Insect Pests and Diseases in Bioenergy Crops

Linda F. Benedict, Beuzelin, Julien, Hoy, Jeffrey W.

Gene Reagan, Ted Wilson, Julien Beuzelin, Mo Way, Jeff Hoy, Yubin Yang, Allan Showler, Matt VanWeelden and Blake Wilson

With plentiful rainfall, abundant land and mild winters, south Louisiana is among the geographic regions with the highest potential for production of dedicated cellulosic bioenergy crops, especially energycane and high-biomass sorghum (Figure 1). Additionally, much of the infrastructure needed for production of bioenergy crops is already in place because the sugarcane industry has been thriving in our state for centuries. However, insect pests and diseases have historically been major yield-limiting factors in the South. LSU AgCenter and Texas A&M AgriLife scientists are working together with the goal of building a landscape- wide pest management program that will mitigate insect pest and disease damage to bioenergy crops in interaction with conventional crops along the U.S. Gulf Coast.

An old foe, the sugarcane borer

The sugarcane borer, Diatraea saccharalis, has been the primary pest of sugarcane in Louisiana for more than a century. The insect also feeds on other crops, including corn and rice, and is expected to be a pest of bioenergy crops including energycane, sweet sorghum and high-biomass sorghum. Sugarcane borer larvae tunnel internally in stalks, reducing the flow of nutrients within the plant. Sugarcane borer injury is most commonly assessed by determining the proportion of bored internodes, which is directly related to reductions in yield. While the pest is controlled in sugarcane with judiciously timed insecticide applications and conservation of natural enemies, management in bioenergy cropping systems presents a new challenge. Insecticide recommendations are developed from insect injury to yield loss relationships, which are different for bioenergy crops than for conventional sugarcane. Studies conducted in the sugarcane production region of St. Mary Parish, where high pest populations occur, indicate sorghum varieties may be more susceptible to sugarcane borer damage than energycane or conventional sugarcane (Table 1). Thus, in areas where sugarcane borer problems are common in sugarcane, sugarcane borer problems are also expected in bioenergy crops. If infestations in bioenergy crops are not controlled, they could increase pest pressure on surrounding fields of conventional crops.

An emerging threat, the Mexican rice borer

The Mexican rice borer, Eoreuma loftini, is the primary pest of sugarcane in Texas and has been making its way eastward since the 1980s (Figure 2). It first arrived in Louisiana in 2008 and is now in eight southwestern parishes (Figure 3). The Mexican rice borer thrives in crops already stressed by factors such as drought. Chemical control of this pest is made difficult because the larvae quickly bore into stalks, escaping exposure to insecticides and natural enemies. Many sugarcane farmers in Texas have abandoned the use of insecticides to control this pest.

Studies at the Texas A&M AgriLife Research Center at Beaumont evaluated Mexican rice borer injury and associated yield reductions in conventional and bioenergy sugarcane and sorghum varieties. Results indicate this pest has potential to have a serious impact on the production of biofuels along the Gulf Coast. The thinner stalks and higher fiber content of energy cane relative to conventional sugarcane and sorghum may reduce susceptibility to Mexican rice borer injury. However, yield losses of 1 to 3 percent per 1 percent bored internodes were observed in all bioenergy varieties evaluated.

Aphids and other pests attack bioenergy crops

The sugarcane aphid, Melanaphis sacchari, has been garnering a lot of attention in recent years. Severe outbreaks have devastated grain sorghum fields from Texas to South Carolina. These tiny insects suck vital nutrients from plants and secrete sticky honeydew, which promotes growth of black sooty mold (Figure 4). Section 18 Emergency Exemption use labels granted by the EPA have allowed a newer, more effective insecticide to be sprayed on grain and forage sorghum to help control recent outbreaks. However, currently labeled pyrethroid insecticides for sugarcane and bioenergy crops often provide poor aphid control and can even flare infestations because of suppression of beneficial insects. Infestations of aphids in research plots of high-biomass and sweet sorghums in Beaumont, Texas, reached damaging levels in 2013 and 2014, despite multiple insecticide applications. In addition, the sugarcane aphid is a vector of several plant viruses, including sugarcane yellow leaf virus. Surveys found this virus in one out of 10 sugarcane fields, with an incidence of 2 percent in 2011 and two out of 10 fields with incidences of 4 percent and 18 percent in 2012. Results suggest mixed cropping systems with sugarcane, sorghum and corn could affect virus incidence; however, the study size was not sufficient to draw definitive conclusions.

In research plots of bioenergy crops in Rapides Parish, high-biomass sorghum varieties were heavily damaged by grass mites, Oligonychus pratensis, and stalk rot, Fusarium spp. (Figure 5). These observations further add to the diversity of insect and disease pests expected in production of bioenergy crops in Louisiana.

Because of overlap in insect and disease pests of sugarcane, grain sorghum and crops produced for biofuels, expanded production of bioenergy crops is anticipated to have wide-ranging effects on Louisiana agriculture. Ongoing cooperative research efforts focus on development of a Webbased regional management program based on landscape-wide simulations of stem borer populations that allow for rapid analysis and selection of optimal field- and regional-level management approaches.

Gene Reagan, Austin C. Thompson Professor of Sugarcane Entomology, Department of Entomology; L.T. (Ted) Wilson, Jack B. Wendt Endowed Chair in Rice Research, Center Director, Texas A&M AgriLife Research Center at Beaumont; Julien Beuzelin, Assistant Professor of Entomology, Dean Lee Research and Extension Center, Alexandria; M.O. Way, Professor of Entomology, Texas A&M AgriLife Research Center at Beaumont; Jeff Hoy, Professor of Sugarcane Pathology, Department of Plant Pathology and Crop Physiology; Y. Yang, Senior Biological Systems Analyst, Texas A&M AgriLife Research Center at Beaumont; Allan Showler, Research Entomologist, USDA-ARS, Kerrville, Texas; Matt VanWeelden and Blake Wilson, Department of Entomology.

(This article was published in the spring 2015 issue of Louisiana Agriculture.)

5/27/2015 12:29:07 AM
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