Features Agronomy Irrigation
Irrigation management to prevent fusarium

Research conducted on fusarium head blight (FHB) has shown that cereals grown
under irrigation face a higher risk of infection than those grown under dryland
conditions. As a result, Alan Efetha, an irrigated crop water use agrologist
with Alberta Agriculture, Food and Rural Development (AAFRD), says that farmers
need to assess their irrigation practices and manipulate them to minimize FHB.

"Durum wheat has the highest risk under irrigation, but other wheats and
even barley are at risk, as well," says Efetha. In fact, durum wheat is
the most susceptible cereal crop to FHB, followed by soft white spring wheat.

Recent field experiments conducted by Debbie McLaren and Byron Irvine, at the
Brandon Research Centre of Agriculture and Agri-Food Canada (AAFC), evaluated
the effectiveness of irrigation management to control FHB caused by Fusarium
graminearum. Funding for this research was provided by the Alberta Agricultural
Research Institute. McLaren and Irvine found that irrigation management had
an impact on the FHB development, where termination of irrigation prior to anthesis
(flowering) produced lower FHB index values than continual irrigation throughout
anthesis.

The type of irrigation management also influenced yield. Higher yields were
observed with flood irrigation than with sprinkler irrigation. Reduced deoxynivalenol
(DON) levels, which is the mycotoxin produced by Fusarium graminearum,
occurred with termination of sprinkler irrigation prior to anthesis in two years
of the study. Similarly, DON levels were significantly reduced with intermittent
sprinkler irrigation as compared to continual irrigation throughout anthesis
during 2002 and 2003.

Also as part of the same study, AAFC and AAFRD staff from Lacombe and Lethbridge
evaluated commercial wheat fields under dryland and irrigation in southern Alberta
from 2001 to 2003. Symptoms of FHB were almost exclusively found in irrigated
fields only. Irrigation levels also appeared to have an important influence
because increased FHB symptoms and seed infection levels were found as the level
of irrigation approached 10 inches or more during the growing season. In contrast,
reduced FHB and seed infection tended to occur with irrigation levels of approximately
seven inches or less.

Since FHB infects cereals during flowering, Efetha says the key strategy in
avoiding infection is to manage the irrigation schedule to prevent the environmental
conditions that favour FHB. Moist and warm environmental conditions at flowering
favour the development of FHB. Avoiding irrigation during this period helps
to reduce FHB infection.

"The problem is that during this growth stage, a cereal crop's water requirements
are highest, at about 0.25 inches of water per day. Most producers irrigate
during this time to avoid drought stress, but that can favour the disease, as
well," explains Efetha. "If you can avoid irrigation activities during
flowering, it will help to keep the canopy dry and prevent infection."

Efetha says this strategy of avoiding irrigation during cereal flowering is
not easily accomplished, but is possible if the soil profile is used as a water
reservoir. For this strategy to be successful, the root zone must be filled
to 100 percent of field capacity just before flowering. The soil within the
root zone must be able to hold enough crop-available moisture for the entire
flowering period. He says this strategy works well on heavier soils but may
not be suitable for cereals grown on very sandy soils.

Know when flowering starts and stops
Most wheat crops start to flower three to four days after heading out. Barley
starts flowering just prior to heading out. The duration of flowering is approximately
10 days for cereal crops, although some barley varieties may flower for a shorter
duration.

A key recommendation for reducing the crop's susceptibility to the disease
is to create a uniform plant stand so that all of the crop is flowering at the
same time. This helps to lessen the period that the crop is susceptible to the
disease and keeps the irrigation-free time period shorter. Seeding at a uniform
depth with recommended seeding rates and using healthy seed helps establish
uniform stands. Avoiding excessive nitrogen fertility also helps to prevent
prolonged flowering.

During this 10 day flowering period, the wheat or barley crop will use approximately
60mm to 70mm (2.4in to 2.8in) of moisture. Efetha says these estimates are based
on long-term averages during the flowering period, and could be higher if conditions
are sunny, windy, dry and hot.

Filling up the soil reservoir
Whether turning off the irrigation pivot can be successfully used as a FHB management
tool depends on the soil texture. Soils with sandy textures may not be suitable,
since the amount of water that can be stored in the soil may not fulfill the
crop's requirements for the entire 10 days of the flowering period, resulting
in moisture stress and yield loss. After flowering, irrigation must also be
able to catch up with crop requirements.

Efetha says that this strategy can be used successfully on heavier soils where
there will be extra soil moisture reserves to draw on after flowering. Pivots
should be able to then keep up with the crop requirements for the rest of the
season. For wheel move systems, the deciding factor becomes a matter of whether
there is enough capacity in the system, labour and equipment, to ensure the
crop does not run out of moisture during heading and filling stages. As well,
the crop may have grown too high for post-flowering wheel move irrigation.

"Managing the rate, timing and amount of irrigation can have a positive
impact on reducing fusarium head blight," says Efetha. "With careful
planning, the cereal crop can be managed for maximum yield and quality while
reducing disease pressures." -30-