ISSUE 10 July 5, 2001
CANOLA FLOWERING AND FUNGICIDE APPLICATION TIMING
A new color publication entitled Canola Flowering and Fungicide Application Timing, NDSU Extension Circular A-1208, has just been printed. It provides information on the percent bloom recommended for fungicides currently registered for Sclerotinia stem rot control and has photos showing various bloom stages. The color photos, provided courtesy of BASF, are a series of photos taken some years ago by Prof. Robin Morrall, plant pathologist, University of Saskatchewan.Information in this publication should help canola producers determine the correct timing of fungicides on canola: 10-25% bloom for Quadris and 20-50% for Ronilan. This information should help producers make timely applications of fungicide. The information, if used in conjunction with general information from the Sclerotinia Risk Map and specific information about each field that might need to be sprayed (includes the Sclerotinia check list), should help make fungicide spray decisions easier for canola producers.
We continue to need reports of apothecia as they appear. This is needed for ground truth to the Sclerotinia Risk Map. Since the upper soils have dried somewhat in much of the state, we may not see many new appearances for a while.
Once apothecia appear, how long do they continue to puff their spores? In response to this question, Dr. Berlin Nelson, plant pathologist at NDSU, stated that he has seen apothecia puff spores intermittently for up to a week in some of his laboratory/greenhouse trials. Apothecia that continue to puff spores for this long must remain moist and not dry out.
Art Lamey, Plant Pathologist Emeritus
Low levels of wheat leaf rust are now being found in commercial fields of winter and spring wheat in the southern tier of counties in the eastern half of ND. One or two rust pustules or trace amounts are being found.
Stripe rust observations were made on 6/29 on winter wheat plots in Ransom Co., by Dr. Jim Miller, USDA cereal rust pathologist. He found fairly high levels on certain winter wheat varieties, such as Foster, Nakota, and Norstar. Incidences of stripe rust on these three varieties was 100%, with severities from 50-100% on Foster winter wheat, 20-50% on Nakota, and 5-40% on Norstar. On 7/2, I examined spring wheat plots adjacent to these winter wheat plots, and a commercial field of Alsen wheat adjacent to the plots. I did not find any rust in the Alsen. The varieties in the plot also appeared rust free, except for my observation of a trace amount of stripe rust in Ingot spring wheat. Dr. Marty Draper, SDSU Extension Plant Pathologist, reports that in South Dakota, some plots of Ingot are showing quite a bit of stripe rust, Oxen has a lower level, and Russ spring wheat was showing none. Some commercial fields in north central SD also are showing quite a bit of stripe rust.
Rusts are explosive diseases and always bear watching. The good news is that the most recent updates of the small grain disease forecasting model in the Fargo and Wyndmere areas show that conditions on July 1 and 2 were not favorable for leaf rust infections.
IPM SCOUT SURVEY REPORTS THROUGH 6/29
Wheat: Tan spot remains the most common disease being observed on wheat by NDSU Extension IPM field scouts this past week, in all parts of the state. Incidences of plants infected in a field are generally high, but severity levels ranged from 0 to 22% on the top leaves. The 22% severity on the flag leaf was observed by Jerry Schneider in a winter wheat field in Logan Co.
Some Septoria infections are also being observed now, and the dark, brown-black specks that are the fruiting bodies of the fungus are noticeable in the greyish centered lesions. Septoria was observed in winter wheat in Ransom Co. and in spring wheat in Barnes and Emmons counties.
Bacterial blight was observed by Holly Semler in wheat in McHenry and Pierce counties and by Nathan Carlson in McLean and Mountrail counties; levels were fairly severe on wheat in the jointing stage. The crops should grow out of bacterial infections when the weather returns to sunny, warm days.
Spot blotch was observed in barley in the NC and NW regions, while net blotch was observed in barley fields in Stutsman, Barnes, and Logan counties. Percent of plants or incidence of infection was high, up to 100%, but severity values averaged under 5%. Terry Gregoire, Area Extension Specialist, Devils Lake, also reported seeing scald fungal leaf spot, as well as net blotch, in barley near Tolna, ND, and he observed powdery mildew in the lower canopy of both wheat and barley in that region. Head scab (Fusarium head blight) has not been reported by the IPM scouts yet. I observed some scattered scab infections in the winter wheat plots in Ransom Co.
POTATO LATE BLIGHT HOT LINE
Late blight has still not been reported in the region, although severity values are high at most irrigated sites. A few of the non-irrigated production areas also have reached the cumulative severity value of 17 or higher. All irrigated sites also have now reached the early blight favorability index value of 300. Irrigated growers should be on a 7-day fungicide application schedule at the high rate.
DOWNY MILDEW IN SUNFLOWERS
Downy mildew of sunflowers may be evident now in sunflower fields that had saturated soils for extended periods after planting. Typical symptoms in seedlings include dwarfing of the plant and yellowing of the leaves. The appearance of white cottony masses of the fungus on the lower leaf surface during periods of high humidity and dew is fairly diagnostic of this disease.
Dwarfing and distortion of leaves are also symptoms typical of herbicide drift damage, especially of 2,4-D and related phenoxy compounds. Herbicide damage, however, will not exhibit the white appearance of the fungus on the underside of the leaves, nor the typical chlorosis (yellowing)of downy mildew.
Extension Plant Pathologist
SUGARBEET: CERCOSPORA SEASON SLOWLY APPROACHING
At this time in the growing season, there is no Cercospora alert since we have not seen any symptoms of the disease in fields. This is of course due to the fact that most sugarbeet planting was done in mid-to late May rather than in late April because of wet fields. As a result, most sugarbeet fields will close rows after the first week of July. Cercospora leaf spot usually start appearing after row closure.
The fungus Cercospora beticola causes Cercospora leaf spot. The symptoms of Cercospora leaf spot are circular spots about 1/8 inch in diameter with ash gray centers and dark brown or reddish-purple borders on leaves.
Bacterial leaf spot, which may be confused with Cercospora leaf spot, has been identified in sugarbeet fields. Bacterial leaf spot produces irregular to circular spots about 3/16 to ¼ inch in diameter. Using a hand lens, you will see spores as tiny black dots in the Cercospora leaf spot. There are no black dots or spores present in bacterial leaf spot.
Cercospora leaf spot is the most damaging foliar disease of sugarbeet, resulting in lower tonnage, reduced sucrose content, poor storage in pilers, and increased impurities. Growers lost $75 million to Cercospora in 1998. As such, it is imperative that we manage Cercospora for long-term profitability of the sugarbeet industry. This is possible by rotating sugarbeet with other crops such as corn, wheat, barley, soybean, and edible beans, for about 3 to 5 years - the longer the better; planting sugarbeet as far away as possible (at least 100 yards) from the previous year infected crop; burying infected debris by tillage in the fall; using more tolerant varieties; and alternating fungicides from different classes when using chemical control.
Dr. Mohamed F. Khan
NDSU Extension Sugarbeet Specialist