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

The Virginia Soybean Field Day is this Thursday

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VIRGINIA SOYBEAN FIELD DAY
Thursday August 20, 2015

Eastern Virginia Agricultural Research & Extension Center
2229 Menokin Road
Warsaw, VA 22572
(804) 333-3485

Sponsored by
Virginia Soybean Association
Virginia Agricultural Experiment Station
Virginia Cooperative Extension

Join us to see the latest research on soybean varieties, disease and weed management, IPM and sorghum varieties. Experts will also demonstrate no-till drill maintenance and update you on the mid-Atlantic double crop initiative. Registration begins at 8:00 am and field tours begin at 8:50 am. The program will end at noon with a delicious meal by Nixon Catering.

Topics include:
– Soybean Disease Management – Dr. Hillary Mehl
– Soybean Weed Management – Dr. Mike Flessner
– Soybean Insect IPM – Mr. Mike Parish and Drs. Sean Malone and Ames Herbert
– No-Till Drill Maintenance – Mr. Keith Burgess
– Grain Sorghum Management – Dr. Joseph Oakes
– Roundup-Ready Public Soybean Varieties – Dr. Bo Zhang
– Mid-Atlantic Double-Crop Soybean Initiative – Dr. David Holshouser

We hope to see you there!

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.

Late season Palmer amaranth

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I have received several calls regarding control of large glyphosate-resistant Palmer amaranth in soybean. In most cases, Palmer amaranth resistant to glyphosate is also resistant to the ALS-inhibiting herbicides (ie Harmony SG, Pursuit, Raptor, Synchrony STS, etc.). So these herbicides offer no help. Resistance to these two chemistries limits the chemical control options growers have left. In Roundup Ready soybean cultivars, the only postemergence options left for control of Palmer amaranth are the PPO-inhibiting herbicides (Cobra, Flexstar, Reflex, Resource, Ultra Blazer, etc.). When targeting Palmer amaranth with PPO-inhibitors, the weed must be small (less than 4 inches in height) to achieve adequate control. It is also important to remember PPOs can cause some soybean injury. In Liberty Link soybean, in addition to the PPOs, growers also have the option of Liberty to control Palmer amaranth. Again, small weeds are necessary to get the most out of Liberty. Once Palmer amaranth exceeds the 4 inch threshold, control by the PPOs and Liberty diminishes. Unfortunately, attempts to control large glyphosate- and ALS-resistant Palmer amaranth are often futile. Faced with this situation, it is necessary to physically remove Palmer amaranth. Prior to the appearance of a seed head, Palmer amaranth can be pulled and left in the field. Remember to shake dirt from the root ball to ensure the weed does not re-root. After seed head emergence, it is critical to remove Palmer amaranth from the field. Female Palmer amaranth are capable of producing over 1 million seed. Even while still green, some seed are viable. In the soil, Palmer amaranth seed remains viable for approximately 4 to 5 years. Assuming the seedbank is not replenished during this time period, daunting populations begin to decrease and management becomes easier. In problem areas, rotating to corn may be a good idea (atrazine and the auxin herbicides remain effective against Palmer amaranth). However, corn harvest occurs relatively early and Palmer amaranth can emerge following harvest and produce seed prior to a killing frost. Gramoxone applied after corn harvest (3 to 4 pints/A) has proven most effective controlling Palmer amaranth and ensuring the weed seedbank is not replenished in this situation.

Palmer amaranth seed produced by on female plant.

Palmer amaranth seed produced by one female plant.

 

Black light trap catches for the week ending August 6, 2015

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Corn earworm moth captures started increasing in area black light traps, ranging from 0.3 to 7.5 per night.  Brown marmorated stink bug nightly averages ranged from zero to 12.9.  Please see the data tables for specifics.  Thanks to the following for their reports this week:  John Allison, Scott Reiter, David Moore, Mary Beahm, Austin Brown, Janet Spencer, Keith Balderson, and Ames Herbert and his entomology crew. BLT_Aug_6