12 April 2002

Dry weather helps to keep control of barley diseases

Net blotch and

rhynchosporium can be

found in most winter barley

crops. But recent dry

weather will have helped to

ease disease pressure, as

our latest baseline advice

article reports

AS GROWERS make the first of two planned fungicide applications to barley crops, ADAS consultant David Parish reminds them that most fungicides used are protectant in their activity.

"Its important to go early with these materials. Being on top of the situation is essential, especially if you are dealing with rhynchosporium and net blotch."

He adds that a two-spray disease control programme will give the most cost-effective response in barley, with the first application going on at GS30-31. "Thats now in most crops. The first spray gives the best yield response, so dont miss this timing."

Barley diseases

Eyespot is likely to be present in winter barley crops and is often difficult to identify, warns Mr Parish.

"Its under-rated in barley and is not obviously visible without close inspection. As barley tends to be grown in a second cereal situation and drilled in September, it is vulnerable."

Rhynchosporium and net blotch, classed as the wet weather diseases, will be present on crops. "Plants have come through the winter with them. The key with both is to prevent them getting established."

Mildew is also around. "It dries up when temperatures get above 25C. So although its been dry, it hasnt been warm enough to slow down mildew yet."

Brown rust comes into crops later in the season and is favoured by warm conditions. "Its especially a problem in East Anglia. Growers must protect the awns where this disease threatens, as they account for 25% of light interception."

Spray programmes

The best approach is to spray at GS30-31 and again at flag leaf/ear emergence, advises Mr Parish.

"The second application doesnt always give the same yield response as the first, but it is very important in a brown rust year."

Disease severity should dictate how early the first application is made. "Theres a case for going even earlier if net blotch and rhynchosporium have got a hold."

Fungicide choice

Strobilurins should feature at both timings, believes Mr Parish. "Weve seen enough evidence of their activity in barley to be persuaded to use them twice."

Twist (trifloxystrobin) and Acanto (picoxystrobin) are the best fungicides available on rhynchosporium, and will also control net blotch. Amistar (azoxystrobin) is especially suited to the second timing for the control of brown rust.

"And Opera (pyraclostrobin) and Landmark (kresoxim-methyl) are also useful. Its a case of using the best product for the disease spectrum present."

Away from the strobilurins, Unix (cyprodinil) is his first choice for eyespot. "It also has activity against rhynchosporium, net blotch and mildew. So its an excellent partner product for the first timing."

Where eradicant activity is needed, epoxiconazole (Opus) is considered the best of the triazoles. "Again, there are a number of reasonable triazoles, depending on the situation. Use the right rate for the disease pressure."

Mr Parish reminds growers that the strobilurins are losing their activity against mildew. "This does apply now to barley mildew, as well as wheat. So use quinoxyfen or a morpholine where you need to control mildew."

Likewise, a reduction in the activity of triazoles on rhynchosporium means that a strobilurin must be used to target it. "Rhynchosporium is the most difficult disease to control. The key is to get ahead of it, rather than letting it get established." &#42

Good news for growers… Winter barleys should be easiers to keep clean this season, thanks to dry conditions at the crucial first spray timing, says Beds-based David Parish of ADAS.

1 Eyespot Often missed and difficult to identify. Unix will give good control.

2 Rhynchosporium Crops have the disease from the winter, aim to get ahead of it rather than have to control it. Triazoles losing their activity, so use a strobilurin.

3 Net Blotch Another wet weather disease already present.

4 Mildew Need temperatures above 25C to dry it up. Strobilurins should be avoided, use quinoxyfen or a morpholine.

5 Brown Rust Comes in later in the season in warm weather. East Anglian crops at highest risk.

6 Spray Timings Spray at GS30/31 and again at flag leaf/ear emerging. First spray gives greatest yield response.

7 Awns Account for 25% of light interception, so protect where brown rust is likely.

8 Strobilurins Use at both timings for yield response and unrivalled disease control.

9 Variety Consider strengths and weaknesses. Around half the area is in Pearl.

10 Disease Pressure Recent dry weather will have helped to ease disease pressure.