Friday, August 7, 2015

Sugarcane Aphids in Grain Sorghum

Threshold levels have been reached are will be soon on late planted grain sorghum (milo).  Every field of grain sorghum that I have looked at in the past several weeks has had some level of infestation from these fairly new pests.

This aphid pest that once only infested sugarcane has quickly become a pest of grain sorghum throughout the Southeast.  Since it is still a relatively new pest we are still learning about pest thresholds and the best tools to control it.  

Planting early and seed treatments can help early infestations, however much of our sorghum is planted later in the season and is untreated seed.  Fields should be scouted early and often to monitor pest levels and to be able to track the increase in populations across the field.

Threshold levels developed in the Delta range from 25% infested leaves with colonies of 50+ or 30% infested plants with colonies of 100+.  Either way once we get near this threshold we need to apply a suitable insecticide to reduce populations and protect yields.

Products that we have available are Transform, Sivanto, Chlorpyrifos (Lorsban, and others), and Dimethoate (Cygon,).  Dimethoate has had variable results and is not one that we would recommend. Chlorpyrifos has done well but the high rate requires a 60 day pre-harvest interval.  Sivanto has couple of labels for sorghum and was effective at the 4 oz. rate in trials.  the pre-harvest interval is 21 days.  Transform is another product that has label specifically for this pest.  it has a 14 day pre-harvest interval and has been effective even at low rates (0.75 oz) providing good coverage is accomplished.

Coverage is the key and can be improved by using at least 15 gallons per acre, by increasing pressure, and with the addition of a non-ionic surfactant at 0.25% v/v.