ISSUE 14 August 16, 2007
SMALL GRAIN SURVEY RESULTS - AUG. 3
NDSU IPM field scouts surveyed 99 wheat fields and 14 barley fields the first week of August, primarily in the northern tier of counties. For wheat, the average growth stage was soft dough (see map), and for barley, the average growth stage was hard dough. Head diseases were the primary focus of these late season crop surveys.
Fusarium head blight, or scab, was reported from the northeast, north central and northwest regions, but generally at low severity levels (see map).
In the NE, scab was found in all but one wheat field surveyed, almost all fields, but the average field severity was 2.1%. In the north central and northwest counties, scab was observed in 23 of the 72 fields surveyed in the region, with the average severity in infected fields at 2.3%, and over all fields surveyed, the average severity was 0.7%. Other head diseases observed at low severity levels included ergot, loose smut, and glume blotch.
Of the 14 barley fields surveyed during this first week of August, all were in the north central or northwest district. Half had some scab symptoms evident, but severities averaged less than 1%. Two of these fields had a 2% incidence of ergot. Loose smut was not observed in these fields.
A FEW DISEASES IN CORN OBSERVED
I have received several corn samples and jpeg pictures from crop consultants and from Greg Endres, Area Extension Specialist, Carrington, in the past week. In each case, some specific hybrids were expressing some leaf spot symptoms, while other hybrids in the area were symptom free.
In one case, the leaf lesions were determined to be those of Northern corn leaf spot (Bipolaris zeicola). This is the most common fungal leaf spot that Iíve observed in ND, but it is seen very infrequently. In another case, large, irregular, purplish brown blotches were due to a condition called Purple Leaf Sheath, a discoloration which occurs when saprophytic fungi develop on pollen and other particulate matter lodged between the stalk and the leaf sheath.
In another case, Alternaria spores were abundantly found associated with long dead areas or lesions on the leaf and on smaller whitish spots with a dark border. The small, dark border lesions were symptomatic of Holcus spot, a common bacterial disease seen in the region. The larger necrotic spots may have been dead due to a number of causes other than fungal, with the Alternaria fungus growing as a saprophyte. However, on rare occasions, Alternaria spores also have been reported to cause similar long necrotic lesions under high dews and with leaf injuries caused by insects or soil particles.
Fungal leaf diseases remain uncommon and non-severe in almost all corn fields in the region.
Ext. Plant Pathologist
DRY BEAN AND SOYBEAN DISEASE UPDATE
Sclerotinia (white mold), bacterial blights, and rust diseases are being observed on dry beans. Sclerotinia, bacterial blights, and some root rots have been showing up in soybeans. Disease levels on both crops have generally been low.
Fungicide applications at late growth stages for sclerotinia are not economical. Temperatures are favorable for development of sclerotinia. For those growers who are irrigating either crop, it is important to irrigate only if the crop needs water, and avoid watering on cloudy days. Prolonged canopy wetness creates a favorable environment for white mold development. Closed canopies are more likely to remain wet for prolonged periods of time.
It is important to know if sclerotinia is present in the crop. The occurrence of sclerotinia even late in the season can increase the amount of sclerotia in the soil, which can cause disease in the future.
Soybean rust has moved into northern Oklahoma. However, because of persistent 100oF + temperatures in Oklahoma and Kansas, little disease development and/or spread in that area is expected in the near future.
Extension Plant Pathologist