Texas Blacklands IPM: Sugarcane Aphid Thresholds

Cotton

Cotton that has been planted and emerged is growing as our saturated soil profile is finally starting to dry down. Cotton in the scouting program was at the 2- to 3-true leaf stage last week.

Thrips are present in all cotton fields in the scouting program but still well below the economic threshold. Higher thrips populations have been observed in fields that are close to wheat that is drying down. As our wheat crop continues to dry down and move closer to harvest we need to keep an eye on potentially damaging thrips populations.

Sorghum

Sugarcane aphids have been found in Hill County on both johnsongrass and sorghum.

On Wednesday while checking wheat north of Brandon I decided to stop and look at some johnsongrass along field edges and in the bar ditch and found small colonies of sugarcane aphids. Most colonies were less than 50, but there was one colony of 100 or more aphids on a leaf. On Thursday while scouting sorghum near the Hillsboro Municipal Airport I found an extremely low population of sugarcane aphids, with only three aphids being found across 4 sorghum fields.

We need to keep in mind that sugarcane aphid populations can quickly increase to the economic threshold when beneficials are not in the field to help manage the population. There were beneficial insects around the aphid population found in the johnsongrass, however, I did not notice any beneficials around the aphids in the sorghum. The lack of beneficials in the sorghum could also be due to the extremely low number of aphids in these fields.

Sugarcane Aphids

There are two economic thresholds for sugarcane aphids used in the state of Texas:

1. The first threshold is based on growth stage and the percent of plants infected with 50 or more aphids per leaf. See Table.
2. The second threshold is based on the average number of aphids per leaf from plant emergence to flowering with an economic threshold of 50 aphids per leaf.

Depending on the threshold you use determines how to scout and record data. To better discuss the scouting procedures for each method I will call plants infested threshold the High Plains Threshold since it is commonly used in the Texas High Plains and the number of aphids per leaf threshold the Central/South Texas threshold.

Texas: Sugarcane Aphid Threshold. Click on table to enlarge.

When using the High Plains threshold, you want to examine 10 plants form at least 4 areas of the field and document the total number of plants checked and the total number of plants with 50 or more aphids. Once you have a percentage of plants with 50 or more aphids, use the threshold in Table 1 to determine if an insecticide application is warranted.

When using the Central/South Texas threshold you want to examine one leaf from the lower canopy and one leaf from the upper canopy on at least 5 random plants from a minimum of four regions of the field. To use this threshold, you will need to estimate the number of sugarcane aphids (will take too long to count) per leaf. Once you have looked at a minimum of 40 leaves in the field, you will need to calculate the average number of sugarcane aphids per leaf, and if the average is 50 or more per leaf an insecticide should be applied.

For fields that average close but still below the economic threshold, one should take into consideration the rate of aphid population growth, future weather conditions, and a potential backlog with ground rigs and/or crop dusters before deciding not to spray.

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Through the years several insecticides have been tested for their efficacy against sugarcane aphids, and their ability to manage a resurgence of the aphid.

Through these trials two insecticides have performed well and preserved the beneficial insects to help keep sugarcane aphid populations form flaring back up. Sivanto and Transformare labeled, but Transform is only labeled through a Section 18 Emergency Exemption label, which has recently been approved by the EPA to include the state of Texas.

• Sivanto labeled rate is between 4 and 7 ounces per acres, with no more than 28 ounces per acre applied per year.
• Transform labeled rate is between 0.75 oz. per acre to 1.5 oz. per acre, with no more than 3 oz. being applied per acre in a single year. Transform also has some restrictions to help minimize negative effects on bee populations, including: no application within 3 days of bloom through seed set. Only 2 applications of Transform can be made to a single field within a year.
• All insecticide applications for sugarcane aphid management should be applied in a minimum of 10 gallons per acre by ground and 5 gallons per acre when applied by air.