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Research Highlights
Enhanced Pest Control Systems for Mid-South Soybean Production

Cercospora leaf blight

By Paul Price III, Louisiana State University Agricultural Center

Soybean growers lose yield to both diseases and pests every year. Disease losses due to anthracnose, Cercospora leaf blight (CLB), frogeye leaf spot, pod and stem blight, Rhizoctonia aerial blight, Septoria brown spot and soybean rust ranged from $142 to $302 million per year over the past five growing seasons in the southern states. The problem is increasing, as many diseases are now showing fungicide (especially strobilurin) resistance. The most sustainable way to manage soybean diseases is by choosing resistant varieties; however, for many of these diseases, including CLB, few or
no resistant soybean varieties have been identified. 

In addition to diseases, insect pests such as stink bugs reduce soybean yield and quality. Estimates from the 2018 USB-funded insect loss survey (USB project #1920-172-0119-J) of southern soybean-producing states reported that stink bugs were the most important insect pest, resulting in an estimated economic loss of $244 million. 

The brown stink bug represents about 50% stink bug damage in soybean overall in southern states. While the redbanded stink bug accounts for only about 3% overall, it causes 70% and 40% of the damage in Texas and Louisiana, respectively. It continues to expand as a threat because it is already tolerant of many insecticides. 

Figure 1. Adult southern green stink bug.

A main goal of this FY19 project was to identify new soybean germplasm with resistance to diseases and stink bugs. The overall budget for the project is $373,851, of which USB has funded $213,851 and the Mid-South Soybean Board funded $160,000. Approximately 500 plant introductions (PIs) from the USDA soybean germplasm collection were planted in 18 locations over three years, in order to identify novel sources of resistance. 

Another goal was to identify commercial and public varieties with resistance to CLB and stink bugs. Entries were planted in 15 locations in seven southern states over three seasons then evaluated for disease resistance, yield and quality. Several locations were planted and monitored for stink bug infestation as well. 

In collaboration with USB project #1920-172-0124A and entomologists throughout the U.S., over approximately 1,000 Cercospora spp. isolates were collected and characterized, revealing that at least three different Cercospora species responsible for CLB. Isolates were also tested for sensitivity to different fungicides and will remain in storage as an important genetic archive and resource. 

CLB resistance screening is time-consuming and inefficient. The group is working on two methods, one involving cercosporin accumulation and the other developing correlation with iron levels. 

To date, eight PIs with very high levels of resistance to CLB have been identified and are being incorporated into elite lines and cultivars adapted to the southern United States. In addition, several breeding lines and PIs with resistance to stink bugs have been identified, and are currently being incorporated into breeding programs. Preliminary results from three seasons indicate publicly available sources of moderate resistance to stink bugs. 

The development of new commercial varieties with improved genetic resistance to diseases and stink bugs will result in higher yields, with less fungicides and insecticides, directly benefiting soybean producers and seed companies across the country. 

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.