Posts Tagged ‘spot blotch and net blotch’

Barley Leafspot Diseases

Friday, April 8th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

As you scout your fields at this time of year it is often easy to find scattered brown spots in barley. Sometimes in wheat and rarely in barley, a minor disease called Ascocyta leafspot can be found on winter damaged tissue that can resemble Septoria leafspot but the plants grow out of it once warm weather arrives. The other brown spot that can be seen now is the early symptoms of net blotch. This is a very common leafspot of barley in our region. Severity is determined by the weather (it likes cool and wet) and the susceptibility of the variety. High nitrogen fertilization early will also favor development. Spot blotch rarely gets severe enough here to warrant fungicide applications. The symptoms that develop on barley can vary depending on the variety of the fungus present (there are several forms or isolates of this fungus) and the barley genetics. Later in the season we see the spot blotch form of net blotch (two leaves on the left) more frequently than the classic net blotch symptom seen on the two leaves on the right in the picture below.

Two leaves on left- spot blotch form of net blotch, on the right classic net blotch symptoms

Sometimes the only symptom development is a small brown spot or fleck that never enlarges or blights a leaf. This is thought to be the barley resistant reaction to the fungus infection.

The picture above, taken two days ago, shows the early symptoms on leaves before jointing has occurred. Typically, as the season warms the older infected leaves at the base of the plants will die and the new leaves may or may not develop more symptoms depending on the weather.

Scout Barley for Disease

Thursday, April 15th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Scouting barley regularly is important to monitor for diseases such as powdery mildew and spot blotch, especially in ‘Thoroughbred’. This variety has great yield potential but is very susceptible to powdery mildew and the disease has been yield limiting. Fungicide applications may be warranted if enough disease is present and yield potential is high. Most other varieties would not likely respond to fungicide control of powdery mildew and/or spot blotch unless disease occurrence was very high.

Small Grain Diseases

Friday, May 2nd, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Barley
Several diseases are present at this time. Powdery mildew, which we had reported earlier, seems to be found primarily on the variety ‘Thoroughbred‘. The spot blotch form of net blotch is also present in some varieties at low levels that should not affect yields. The latest “new” disease that appeared at heading is loose smut. This fungus is present in the seeds at planting and grows with the germinating plant and systemically infects the head and replaces the seed with its dark brown spore masses. Grain harvested from infected fields should not be used for seed unless it is treated with a systemic fungicide such as Baytan, Dividend, and Raxil. Because the spore masses weather and are absent during harvest the fungus does not cause surface contamination of the harvested grain so the feed value is not affected. Plant certified smut free seed and/or treat with a fungicide for loose smut control.

 

Loose smut of barley caused by Ustilago nuda

 Spot blotch and net blotch

Spot blotch on left two leaves, net blotch on right two leaves

 

Barley scald caused by a fungus Rhynchosporium secalis.

The last disease that I am seeing in barley is scald. This disease overwinters in old barley debris or can be seed borne. Look for the water-soaked gray-green spots that appear initially. As the lesion the dries out the center becomes bleached then tan with a brown margin (see photo). Some lesions can be very large and several spots can merge and kill the leaf. Rotation and use of resistant varieties is the best control method.

Wheat
Powdery mildew is still the most prevalent disease present. Continue to scout and remember that the end of flowering is the last opportunity to apply a fungicide for control. We have not confirmed it yet but I believe we have seen barley yellow dwarf mosaic virus (BYDMV) in wheat this week. A late fall infection or early spring infection produces symptoms of off-color wheat, which may be stunted in varying degrees, as well as red-purple flag leaves (the uppermost leaf). Since this virus is aphid transmitted, fields that are early planted or have had high aphid infestations are the most at risk. The later the infection occurs the less the effect on yield. Aphid control, including seed treatments, may prevent BYDMV as well as avoiding early planting.

 

Barley yellow dwarf causing reddened flag leaves

Flowering has begun for many wheat fields due to the warm weather last week. The remainder will be flowering in the next week or two. If you want to check the Scab Forecasting website visit: http://www.wheatscab.psu.edu/ for more info. Right now the risk for scab statewide for the next 48 hours is low.