COLORADO WHEAT DISEASE NEWSLETTER

May 9, 2023

DISEASE OBSERVATIONS

Root Rot

A root rot disease was found in a few fields in Kit Carson county in spotty areas (Figure 1). Root rot pathogens generally favor wet weather and mild soil temperatures for infection. However, symptoms usually appear after the weather becomes warmer and dryer. Root rot diseases typically develop in nutrient-deficient soils with poor drainage, and/or high nitrates. Wheat with root rot initially appear chlorotic (yellow), stunted, and have poor tiller development. Roots are blackened and rotten with visible fungal mycelia. Root rot diseases are more common in fields that have not been in rotation.

Figure 1. Root rot disease found in samples from Kit Carson county. Note the yellowed leaves and blackened roots and crowns.
Photo: Dr. Ana Cristina Fulladolsa.

Management and Prevention: ensure fields have proper drainage and adequate nutrients to prevent infection. Kill volunteer hosts between harvest and planting, since infected plants can carry the pathogen to next season’s crop.

DISEASE WATCH AND MANAGEMENT

Stripe Rust

There are currently no reports of stripe rust in Colorado, but stripe rust was recently reported in Texas (Castroville, southeast TX), and Oklahoma (Chicksha, southwest central OK). Disease incidence and severity is low; however recent rain and nighttime temperatures have been conducive to disease development in these areas (Figure 2). Stripe rust disease is dependent upon cool, wet weather, and the dry conditions in Colorado will likely inhibit and/or limit rust diseases in the near future.

Figure 2. Recent weather in states reporting stripe rust is conducive to disease development, though risk for Colorado remains low. The stripe rust pathogen requires both cooler temperatures and wet conditions to cause disease. States that have reported stripe rust (Texas and Oklahoma, at low incidence and severity) have recently had cooler nighttime temperatures (left panel) and more moisture (right panel), which is conducive to disease development. While nighttime temperatures in Colorado are low, the precipitation is also low, which does not support disease development. Data from the National Weather Service Climate Prediction Center.

Soil moisture levels are often correlated with stripe rust incidence and can be used as a predictive tool in determining if stripe rust will emerge. This time of year, we look at the soil moisture levels in the south, particularly Texas and Oklahoma (Figure 3). Most of Texas and Oklahoma has been very dry since last fall, and is currently experiencing low soil moisture; however, recent weather conditions have been conducive for disease development. At this time, it seems that stripe rust spore levels will remain low, suggesting a low risk for an epidemic in Colorado. We will continue to monitor for rust and provide recommendations as we reach critical growth stages. Please help us protect our fungicides and prevent fungicide resistance by carefully timing applications, following the label, and applying only when the disease pressure is appropriate. If you think you see symptoms, please feel free to send photos.

Figure 3. Soil moisture levels as a predictive tool for stripe rust risk. Higher soil moisture levels are typically associated with higher risk. We closely watch the southern states (Texas, Oklahoma) for soil moisture levels and the emergence of stripe rust as one tool to predict risk in Colorado. Low soil moisture levels support less stripe rust disease development. Data from the National Weather Service Climate Prediction Center.

Viruses

We haven’t found any viruses yet this year, but stay on the lookout as things start to green up. Growers are strongly encouraged to regularly scout wheat fields for diseases. Particularly, scout for stripe rust and viruses in the coming weeks.

Additional Resources

1. The North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) Fungicide Efficacy for Control of Wheat Diseases Table
2. Wheat variety database with stripe rust and virus resistance ratings from field trials

CONTRIBUTORS

Many thanks to all who contributed to this report: Tyler Benninghoven, Dr. Esten Mason, Emily Hudson-Arns, Ron Meyer, and Dr. Todd Ballard.