Wheat Disease Update
Figure 1. Figure 1. Septoria tritici blotch in research plots at the ARDC near Mead on June 9.
Figure 2. Leaf rust in research plots at Havelock Farm in Lincoln on June 12.
Figure 3. (left) Fusarium head blight in a commercial field in Jefferson County on June 12. Only trace levels of the disease were observed in this field.
Figure 4. Black chaff on wheat heads in research plots at the ARDC near Mead on June 9.
A survey of wheat fields on June 9, 11, and 12 in Dodge, Lancaster, Jefferson, Saline, and Saunders counties showed generally low levels of foliar fungal diseases. The predominant foliar fungal diseases were Septoria tritici blotch (Figure 1) and tan spot. Leaf rust (Figure 2) was found at low levels at Havelock Farm in Lincoln (Lancaster County). Recent rains have favored development of foliar fungal diseases; however, due to the late onset of these diseases, their effect on yield is expected to be minimal.
Fusarium head blight (FHB, scab, Figure 3) was found at trace levels in research plots at UNL's Agricultural Research and Development Center (ARDC) near Mead (Saunders County) and in a commercial field in Jefferson County. It was found at low to moderate incidence (percentage of heads affected) in research plots at Havelock Farm in Lincoln and in two commercial fields, one in Dodge County and the other in Saline County. Severity (percentage of bleached spikelets on a head) was generally low.
The rains that occurred on Memorial Day weekend and subsequent rains favored development of FHB. However, because most infections occur at flowering, fields that did not receive rain just before flowering or during flowering escaped infections. This explains the sporadic occurrence of FHB that we are seeing. In addition, rain has not been continuous and the dry periods between rain events have slowed down progression of FHB in affected fields.
Bacterial leaf streak, also known as bacterial streak (see previous CropWatch report) remained the most widespread disease in breeder nursery plots at Mead and Lincoln. Low levels have been observed in some commercial fields in southeast Nebraska. The head phase of this disease, known as black chaff (Figure 4), is now visible on heads at Mead and Lincoln.
Fungicide applications effectively control foliar fungal diseases (rusts, Septoria, tan spot). Given the late onset of these diseases this year, it has not been necessary to apply fungicides to control them in most fields. FHB can be suppressed by applying a suitable fungicide at early flowering. Integration of resistant cultivars and fungicide application is the most effective strategy in managing foliar fungal diseases and FHB.
Most wheat fields in the southern half of eastern Nebraska are currently past the stage when a fungicide can be applied. Do not apply a fungicide if your wheat is past the flowering growth stage or will be harvested within 30 days of fungicide application.
Fungicides do not control bacterial streak/black chaff. However, this disease has been observed at high levels only in breeder nurseries. It is not expected to cause significant yield loss in commercial fields.
Because of the generally low levels of disease in commercial fields, yield loss from diseases is expected to be minimal. Factors other than disease, such as low moisture and freeze damage, will account for the majority of yield loss this year.Stephen Wegulo, Extension Plant Pathologist
Nathan Mueller, Extension Educator, Dodge County
Everlyne Wosula, Post-Doctoral Research Associate, UNL