ISSUE 12 July 19, 2001
SMALL GRAIN DISEASE UPDATE, 7/18
The NDSU IPM field scouts surveyed 156 wheat and barley fields from July 2 to July 13 and found some increase in leaf and head diseases as the crop continues to mature and precipitation returns. Modest to heavy rainfalls across the state this past weekend and on Monday and Tuesday will increase leaf and head disease potential in small grain crops that have not reached soft to hard dough stage yet. Wheat and barley observations from this past week include:
Leaf rust: Low to high incidences of wheat leaf rust were observed in spring wheat and winter wheat this past week (see map). The majority of leaf rust observations have been in the SE, SC, and central counties, although trace levels are starting to be observed in other crop reporting districts, as well. Field scouts from the North Central Research Extension Center (NCREC), Minot, are now finding trace amounts of leaf rust in a few fields in their districts, and leaf rust, at 5-10% severity levels on the flag leaf, was observed on some varieties in plots at the NCREC on 7/18. The highest incidences and severities of leaf rust have been observed in winter wheat. Crown rust on oats was common in the Otana oat variety at the NCREC on 7/18, and Terry Gregoire found trace levels of barley stripe rust in barley plots in Grand Forks on 7/16.
Tan spot: Tan spot continues to be the most common disease observed in wheat, with incidences often above 75% now (see map) and severities on the flag leaf ranging up to 23% in winter wheat, and more commonly 1-5% in spring wheat.
Septoria: Detections of Septoria have really picked up this past week as crops begin to flower or enter grain fill stages. Jerry Schneider, field scout operating out of Carrington, has detected the most Septoria, but Matt Gregoire in the SE, Kelly Novak in the NW, and Holly Semler and Nathan Carson in the NC areas also have detected Septoria. In the SW, Jeanna Jambor primarily concentrated on a downy mildew survey this past week, but Roger Ashley, Area Extension Specialist from the Dickinson REC, and I examined variety plots at Regent on July 10 and observed considerable tan spot and Septoria on certain wheat varieties that were planted into wheat stubble. Septoria lesions have a greyish center and contain tiny black to brown fruiting bodies called pycnidia. Tan spot has the brown center of the lesion with a yellow halo, and no fruiting bodies visible.
Stem rust: Traces of stem rust were observed in plots of the winter wheat variety 2137 in Ransom Co., and Dr. Jim Miller, USDA, observed 30% severity levels in Norstar winter wheat at Casselton.
Head scab: Head scab (Fusarium head blight) infections were common in winter wheat fields in the SE and in plots in Ransom county. Varieties Nakota, 2137, and Wesley had the highest incidence and severity. These winter wheat crops flowered during the rainy period of latter part of June. Traces of scab also were observed in spring wheat plots planted into wheat stubble near Regent in the SW, and traces of head scab were visible on susceptible spring wheat and barley varieties in plots at the NCREC in Minot on 7/18.
Loose smut: Loose smut was observed in 24 of the 156 fields surveyed from 7/2-7/13. Incidence ranged from 2 to 14% and was highest in barley.
Barley leaf spots: High incidences and low severities of net blotch and spot blotch have been observed by the NDSU IPM field scouts. Most frequent occurrences of barley leaf spot have been observed in fields in NW and NC counties.
DISEASE FORECASTING MODEL UPDATE
The small grain disease forecasting model ( http://www.ag.ndsu.nodak.edu/cropdisease/ ) indicates that recent rains have been very favorable for possible infections by the leaf spot and leaf rust pathogens. For example, along the northern tier of counties, conditions were favorable for tan spot and leaf rust infections everyday from 7/12 through 7/17 at Rolla, Bottineau, Minot, Mohall, and Berthold, and most of these days also were favorable for Septoria blotch infections. Similar conditions existed at Langdon, except for 7/13, when wet periods were only for 3 hours. Scab spore detections also have occurred at all of these sites on 7/13 and 7/16. Low counts were found at Langdon, Rolla, and Minot, but high counts were observed in spore traps from Mohall, Berthold, and Bottineau. This information indicates the risk is high for disease in those crops in these areas that are approaching flowering or are in flowering now and good yield potential crops would warrant a fungicide application.
GROWTH STAGE AND APPLICATION OF FUNGICIDES FOR CONTROL OF SCAB
With recent rains, producers are again thinking about fungicides to protect their small grain crops. Some crops are still approaching flowering, or are in flowering or immediately past flowering.
Application of systemic fungicides to control head scab are most effective when applied at early flowering (approx. 25% of the main stems with flowers appearing in center of head), as shown in several research studies at NDSU or at the research and extension centers. Control drops off after flowering; studies with spring wheat and durum showed that control dropped dramatically (from 89% down to 29%) if fungicides were applied after the kernel was formed and in the watery ripe stage. For barley, control was optimum when a systemic fungicide was applied at early full head emergence and dropped off by 20% if the fungicide was applied at kernel watery ripe stage.
In regions where the spring wheat or durum crop is just beginning to flower and wheat midge is also a threat, work by Jan Knodel and Kent McKay of the NCREC at Minot has shown excellent control of scab and midge with application of Folicur + Lorsban at early flowering.
POTATO LATE BLIGHT HOTLINE
Isolated thunderstorms over the past weekend and on Monday and Tuesday caused severity values to increase in a number of potato production areas. No late blight has been reported in ND or MN, but weather conditions have been conducive for infection. Fields need to continue to be scouted, and if late blight is suspected, leaf and/or stem samples should be sent for confirmation to Dr. Neil Gudmestad or Dr. Gary Secor, in care of the Plant Pathology Department, Walster Hall 306, NDSU, Fargo, ND 58105.
Extension Plant Pathologist
PLANT DIAGNOSTIC LAB SAMPLE SUMMARY
There have been a variety of crops coming into the lab this past week. Many of them involve herbicide injury: growth regulator herbicide injury on Roundup Ready (RR) soybeans, sugarbeets, sunflower, tomato; dinitroanaline injury on sunflowers, ALS-inhibitor injury on corn, roundup injury to non-RR canola, and a late application of roundup on RR canola. In this case, the canola had already bolted and was only a day or two away from flowering when the application was made. There was complete pod abortion on the plants in the sample.
Other samples diagnosed this week include iron chlorosis on RR soybeans, Rhizoctonia root rot on sugarbeets, Cercospora on sugarbeets, Downy mildew on sunflower, heat stress and possible soil compaction on RR canola, Loose smut, Common root rot, and Tan spot on wheat, hail damage to corn, Septoria brown spot on soybeans, Rhizoctonia and Pythium root rot on dry beans, copper deficiency on wheat, transplant shock on ane elm, Fireblight on apple, and iron chlorosis on maple. Plant identifications included a linden tree (Tillia), and common ragweed (Ambrosia artemisiifolia); and insect identified as larder beetles (Dermestes lardarius), adult mealworms (Tenebrio sp.), and thistle caterpillar (Cynthia cardui) on borage.
Stay tuned for next week’s report on symptoms, diagnostic tips, and management strategies for soybean cyst nematode (SCN).
SCLEROTINIA RISK MAP FOR CANOLA
The Sclerotinia Risk Map will continue until the end of the month. By that time even the latest planted canola should be well past 50% bloom, which is the latest bloom stage recommended for fungicide application.
It looks like the weather dried off at just the right time for much of the crop, so that early flowering occurred when the soil surface was drying off and the Sclerotinia risk was becoming reduced. With recent rains the risk has been increasing in the northwest and north central parts of the state; however much of the crop is past the 50% bloom period. Infections in late bloom may cause some damage, but usually are not as devastating as early infections. Time will tell as we get into the swathing season and as we get some disease survey data.
RAINFALL, RECORDED RAINFALL AND DISEASE
Some recent locally heavy rains do not show on the NDAWN (North Dakota Agricultural Weather Network) rainfall maps because these heavy showers occurred between NDAWN stations. Using the radar records on the Intellicast Web site may help to show where locally heavy rainfall occurred. Click:
Then click on Bismarck, then radar imagery, then historic weather. This will show the past 24 hours of precipitation. From there you can also click on the past week of rainfall. This will help define small local areas of heavy rainfall where disease risks might be greater than that indicated by disease models using NDAWN data.
Plant Pathologist Emeritus