ISSUE 14 August 1, 2002
NDSU FIELD SCOUTING UPDATE FOR SMALL GRAIN DISEASES, 7/27
Small grain fields scouted the past week by NDSU IPM field scouts were generally in the milk to ripening stages of kernel development. These fields were in the SW, SC, C, SE and EC parts of the state. Fields in the NC and NW districts were in heading to flowering stages, while no fields were surveyed in the NE the past week.
Leaf diseases of tan spot and leaf rust continue to be the dominant diseases detected in maturing fields. Head scab also was detected in fields in some fields, with average field severities (incidence x head severity) in the 1-5% range. Areas of highest potential risk for head scab, in heavy rainfall areas of the NE, have not been surveyed yet.
DISEASE FORECASTING UPDATE, 7/31
The NDSU small grain disease forecasting site:
indicates that on July 30, the risk of infection of Fusarium head blight (scab) was low in most areas of the state where crops are still in vulnerable flowering stages. The highest weather related risk was in the SE part of ND and into MN, areas where the crop has already matured. Favorable infection periods continue for wheat tan spot and for leaf rust in many areas.
BACTERIAL BLIGHT IN SMALL GRAINS
In the last issue of NDSUís Crop and Pest Report (issue #13), I indicated that a considerable amount of bacterial blight had been observed in wheat in some locations in the state. This bacterium, Xanthomonas translucens pv. translucens, also can cause bacterial blight in barley and oats, and symptoms in those crops also have been observed recently. Flag leaves are generally necrotic from the leaf tip downward.
Certain varieties of wheat appear to be more vulnerable to bacterial blight. Terry Gregoire, Extension Area Agronomist at Devils Lake, observed varietal differences in the variety plots at Grand Forks. Ken Nichols, Grand Forks County Extension Agent, provided me plants from these variety plots for examination of bacterial blight symptoms. Keeping in mind that these were plants from just ONE of the four replicated plots at Grand Forks, I observed the following differences among varieties.
Severe bacterial blight: Laser, Granite, Gunner, HJ98, Ingot, Oxen, Mercury, Reeder, and Russ;
Moderate bacterial blight: Briggs, Dandy, Hanna, Lars, Norpro, Wallworth
Least severe to non-detectable bacterial blight: Alsen, Keystone, Knudson, 2375, Parshall, Butte 86, Grandin.
Abundant bacterial black chaff also was observed on grain heads of Mercury and HJ98. These observations donít preclude that bacterial blight could be severe on other varieties if weather conditions were favorable. We donít have a strong research data base on this disease.
On leaves of some wheat varieties, the bacterial blight symptoms were overlayed on abundant rust pustules. The rust fungus obviously had infected first.
Ken Nichols also brought me leaves of barley varieties; all appeared equally impacted by bacterial blight.
The most recent Cereal Rust Bulletin (# 9, July 22) indicated that wheat stem rust was observed in susceptible wheat varieties in plots in southeastern North Dakota (detected by Jim Miller, USDA rust pathologist). These susceptible varieties (Baart and Max) are indicator varieties and not grown commercially in ND. Commercially grown varieties of spring wheat are resistant to stem rust. The same is not true for all winter wheats, and stem rust was detected in Seward winter wheat plots near Lisbon, ND on July 9.
The Cereal Rust Bulletin also indicates that scattered oat stem rust infections have been observed in the region and some of the currently grown oat cultivars have susceptibility to stem rust. We have been detecting stem rust in barley in plots and commercial fields, at very low levels. All of our commercial barley varieties are susceptible to stem rust. Stem rust collections are being sent to the Cereal Disease Lab in St. Paul for race identification.
POTATO DISEASE HOTLINE UPDATE, 7/31
All non-irrigated and irrigated production areas, with the exception of Williston have now reached late blight severity threshold values.
Morning dew, high humidity and cool temperature in some locations continue to provide conditions favorable for late blight development and spread, and because plant growth rate has been very rapid and late blight can develop if new foliage is not protected. Continue to scout fields often for the presence of late blight and continue fungicide application on a regular basis to protect against late blight and early blight. If late blight is found or suspected, please send samples to NDSU for positive identification and genotype evaluation. Remember to destroy any late blight Ďhotspotsí in fields to prevent further spread.
Remember that the potato field day will be held Tuesday August 6 from nine to noon at NPPGA irrigated potato research site at Tappen.
Extension Plant Pathologist