Recent rainfall has sorghum and all other crops across the Coastal Bend Region 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 moved into the Lower Coastal Bend.
In Nueces County it was first observed in numerous fields around May 16th, but generally in low populations of 5 or so aphids on a leaf with 1 to 5% of the leaves infested. Although, some fields had 49% of leaves infested. On May 20th, we had our first grower report of heavy infestations in a field. The sample brought into the office had several 100s of aphids on it and the grower reported that it was representative of about 20% of the plants in the field. 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, including Nueces County, and neighboring states. Infestations detected were very heavy, often with hundreds of sugarcane aphid 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. A repeat of what occurred in 2013 can already be observed in the Rio Grande Valley and Northern Mexico. 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.
Entomologist have emphasized that growers will not need to treat at the first sign of this pest, because it does not appear to vector any plant disease. 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 2 applications with a maximum amount of 3oz 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, 2 applications of Transform at a 1oz rate followed by Dimethoate. However, the Transform label does allow you to go as high as 1.5oz for a single application.
Dr. Mike Brewer, Entomologist with AgriLife Research, has scouted several fields in the area and realizes determining where to focus scouting efforts is a major challenge. Therefore, he has outlined several suggestions to maximize scouting efforts for this pest.
Detection survey first: Check all fields for early infestations low in the plant traveling upward, and recent infestations of winged aphids middle and top leaves of plant. Walk into fields on all sides and part plants to detect established colonies on leaves with honeydew/aphids in the lower part of the plant (check 50 plants). Next, turn over 50 leaves on the upper part of the plant to detect winged aphids/new colonies. Follow detection surveys in fields with aphids with delineation surveys (see below), and continue detect surveys weekly in fields with no aphids detected.
Delineation surveys in fields with lower plant infestations and lower/upper plant infestations: These fields need a lot of attention to make a best assessment of whether aphids are very abundant (patches of plants with thousands of aphids) possibly causing some direct damage and likely to cause honeydew contamination of the heads. These fields are at risk and decision-making based on good observations is needed. Note that these aphids have not been associated with injecting plant toxins and plant disease, but the population increase and associated honeydew issues are a concern here. Schedule sprays accordingly.
Delineation surveys in fields with only upper plant new infestations: These fields need watching, but less time critical in making a spray decision. He advises sampling twice weekly possibly flagging sections of fields to check on how the infestation is advancing. Population increases and associated honeydew issues may result in late season issues, particularly harvest problems. These fields are worth regular inspection, twice weekly if possible to determine the extent of aphid colony increase in the field.
While no economic threshold has been established for this pest the IPM Agent on the upper coast, Stephen Biles, had the following suggestions in his weekly newsletter on May 21st.
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% of plants are killed; Boot to heading, treat at death of one functional leaf on 20% of plants; Heading to hard dough, treat when aphids cause death of two normal-sized leaves on 20% 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”.