ISSUE 3    May 18, 2006

RECENT RAINS WILL BRING EARLY SEASON TAN SPOT IN WHEAT

Recent rains may activate fungi that cause early season leaf spot diseases in small grains. The most common early season leaf disease is tan spot of wheat caused by the fungus Pyrenophora tritici-repentis The fungus survives in wheat residue, and when conditions are wet and rainy, the fungusís fruiting bodies on the straw (see figure of fruiting bodies) swell and release spores that can infect during wet conditions. The early infections show as small tan to brown spots with yellow halos (see figure of symptoms). This disease has already been observed in some winter wheat fields.


Tan spot fruiting bodies on wheat straw


Early season tan spot symptoms

When tan spot is present and wheat crops are in the appropriate stage for early herbicide application, generally the 4-5 leaf stage, a fungicide often is applied or tank mixed with the herbicide application.

The fungicides are often applied in combination with herbicides applied to the crop at these early leaf stages. Some combinations of products may cause slight injury, so herbicide and fungicide labels should be checked before tank mixing. A spreader/sticker addition is NOT needed for the fungicide, if applied in combination with a herbicide. Also, most manufacturers of the above products have a later season use rate that is generally twice the early season fungicide use rate. Early season fungicide use rates generally cost approximately $4.00 to $5.00/acre, or less.

A number of fungicides are available for control of early season leaf spot diseases in wheat. Several are also registered for barley, if early net blotch or spot blotch should occur.

The following table indicates products available, use rate, and if registered for barley, too.

Product

Active ingredient

Early season use rate

Crop

Tilt, Propimax,

Bumper

Propiconazole

2 fl oz

Wheat Barley

Stratego

Propiconazole + Trifloxystrobin

4-5 fl oz

Wheat

Quadris

Azoxystrobin

6.2 fl oz

Wheat

Barley

Headline

Pyraclostrobin

3 fl oz

Wheat Barley

Quilt

Propiconazole + Azoxystrobin

7 fl oz

Wheat

Barley

Penncozeb, Manzate, Dithane

Manex II

Mancozeb

1-1/12 lb

Wheat

Barley

All of the products have good activity against leaf spot diseases at the 4-5 leaf stage. The mancozebs are protectants and generally are less rain fast than the other products.

NDSU research trials with winter wheat and with tan spot susceptible spring wheats have shown yield responses generally in the range of 4-5 bushels in wet years, and some responses up to 8 bushels. The majority of these trials have been with wheat planted into various levels of wheat stubble. The greatest economic response from early season fungicide use is generally seen under the following conditions:

* susceptible cultivar

* wheat planted into wheat ground

* rainy weather during early leaf stages

Producers who had wheat in a field two years ago may have enough remaining wheat stubble to see some tan spot infection.

 

NDSU WHEAT LEAF DISEASE FORECASTING SITE INDICATES DAYS FAVORABLE FOR TAN SPOT INFECTION

The NDSU Wheat Disease Forecasting web site is now operational for the season. The web address is:

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

Dr. Shaukat Ali and Dr. Tika Adhikari of the NDSU Plant Pathology Dept. are responsible for maintaining this web site.

Predictions are now available for risk of fungal infections that cause tan spot, Septoria leaf blotch, and leaf rust. Fusarium head blight (scab) forecasts will also be available as the crops approach flowering. Disease forecasting at this site is based on models using weather data downloaded hourly from the NDAWN weather stations. A user of this web site needs to pick the closest NDAWN station and the growth stage, and then will get a prediction of which days within the past thirteen days were favorable for infection. At early leaf stages, a user of this site should pick the "flagging" leaf stage, as this is the earliest leaf stage indicated.

For example: on May 16th at the Prosper location of the NDAWN weather sites, the disease forecasting web site indicates that 5 days within the last 10 days had a Yes. The Yes means the weather on those 5 days was favorable for tan spot infection. Some other NDAWN sites across the state had less rainfall recently and had fewer days that were favorable for tan spot infection.

 

CEREAL RUST DEVELOPMENT - SOUTHERN PLAINS

The 5thd edition (May 16) of the Cereal Rust Bulletin (USDA/ARS - St. Paul, MN) indicates that wheat leaf rust is widespread but at low severity levels in winter wheat fields from north central Texas to south central Kansas. Drier than normal conditions in late April and early May in these regions slowed leaf rust development, but recent rainfalls in those areas will increase leaf rust infections and provide some inoculum for our wheat. Wheat stripe rust is not being reported from Kansas or Oklahoma.

Dr. Bob Hunger, Plant Pathologist in Oklahoma, reported on May 13th that wheat leaf rust was present on susceptible cultivars in Oklahoma, but levels were too low and the crop was too advanced to cause any significant losses. He reported that barley yellow dwarf virus was still the most common disease present in winter wheat in his state.

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

 

USE POWDERY MILDEW RESISTANT PEAS WHEN PLANTING LATE

Research from trials conducted at NDSU Research Extension Centers has shown that dry peas planted later than normal may have a greater chance of suffering losses from powdery mildew, a fungal disease of pea. Although foliar fungicides are available that control powdery mildew on pea, resistant varieties are the most economical way to control the disease. Several yellow cotyledon varieties have resistance to powdery mildew, and a few green cotyledon varieties also have resistance. Below is a partial list of powdery mildew resistant dry pea varieties:

Yellow cotyledon
-AC Melfort
-AC Minuet
-AC Miser
-CDC Bronco
-CDC Golden
-CDC Handel
-CDC Mozart
-CDC Sonata
-Cutlass
DS Admiral
DS Stalwarth
Eclipse
Highlight
SW Carousel
SW Midas
SW Salute
Topeka
Tudor
Green cotyledon
AC Advantage
Bluebird
Camry
CDC Montero
Cooper
Stratus
SW Parade

 

CERTIFIED SEED IS FIRST LINE OF DEFENSE AGAINST ANTHRACNOSE AND BACTERIAL BLIGHTS OF DRY BEAN

Anthracnose and bacterial blights are diseases that can reduce the yield and quality of dry beans grown in North Dakota. Because these diseases are readily seedborne, the first line of defense is the use of certified seed. Certified seed relies on field inspections and seed assays to monitor for diseases. No fungicide seed treatments are registered in the United States that can eradicate seedborne Anthracnose infections. Streptomycin sulfate is registered for control of bacterial blights on the seed surface of dry bean, but cannot eradicate internal infections. In addition to certified seed, crop rotations are important in reducing the population of these pathogens in the fields.

Carl A. Bradley
Extension Plant Pathologist
Carl.bradley@ndsu.edu  

 

PLANT DIAGNOSTIC LAB UPDATE

Wheat samples, both spring and winter types, are beginning to arrive at the plant diagnostic lab. Environmental injury was noted on one winter wheat sample (no pathogen was detected). Another winter wheat sample had symptoms of tan spot. It also appeared to have symptoms consistent with wheat streak mosaic virus. Testing is underway to verify the presence of the virus.

Root injury due to wet conditions was determined to be the probable cause of symptoms on a recently-submitted spruce sample from a relatively newly planted row in a wind break (based on images only). Turf samples continue to arrive in the lab. Necrotic ring spot was diagnosed on one sample. Another sample appeared to be infected with Fusarium patch. Excessive thatch layers probably contributed to both disease problems.

Kasia Kinzer
NDSU Plant Diagnostic Lab
diaglab@ndsuext.nodak.edu
http://www.ag.ndsu.nodak.edu/diaglab
701-231-7854
206 Waldron Hall, PO Box 5012
Fargo, North Dakota 58105


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