Insect Strip

Insect Strip

Tuesday, November 11, 2014

Texas Panhandle Sugarcane Aphid Update with comments about Sorghum Ergot

In the last issue of the Panhandle Pest Update (vol.6 issue 17), I reported on sugarcane aphids (SCA) being confirmed on the Texas Panhandle in Moore County. I provided a description of the conditions in the field where there were very few SCA numbers but sorghum heads with a lot of honeydew. After finding SCA in Moore County Tuesday, Nov 4th, I was in Lubbock on Thursday, Nov. 6th, and talked with Dr. Calvin Trostle, A&M Extension Agronomist - Lubbock, and Dr. Gary Peterson, A&M Sorghum Breeder - Lubbock, about SCA and ergot symptoms of sticky honeydew in sorghum heads. This is because a report came out on Nov. 6th that ergot was showing up in some sorghum fields on the High Plains.
Dr. Calvin Trostle found a small colony of SCA while looking at a sorghum variety trial near Vega, TX (Oldham County) on Thursday, Nov. 6th. I went to the field on Nov. 7th and could not find anymore SCA. I was able to ID the aphids as SCA from a sample saved by Dr. Trostle. But, this field did not have ergot infected heads.  Because Vega, TX is not far from the USDA - ARS / Texas A&M AgriLife Research station at Bushland, TX, Dr. Jourdan Bell, A&M Extension Agronomist - Amarillo, and I looked for SCA in sorghum fields at the Bushland station on Nov. 7th. With the help of Mr. Grant Johnson, USDA Technician, we found one nice size SCA colony in a dryland field. We were not able to find another colony this size, but found individual aphids on other leaves in the dryland field and in an irrigated field. Also, it was not difficult to see that the secondary tiller heads were infected with ergot in the dryland field.
Sugarcane aphid colony from a sorghum field at Bushland, TX
Dr. Gary Odvody, A&M Plant Pathologist - Corpus Christi, TX, provides this description of sorghum ergot. “…. honeydew on the sorghum heads is almost surely sorghum ergot caused by Claviceps africana.  It is probably very common across the area as the ever cooler nights promote male-sterility in the late-developing heads which favors infection by C. africana.  Typically, sorghum ergot is readily controlled or prevented through rapid pollination and seed set.  The longer dew periods also contribute to infection by C. africana and the dripping of honeydew onto the ground also indicates extended dew periods”. And comments by Dr. Ron French, A&M Plant Pathologist - Amarillo, are “We had ideal low temperatures that favored disease at some time in September which affected late planted sorghum, suckers, volunteers” and “We have had several cases of sorghum ergot based on reports from others and phone calls/emails I have received".

So, for our situation of light SCA infestations in the Panhandle, the issue of “gummy” honeydew in late-developing heads is from Ergot and not SCA.

Wednesday, November 5, 2014

Sugarcane Aphid confirmed on the Texas Panhandle

I received a call from a producer in Moore County yesterday. While walking down a row of his sorghum field he saw spots of honeydew drippings underneath some sorghum plants and the heads of these plants were covered with honeydew.  He remembered reading about the sugarcane aphid (SCA) from a previous newsletter and decided to call. The field was located just west of Dumas. 

What is interesting is that plants with honeydew were in one row and were not as mature as other plants in the field. Also, SCA numbers were very low. The producer and I only found two small colonies on two leaves and a couple of individual aphids on two other leaves. But, there was too much honeydew in the heads for the few aphids that we found. From what our fellow entomologists have seen down state and in other states, I was expecting to find greater infestation levels all across the field. What may have contributed to the low aphid numbers is that the top leaves of the plants had freeze injury (leaf die back) from a light freeze last Friday. It is difficult to actually say what impact the freeze had on the aphid population, because we did not know about this field prior to the freeze. The weather service was predicting another freeze.last night in the majority of counties north of Amarillo. 

Hopefully, with the freezes and predicted colder temperatures any surviving SCA will be held in check until our sorghum fields can be harvested. In the last issue of the newsletter, October 22,, information was given about management options for SCA infestations. One of these options was to use Transform insecticide for aphid control. However, the Section 18 emergency use exemption for this product expired October 31, 2014. This means that, in the event, SCA do present a problem there are two remaining management options this late in the season.

1. Harvest early: Take the dock at the elevator rather than loose so much yield to the aphid. This aphid can also cause serious lodging and ‘gummy harvest’ issues and losses pushing 60% of yield potential.

2. Harvest aid the infested sorghum field: Treatments of Aim or Roundup might help dry the plant faster and leave the aphid with nothing to feed upon. This was tried with limited success in the LRGV in 2013.

SCA from Moore County, TX field