scouts have recently reported finding large numbers of soybean aphids in many soybean fields. Threshold levels have been found in soybean fields in 11 counties (Goochland, Buckingham, Cumberland, Culpeper, Fauquier, Rappahannock, Warren, Clark, Fredrick, Shenandoah and Rockingham). We typically see only a very limited number of fields infested with soybean aphids so this widespread infestation is very unusual. From past investigations we determined that soybean aphid likely does not overwinter in Virginia, as their required winter host plant, buckthorn, is very uncommon in our state. We believe it migrates in from the north central states and Canada when large infestations develop in those areas. The alates, or winged forms, take flight and can be transported long distances by prevailing winds and storm events. What is unusual is that soybean aphid seems to prefer a climate that is cooler than our normal summertime temperatures so have been the most troublesome only in summers that were cooler. I think we can all agree that our summer has NOT been a cool one. So why this widespread infestation? Not sure!

Soybean aphid is not hard to identify on soybean as there are no other aphid species that reach these high numbers—basically a light yellow/green aphid with black tips on the cornicles. There are good economic thresholds for determining if a field needs to be treated. A treatment is suggest when an average of 250 or more are found per plant, in two consecutive field visits 5-7 days apart, and beans are in the R2-R5 growth stage (see the attached threshold chart). Between R5 and R6 the number can be much higher and after R6, fields are safe. From our past experience, if a treatment is warranted most pyrethroids registered for use in soybeans will do a good job of controlling them.

soybean_aphid

SBA_threshold

 

Sugarcane aphid update—spread and control options

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Sugarcane aphid has advanced as far north as Halifax County, North Carolina—about 30 miles south of the Virginia border. To prepare for the possibility of sorghum field infestations, we have pursued a Section 18, Emergency Exemption for the use of Transform insecticide. This process involved a lot of good cooperation by VDACS who put the request together and forwarded it to the US EPA. We are awaiting approval. If approved, Transform (sulfoxaflor) can be used at 0.75-1.5 oz/acre and has a 14 day preharvest interval. Having Transform will give us access to the two insecticides that most states are relying on to combat sugarcane aphid—Transform and Sivanto. Since controlling heavy infestations it is taking two applications, having these options provides insecticides with different chemistries—always a good strategy.

We do not know if sugarcane aphids have infested sorghum fields in Virginia as we do not have a statewide sorghum pest surveillance program. According to FSA records, 12,245 acres of sorghum are grown for grain in 45 different Virginia counties, ranging from as few as 10 acres to as many as 1,000 depending on the county (view the attachment for a summary and FSA web site acreage source). With a crop that is this variable and widespread, it will be up to growers, crop advisors and local VCE agents to check fields for sugarcane aphids. As we have mentioned in earlier advisories, the crop is vulnerable until harvest.

Please let us know if an infestation is found so we can track this pest for future program development.

Sorghum acreage 2015

Sugarcane aphid nearer to VA and threat to sorghum

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Sugarcane aphid (SCA) is inundating sorghum in a lot of the southeast and mid-South. As of this week (Aug. 26) we know that a field plot in Kinston, NC (see images below) is heavily infested and at least some have been seen in plots in Lewiston, NC. There is a preliminary siting in the Roanoke, VA area but as of today, this is not confirmed. We have every reason to expect SCA outbreaks in our sorghum fields this season—it’s just a matter of time.

Sorghum is susceptible until harvest and heavy aphid infestations need to be controlled up to that time. From what I have been hearing and seeing, only Sivanto at 4 oz/acre (Bayer CropScience) and Transform at 1.5 oz/acre (Dow AgroSciences) are effective in controlling heavy infestations of this aphid—and for good control it is critical that the applicator focus on coverage all the way to the bottom of the plant. You might have to spray again in 2 weeks following the initial spray and should be prepared to do so though harvest. The crop is not safe until the grain is in the combine. Sivanto has a 21 day pre-harvest interval, and 28 oz can be applied through the season. There is a 14 day pre-harvest interval restriction with Transform, and a maximum of 3 oz can be sprayed for the season. Once nights start to drop into the 50’s efficacy drops—but hopefully, so will aphid activity.

SCA_Mehl_aSCA_Mehl_b

Corn earworm advisory

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The corn earworm moth flight is underway, but is still pretty light compared to past years. Worm numbers are gradually increasing in soybean, peanut, cotton, and sorghum fields, but are still not at economic levels.

Worms are rarely, if ever, an economic threat to peanuts as they feed only on leaves, feed for only a short time, and do not remove enough leaf area to result in any yield loss. So why do most peanut farmers spray their fields for worms when there is no chance that those sprays will improve the yields?

We are finding a few worms in soybean fields, but not many. And, if fields are not in the R5 growth stage (seed forming in the pods), worms are not a threat. They are only a threat when they start eating seed, so if no seed are present, there is no need to treat. If seed are present, a good rule-of-thumb threshold would be to treat if you catch an average of 1 to two per 15 sweeps—but only if seeds are present.

Most cotton, unless very late planted, is mature enough to be safe from worms. At this point in the season, it would be very hard to justify treating most cotton fields for worms.

Sorghum is a different story. Corn earworms are highly attracted to sorghum heads, especially late planted sorghum. For more information on this, read to sorghum insect pest advisory that was just posted.

We are detecting a pretty high level of pyrethroid resistance in the corn earworm moths we are testing. The attached figures show this. With 705 moths tested so far this year, we are seeing an increase in the number surviving with a cumulative average of 37.5 percent survival. From the attached figure, you can see that this is high compared to previous years. Non-pyrethroid insecticides will need to be considered, especially if heavy infestations occur.

vialtest_Aug19

 

AVT_barchart_Aug19

Sorghum insect pest update—and sugar cane aphid alert

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Sorghum is susceptible to several insect pests. Both stink bugs and corn earworm are highly attracted to the heads once seed begin to form and both feed directly on those seed. Later planted sorghum is especially attractive to these pests as late sorghum heads offer a nutritious food source when many other host crops are reaching a stage that is no longer preferred.

We have seen sorghum heads in Virginia with large numbers of worms and severe head damage. We have also seen heads with stink bugs feeding. Growers should check all fields to determine if insecticide sprays are needed. The best and only efficient way to sample heads is to shake individual heads into a white 5 gallon bucket. Worms and stink bugs show up well in these buckets and can be easily counted. Sample several heads throughout the field and determine the average number of stink bugs and worms per head. Thresholds taken from several other states are pretty consistent:

Head worms (mostly corm earworm in Virginia)—an average of 2 worms per head

Stink bugs—2-4 per head at seed milk stage; 4-8 per head during soft dough stage

There are several insecticides labeled for use in sorghum that will provide good control of both pests. In general, pyrethroids are effective against stink bugs. To ensure the best control of corn earworm, use a non-pyrethroid such as Belt, Besiege, Prevathon, or Blackhawk.

IMPORTANT. Sugar cane aphid is also a potential problem for sorghum in Virginia. This is a new pest of sorghum in the US where it started in Texas and moved rapidly into the eastern states. Infestations have been reported as close to us as mid North Carolina and there is every indication that this pest could reach Virginia fields early enough to cause significant problems. These aphid populations can increase very rapidly and if numbers are high enough, the sticky ‘honey dew’ that they secrete while feeding can ruin heads and interfere with combines at harvest time. Please open and read the pdf below we have prepared that provides a lot of good information on this pest with color images to help with identification, sample procedures, thresholds, and recommended insecticides.

Sugarcane Aphid advisory_Aug_19

Bollworm treatments may be needed in Virginia cotton

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As of last week, we found bollworm eggs in cotton fields in numbers high enough to indicate that fields may need to be treated. The bollworm (= corn earworm) moth flight from corn is light and spotty, but it does not take many moths to cause concern in cotton.

In the old days before Bt cotton, we relied on the two spray system to control bollworms—the first spray applied at egg threshold followed by an automatic second spray 5 to 7 days later. This system worked very well to protect cotton from economic levels of boll damage.

With the advent of Bt cotton varieties (now TwinLink, BG2 and WideStrike) we found that even with these technologies, there were enough worm escapes (worms not killed by feeding on the plant toxins) to warrant a single insecticide spray. And—we determined that the best time for that single worm spray coincided with the second of the original two spray system—i.e., 5 to 7 days after the egg threshold.

Egg thresholds were found towards the end of last week in fields near the Tidewater AREC. The same is likely happening in fields across the region. So now is the time for applying a bollworm treatment. Based on our history of bollworm resistance to pyrethroids, the best control results will be obtained using a non-pyrethroid (e.g., Steward, Belt, Prevathon, Blackhawk). But we also recommend adding a pyrethroid to clean up any stink bugs that may be in the cotton. There are several pyrethroid options, and I would use the highest labelled rate for stink bugs—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 from the neonicotinoid class as they do not provide good control of either bollworms or stink bugs.

Soybean loopers are infesting soybeans in North Carolina

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I have gotten reports that soybean loopers are already infesting soybean fields in North Carolina in large numbers. This is basically about a month earlier than we normally see them in this area of the US. Loopers migrate from the south and typically infest fields in Virginia in early to mid September, but based on what is happening in NC, we should be on the lookout.

We are also in a high risk environment for having looper infestations. We usually have more problems with them in dry seasons, and they most often develop in soybean fields that have been previously treated with pyrethroids. Our current research is proving what we have been suspecting—that pyrethroids are non-selective insecticides which kill many of the natural enemy species that feed on looper eggs and small larvae—which if undisturbed, can prevent outbreaks in many situations. So previously treated fields are at the highest risk to loopers.

If we begin to hear about infestations in Virginia, we will post updates and include some recommendations in terms of thresholds and products that will work best. But generally, you cannot get control of loopers with pyrethroids—none of them—so you will have to turn to non-pyrethroid options, and there are several.

Looper

Annual Corn Earworm Field Corn Survey–2015

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Annually, we conduct a survey to estimate Helicoverpa zea (corn earworm) infestation levels in field corn in mid- to late July. Corn is considered a nursery crop for corn earworm, allowing the pest to complete a lifecycle and then move on to other crops such as soybean, cotton, and peanut in August. Over 30 years of data show that there is a linear correlation between the infestation level in corn and the amount of soybean acreage that gets treated with insecticide for this pest.

To conduct the survey this year, the number of corn earworm larvae found in 50 ears of corn was recorded in 5 corn fields in each of 25 counties, totaling 6,250 ears and 125 fields sampled. When fields were known to contain Bt or non-Bt corn, this was noted. Otherwise, samples were considered to be random and assumed to be representative of the actual Bt/non-Bt composition in each county. Age of corn earworms, or if they had already exited the ears, was also recorded (data not shown). We greatly appreciate the help of Virginia Cooperative Extension Agriculture and Natural Resource (ANR) Agents, Virginia Tech faculty and staff, summer agricultural assistants, and interns in this effort. These cooperators are acknowledged in the attached Figure. We also would like to thank the many growers who graciously allowed us to inspect their fields for corn earworm larvae.

Results of the survey are provided in the Figure (CEW_survey_2015). Statewide, approximately 17.5% of ears were infested with corn earworm. This is even lower than the numbers reported in 2014 (20%) and 2013 (18%)—both years with very few cotton, peanut or soybean fields being infested with treatable numbers of worms. Regional averages for 2015 were 4% infested ears in the Northern Neck, 13.4% in Mid-Eastern, 9.5% in South-Central, and 27.7% in the Southeast.

So far, all indicators point to another year with few fields reaching thresholds. We will continue monitoring and posting updates.

This survey is intended to be a representative sample, not a complete picture. We always recommend scouting individual fields to determine exactly what is happening in terms of corn earworm as well as other pests and crop problems. Also, please check the black light trap reports on the Virginia Ag Pest and Crop Advisory and other reports posted weekly to keep up-to-date on the insect pest situation.


Update on soybean insect pests in Virginia

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In mid July we initiated our annual soybean insect pest survey, our black light trapping program, and our corn earworm pyrethroid resistance monitoring program. Following are short updates.

BMSB (brown marmorated stink bug): So far this summer, only a TOTAL of 4 BMSBs have been found in soybeans—one in a field in Amelia Co. and 3 in a field in Bedford Co. (see the attached BMSB occurrence map). This breaks all records for the fewest for this time of year. Was it the cold winter, or those unusually hot days in June (BMSB does not do well when temperatures exceed the mid 90s)? We will continue posting our field survey results but all indicators point to a season with very low risk to BMSB infestations in the Virginia soybean crop.  BMSB_map_30_July_2015

Kudzu bug: As of the end of July, kudzu bugs have been found in soybean fields in 21 southern/eastern counties (see the attached kudzu bug occurrence map)—but in all cases, these have been adults only, and at very low numbers. Most counts reported by our scouts were 1 or fewer adults in 15 sweeps, and occasionally 2 per 15 sweeps. These numbers are way too low to be a threat to fields and DO NOT warrant treatment. These adults represent the first generation that will set up the nymphs that could cause concern later, but only if numbers increase a lot. Our best guess based on what we are seeing in fields now, and the lower number that successfully overwintered compared with last year, is that not many, if any, fields that will reach the nymphal threshold.  KB_map_30_July_2015

Corn earworm moth activity: We are seeing an increase in CEW moth activity just in the last week and what we think is the beginning of the flight from field corn. Our local pheromone traps have gone from just a few caught in a week, to averaging in the teens and twenties. We are just beginning to see moths fly up in crop fields as we walk the rows, and some local growers are seeing the same. On a separate advisory we have posted the results of the annual corn earworm field corn survey—which showed a statewide average of only 17.5% ears infested. This is even lower than the numbers reported in 2014 (20%) and 2013 (18%)—both years with very few cotton, peanut or soybean fields being infested with treatable numbers of worms. So far, all indicators point to another year with few fields reaching thresholds. We will continue monitoring and posting updates.

Corn earworm pyrethroid resistance: To date we have tested 255 moths (see the attached line graph). We started the season with about 15% survivorship at the end of June and as of the end of July are up to 40% survivorship. This level, this early in the season is cause for some concern. We will be posting updates often.  Vial_tests_30_July_2015

Advisory on Pollinator Protection and the Use of Foliar Insecticides in Flowering Cotton

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We have received several calls about the issues regarding the foliar application of insecticides to flowering cotton. Because of the oil and livestock feed uses of cotton, it is considered to be a food crop—so many of the insecticides used in cotton now include pollinator protection statements on their labels. These insecticides include, but are not limited to the neonicotinoids: Admire Pro, Centric, Belay, Endigo, Leverage, and others.

According to the new label restrictions, these insecticides are not to be used on cotton while bees are foraging, and they are not to be used until flowering is complete and all petals have fallen unless one of the following conditions is met:

1) The application is made to the target site after sunset and before sunrise.

2) The application is made to the target site when temperatures are below 55˚F.

3) The application is made in accordance with a government-initiated public health response.

4) The application is made due to an imminent threat of significant crop loss, and a documented determination consistent with an IPM plan or predetermined economic threshold is met.

Conditions 1, 2, and 3 are either not practical or will likely not apply to the cotton crop.  But condition 4 could be a viable option for growers but it needs some clarification—specifically, what is an imminent threat, who makes the determination, and how is the determination documented?

WHAT CONSTITUES AN IMMINENT THREAT OF SIGNIFICANT CROP LOSS, AND WHO DECIDES?

  • According to a guidance document by the State FIFRA Issue Research and Evaluation Group (SFIREG) (further details follow), the criteria to determine when an imminent threat exists would need to be determined by the applicator in consultation with a Cooperative Extension agent, crop consultant, certified crop advisor, or a state recognized pest management model/tool.
  • According to VDACS, “….ideally the determination of what an ‘imminent threat of significant crop loss’ is would be made and supported by a subject expert, for example, extension agent, crop advisor etc., prior to the application and the decision to apply can be shown to be consistent with an IPM plan or based upon an established economic threshold.”

HOW IS THE DETERMINATION DOCUMENTED?

  • According to VDACS, regarding required documentation, “…the label does not contain, thus there does not exist, a requirement for any specific records or documentation to be kept by the applicator. It is, however, in everyone’s best interest to have thorough application records and that would include documenting ‘imminent threat’. It would be prudent for the applicator to have some ‘evidence’ to support their use of the product as an outdoor foliar application on a labeled crop. The ‘evidence’ could be a letter or email from one of many experts, or a reference to a pest management guide or other such literature.”
  • Our current insect pest management recommendations for Virginia cotton can be accessed in the VCE publications, Pest Management for Field Crops, http://www.pubs.ext.vt.edu/456/456-016/456-016.html, and Managing Stink Bugs in Cotton: Research in the Southeast Region, http://www.pubs.ext.vt.edu/444/444-390/444-390.html.
  • Also according to VDACS, the label language (regarding documentation) is purposely vague to allow flexibility and rather than making the documentation requirement too prescriptive, they are following the general guidance document from the State FIFRA Issue Research and Evaluation Group (SFIREG), http://www.aapco.org/documents/bee_label_guidance_2014.pdf, and will consider the documentation provided to satisfy the condition has been met on a case by case basis.

So, as I see it, cotton can be treated with a neonicotinoid insecticide during flowing if the need is determined by a trained professional or there is some evidence that the treatment was based on published thresholds—and it would be best to document it via a letter, email, or some other written record.  Using any insecticide with the pollinator protection label language (and it is likely that in the future these restrictions will be applied to more products) will raise the bar in terms of both understanding and adhering to insect thresholds in not only cotton, but all food crops where pollinators forage during flowering.  This would leave no room for ‘automatic’, ‘tank mix’, ‘convenience’, or ‘insurance’ treatments—as these could not be justified as adhering to thresholds.

Note that there are a number of other requirements regarding notifying nearby beekeepers prior to insecticide applications. Details are provided in the SFIREG document mentioned, above. Always read and follow the label.  If you have further questions about the pollinator protection label language or how VDACS will handle this, you should contact your local Pesticide Investigator http://www.vdacs.virginia.gov/pesticides/directoryinvest.shtml or the Office of Pesticide Services at 804-786-3798. If you need further help in understanding the thresholds, please contact your local VCE ANR Agent, or Ames Herbert at the VT Tidewater Agricultural Research and Extension Center.