University of Illinois researchers identified the top pathogens, pests, and weeds affecting soybean production in a recent article in the journal Food Security, "Crops that Feed the World. 2: Soybean--Worldwide Production, Use, and Constraints Caused by Pathogens and Pests." Soybean aphid, soybean rust, soybean cyst nematode, sclerotina stem rot, and the exotic pathogen red leaf blotch were identified as top biotic constraints that may affect soybean production now and in the future.
Enormous potential exists to increase future soybean production. Genetic resources, used through both traditional breeding and bioengineering, may provide the solutions needed to combat these problems.
As soybean production has increased over the past 50 years, so has the intensity of biotic constraints that ultimately threaten yield. Where soybean is grown every year or even every other year, pathogens often have increased in density to cause economic losses in yield. Parasitic microorganisms, including bacteria, fungi, nematodes, Oomycetes, and viruses, all contribute to economic damage. The story is similar for pests; many, including aphids, beetles, mites, and stinkbugs, cause considerable economic damage to the soybean crop.
Although aphids, rust, nematode, and Sclerotina stem rot are commonly known and recognized by soybean growers, less is known about red leaf blotch, an exotic disease caused by the fungal pathogen Phoma glycinicola. Red leaf blotch, which is listed on the USDA Agricultural Select Agent List--the same list that includes anthrax--has so far only been reported in Africa. However, if it is found in the United States, a recovery plan developed through the USDA-APHIS program outlines a course of action to prevent it from spreading.
Red leaf blotch symptoms include lesions on foliage, petioles, pods, and stems. The fungus does not appear to be seedborne, but it may be transported along with soil and other debris in grain. Yield losses of up to 50% were documented in Zambia and Zimbabwe in the 1980s.
Though red leaf blotch has not been found in the U.S., we want growers to be aware of it because they are typically the ones to find new pathogens, pests, and weeds in their fields. The goal is to build awareness among crop specialists and producers in order to stay ahead of the disease.
More research is needed to develop molecular diagnostic techniques to distinguish this pathogen from other common foliar soybean pathogens, to provide better information on fungicide chemistry and application timing, to develop varietal resistance, and to gather more data to develop predictive models for potential containment and management.
To successfully reduce losses due to pathogens and pests, a number of practices, used alone or in combination, may be needed; these include cultural and seed sanitation techniques, pesticide applications, and deployment of soybean cultivars with resistance. Biosecurity of food crops is important because we don't want to suffer food shortages, whether due to natural disasters or to pathogens and pests that can sometimes be controlled. Achieving food and crop improvement always involves talking about reducing diseases and pests.
Funding for the work reported in Food Security was provided by the Illinois Soybean Association, the North Central Soybean Research Program, and the Elizabeth Hageman Endowed Graduate Research Fellowship. The researchers, in addition to me, were Ellen West and Theresa Herman.
You can learn more about these pathogens and pests and their threat levels during my presentation at Agronomy Day on Thursday, August 18. For more information on speakers and displays, "like" University of Illinois Agronomy Day on Facebook, or go to agronomyday.cropsci.illinois.edu.