ISSUE 7 June 18, 1998
SMALL GRAIN FUNGICIDE UPDATE
Small grain crops are developing rapidly, and in some counties spring wheat is in the boot stage, and barley is heading to flowering. In some of these same counties heavy rains have recently occurred and heading stage is coinciding with saturated soils, heavy dews, and morning fogs. As many growers know, these weather conditions can be very conducive to leaf diseases and Fusarium head blight. I have had a lot of questions about use of fungicides in the past few days. Guidelines for use of fungicides in wheat look at yield potential, presence of diseases in canopy or history of head scab, favorable weather for infection, presence of wheat, barley or corn stubble in field, and also market price. The likelihood of economic response is greater if the yield potential is good, leaf diseases are present on lower leaves, scab was severe in area last year, heavy dews are persisting, and if wheat or barley is planted back into ground containing diseased stubble from last year.
The big drawback this year that affects economics is the market price of wheat and barley, prices which not only fail to rally, but continue to fall. However, based on last years wheat yield responses to fungicides applied at early flowering, economic returns could still be gained on wheat with high yield potential and if there is a high potential risk of leaf and head disease. In 1997, NDSU plot trials on wheat at various locations across the state averaged from 17-21% yield response with fungicides applied at early flowering and which are currently registered for heading application to wheat. Fungicide applications monitored by Ostlund Chemical Co., Fargo, showed similar or slightly better yield response in commercial wheat fields, with improved quality, as well.
Fungicides applied at heading on barley did result in some good yield responses in 1997, BUT the vomitoxin (Deoxynivalenol) levels were never reduced enough to achieve the low ppm required by the malting industry.
SMALL GRAIN FUNGICIDE COSTS
Information received from one chemical distributor indicated the following retail prices for small grain fungicides:
|Tilt||$292.00/gallon (use rate = 4 fl.oz/acre)|
|Folicur||$292.50/gallon (use rate = 4 fl.oz/acre)|
|Benlate||$ 15.75/lb (use rate = ½ lb/acre for scab suppression)|
|Mancozeb||$2.40-2.60/lb (use rate = one lb/acre generally combined with Benlate for scab suppression OR 2 lbs/acre if applied alone)|
* Above prices may vary depending on distributor, location, and availability. The primary bulk of testing with these fungicides has been at recommended label rates, as indicated above. Results with reduced rates may be less than optimum.
*Optimum time for application of above fungicides for scab suppression is at early flowering, when about 25% of the main stem tillers have flowered. Yield responses with fungicides for scab suppression have been lower if the fungicides were applied before flowering, or after flowering-during early milk.
TIPS FOR IMPROVING APPLICATION OF FUNGICIDES FOR SCAB SUPPRESSION
This past winter and spring several NDSU personnel have examined
ways to improve delivery of fungicides to wheat and barley heads, so that improved
coverage and retention would occur. This work followed some preliminary results from
trials at the Langdon Research and Extension Center during the summer of 1997. Research
done by Terry Gregoire, NDSU Extension Agronomist, Ron Stover, Langdon REC Plant
Pathologist, Jim Harbour, NDSU Extension Crop Protection Specialist, and Vern Hofman, NDSU
Extension Agricultural Engineer, has shown that, for ground application, creating
an angled spray pattern towards the wheat and barley heads greatly increases the
deposition of fungicides on the heads, as compared to the standard vertical positioning of
Research has shown that deposition on the head improves using either a twinjet nozzle (type 8004), or a double swivel nozzle body equipped with two 8002 flat fan nozzles. The twin jet nozzle has two flat fan cavities angled at 30° of vertical. The double swivel nozzle body allows for any angle, but 60° of vertical (equal to 30° of horizontal) provided the best deposition. Most existing spray equipment can be retrofitted with either the twinjet nozzles or the double swivel nozzle body. With a 20" spacing of the nozzles on the boom, the boom should be raised 14" above the crop for the twinjet nozzles, and 11" above the crop for the double swivel nozzle body angled at 60o from the vertical.
For aerial application, very little research to date has been done with fungicides aimed at controlling scab in small grains . Two factors that may increase the efficacy of fungicides aimed at wheat or barley heads is to increase the spray volume to 5 gallons/acre, and to spray in the early morning when heavy dews are present, with the dew functioning as additional spray volume. An aerial application trial is planned for barley this week.
SMALL GRAIN DISEASE SURVEY UPDATE
Surveys of wheat this past week in the south central and central counties have indicated a slight increase in incidence of wheat leaf rust. Septoria tritici has now been confirmed on bottom leaves of many of these same fields. In Ward and McLean counties, very little disease was observed this past week, with only tan spot evident on the bottom leaves of wheat. Barley crops in North Dakota are showing very little evidence of diseases at this time.
A fungal spore trap located at Fargo and operated by Dr. Len Francl, NDSU Plant Pathologist, has indicated that ascospores of Septoria were commonly found this past week, but only an occasional ascospore of Gibberella zeae ( = sexual stage of Fusarium graminearum) was observed. This spore trap is located in a wheat trial on the Fargo station.
I received a report of high levels of loose smut infection in a few wheat fields heading out in Richland Co. The grower indicated that the fields showing loose smut were from bin run seed that had not been treated with a seed treatment.
Extension Plant Pathologist
SECTION 18 FOR QUADRIS ON SUGARBEET
The Environmental Protection Agency granted a section 18 for the use of Quadris on sugarbeet for control of Cercospora leafspot. Quadris, manufactured by Zeneca, is a strobilurin, a new class of fungicide with a new mode of action. It is locally systemic and has several days of post-infection activity. It has shown somewhat better activity against Cercospora than TPTH in two years of trials over a wide geographical area.
A maximum of 125,000 acres may be treated. Quadris is to be applied by ground or air at 9 fl oz/A (0.15 lb ai), with a maximum of 3 applications. Quadris cannot be applied through irrigation equipment. The use of Quadris in areas where soils are permeable, particularly where the water table is shallow, may result in ground water contamination.
In order to maximize resistance management, Quadris should be applied in alternation with an unrelated fungicide. The preharvest interval is 7 days. There is a 12 hour re-entry interval.
POTATO LATE BLIGHT HOTLINE
The potato late blight hot line is available at 1-800-482-7286. It provides severity values for 12 non irrigated sites in eastern North Dakota and western Minnesota, and also provides severity values for 6 irrigated sites in the eastern half of North Dakota. It also provides recommendations on fungicide applications required for late blight control.
This is the first year that severity values for irrigated sites were available.
A web site provides the late blight hot line information, as well as weather data, results of fungicide trials, information on late blight and photos of late blight, and information on potato diseases. The web site can be found at: http://www.ndsu.nodak.edu/instruct/gudmesta/ lateblight.
Extension Plant Pathologist
PLANT DIAGNOSTIC LAB REPORT
The chemical injury samples continue to predominate, in crops such as wheat, corn, soybean, and dry bean. There have also been samples of trees that border fields where herbicide applications are being made. The Plant Diagnostic Lab does not do chemical residue analysis on soil or plant samples. Groups of compounds with like modes of action will produce documented symptoms on specific plants. Our diagnosis is based on a visual evaluation of the consistency of the symptoms observed on the sample with those known to occur when injury is caused by chemical drift or carryover. Chemical residue analysis can be done at several labs around the country. This testing is specific for the compound of interest and can be costly. If you would like a list of those labs that perform these tests, it is available from the Plant Diagnostic Lab.
It is not too early to begin watching for diseases. Fireblight may begin to be noticeable soon. Fireblight is a bacterial disease (causal organism - Erwinia amylovora) that causes a characteristic blackening and often crooking of the end of the stem, referred to as a shepherds crook. The bacterium can be spread by splashing rain and insects, at temperatures above 65° F. It overwinters in a canker under the bark of apple, pear and many ornamental tree species. In the spring, under the proper environmental conditions, the bacteria will ooze out in plant sap and spread via insects and water. Hail can be of particular concern as a predisposing factor since it creates fresh wounds that are easily invaded by the bacteria. Symptoms to watch for include wilting and scorched blossoms and stems. In pears, the leaves may turn black.
This disease can spread very rapidly if the weather conditions are favorable. If you see any of these symptoms, it is wise to prune out the infected material as soon as possible. Pruning cuts should be made approximately 8-12 inches below the infected area, and you should disinfect the cutting instrument with a 10% household bleach solution between cuts to ensure that you dont spread the pathogen (bacteria) to a new cut.
Plant Pest Diagnostician