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Sugarcane aphids found in Wilson County area
Recent rainfall has sorghum and all other crops across South Texas in good condition and set up well for a good harvest. However, in the case of sorghum, growers need to be aware that the sugarcane aphid has been observed in Wilson County.
The Wilson County AgriLife Extension Service had the first grower report of heavy infestations in a field in late May. Since then numerous other fields have been observed with heavy infestations and growers have been opting to treat for the pest in many cases.
Therefore, careful monitoring of sorghum fields is encouraged. Growers are also being reminded that sorghum should be able to tolerate a fairly heavy population before treatment is necessary.
In 2013, an outbreak of this invasive aphid was discovered damaging grain sorghum in Texas and neighboring states. Infestations detected were very heavy, often with hundreds of sugarcane aphids per leaf. Leaves became sticky and shiny from honeydew and coated with sooty mold fungus (grows on honeydew), which hampered harvesting operations.
The 2013 outbreak caused severe damage in fields affected by it. The aphid may be a new variant of sugarcane aphid, Melanaphis sacchari, which has a high preference for sorghum. It should be emphasized that this aphid does not currently appear to vector any type of plant disease and plants do not show “warning signs” such as yellowing of lower leaves as they typically do for other aphid species. However, as the aphid load builds up on individual plants they eventually succumb and quickly defoliate.
Entomologists have emphasized that growers will not need to treat at the first sign of this pest. Sorghum should be able to tolerate a fairly heavy population before treatment is necessary. However, when populations of sugarcane aphids are increasing rapidly, insecticides may be needed to prevent yield losses and honeydew buildup before harvest.
The Texas Department of Agriculture has obtained a Section 18 label from the Environmental Protection Agency so that pesticide applications of Transform WG can be made to control this pest. Dimethoate has also received a Section 2ee label for this pest. The Transform WG label allows for up to two applications with a maximum amount of 3 ounces per season. The IPM Agent in the valley, Daniella Sekula, was suggesting an application of Transform followed by an application of Dimethoate in lower populations. For heavy infestations, two applications of Transform at a 1-ounce rate followed by Dimethoate. However, the Transform label does allow you to go as high as 1.5 ounces for a single application.
Treating sugarcane aphids in sorghum
While no economic threshold has been established for this pest, the IPM Agent on the upper coast, Stephen Biles, offers the following suggestions in his weekly May 21 newsletter.
If leaf death occurs he would treat based on the greenbug economic thresholds (but remember the sugarcane aphid does not inject a toxin):
•Preboot treat before entire leaves on 20 percent of plants are killed.
•Boot to heading, treat at death of one functional leaf on 20 percent of plants.
•Heading to hard dough, treat when aphids cause death of two normal-sized leaves on 20 percent of plants.
If honeydew production is the concern, treat if aphids are in the head and producing honeydew but remember, a rainfall event could clean up the honeydew.
More detailed information about the sugarcane aphid can be found in a newly released extension publication, ENTO-035 “Sugarcane Aphid: A New Pest of Sorghum” or visit http://bit.ly/1oAHpW6.
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