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.

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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

BMSB and kudzu bug distribution maps for the week ending August 27, 2015

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Brown marmorated stink bug and kudzu bug were found in soybean in several additional Virginia counties this week–please refer to the distribution maps below.  Fields at or above the BMSB threshold of 3 to 5 total adults + medium and large nymphs in a 2-minute visual count were found in the following counties:  Bedford (12 BMSB per sample), Shenandoah (8 BMSB), Nelson (4 BMSB) and Henry (3 BMSB).   Thanks to our scouts Ed Seymore and Jamie Hogue, and to ANR Agent Scott Reiter for their reports this week.  BMSB_map_27_Aug_2015KB_map_26_Aug_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

Soybean disease update – frogeye leaf spot

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I have received numerous reports of soybean fields with moderate to severe frogeye leaf spot (FLS) over the past several weeks. In most cases, the disease is showing up in fields planted to a FLS susceptible variety and/or in fields that have been in continuous soybean. FLS can cause significant yield loss in susceptible varieties, so fungicides may be needed to control the disease in high risk fields (see accompanying blog post “Foliar fungicide applications in soybean”). Unfortunately, FLS isolates resistant to strobilurin (QoI, Group 11) fungicides have been confirmed from some locations in Virginia, so fungicide control failures can occur if the proper fungicide chemistries are not selected as illustrated in the pictures below. A soybean fungicide efficacy table with ratings based on data from multiple field trials in multiple states can be downloaded below. We are currently surveying fields in Virginia for strobilurin-resistant FLS and will have data on the frequency and distribution of resistance later this year. In the meantime, it should be assumed that FLS will not be controlled by strobilurin fungicides, and other fungicide chemistries (e.g. triazoles) should be applied in fields with FLS either alone or in combination with a strobilurin. Keep in mind that strobilurin fungicides still provide good control of other diseases that can occur in soybean.

FLS - untreated

FLS – untreated

FLS - 2 fungicide applications

FLS – 2 fungicide applications

Soybean disease scouting & fungicide guide 2015

Foliar fungicide applications in soybean

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If and when to make a foliar fungicide application is a decision soybean producers must make each growing season. Every year is slightly different, and it is difficult to predict whether or not a fungicide application will be profitable. However, the risk factors listed below can be used to make an educated decision of whether or not to spray. The greater the number of risk factors in your field, the more likely it is that a fungicide application will be profitable.

  1. Growth stage of the crop. Disease is most likely to impact yield during pod and seed development since this is when the yield of the crop is being formed. Fungicides are more likely to result in a yield response if disease occurs between the beginning pod (R3) and full seed (R6) growth stages, a period that lasts approximately 30 days. Results from research conducted in 2014 suggest that a fungicide application is most likely to result in a yield response if weather conditions (see #2 below) conducive for disease development occur within two weeks of the R3/R4 growth stage. Overall, the optimum timing for a fungicide is at the R3/R4 growth stage, though later applications can be beneficial if diseases develop later in the season. Fungicide applications after the R5 growth stage are not recommended.
  2. Weather conditions. Currently, research is being conducted to develop a weather-based fungicide decision aid for soybean. Infection, growth, and sporulation by foliar pathogens occurs when temperatures are moderately warm and during periods of rainfall or high humidity. To determine the relative disease risk based on weather conditions, find a source of hourly temperature, rainfall, and relative humidity data (e.g. Weather Underground or a personal weather station). If over the past week the following conditions occurred on two or more days, the risk of disease development in the crop is high:
    • Average daily temperatures from 65-80 °F AND
    • 10 or more hours of relative humidity at or above 95% OR a rainfall event
    These conditions have occurred in many areas throughout Virginia over the past week as storms have moved through. However, before making a fungicide application consider the other risk factors below.
  3. Susceptibility of soybean variety to disease. Soybean varieties vary in their susceptibility to diseases, and more susceptible varieties are more likely to need a fungicide to protect yield. Keep in mind that a variety may be relatively resistant/tolerant to one or a few diseases but susceptible to others, so be aware of which diseases are most likely to occur in your field (see #4 and #5 below).
  4. Field history. Soybean debris is a source of pathogen inoculum, so diseases will show up earlier and be more severe in fields planted to soybean year after year compared to those in rotation with corn or another crop. History of a particular disease in a field should also be considered since it is likely to occur year after year.
  5. Confirmation of disease in a field. If you see a foliar disease starting to develop in your soybean crop, it may be a sign that it is time to apply a fungicide. Scouting may be useful for some diseases such as frogeye leaf spot, but other diseases (e.g. Cercospora blight) do not show symptoms until long after infections have occurred. Fungicides are more effective when applied preventatively, but applications shortly after the onset of symptoms will slow the progress of the disease. Thresholds have not been established for frogeye leaf spot or other foliar diseases of soybean.
  6. Yield potential. This year some soybean fields got off to a poor start and never really recovered. If growth is poor and yield potential is low, you do not have much yield to protect and fungicide applications are less likely to be profitable. In contrast, if a crop has high yield potential, a fungicide application can help to maximize that yield, especially if the variety is susceptible to disease.

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