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.