ISSUE 13 July 27, 2006
WHEAT & BARLEY OBSERVATIONS, July 17-21
Wheat: NDSU IPM summer field scouts surveyed 83 wheat fields during the week of July 17-21. The average growth stage of these crops during that week was Zadoks 79 = early milk stage to early soft dough. Field scouts found a little more leaf rust developing in the counties of Stutsman, Renville, and McHenry, with an average of 10.2% severity on flag leaves. The NDSU small grain disease forecasting system indicated some favorable weather for leaf rust infections in these locations the past week. Statewide, leaf rust averaged only 2% severity.
Fusarium head blight was observed in only four of the 83 wheat fields surveyed, with detection in fields in northeast counties. Fusarium field severities in these fields were very low, from 0.1 to 2.5%.
Barley: Ten barley fields were surveyed across the state during the week of July 17-21, five in the northeast district, four in western districts, and one in the east central district. These barley fields were in the late milk growth stage, on average. Very little leaf disease was detected in these barley fields and no Fusarium head blight was observed.
Most of the field scouting of small grains will be done the last week of July, except for some northern tier counties where crop development is slightly later.
The next Crop and Pest Report bulletin will not include contributions from Extension Plant Pathologists, because of our attendance at the annual meeting (July 30-Aug. 3) of our professional society, the American Phytopathological Society. A final pathology report will be included in the Aug. 17th edition of the Crop and Pest Report.
Extension Plant Pathologist
DISEASES UNDER DROUGHT CONDITIONS
The majority of plant diseases require cool and wet conditions to be severe and cause yield reductions; however, a few diseases are favored or can still cause yield reductions under dry conditions. With the dry weather that most of North Dakota is currently facing, the following are diseases that may be observed under these conditions.
Root rots. Infections by root rot pathogens are generally favored by wet weather; however, the effects of root rots on crops may be more severe under dry conditions. Under dry soil, plants that have poor root systems will be the first ones to wilt and die.
Charcoal rot. Charcoal rot, caused by the fungus Macrophomina phaseolina, can cause damage to soybean, dry edible bean, and sunflower. Plants affected by charcoal rot may die prematurely, and the diagnostic sign of this disease is the presence of tiny microsclerotia (small "pepper grains") that can be found in the lower stem area when split open.
Soybean cyst nematode. Under dry conditions, the above-ground symptoms caused by soybean cyst nematode (SCN) are more likely to be observed. Above-ground symptoms include wilting, chlorosis of the leaves, and premature death. On affected plants, the SCN females may be observed on the roots as tiny (smaller than nodules), lemon-shaped objects that are white to yellow in color. Soil samples from affected areas may be collected and sent to some diagnostic and soil labs for confirmation.
Insect-transmitted diseases. Because some insect pests are more active in dry conditions, insect-transmitted diseases can also increase under dry conditions. Viruses and phytoplasma diseases can be vectored by aphids, beetles, and leafhoppers. Depending on the disease and crop, control of the insect vectors may or may not impact the disease.
Carl A. Bradley
Extension Plant Pathologist