It has been a while since I have seen corn leaf aphid on sorghum but they are abundant this year. I have seen them in about every sorghum field from the Rio Grande Valley into San Patricio county. They are creating a little confusion among some folks confusing them for sugarcane aphid. I think a short refresher on separating the two species is in order so lets take a closer look at the two aphids and their biology. The following fast paced video produced by my grad student, Jason Thomas, is a helpful resource to help you know whether you have a sugarcane aphid or not. It also discusses estimating populations.
We just released a number of videos on the sugarcane aphid to see the full list click here. If you are new to the sugarcane aphid I suggest you click here to view the sugarcane aphid basics page to view some highly simplified training that can either be read or watched as a video.
CORN LEAF APHID: The corn leaf aphid is an olive colored aphid with a dark head. The characteristics that set it apart from the sugarcane aphid (aside from the coloration) are the dark legs,
The corn leaf aphid is commonly found in the whorl of vegetative sorghum. They may occur in large numbers but are very rarely considered an economic issue on sorghum. As the plants advace to the boot stage corn leaf aphid may move to the underside of leaves, stalks, and the head. The populations generally collapse once they are outside of the whorl.
They can be somewhat beneficial because their presence allows for the early establishment of predators (ladybugs, lacewings, syrphid larvae, etc…) and parasites that will feed on sugarcane aphid. In rare cases their feeding may stress plants resulting in secondary infection by charcoal rot.
If you see aphids in the whorl, they are not sugarcane aphid. If you do find aphids on sorghum leaves or stalks please look carefully at the key characteristic for proper identification. The black legs alone will eliminate the aphid as a sugarcane aphid. So, lets revisit the sugarcane aphid.
SUGARCANE APHID: The sugarcane aphid color may vary from light yellow to dark tan (darker coloration is most common at low temperatures during late fall and winter). Key characteristics used to identify sugarcane aphid include dark feet (not the legs), dark cornicle tips and the tips of the antennae will be dark. The head will be the same color as the body.
Although rare, corn leaf aphid may be found in colonies on the underside of leaves. Therefore, it is possible that mixed populations of corn leaf aphid (as well as other aphids) and sugarcane aphid to occur on sorghum. I saw this in the Valley a couple of weeks ago. Just remember the key characteristics of the sugarcane aphid and you will never confuse it with other aphids. My Graduate student, Jason has come up with a phrase that will ensure you never get confused as to what is a sugarcane aphid to learn more about that watch his video above or visit this page here.
What is the current status of sugarcane aphids on sorghum in South Texas? Sugarcane aphid populations continue to increase on sorghum in the Rio Grande Valley. Numerous field in the Lower Rio Grande Valley have been or soon will be sprayed for sugarcane aphid.
Sugarcane aphid on sorghum has been documented in Kleberg, Nueces, Jim Wells, San Patricio, Goliad, Refugio, and Fort Bend Counties. It is likely that some fields in all south Texas sorghum are supporting some population of sugarcane aphid. We just have not gotten around to sorghum in all counties to document their presence.
It should be noted that, outside the Lower Rio Grande Valley, sugarcane aphids on sorghum are most common along field edges, especially if volunteer sorghum or Johnson grass is neighboring the field. Their presence on sorghum is the result of local movement from overwintering hosts onto the neighboring sorghum. Their population, thus far, have been spotty and only small colonies (less than 50 aphids) have been observed. However, their presence should be motivation to initiate scouting for sugarcane aphid on your sorghum.
The major source of field-wide sugarcane infestations are coming. Sugarcane aphid populations have been quite high in Mexico and, most recently, in the Lower Rio Grande Valley. Sorghum in Mexico is maturing and the crop is ahead of normal in the Valley. Numerous winged sugarcane aphids are being reported across the border and in the Valley. Once these aphids become wind-borne they will be moving northward the will be more scattered across fields rather than the border effect we are currently seeing on sorghum from the Lower Coastal Bend into the Winter Garden area.
It is important to remember that the aphid can build in populations to extremely large numbers in a very short period of time. Start scouting sorghum for sugarcane aphid now if you have yet done so.
Labeled Insecticide Rates: It is important to recognize labeled insecticide rates are not merely suggestions but the law and important for any implied warranty by the company manufacturing the product. Although rates lower than labeled may be effective, using lower rates may be against the law in some states (not so in Texas). There are several reasons this is not recommended, many of which deal with biological aspects around pesticide and target organism. The major consideration when an off-label application is made, such as using lower than labeled rate, is that it will nullify any implied warranty on the product. If the off-label application fails to work in a satisfactory manner, then the company may not warranty the product in cases of performances failure. Please check with your local chemical representative before making any off-label application to learn of possible consequences of such an application.
Transform: The EPA approved the use of Transform on sorghum for 2017. There are label changes for its use on sorghum from the 2016 Section 18. As a reminder here are the major restrictions for its use on sorghum against SCA:
- Preharvest Interval: Do not apply within 14 days of grain or straw harvest or within 7 days of grazing, or forage, fodder, or hay harvest.
- A restricted entry interval (REI) of 24 hours must be observed.
- Do not make more than two applications per acre per year.
- Minimum Treatment Interval: Do not make applications less than 14 days apart.
- Do not apply more than a total of 3.0 oz of Transform WG (0.09 lb ai of sulfoxaflor) per acre per year.
- Do not apply product ≤ 3 days pre-bloom until after seed set.
Please refer to the following link for the full section 18 label: https://www.texasagriculture.gov/Portals/0/Publications/PEST/Sect18/16TX02%20Transform%20WG%20Sec%2018%20Directions.pdf
- Residual activity of insecticide seed treatments is generally 30 up to 50 days after planting. Regardless of insecticide seed treatment and planting date, now is a good time to initiate early detection of sugarcane aphid in your sorghum. Pay close attention to field borders, more especially if volunteer sorghum remnant sorghum, or Johnsongrass borders these fields.
- Scout all sorghum! Many farmers will plant sugarcane aphid tolerant sorghum this year. It is important to remember that no sorghum hybrid is immune to sugarcane aphid. All fields should be treated as though they were susceptible to the aphid to avoid possible surprises.
Current environmental conditions are favorable for sugarcane aphid migration and optimal for its reproduction. But, early detection of sugarcane aphid in the Valley does not necessarily mean this will be an aphid year on sorghum. However, the best way to handle any crop pest is routine scouting, utilizing thresholds (average of 50 to 125 aphids per leaf for Texas with exception to the High Plains), spraying once thresholds are reached (highly suggested to do so within 3 days after the population reaches the threshold), and use enough carrier (minimum of 10/gallons per acre by ground or 5 gallons per acre by air) to penetrate the canopy and maximize coverage on lower leaves.
Robert Bowling, Ph.D.
Assistant Professor and Agrilife Extension Entomology Specialist
Texas A&M Agrilife Research and Extension Center at Corpus Christi
10345 Hwy 44
Corpus Christi, TX 78406
Work: (361) 265-9201