Monday, August 1, 2016

Sugarcane Aphids Have Reached Threshold in Lubbock County

Sugarcane aphids have reached treatment thresholds in sorghum in east Lubbock County. Last week we were optimistic that the beneficials were doing their jobs and preventing the aphids from exploding, but the aphid reproductive capabilities have proved too great. I was in a field today that had approximately 50% plants infested with aphid colonies, some as big as several thousand, with heavy honeydew in some areas. I am also seeing more winged adults. While beneficial activity is still high, they cannot compete with the exponential growth rate of the aphids once pest populations get this high.


Tommy Doederlein (EA-IPM, Dawson and Lynn Counties) reported today that SCA exploded over the weekend. Where there were 10-20 aphids late last week, there are now several hundred if not thousands, and honeydew is heavy. They are currently treating.

Greg Cronholm, independent crop consultant in Hale County, reported today seeing SCA colonies on the upper one third of the plant. Colonies are substantial with winged adults present.

Scouting for Aphids – Whole Plant Method
SCA will start colonies on the underside of leaves, so you must look there when scouting your fields. One method that is quick and easy is to cut the entire plant with your pocket knife and turn it upside down to inspect the bottom of each leaf individually. The smaller colonies will be harder to spot so examining the plant up-close will give you a better chance of spotting them.

Thresholds
Pre-boot: 20% of plants with aphids.
Boot: 20% of plants infested with 50 aphids per leaf.
Flowering to Milk: 30% of plants infested with 50 aphids per leaf.
Soft dough through dough: 30% of plants infested, localized areas with heavy honeydew, and established aphid colonies.
Black layer: Heavy honeydew and established aphid colonies with treatment only for preventing harvest problems.

What to Spray
It is crucial that you preserve your beneficials while still getting high efficacy. Insecticide efficacy trials on the High Plains last year confirmed that there are only two good choices when it comes to SCA: Sivanto and Transform. (FYI – Both of these products will take out both SCA and Yellow SCA!).

The data below are from Dr. Ed Bynum and Dr. Pat Porter’s SCA trial in Bushland in 2015. The significant spikes in aphid numbers following treatments of Karate and Nufos (Chlorpyrifos, also sold as Lorsban) are because the treatment also killed the beneficials. Nufos (Chlorpyrifos) at one pint, and Karate at 1.92 oz provided poor control but, to make matters worse, any aphids that escaped the treatment were allowed to reproduce without any pressure from predators.

Chlorpyrifos can be effective at one quart per acre (while killing beneficials and allowing population resurgence), but at this rate has a preharvest interval (PHI) of 60 days. Transform has a PHI of only 14 days for grain or straw harvest and 7 days for grazing, or forage, fodder, or hay harvest. Sivanto has a PHI of 7 days for forage and 14 days for dried grain, stover, or straw. Always make sure to read your labels before using any chemical.