ISSUE 11 July 15, 2004
NDSU IPM CROP SURVEY, 7/5 TO 7/9 UPDATE
During the first full week of July, NDSU IPM field scouts found increasing levels of fungal leaf spots and wheat leaf rust in their surveys. Several occurrences of wheat stripe rust also were observed in the Southeast and in the Carrington area.
Septoria and tan spot levels in wheat are increasing across ND and are being observed on flag leaves of crops in the flowering to dough stages of development. These infections will impact yield and quality on susceptible cultivars, if not controlled with fungicides.
Wheat leaf rust was observed in 31% of the wheat fields surveyed by the NDSU scouts during the first full week of July. Leaf rust will continue to develop and spread with the heavy nighttime dews across much of eastern ND. For example, at the Carrington Research Extension Center field day on July 13, very heavy infections of leaf rust were observed in susceptible cultivars of spring wheat that were in the late flowering stage, cultivars such as Ingot, Oxen, AC Amazon, AC Superb, and Gunner.
In barley, disease levels remain fairly low, with occurrences of spot blotch or net blotch being most common, but not severe.
Loose smut was observed in 21% of the wheat fields surveyed and in 25% of the barley fields surveyed. In wheat, the percent of heads infected with loose smut ranged between 1 to 15%, while in barley the majority ranged between 1 and 15% infection, but one field had greater than 15% infection of loose smut.
Field scouts have not observed head scab yet in their surveys of wheat or barley. I observed extremely low incidences of scab in winter wheat plots in Lisbon and Ellendale and these winter wheat crops were in soft to mid-dough stages.
DISEASE FORECASTING UPDATE
The NDSU Small Grains Disease forecasting web site (http://www.ag.ndsu.nodak.edu/cropdisease/cropdisease.htm) indicates continued favorable weather in the eastern ½ to 2/3 of ND for infection by the leaf disease fungi and the Fusarium head blight (scab) fungus. Growers need to assess their crop yield potential, variety susceptibility and crop growth stage to determine need for fungicide application at this time. Much of the south central and southeastern crop is past the fungicide application window, while much of the northern crops are still very vulnerable to disease.
FUNGICIDE RESULTS ON WINTER WHEAT AT ELLENDALE, ND
Ducks Unlimited and the Dickey County Extension office have established a winter wheat demonstration plot on the Larry Anderson farm near Ellendale. Included in the plot are various nitrogen treatments and a fungicide vs no-fungicide treatment.
The fungicide treated plots were treated with Stratego at 5 fl oz/A on May 18 and then a 4 fl oz/A treatment of Folicur at early flowering, on June 11. I rated leaf diseases on the split nitrogen treated plots on July 8, at early soft dough.
I observed that Septoria leaf spot was the predominate disease across all varieties. The plots treated with fungicide had an average of 2.5% severity of Septoria on the flag leaf, while the plots without fungicide treatment had an average of 34.4% severity of Septoria on the flag leaves. The % reduction in leaf disease was over 90% with fungicide treatment, for this date of disease rating. Leaf rust levels were very low in these plots and scab was not present.
Extension Plant Pathologist
NDSU PLANT DIAGNOSTIC LAB 7-14-04
Correction: Last week, a fungus observed on sugarbeet roots was mistakenly referred to as Aphanomyces euteiches. The actual fungus observed on the roots (in water culture) from two sugarbeet samples was Aphanoymyces cochlioides.
Recent Diagnoses from the Plant Diagnostic Lab:
The cause of a brown spotting on the upper surface of older soybean leaves has not been found. However, the brown spots are not soybean rust, a disease which has not yet been reported to be in the United States. New growth does not seem to have this spotting.
A few other items that came to the Plant Diagnostic Lab this past week include Pythium species observed on roots of two small grain samples, probable bacterial blight (Pseudomonas species) diagnosed on two small grain samples, spider mites and needle cast diagnosed on a spruce sample, Botrytis blight on rose, apple scab, two samples testing positive for Dutch elm disease, downy mildew identified on sunflower samples, Pythium species observed on sugarbeet roots, and a weed identified as Rumex acetosella (red sorrel).
Plant Pest Diagnostician