ISSUE 6   June 14, 2007

BACTERIAL SYMPTOMS SEEN IN SOME WHEAT FIELDS

Some winter wheat crops are showing symptoms typical of bacterial stripe (blight) infections. The flag leaves are showing dark brown streaks, with a water- soaked edge, and in some cases, the dried bacteria are also evident on the leaf surface, appearing as shiny residue. The following figures are various types of symptoms seen:

Bacterial blight on leaf bacterial blight on leaf
bacterial leaf blight (stripe)

Bacterial infections also have been seen in some spring wheat crops, evidenced as a leaf tip browning that is obvious once the bacterial infections dry up. The leaves look wind-whipped, but bacterial infection has been confirmed in some fields.

Bacterial infections of wheat leaves often are seen following wind-driven rains. The wind-whipped tissue and particles moving with the wind create tiny wounds that allow the bacteria to enter and infect during the rainy periods.

Fungicide applications will not control bacterial infections. Generally, damage due to bacterial blight is minimal once the weather turns sunny and dry. Bacterial infections may continue, however, under prolonged periods of wet, windy weather.

 

NDSU IPM CROP SURVEY

The NDSU scouts examined 151 wheat fields last week across all parts of the state; 21 fields were winter wheat and 130 were spring wheat or durum. Winter wheat fields were in the late jointing to heading stage, and spring wheats were in the one leaf to jointing stages.

Tan spot leaf infection was observed in 87% of the fields surveyed, with high severities observed in winter wheat fields. Leaf rust was observed in 20.5% of the fields surveyed, and average severity of leaf rust ranged from 1-6% in symptomatic fields. Grain aphids were most abundant in observations in Cass and Richland counties, with up to 33% of tillers having at least one aphid.

 

CEREAL RUST BULLETIN UPDATE

The June 12th edition of the USDA’s Cereal Rust Bulletin indicates that wheat leaf rust is widespread throughout the Great Plains, with high severities in winter wheat in Nebraska and becoming increasingly severe in southern South Dakota winter wheat. Stripe rust also has developed in the central Plains, but to a lesser extent. Night time temperatures need to stay below 65 degrees to allow additional development of stripe rust. Oat crown rust has been observed in a field in Minnesota and is increasing on spreader rows in nurseries at St. Paul, MN. Barley rusts currently are not being reported in the Plains states.

 

NEW PUBLICATION ON AERIAL APPLICATION OF FUNGICIDE

The NDSU Extension Service has recently published a new circular titled Aerial Application of Fungicide for the Suppression of Fusarium Head Blight (FHB) in Small Grains. The publication number is AE-1327, and may be viewed on-line at:

http://www.ag.ndsu.edu/pubs/plantsci/pests/ae1327.htm

This publication provides recommendations for fungicide application techniques for FHB suppression when using aerial application. The recommendations are based on research work done through regional aerial application trials in recent years, work supported by the US Dept. of Agriculture as a cooperative project of the US Wheat and Barley Scab Initiative. Six individuals from four states co-authored the publication, with Vern Hofman, retired NDSU Extension Ag. Engineer, as the first author.

Marcia McMullen
Ext. Plant Pathologist
marcia.mcmullen@ndsu.edu

 

GROWTH STAGING SMALL GRAINS FOR FUNGICIDE TIMING FOR SCAB CONTROL

Research has shown that fungicides can be effective in reducing Fusarium Head Blight (Scab) severity and vomitoxin (DON) in small grains when conditions are favorable for scab development and if applied in a timely manner. Winter wheat has reached or is fast approaching the optimum stage for applying fungicide for scab control. The intent of this article is to describe when to apply fungicides for optimal scab control in wheat and barley.

Timing in wheat

The optimum growth stage for applying fungicide for scab control in wheat, the Feekes 10.51 stage, is the same for all classes of wheat (winter, spring and durum). The Feekes growth staging system is used as it describes development from spike emergence to graining-filling in more detail than other systems and is summarized in the following table. In wheat, the scab fungus causes the most damage when it infects the floret during pollination. Applying fungicide during early flowering helps to protect vulnerable florets during fertilization and early grain-filling. The center spike in the following photo is at the ideal stage for applying fungicide. The spike on the left has emerged from the boot, but has not yet started to flower (note that there are no visible anthers extruded from the glumes). The spike on the right is past the optimum stage. Note that the anthers are bleached and dried, unlike the turgid, yellow anthers in the center spike. The length of time from head emergence to the beginning of flowering is temperature dependent, but usually takes about three days. Experience has shown that it is better to apply fungicide too early rather than too late, so the beginning of heading is a good trigger to indicate when to get serious about spaying for scab in wheat.

Durum heads

Feekes scale values described from the start of heading to early grain filling

Scale

Description

10.1

First spikelet of head just visible

10.2

One-fourth of head emerged

10.3

One-half of head emerged

10.4

Three-fourths of head emerged

10.5

Head emergence complete

10.5.1

Beginning of flowering (for wheat)

10.5.2

Half of florets have flowered

10.5.3

Flowering complete

10.5.4

Kernel watery ripe

Timing in barley

Flowering in barley begins just before head emergence, so barley florets are not overly susceptible to scab infection. Scab infections do not generally impact yield. The scab fungus, however, is able to infect the glumes and produce DON which impacts the value of the grain in the market. The optimum stage for applying fungicides to protect the glumes of barley from infection is when the spike is fully emerged from the boot (Feekes 10.5). The spike third from the left demonstrates the optimum stage, with those further to the left too early and the one on the right approaching too late. With barley the appearance of the first spikelet from the boot is a good indication that the best stage for spraying is only a few days away.

Barley heads

Joel Ransom
Extension Agronomist
Joel.ransom@ndsu.edu

Marcia McMullen
Extension Plant Pathologist
Marcia.mcmullen@ndsu.edu

 

DOWNY MILDEW ON SUNFLOWER PHOTOS

Last week, three photos were accidentally omitted from the report on Downy Mildew.

downy mildew

Symptoms of systemic downy mildew include stunting and distorted growth.

downy mildew

Foliar symptoms of systemic downy mildew include yellowing leaves and chlorosis (yellowing) along leaf veins on the upper side of the leaf, and a white cottony growth on the underside of the leaf.

downy mildew

Symptoms of non-systemic downy mildew (also called secondary infection or local lesions) include local chlorotic lesions on the upper side of the leaf surface and white spores on the underneath. These lesions are caused when spores blow in the air and land on the leaves and cause infection. Unlike systemic infection, symptoms do not appear to radiate from leaf veins.

(Photos by Tom Gulya)

Sam Markell
Extension Plant Pathologist
samuel.markell@ndsu.edu

Tom Gulya
Sunflower Pathologist USDA-ARS
Thomas.Gulya@ARS.USDA.GOV

 

WET WEATHER MAY FAVOR ROOT ROTS

Rains in the last few weeks may favor root rot development in many crops. Root rots are commonly caused by multiple species of fungi, including Phytophthora, Pythium, Aphanomyces, Fusarium and Rhizoctonia. Root rot pathogens are often soil borne and/or seed borne, and can survive in the soil for several years. Infection takes place when roots come into contact with the pathogens.

Symptoms vary among crops, but damping off, wilt, and yield loss often occur in wet years. Control of root rotting pathogens requires an integrated approach. Crop rotation provides some control from virtually all root rotting pathogens, resistant varieties are available in some crops, and certified seed can limit seed borne infection. Seed treatments are registered for many crops, but because two different types of fungi cause root rots, many chemicals control only Pythium, Phytophthora, and Aphanomyces, OR Fusarium and Rhizoctonia, but not both. Seed treatments with a combination of chemicals conferring activity against both groups of fungi give you the broadest spectrum of control.

Although most seed is in the ground this year, it is time to think about control in the future. Because many root rot pathogens survive in the soil, the possibility of root rots re-appearing in fields is a concern. Preventative control measures will likely pay off in the future, especially if there are other wet springs.

Sam Markell
Extension Plant Pathologist
Samuel.markell@ndsu.edu


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