Sugarcane aphid on south Texas sorghum plummeted shortly after a series of rain events starting on Memorial day. We have seen this across multiple years. The sugarcane aphids seem to have some sort of hypersensitivity to the rain and humidity or possibly some other undocumented factor(s). In almost all of our field plots we saw major declines in the sugarcane aphid. Although not fully understood, it is likely that the sudden collapse of sugarcane aphid in south Texas has been caused by multiple factors some of which include:
- Natural enemies. Abundant corn leaf aphid on sorghum provided an early season food source for aphid predators and parasites. There was a ready supply of natural enemies once the sugarcane aphid began to establish in south Texas. We were somewhat surprised to see a new sugarcane aphid parasitoid this year…a braconid. This parasitic wasp produces a brown mummy rather than the black mummy we have become accustomed to in the sugarcane aphid. The braconid was quite effective at reducing sugarcane aphid populations. The video above is of an Aphelinus wasp that produces black mummies. The video was by Jason Thomas.
- Following the recent rain events there has been an increase in aphids that appear to be diseased. Pathogen derived mortality is a real possibility as a factor for the sudden collapse of sugarcane aphid on sorghum in south Texas.
- Heavy rain events may have physically washed aphids from lower leaves possibly drowning or physically injuring aphids.
- Adoption of sorghum ‘Highly Tolerant’ to sugarcane aphid. Sorghum acres planted to hybrids categorized as ‘Highly Tolerant’ to sugarcane aphid have increased over the last two seasons. sugarcane aphid are very slow or fail to establish in these fields.
The sudden collapse of sugarcane aphid is likely not the result of any one of these factors but most likely a combination of these and other elements. The good news is that less than 20% of the sorghum acres in south Texas (from the Lower Rio Grande Valley to the Upper Gulf Coast) have been treated for sugarcane aphid. This was very good news for farmers in the Valley as this is the first year since the arrival of sugarcane aphid that the majority of sorghum acres did not require an insecticide (with many acres requiring 2 insecticide applications) for the aphid!
This is the third season the sugarcane aphid has not presented itself as a main entomological issue in south Texas sorghum (only exception would be the Lower Rio Grande Valley in 2015 and 2016). A close association among Research and Extension Entomologists and other specialists, county extension agents, the Texas Sorghum Growers Association, Sorghum Checkoff, industry partners, and area farmers have made possible development of sugarcane aphid management strategies. A science based economic threshold, natural enemy surveys, insecticide efficacy trials, identification of an entomopathogen, and numerous field trials evaluating sugarcane aphid tolerance in sorghum have been major contributions to managing this aphid on south Texas sorghum. This is a challenging insect pest but the field work and countless educational programs around managing the aphid has been rewarding. I look forward to future challenges in working with this aphid and developing additional management strategies around the sugarcane aphid.
Although our replicated sugarcane aphid trials have not achieved the desired results we do have a couple of demonstration locations that will shed light on sorghum touted at ‘Highly Tolerant’ to sugarcane aphid. We will hand harvest one location next week and share results of this trial in the near future. Also, it looks like I will be conducting some fall trials as well…anyone interested in helping count sugarcane aphid this fall?
Assistant Professor and Agrilife Extension Entomology Specialist
Texas A&M Agrilife Research and Extension Center at Corpus Christi
10345 Hwy 44
Corpus Christi, TX 78406