Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu
The fungus that causes fusarium head blight (FHB) produces chemicals that can be toxic to humans and certain animals. The primary mycotoxin associated with FHB is deoxynivalenol (DON), and levels of DON are regulated by the USDA and FDA (Table 1). DON can also be a factor in grain or silage infected with the FHB pathogen. This year it is likely that your loads will be assayed for DON at the elevator or mill. Therefore it is important to understand the sampling process and the various DON testing methods before your loads are sent to the elevator.
Table 1. Deoxynivalenol (DON) Advisory Levels established by the FDA.
Elevators use endgate or probe sampling to assess grain quality. In order to accurately assess DON levels for a grain sample samples must be representative of the entire truckload. Grain particles differ in size and weight and tend to separate and collect in different parts of the bin. Often smaller, denser material settles near the center of the bin and the larger, lighter material is near the outside edges of the container. Since DON levels vary between kernels of similar size or density several samples must be taken from various locations in the bin. A properly conducted endgate sample should be taken from multiple points in the bin representing different bin depths and lengths. Samples taken from the ends of the load will not result in a representative sample. For probes, the edges or center of the bin should not be sampled and the probe should collect the sample from as much as the depth of the bin or truckload as possible. Similarly, multiple samples (5-10) should be taken if probes are used. The probe method is the only method approved by USDA-GIPSA for stationary lots. Guidelines sampling can be found at the following link:http://www.gipsa.usda.gov/fgis/insp_weigh/inspwgh/don.pdf
Grain elevators and mills often test for DON using a test known as ELISA. These tests are quick and provide fairly accurate levels of DON. Other methods, such as those using a gas chromatograph, are more precise but also more time consuming and expensive. There are kits that a concerned grower can purchase to test for DON at the farm. The USDA-GIPSA approved test kits can be found by following this link: http://www.gipsa.usda.gov/fgis/tech-servsup/metheqp/GIPSA_Approved_Mycotoxin_Rapid_Test_Kits.pdf. Kits with a visual assessment method, such as the Neogen 8310 or 8315 rapid tests for DON, tend to be fast, easy, and do not require advanced equipment or readers. These tests are similar to the immunostrip tests that are available for rapid detection of some plant pathogens. Kits are not as accurate as tests used by mycotoxin testing laboratories, but provide general information needed for decision making. Alternatively, one can send a sample to a mycotoxin testing lab for a fee, such as Cumberland Valley Analytical Services located in Maryland:http://www.foragelab.com/Lab-Services/Forage-and-Feed/Mycotoxin-Evaluation. Prices for ELISA tests tend to be much lower than the more advanced tests using HPLC or GC.
Levels of scab in wheat this year appear to be low, around 1-2% in the most severe cases. This is a stark contrast to last year where fields had levels approaching 80% and many fields well over 50%. FHB pops out at this time of year, so you may notice white or light brown heads in a field of green heads. The stark contrast in the color of the head makes the disease appear worse than it actually is in many cases.