ISSUE 14 August 6, 1998
SMALL GRAIN DISEASE UPDATE
Surveys of durum and hard red spring wheat the week of July 27th in Ward, McHenry, Bottineau, McClean, Burke, and Williams counties indicated that tan spot and Septoria were detected on the flag leaves in all of the fields surveyed, with severities on the flag leaf ranging from 1 to 30%. Leaf rust was detected in 22% of the fields, and scab was detected in 38% of the fields. Severities of scab were less as the surveyor, Shane Crawford, went north and west, with no scab observed in fields surveyed in Burke county and a less than 1% field severity recorded in one field in Williams county. Loose smut was observed in 28% of the fields, with an incidence from 1-10%.
Many of the fungicide trials on wheat and barley that were established to evaluate efficacy of fungicides for scab and leaf disease suppression and to evaluate optimum fungicide application techniques are now being rated for scab and leaf disease levels, and only a few have been harvested. After harvest and determination of yields, test weights, and vomitoxin levels, a considerable amount of data from various locations and numerous trials will be available to provide some answers on best products and methods for coverage of grain heads and disease control.
Some preliminary information from small plot research and ground equipment application on several trials at Fargo and Langdon indicate that the best treatments on hard red spring wheats gave from 75% to almost 90% reduction in field severity of scab. A replicated small plot study with fungicides at Fargo on barley indicated up to a 65% reduction in field severity of scab, whereas a fungicide study on a commercial barley production field indicated a 45% reduction of field severity of scab. Leaf disease control also has been substantial with fungicide treatments. Yield and quality comparisons have not yet been made on these trials. Some early reports from producers wheat fields have indicated some substantial yield increases and test weight increases with use of fungicides in 1998.
Extension Plant Pathologist
CRISIS EXEMPTION DECLARED FOR USE OF QUADRIS ON POTATO
The North Dakota Department of Agriculture has declared a crisis exemption for the use of Quadris on potatoes for the control of early blight. The crisis exemption became effective on July 31, and will be followed by a section 18, which was submitted to EPA earlier. The crisis exemption followed by the section 18 will be in effect through September 25.
Quadris is to be used at 6.2 fl oz/A for early blight control. It can also be used at 12.4 fl oz/A for late blight control. Quadris should be used in alternation with Bravo on a 7-10 day schedule. There is a limit of 6 applications per year with Quadris. Do not apply Quadris within 14 days of harvest. The label submitted for the section 18 also indicated that Quadris should be applied with ground equipment or aircraft. For aerial applications, volumes should be 5-10 gal/A. A spreader-sticker could be used, but do not tank mix Quadris with COC, MSO, silicon or other adjuvants.
Quadris (active ingredient azoxystrobin) belongs to a new class of fungicide called strobilurins or methoxyacrylates. Quadris has a different mode of action than any currently registered fungicide. It is locally systemic, is taken up by the leaf and distributed within the leaf, providing protection to both leaf surfaces. It can also be taken up by green stem tissues and be translocated upward in the xylem. Quadris has some post-infection activity but is most effectively used as a protectant.
Quadris at 6.2 fl oz, used in alternation with Bravo, provided better early blight control in 1996 and 1997 Wisconsin trials than Bravo alone, mancozeb alone or mancozeb plus Super Tin. When used in alternation with Bravo, it also provided late blight control in 1997 trials at Prosper, ND that was superior to that of Bravo or mancozeb alone. Late blight control at the 12.4 fl oz rate was outstanding, and the yield was 60-70 cwt/A greater than that with Bravo or mancozeb alone, and 145 cwt/A greater than the untreated check.
Extension Plant Pathologist
PLANT DIAGNOSTIC LAB REPORT
Now that many homeowners are starting to harvest the produce from their gardens, diseases of fruits and vegetables are beginning to show up. There have been a few inquiries to the lab about a disease called Blossom-End Rot on tomato. This is a nutritional disorder that results form a localized calcium deficiency in the bottom of the tomato. Blossom-end rot is observed first as light tan, water-soaked lesions at the end of the tomato (opposite the stem end). These lesions then expand and become black and leathery. Often, secondary infections can occur on the lesions producing a moldy looking tomato. These lesions may also occur on the side, and less commonly, will not be visible from the outside appearing instead as a black lesion on the inside of the fruit when it is cut.
Calcium is not a very mobile element in the tomato plant and so a fluctuation in the water supply, plants repeatedly being allowed to wilt down and then watered thoroughly, may promote occurrence of this disorder. High salt concentrations in the soil, use of ammonium nitrogen fertilizer, and high relative humidity may also increase the likelihood and severity of blossom-end rot.
Managing this disorder should start with planting tolerant cultivars, using appropriate fertilizers and regular watering. A soil test can determine if there is a calcium deficiency, and treating dolomite or high calcium limestone 2-4 months before planting will help avoid this problem. During the growing season, foliar sprays of anhydrous calcium chloride may help alleviate symptoms if a calcium deficiency is detected or if a high salt concentration occurs.
On the field crops end, we continue to culture sugarbeets for Aphanomyces and Rhizoctonia root rot. Potato samples coming in have been diagnosed with late blight, early blight, and white mold. Dry bean samples have come in with bacterial blight and Bean Common Mosaic Virus. Green snap is occurring on corn as well as sunflower samples submitted, and many of the soybean samples submitted show mild to severe symptoms of iron chlorosis.