Posted on Oct 04, 2016
Grain sorghum harvest is getting close for many producers in the Texas Panhandle and throughout Kansas, with a few fields already being cut. Unfortunately, sugarcane aphid (SCA) continues to be an issue in some regions. I made a trip up to Manhattan, Kansas, from Amarillo, Texas, this week and stopped at several fields along the way. SCA populations were highly variable, from very few in some fields to significantly above threshold in others.
Growers should keep in mind that SCA can significantly reduce yield through the soft dough stage and very likely during early hard dough. See table below.
Even if yield is not reduced at the hard dough stage, SCA can affect stalk integrity leading to stalk rot infection which can lead to lodging. It takes approximately 24 to 30 days to reach hard dough stage AFTER flowering. Depending on weather conditions, another 10 to 15 days is required to reach physiological maturity. Look for the black spot at the base of the sorghum kernel that indicates physiological maturity has been reached.
The decision to treat becomes difficult when SCA is present close to harvest. Although SCA is no longer directly affecting yield, they can cause harvesting issues due to honeydew production. We do not have any good threshold numbers on when to treat in order to prevent harvesting problems. A few SCA are not going to be an issue. However, when heavy uniform infestations are present an insecticide application is warranted, particularly if SCA are moving into the head or poor head exertion is going to result in significant honeydew covered leaves being harvested with the grain heads. When poor head exertion is present, then the addition of glyphosate or sodium chlorate to desiccate the leaves should be considered. Both Sivanto Prime and Transform have 14 day pre-harvest intervals in Texas, Oklahoma and Kansas.
Once SCAs are killed, the honeydew seems to dry up rather quickly. A good rain can also wash off some of the honeydew.
It is very hard to predict when SCA numbers will crash. SCA can be present in large numbers one day and within a few days almost completely disappear. We think cooler temperatures, particularly below 60 F, will have a negative effect on SCA.
In spite of SCA, the sorghum yield potential still looks good throughout most of the upper Texas Panhandle and in Kansas.