Overview
A crop pest
Fusarium head blight (FHB), also known as scab or tombstone, is a serious disease of cereals and grasses. It is caused by several species of Fusarium; however, F. graminearum is the primary species involved. Wheat and barley infected by FHB may contain mycotoxins that are toxic to animals and can negatively affect marketability of the grain.
For more information on FHB, see: Fusarium head blight – Overview.
Irrigation management basics
Irrigation management is one of several recommended strategies for managing FHB.
Irrigation management is the determination and control of the rate, amount, and timing of the application of irrigation water. This involves:
- determining soil moisture to determine how much water must be added to meet crop water requirements
- ensuring application rates do not exceed the infiltration rate of soil
- 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.
FHB risks from irrigation
If not properly managed, irrigation can pose the following FHB infection risks in crops:
- 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.
Preventing infection
If possible, limit irrigation just prior to and during the flowering period to reduce humid conditions in the crop canopy which would otherwise favour FHB infection.
The following irrigation management strategies help prevent FHB infection in crops:
- Irrigate to meet the crops water requirements throughout the growing season (do not under or over-irrigate), especially during drought - sensitive growth stages.
- 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).
- Know when flowering begins and ends.
- Irrigate to fill up the root zone (soil reservoir) prior to flowering and avoid irrigation during flowering. This ensures:
- enough water is available to the crop during flowering
- the canopy is kept dry during flowering period (the infection of FHB is discouraged by dry conditions)
- Resume proper irrigation management after flowering is done for quality (know your soil texture and daily crop water consumption).
Cereal flowering period
Length of flowering period
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 plants are uniform (minimize tillering) include:
- minimize excessive nitrogen fertility
- uniform seed depth
- increase seeding rates
Moisture during flowering
During a 10-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.
Flowering without irrigation
Soils can provide enough moisture to cereals during flowering without irrigation, depending on soil type. Table 1 shows irrigation management recommendations based on soil textural classes and a 10-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 |
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