BMSB and kudzu bug in soybean: update for Aug. 25, 2016

This past week our scouts found four new Virginia counties with brown marmorated stink bug (BMSB) in soybean (Caroline, Shenandoah, Rockbridge, and Henry).  Thresholds for field edges where BMSB is the predominant stink bug species are 3-5 adults + medium and large nymphs per 2-minute visual count, or 3-5 in 15 sweeps.  The Shenandoah field (R5 growth stage) that was sampled was above threshold with 8 BMSB per 2-minute count; six counties were approaching threshold (please see the map for specifics).

BMSB_map_25_Aug_2016

Kudzu bugs were found in three new counties (Prince George [reported by ANR Agent Scott Reiter), James City, and Franklin).  No counties had threshold levels of kudzu bugs (threshold is one nymph per sweep, which equals 15 nymphs per 15 sweeps).

KB_map_25_Aug_2016

Corn earworm soybean update.

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

 

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