Published on Tuesday, April 21, 2020
Fusarium Head Blight (FHB), also called head scab, is a disease that can affect many small grain crops, but its economic impact is the largest on wheat. The causal pathogen of this disease is Fusarium graminearum, and it can significantly impact yield and grain quality. The disease can produce many mycotoxins. Deoxynivalenol (DON), also known as vomitoxin, is the primary mycotoxin screened for at grain delivery points.
DON can be extremely toxic to people and animals, specifically monogastrics like swine, and horses; therefore, it is crucial to monitor mycotoxin levels. Infected grain stored for livestock consumption should be immediately dried to less than 15% moisture to stop the pathogen and prevent further mycotoxin production. The grain will then need to be dried to 13% if being stored for extended periods.
Referred to as “head scab,” the symptoms of this disease are limited to the wheat head and sometimes in severe infections, the peduncle. Spikelets on the wheat head will appear to be bleached while others will remain healthy and green (Figures 1 and 2). The infection typically spreads up to the tip of the spike from the infected glume.
Pink and orange spore masses may be observed on the bases of individually infected spikelets (Figure 3). Infected seeds are commonly referred to as “tombstones” because of their lightweight and shriveled discolored appearance.
The F. graminearum pathogen can survive on crop residue, and since corn is an alternate host, rotation can affect disease pressure. Warm, wet conditions with periods of high humidity favor early spore production in the spring. These spores can then be dispersed and deposited via air currents. Wheat is vulnerable to infection from flowering through early dough stage or Feekes 10.5.1-11.2.
Good disease management begins with variety selection. Currently, there are no highly-resistant FHB varieties commercially available; however, there are some rated moderately resistant. Resistance ratings can be obtained from your local Beck’s dealer. The Fusarium pathogen associated with FHB can be carried over in the progeny from infected seed; therefore, planting certified seed can help reduce seedling blight. Also, using a fungicide seed treatment can reduce early-season blight.
Foliar fungicides can be an effective management strategy. Several factors influence a fungicide’s ability to suppress FHB including spray coverage, timing, and disease pressure. Research has shown that Group 3 (DMI/triazole) fungicides are most effective at suppressing the disease if they are applied at early flowering or Feekes 10.5.1. If favorable conditions are present for disease development, applications can continue to be successfully made up to seven days after Feekes 10.5.1. Recently, there has been research showing that some Group 7 (SDHI/carboximide) fungicides can help suppress FHB while lengthening the application window from 50% heading through seven days after flower initiation. It is also important to note that Group 11 (Qoi/strobulurin) fungicides should not be used to suppress FHB as they can increase mycotoxin levels in the grain.
There is an online Risk Assessment Tool that was developed to help producers evaluate whether FHB could potentially be a threat in their local area. This tool can be found accessed online at: wheatscab.psu.edu.
Author: Austin Scott
Categories: Agronomy, Agronomy Talk