What is FHB?
Fusarium head blight (FHB), also known as scab or tombstone, is a disease of cereals and grasses. It is caused by several species of Fusarium; however, F. graminearum is the primary species involved. F. graminearum is a declared pest under the Alberta Agricultural Pests Act. Wheat and barley infected by FHB may contain mycotoxins that are toxic to animals and can negatively affect marketability of the grain.
(Agdex 110/632-1 "Fusarium Head Blight of Barley and Wheat")

What is irrigation management?
Irrigation management is the determination and control of the rate, amount, and timing of the application of irrigation water. This involves:

  1. Determining soil moisture to determine how much water must be added to meet crop water requirements
  2. Ensuring application rates do not exceed the infiltration rate of soil
  3. Scheduling irrigation timing and farming practices to avoid water stress (under or over irrigation)

The purpose of irrigation management is to efficiently use available irrigation water to manage and control the moisture environment of crops in order to promote desirable crop response (yield and quality), while taking care of environment and water quality.

Irrigation and FHB in cereals

  • Cereal crops grown under irrigation face a higher risk of infection than those grown under dryland production
  • Infection risk is greater under sprinkler irrigation compared to gravity (flood) irrigation systems
  • Infection occurs during flowering. It is during this growth stage that cereal crop water requirements are highest and also when most producers irrigate to avoid drought stress. The warm, humid environment within the crop canopy encourages the development and spread of FHB disease

Irrigation management to prevent FHB infection

  1. Irrigate to met the crops water requirements throughout the growing season (do not under or over-irrigate), especially during drought - sensitive growth stages.
  2. Manage irrigation to discourage drought stress at the tillering growth stage (the aim is to shorten flowering duration by not encouraging late and prolonged tillering)
  3. Know when flowering begins and ends
  4. Irrigate to fill-up the root zone (soil reservoir) prior to flowering and avoid irrigation during flowering
    1. Ensures enough water is available to the crop during flowering
    2. The canopy is kept dry during flowering period (the infection of FHB is discouraged by dry conditions)
  5. Resume proper irrigation management after flowering is done for quality (know your soil texture and daily crop water consumption)

When do cereals start and finish flowering and how long does it last?
Differences exist in flowering characteristics and duration among cereal crops. Barley starts flowering prior to heading, whereas most wheat crops start to flower three to four days after heading out. The flowering duration of a uniform barley or wheat crop is approximately ten days. Barley might have a shorter flowering duration, depending on variety.

In order for cereals to complete their flowering uniformly, proper irrigation and agronomy management must be practiced during early growth stages and especially during tillering. Additional ways of making sure that the plants are uniform (minimize tillering) include: (a) minimize excessive nitrogen fertility, (b) seed deep, and (c) increase seeding rates.

How much moisture does a cereal crop use during flowering?
During a ten-day flowering period, barley or wheat will use approximately 60 to 70 mm of moisture. These approximate water use numbers are based on long-term averages during the flowering period and could be higher if conditions are sunny, windy, dry, and hot.

Can soils provide enough moisture to cereals during flowering without irrigation?
Yes / Maybe. Table 1 shows irrigation management recommendations based on soil textural classes and a ten-day flowering window.

Table 1: A soil-texture-based irrigation strategy for preventing FHB

Soil Type Total plant available moisture at field capacity
(mm/m)
Allowable depletion (50% of total available) (mm/m) Crop water use during flowering (10 days)
(mm)
Plant available moisture at the end of flowering (mm/m) Next irrigation event after flowering
(days)
Loamy sand 112 56 64 48 Moisture stress starts before flowering is over
Sandy loam,
Sandy clay loam
140 69 64 76 Right at after flowering is done
Loam,
Sandy clay loam
178 89 64 114 2 to 3 days after flowering is done
Silty loam, Sandy
clay, Silty clay loam, Silty clay, Clay loam, Clay
204 102 64 140 4 to 5 days after flowering is done