Grain sor
ghum fields in the Mid-Coast vary in maturity from soft/hard dough to pre-bloom. These fields should be scouted weekly for insect pests.
Today, we found sugarcane aphids in fields near Bayside. While these fields are not at a level needing treatment, the population should be monitored twice weekly to ensure they don’t get out of hand.
Sugarcane aphids can cause grain yield losses until a few weeks prior to harvest, but the crop is more sensitive to the aphids earlier in the season. As the sorghum grain heads mature, they become less susceptible to yield losses.
Control measures should be taken when the population rises above an economic threshold.
Threshold Based on SCA per Leaf
1. Examine the underside of one completely green leaf from the lower canopy and the upper most leaf (or leaf below the flag leaf at boot to heading). Estimate and record the number of SCA per leaf.
2. Examine two leaves (one upper and one lower) from each of five randomly selected plants for a total of 10 leaves per location.
3. Repeat at four locations for a total of 40 leaves per field.
4. Calculate the average number of aphids per leaf for the field (total aphids counted/total leaves inspected).
If the field average is above 50 aphids or more per leaf, apply an insecticide within one to three days.
Thresholds Based on Sorghum Growth Stages
1. Walk 25 feet into the field and examine the underside of green leaves from the lower canopy to the uppermost leaf for aphids. Watch for honeydew that indicates aphids on the leaf above.
2. Record of the number of plants infested with 50 or more aphids. Also, record the number of un-infested plants and plants with fewer aphids.
3. Examine a minimum of 10 plants at four locations across the field. Calculate the percentage of plants infested with 50 or more aphids (divide the number of plants with 50 or more aphids by the total number of plants and multiply by 100).
| Thresholds Based on Sorghum Growth Stages | |
| Growth stage | Decision threshold |
| Preboot | 20% of plants infested with 50 or more aphids |
| Boot | 20% of plants infested with 50 or more aphids |
| Flowering – milk | 30% of plants infested with 50 or more aphids |
| Soft dough | 30% of plants infested with established aphid colonies and localized areas with heavy honeydew |
| Dough | 30% of plants infested with established aphid colonies and localized areas with heavy honeydew |
| Black Layer | Heavy honeydew and established aphid colonies. Treat only to prevent harvest problems. Observe preharvest intervals for insecticides |
While scouting for sugarcane aphids, continue to look for stink bugs and headworms until hard dough and treat them if they exceed economic thresholds.
The Sorghum Economic Threshold Calculator Link is HERE.
