Kurt Guidry, Beuzelin, Julien, Kerns, David L., Brown, Sebe
David Kerns, Sebe Brown, Julien Beuzelin and Kurt M. Guidry
The sugarcane aphid first appeared in Louisiana in 1999 in sugarcane. Although this aphid is a known pest of sorghum in other areas of the world, it was relegated as a pest of sugarcane in the United States. In 2013, sorghum producers in southwest Louisiana began reporting large numbers of aphids in their crops (Figure 1). Within a few months, the infestation had spread south along the Gulf Coast of Texas into Mexico, northeast through Louisiana and into Mississippi, and northwest to southern Oklahoma. By 2014, the infestation had further spread throughout the southern United States. Little is known as to why this aphid began feeding on sorghum, sorghum-related crops and weeds, but interestingly, LSU AgCenter entomologists observed that the new variant that feeds on sorghum does not survive well on sugarcane.
A new threat to sorghum production
Sugarcane aphids are small, soft-bodied insects that feed on plant sap (Figure 2). Plant sap is rich in sugars and water, and once nitrogen-containing nutrients are filtered from the sap, the sugary waste, or honeydew, is expelled. Feeding occurs on the underside of the leaves and stems, causing reddening, purpling and sometimes death of leaf tissue, and honeydew and subsequent sooty mold accumulation on plants (Figure 3). One of the interesting traits of the sugarcane aphid is its ability to cause injury and economic loss from the time the sorghum crop emerges through harvest. Seedling sorghum can be outright killed by the sugarcane aphid, or severely stunted. The most susceptible stage to sugarcane aphid injury appears to be at pre-boot, when heavy infestations will often cause sorghum to produce sterile seed heads (Figure 4). Significant loss can also occur during harvest. Because of sticky leaves covered in aphids and honeydew, combines become clogged and as much as 50 percent of the grain may be expelled from the combine discharge. Combining an aphid-infested field results in significant machine breakdown and time devoted to cleaning and repairing the machinery.
Although the sugarcane aphid can be a devastating pest to grain sorghum, research and extension efforts conducted by the AgCenter and others have demonstrated that it is a manageable threat. Several insecticide efficacy trials were conducted to evaluate labelled insecticides and several non-labelled alternatives for aphid control. Based on these trials, the only insecticide that offered acceptable control of the sugarcane aphid was the non-labelled product Transform. The LSU AgCenter worked with the Louisiana Department of Agriculture and Forestry to submit a Section 18 emergency exemption request to the U.S. Environmental Protection Agency to permit the use of Transform for managing the sugarcane aphid in sorghum. The cooperative effort exhibited by the AgCenter, the LDAF and the EPA was a textbook example of how research, extension, and state and federal regulatory agencies can work together to solve unexpected pest management problems for U.S. farmers.
Economic impact of the sugarcane aphid
In 2013 a survey was conducted among Louisiana sorghum producers to quantify the economic impact of the sugarcane aphid. The survey showed a 27 percent reduction in sorghum yield and increased production costs due increased usage of desiccants, slower harvest speeds (22 percent reduction) and machinery breakage (more than 40 hours on average). Results of the survey were used in conjunction with AgCenter Enterprise Budget data to estimate economic impacts of the sugarcane aphid to the Louisiana grain sorghum industry. The total economic impact was estimated at $7.6 million (Table 1). In 2014, AgCenter entomologists estimated that 85 percent of the grain sorghum acres had economically significant levels of sugarcane aphids. Given the severity of the infestations, it was estimated that yields across the state were reduced by roughly 10 percent. However, on those acres with economically significant levels, the improved management tactics and availability of a more effective insecticide, thanks to the Section 18 registration of Transform, was estimated to protect roughly 50 percent of yield potential. In other words, the improved management tactics were able to result in yields that were as much as 50 percent higher than without those tactics.
To determine the total economic impact of the improved management strategies available in 2014, both the positive impacts (revenue savings) and the negative impacts (increased costs) were considered (Table 2). Revenue savings were estimated at $14.9 million while increased production costs were estimated at $2.2 million. The net results show that AgCenter efforts in providing improved management tactics resulted in a net positive impact of $12.7 million, nearly 33 percent of grain sorghum’s total farm gate value in 2014. AgCenter efforts helped to turn a situation that caused more than $7.6 million in economic harm in 2013 into a situation that helped protect more than $12.7 million in net returns to the state’s grain sorghum industry.
Research for management of the sugarcane aphid
In 2014, AgCenter entomologists greatly expanded their research effort in the management of the sugarcane aphid in sorghum. Efforts included identifying alternative insecticides, evaluating insecticide seed treatments, managing insecticide resistance, screening sorghum germplasm for resistance and determining an economic threshold for timing insecticide applications. It was obvious that managing sugarcane aphid populations would require an integrated approach, including a combination of management tactics used when needed.
Early or timely planting will help avoid early sugarcane aphid infestation, and research at the Macon Ridge Research Station and Dean Lee Research and Extension Center has demonstrated that commonly used neonicotinoid seed treatments may provide as long as 40 days’ control of the sugarcane aphid. AgCenter entomologists have also identified several commercial hybrids with resistance or tolerance to sugarcane aphid feeding. Cooperative research by the LSU AgCenter and Texas A&M AgriLife has set a preliminary treatment threshold of 50 aphids per leaf colonizing 20 percent of plants in the field.
The long-term solutions for managing the sugarcane aphid in sorghum will undoubtable rely heavily on breeding resistant cultivars. But in the interim, the key to controlling the sugarcane aphid on susceptible hybrids is to not allow the aphid population to build to high numbers.
Detailed sugarcane aphid management recommendations are available at www.lsuagcenter.com.
David Kerns is an associate professor at the Macon Ridge Research Station, Winnsboro; Sebe Brown is an assistant area agent in the AgCenter Northeast Region, Winnsboro; Julien Beuzelin, is an assistant professor at the Dean Lee Research and Extension Center, Alexandria; Kurt Guidry, is a professor in the Department of Agricultural Economics and Agribusiness.
The summer 2015 issue of Louisiana Agriculture magazine includes articles on a variety of topics that affect Louisiana’s agriculture industry and the environment – water management at Catahoula Lake, 4-H youth wetland programs, artificial reefs for water conservation, corn nitrogen management in saturated soil conditions, and more. 36 pages