Figure 1. Bacterial leaf streak symptoms on winter wheat leaves.
Bacterial leaf streak (BLS) was found in several winter wheat fields scouted this week. This continues to be the main disease currently observed in winter wheat, whether a fungicide was utilized. The BLS severity ranged from mild (Figure 1) to severe (Figure 2) especially for wheat on wheat fields planted with a susceptible cultivar. For the majority of fields observed with BLS, there were scattered clusters of a few plants with BLS seen. Just one field had wide spread BLS throughout the entire field (Figure 3).
Figure 2. Winter wheat plants with severe bacterial leaf streak symptoms.
Causal Agent and Symptoms
Bacterial leaf streak is caused by a bacterium called Xanthomonas translucens pv undulosa. The bacteria survive mainly on seed but can also survive on plant debris, volunteer cereals, and other wild hosts. Pathogen spread amongst plants is achieved by plant to plant contact, insects, and rain splash. The bacteria enter the leaf through natural openings of the plant or wounds caused by high winds. Symptoms start as small regular brown to dark brown water soaked lesions limited within the veins (Figure 1). These later coalesce to form larger lesions and can cause the leaf to start dying from the tip (Figure 2). The lesions are transparent when held against the light. Symptoms start to develop after flag leaf growth stage under wet and warm weather.
Figure 3. A winter wheat field with plants yellowing due to bacterial leaf streak. This field had wheat residue (non-rotated) and was planted with a BLS susceptible cultivar.
Yield Loss and Management
Bacterial leaf streak infection can result in significant yield loss under heavy disease pressure before grain fill. This is because the disease can cause flag leaf and the leaf below flag leaf to die prematurely (Figure 2). BLS can be managed through using pathogen-free certified seed. Although the bacteria can survive on residue, the main inoculum is thought to be from the seed. Crop rotation which includes utilizing broad-leaf crops can help to reduce the inoculum from the residue. Breeders are developing BLS-resistant cultivars but information on BLS ratings of cultivars is not yet available.