NDSU Crop and Pest Report
Plant Pathology


ISSUE 8  June 20, 2002

 

SMALL GRAIN CROP STAGES AND FUNGICIDE APPLICATION

Wheat and barley crops are at many crop growth stages across the state. Early planted spring wheat and barley are in the late jointing to early flag leaf emergence stages, while late planted spring grain is in the 2 - 4 leaf stages. Winter wheat is heading out across the state.

Crops in the early leaf stages may still be candidates for early season fungicide application. Some other crops are fast approaching the fungicide application decision time for late season application.

 

EARLY SEASON FUNGICIDE UPDATE

Tan spot of wheat is common now in areas where rains occurred on June 8-9. In some areas with nitrogen stress, tan spot is more severe on the wheat. For these areas with crops still in the tillering stage and with tan spot, early season fungicide application may be an option for producers also applying herbicides. NDSU Crop and Pest Report # 3 (May 16 issue) discussed early season application.

Some questions have come up about rates of fungicides even lower than half the full label rate for early season disease control. NDSU does NOT have data to support a rate lower than half the full label rate, and the fungicide 2(ee) labels for early season application call for ½ full label rate. Adjuvants are not necessary for these early season fungicide applications if combined with herbicides, unless the herbicide product requires a specific adjuvant.

 

LATE SEASON FUNGICIDES FOR SMALL GRAINS

The need for late season application of fungicides on small grains depends on: 1) yield potential; 2) variety response to leaf spot diseases, rust and scab; 3) disease presence as determined by field scouting; and 4) indications of infection periods as described by the NDSU Disease Forecasting System or other weather data.

As some winter wheat crops are now headed and early planted small grains are starting to flag, some producers may soon be making late season fungicide decisions. The following fungicides are registered for small grains in ND as of June 2002.

 

Product

Chemistry

Company

Growth stage limitation or PHI

Champ, Kocide

Copper

Nufarm, Griffin

early heading, 10 days later

Dithane, Manex II, Manzate, Penncozeb

Mancozeb

Various

26 day PHI (often applied 2x)

Tilt; Tilt 24(c)

Propiconazole

Syngenta

Feekes 8; Feekes 10.5 or 40 day PHI

Quadris

Azoxystrobin

Syngenta

45 day PHI

Stratego; Stratego 24(c)

Trifloxystro-bin + Tilt

Bayer

Feekes 8; Feekes 10.5 or 40 day PHI

Folicur Sec. 18

Tebuconazole

Bayer

50% heading or 30 day PHI

PropiMax; PropiMax 24(c)

Propiconazole

Dow

Feekes 8; Feekes 10.5 or 40 day PHI

 

SMALL GRAIN LEAF DISEASE FORECASTING AND FUSARIUM HEAD BLIGHT RISK MAP UPDATE

As of June 16th, many of the NDAWN locations that received substantial rainfall in the previous 10 days had 5 to 7 of those days with weather conditions favorable for tan spot infection. The information at the web site:

http://www.ag.ndsu.nodak.edu/cropdisease/cropdisease.htm

provides tan spot, Septoria and leaf rust information up to through the flowering growth stage.

To get information about the risk of Fusarium head blight (FHB = scab) and scab spore count results, a viewer of the above web site needs to select an NDAWN location, then select the flowering growth stage, and click on "Get Forecast" to see information about FHB. Scab spore counts for certain sites and a forecast of FHB severity across the state are provided. Selecting the Model 1 link provides a map of North Dakota indicating FHB risk in various colors. The model is based on epidemiological information developed at Ohio State University.

Individuals determining the risk of FHB for fungicide decisions at heading should examine the risk map several days before flowering, to get timely information on FHB risk. Currently, the Model I map indicates very low risk of FHB across ND.

 

TAN SPOT AND VARIETIES

Alsen HRSW is being grown on more acres this year and producers are seeing tan spot on the leaves. Alsen is rated susceptible to leaf spot diseases and is similar to Russ, Oxen, 2375, and Ingot in reaction to tan spot. Varieties such as Gunner, Keene, Hamer, Parshall and Reeder have intermediate to moderately resistant reactions to leaf spot diseases.

 

RUST REPORT - SMALL GRAINS

One pustule of leaf rust was detected by NDSU IPM field scout Matt Gregoire on June 18, in a field of spring wheat south of Highway 13 in Richland county. Up to then, leaf rust had not yet been observed in North Dakota and it has not yet been reported from South Dakota. The USDA/ARS Cereal Rust Bulletin # 6 (June 5, 2002) reports that leaf rust levels in southern plains states "will provide much more leaf rust inoculum for the northern wheat growing area than last year." Our late season crop may be at risk, so field scouting is important to determine development and spread.

Wheat stem rust and barley leaf and stem rust levels were very low in southern states this year, as were stripe rust levels in Oklahoma and Kansas. However, oat crown rust infections on the alternate host, buckthorn, are at high levels, and may signify increased risk for oats this year.

 

TAKE-ALL ROOT ROT AND WET SOILS

According to NDSU Plant Pathologist, Prof. Bob Stack, who has studied root diseases of small grains for over a quarter century, the current wet soil conditions in northeastern North Dakota and northwestern Minnesota may favor the Take-All root disease on wheat and barley. Take-all destroys the root system and symptoms show up at heading time. Plants are stunted or killed and quickly bleach out, almost white. These ‘white head" plants may occur singly, in small groups, or in large patches. "White head" plants can be lifted from the soil with little effort because all roots are rooted away by a black rot. Often, the stem base of affected plants shows a shiny black or greyish metallic appearance. Plants affected by take-all are killed before they can set any grain – hence the name ‘take-all".

No useful resistance among commercial grains exists, but crop rotation may reduce future risk. Certain, higher rates of Baytan and Dividend seed treatments provide some take-all suppression. Fields at high risk of take-all or other root rots, because of extended periods of excessive soil moisture, will have to be carefully evaluated for further inputs, such as fungicides.

A more extended description of take-all and how to tell it from other kinds of root rot is given in the NDSU Extension Circular PP-785 on Root and Crown Rots of Cereals, available from county extension agents, or found on the web at:

http://www.ext.nodak.edu/extpubs/plntdise.htm

Marcia McMullen
Extension Plant Pathologist
mmcmulle@ndsuext.nodak.edu

 

PLANT DIAGNOSTIC LAB SUMMARY

The most represented category of plant samples in the lab this past week is still trees. The spruce tree samples (6) diagnoses include Rhizosphaera needlecast, Cytospora canker, spider mites, drought, and yellow headed spruce sawfly. Two (2) pines just came in, one with winter injury and one undiagnosed yet. We are culturing an elm (1) for Dutch Elm Disease (DED). The ash tree samples (2) both showed symptoms of growth regulator herbicide injury. There is also a mountain ash (1) showing symptoms of both environmental as well as disease problems. There have been several samples in recently of herbicide injury to trees. While woody plant species are somewhat tolerant of low dose exposure to herbicides, this type of injury is not without impact on trees. Besides creating unsightly symptoms, herbicides can weaken and stress trees making them more susceptible to insect and disease problems.

We also got a corn sample (1) with early season phosphorus deficiency symptoms. We received a mint sample (1) that we are culturing for leaf spot disease, a wheat sample (1) that showed symptoms of being in saturated soils, a potato (1) that had been burned by a urea application, and an alfalfa sample (1), dry bean sample (1), and pine samples (2) that are still being evaluated.

Cheryl Biller
Diagnostician

diaglab@ndsu.nodak.edu

 

SCLEROTINIA RISK MAP UPDATE

As of June 16, the Sclerotinia risk map shows moderate and high risk in some areas of North Dakota and Minnesota. Light areas on the map are moderate risk, and all dark areas are low risk, with the exception of the dark area located near the tri-county border of Montrail, Ward, and McLean counties in west-central ND, which is a high risk area. The potential risk is only a threat to flowering canola, which still may be a few weeks away in most areas. The Sclerotinia risk map is available on the web at the NDSU Extension site at:

http://www.ag.ndsu.nodak.edu/aginfo/sclerotinia/sclerotinia.htm

The map is also available at the Northern Canola Growers Association site at:

http://www.northerncanola.com/growers_map_default.asp

Sclerotinia Risk Map

 

POTATO BLIGHTLINE UPDATE

As of June 19, severity values have accumulated for irrigated production areas in Hoffund, Northwood, Robinson, Karlsruhe, and Mandan. Growers should continue to scout for seed-borne late blight in emerging fields, and destroy volunteers in those areas and in rotation crops. Fungicide application should begin as row closures approach 50%. All irrigated fields should receive 2 fungicide treatments prior to row closure. For the most current information call the Bravo/Quadris Blightline at 1-800-482-7286. The information is also available on the web at:

http://www.ndsu.nodak.edu./instruct/gudmesta/lateblight/

Carl Bradley
Extension Plant Pathologist

cbradley@ndsuext.nodak.edu

 

CHICKPEA PRODUCERS ADVISED TO SCOUT FOR ASCOCHYTA

Ascochyta blight, caused by the fungus Ascochyta ?, has been identified in isolated chickpea fields in western North Dakota. Ascochyta blight leaf lesions were found as of June 17th, near Beach, Roseglen, and Minot, ND. Chickpea producers are being advised to scout their fields on a daily basis for lesions. Ascochyta blight is of particular concern with the large kabuli chickpea varieties. The disease can be first identified as light to dark-brown spots that occur on leaflets or stems. Lesions will expand rapidly under wet, humid conditions. Fruiting bodies, called pycnidia , will develop in the center of the lesions. The pycnidia are small, round, and black in color. A hand lens may be needed to observe the pycnidia. Severly infected leaves will turn yellow, wilt, and die. Stem lesions may be a dark-brown color and may cause the stem to break. It is very important to scout fields for the disease, and spray chlorothalonil fungicide as soon as the first lesion is detected.

Chlorothalonil fungicides, Bravo Weatherstick ZN, Bravo Ultrex, and Equus DF are labeled for early season control of Ascochyta blight of chickpea. As of June 18, most chickpea plants in ND are only 3 to 5 inches high, and are 2 to 3 weeks from flowering. Fungicide trials at Minot indicate that chlorothalonil will effectively control Ascochyta blight when sprayed in the early vegetative stages, prior to the onset of the disease. If the disease is already present and stem lesions have occurred, then chlorothalonil will not be as effective in controlling the disease.

The recommended rate of Bravo Weatherstick Zn is 1.5 pints/acre, and the recommended rate for Bravo Ultrex and Equus DF is 1.25 lbs/acre. A minimum spray volume of 15 gallons per acre is required, but 20 gallons per acre is recommended.

A request for a section 18 label has been submitted for the use of Quadris to control Ascochyta blight of chickpea in ND. Hopefully, Quadris will be labeled soon for later applications when the crop is in the pre-flowering to flowering stages.

Kent McKay
Area Extension Agronomist

kmckay@ndsuext.nodak.edu


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