Timely fungicide application may be warranted
Figure 2. Stripe rust. Stripe rust (Figure 2) continues to develop in wheat fields, particularly in southern and eastern Nebraska. It was confirmed in Saunders and Lancaster counties on April 24 and there was an unconfirmed report of the disease in southwest Nebraska this week. Stripe rust assessment in a state wheat variety trial in Saline County on April 26 showed high levels of disease in some lines.
Warm, dry weather April 24-25 slowed development of stripe rust; however, the change to cool, wet weather toward the end of week should favor stripe rust. Regular scouting of wheat fields for stripe rust should continue and fungicide should be applied if the flag leaf is at risk of infection. The decision to spray should be based on
- yield potential,
- variety susceptibility, and
- forecast weather conditions.
New Stripe Rust
There is evidence that the race of stripe rust this year may be new since some previously resistant varieties are showing susceptibility. Even if the variety planted is considered to be resistant, it is possible that the resistance may be overcome by the current race of stripe rust.
Leaf spot diseases (mainly tan spot) and powdery mildew are also present in wheat fields and should not be overlooked. Any fungicide applied to control stripe rust will also control these diseases.
Figure 3. Barley yellow dwarf virus. Wheat Viruses
Wheat streak mosaic virus and Triticum mosaic virus have consistently been confirmed in samples submitted to the UNL Plant and Pest Diagnostic Clinic, and virus symptoms have been seen in surveyed fields with varying degrees of incidence and severity. There have been reports of some fields that have been severely affected by virus infections (Figure 1). Barley yellow dwarf (Figure 3) has been seen at low levels in most fields and at significant levels in a few fields.
Little can be done during the current growing season to control virus infections. The wheat curl mite that transmits both wheat streak mosaic virus and Triticum mosaic virus survives best on wheat, but can also survive on grassy weeds. To reduce wheat virus problems in the next growing season:
♦ Control volunteer wheat and grassy weeds in the field before planting this fall.
♦ Plant resistant/tolerant varieties.
♦ Avoid early planting.
♦ Control weeds and aphids (the vectors of barley yellow dwarf virus).
Panhandle Also Should be Scouting
While stripe rust hasn’t appeared in the Panhandle yet, current wet conditions are favorable for its development and growers should be scouting for it.
If the flag leaf hasn't already emerged, it soon will. To protect yield potential, it’s critical that the flag leaf be protected from leaf diseases like stripe rust and tan spot.