By Robert Harveson
Associate Professor
University of Nebraska - Lincoln
Department of Plant Pathology
Panhandle Research and Education Center

Panhandle Plant Disease Diagnostic Lab

Diseases are a major yield-limiting factor to many crops grown in the Nebraska Panhandle. Sugar beets are particularly susceptible to many diseases, including Cercospora leaf spot, and root rots such as rhizomania, Rhizoctonia and Aphanomyces. It is important for these diseases to be properly and rapidly identified so that control measures may be implemented. Therefore, a service was begun in 1999 to diagnose crop samples submitted to the plant pathology lab at the Panhandle REC.

This diagnostic service includes all crops, but 60-65% of submitted samples consist of sugar beets or soil samples from sugar beet fields - 700 sugar beet and (>1100 total) samples in 2004, and is funded primarily by Western Sugar Cooperative. We also test soil samples (>200 in 2004) over the winter for the presence of BNYVV (cause of rhizomania) in fields to be planted to sugar beets the following spring as another part of this service. This attempts to proactively determine whether rhizomania is present, and allows growers to at least choose a cultivar that may help counteract the disease.

This has recently been expanded further (>100 additional soil samples in 2004) to include an estimate for root rot potential during the season based on a disease index assay using sugar beet seedlings (see link). This provides information that also gives growers the opportunity for some decision making (i.e cultivars) before the crop is planted. This new disease index concept is also being used concurrently as a research tool to develop a risk assessment system (forecasting?) for root diseases in sugar beets in concert with soil environmental conditions.

The expansion of diagnostic services also addresses any diseases of any crops. All other crops grown in this region are evaluated as the grower or consultant wishes. Including all crops (both plant and soil samples) between almost 8000 samples have been submitted and processed in the plant pathology lab in Scottsbluff. We have published new reports (Disease Notes, NebGuides, or NebFacts) on these particular diseases which were identified and brought to light due to the diagnostic service including:

a) Aphanomyces root rot of sugar beets
b) Rhizopus head rot of sunflower
b) Ascochyta blight of chickpeas
c) Sterile white basidiomycete (new hypocotyl and stem disease) on dry beans
d) Sexual stage of powdery mildew of sugar beets
e) New epidemics of bacterial wilt in dry beans
f) Cucurbit yellow vine disease - bacterial disease of pumpkins (in review)

Additional new and/or unusual diseases identified in Panhandle REC plant pathology lab during 2000-2005 include:

1) Crown gall of:
a) sugar beets
b) dry beans
c) chicory
2) Bacterial leaf spot of proso millet
3) Bacterial root rot of chicory
4) Alternaria leaf spot of chicory
5) Alternaria leaf spot of dry beans
6) Alternaria head rot of sunflower
7) Septoria leaf spot of sunflower
8) Violet root rot of sugar beet
9) Pythium blight and ashy stem blight in dry beans
10) Pythium stem rot in amaranth
11) Fusarium root rot of lupines
12) Downy mildew of alfalfa
13) Phytophthora root rot of chickpeas
14) Bacterial leaf spot of forage peas
15) Pythium root rot of lentils
16) Bacterial stalk rot of corn
17) Beet soilborne mosaic in sugar beet
18) False root-knot nematode (Nacobbus aberrans) in lambsquarters
19) Septoria leaf spot, and rust of common mallow
20) Downy mildew, Cercospora leaf spot, and Ascochyta leaf spot of common
lambsquarters
21) Multiple root diseases (caused by Rhizoctonia, Pythium, and Fusarium) from
common weeds, including pigweed, lambsquarters, and Kochia.