Friday, June 29, 2018

Sugarcane Aphids in Grain Sorghum






Sugarcane aphids have been observed in several grain sorghum fields in northeastern Travis County in the area of Carlson Lane, Harry Lind Road, Lund Carlson Road and in northern Travis County, west of FM 973.  Some of the fields had treatable infestations of sugarcane aphids, while others had low numbers of sugarcane aphids.  Conditions in Travis County are conducive to rapid increases of sugarcane aphids, so fields should be monitored carefully and regularly to get ahead of any potential problems with this pest. 

Scouting for sugarcane aphids - Once a week, walk at least 25 feet into the field and examine the plants for honeydew along 50 feet of row.  If honeydew is found, look for sugarcane aphids on the underside of the leaves above the honeydew.  Inspect the lower leaf surface of one leaf from the upper and one from the lower canopy for each of 15 to 20 plants along the row.  Sample plants from each side of the field and areas near Johnsongrass or tall mutant plants (at least four areas per field) for a total of 60-80 plants per field.   If no aphid is found or only a few wingless or winged aphids are found on upper leaves, continue once-a-week scouting in that field.  If sugarcane aphids are found on lower- or mid-canopy leaves, begin twice-weekly scouting in that field.  Note:  Sugarcane aphids are capable of increasing from 50 per leaf to 500 per leaf in two weeks.

South-Central Texas Treatment Thresholds - Once sugarcane aphids are established in a field, use the following sampling protocol: 
Field Sampling
  1. Examine the underside of one completely green leaf from the lower canopy and the uppermost leaf.  Estimate and record the numbers of sugarcane aphids per leaf. 
  2. Examine two leaves from each of five randomly-selected plants per location for a total of 10 leaves per location. 
  3. Repeat this process in each of four locations per field for a total of 40 leaves per field. 
  4. Calculate the average number of aphids per leaf for the field (total number of aphids divided by the number of leaves).  Since it is impractical to count large numbers of aphids, an aphid estimation tool may be found at:  http://ccag.tamu.edu/sorghum-insect-pests/  to assist in estimating sugarcane aphid numbers.
Economic threshold
  1. If the field average is 50-125 sugarcane aphids per leaf, or greater, apply an insecticide within four days and evaluate the control after three to four days.  Continue to monitor sugarcane aphids until harvest to determine if a second insecticide application is necessary. 
  2. Consider treatment at 50 sugarcane aphids per leaf if scouting is limited to once a week or the weather is warm and dry.
  3. If the field average is below the threshold level, continue scouting twice a week. 

Insecticides for sugarcane aphid control
  1. Sivanto insecticide is labeled for sugarcane aphid control at rates of 4.0 to 7.0 oz. a.i., per acre.  There is a 21-day pre-harvest interval for Sivanto on grain sorghum.
  2. Transform WG has a Section 18 label for sugarcane aphid control at rates of 0.75 to 1.5 oz. a.i., per acre.  There is a 14-day pre-harvest interval for Transform WG on grain sorghum.
  3. Other insecticides that are labeled for sugarcane aphid control are chlorpyrifos, dimethoate, and malathion.