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Disease Watch 2016 3rd Edition

Arable Fungicides Disease Watch Bayer

Welcome to Disease watch, a season long programme designed to keep you informed and ready to tackle diseases invading arable farms around the country.

14 November 2016 - Developing disease & what to look out for

Welcome to the latest edition of Disease watch, a season long programme designed to keep you informed and ready to tackle diseases invading arable farms around the country.

After reviewing the latest findings from the Bayer Sales and Development teams, it is apparent that there is an aggressive development of Septoria leaf blotch and wheat leaf rust on the lower North Island. In Canterbury, the ones to watch are Ramularia leaf spot and scald. Find out what the disease threat looks like in your region below.

Aorangi-Septoria

Wheat - Lower North Island

A recent trip to the Bayer fungicide trial at the Aorangi Plant and Food Centre near to Fielding revealed that Septoria leaf spot had been developing rapidly during the past three weeks. Where left uncontrolled, Septoria is now severely affecting the flag leaf with leaf two already almost dead.

Considering these leaves account for 70% of yield production we expect the Aviator® Xpro programmes we are testing to deliver very profitable returns.

Image: Septoria aggressively infecting wheat at Aorangi Research Centre. Note that leaf 2 has been very severely affected.

Leaf rust is also developing quickly. In fact, due to the very heavy rain experienced in the Manawatu recently, a lot of the leaf rust spores have been washed off making the disease harder to see. But don’t be fooled, it is still there and will recover.

Interestingly, the Bayer team came across some symptoms that had them scratching their heads; a general yellowing in patches, but without recognisable symptoms - see photographs below. This was later identified as the over wintering stage of leaf rust - occurring in November!

Leaf Rust

To ensure that your crops are protected apply Aviator Xpro now at GS39-45. Then, to ensure you don’t get caught out by leaf rust infecting during December, follow up with an application of Proline® + a strobilurin fungicide or Prosaro® + a strobilurin fungicide at full ear emergence.

Illustrated below is the performance of Aviator Xpro. Contrast a two spray Aviator Xpro programme where the flag leaf is very healthy and fully intercepting sunlight for yield production with untreated crop where the flag leaves are already losing green leaf area to Septoria leaf blotch infection.

Sporulating Septoria Aviator Xpro

Image above (left): untreated wheat with Septoria infecting the flag leaf. Image above (right): crop treated with Aviator Xpro at GS31-32 and GS39.

Barley- Mid-South Canterbury

2016 is proving to be an interesting year in this part of the world for barley growers. Scald has been present all spring and has continued to develop when not adequately treated. The surprise has been the amount of net blotch present and the early development of Ramularia leaf spot. In addition powdery mildew can be found.

The fungicide approach you take to control these diseases will vary depending on whether you are treating winter planted barley now at ear emergence or spring barley now which will be around the end tillering to GS30.

Image right: Net blotch developing on spring barley. Bayer SeedGrowth trial, Lincoln.

Spring Barley infected with net blotch
Ramularia leaf spot

Image: Ramularia leaf spot developing during October in South Canterbury.

For winter barley most crops will have received their GS39 application and this will help protect against scald, net blotch and Ramularia leaf spot.

If powdery mildew is present, it is likely to be in the base of the crop and is unlikely to now cause economic yield losses.

The question is, should a later application of Aviator Xpro be made?

This can be justified for high yield potential crops as this application, which can be made until 56 days prior to harvest, will help suppress Ramularia.

Ramularia leaf spot

Image: Ramularia leaf spot, disease in the early stages of establishment. Mid-Canterbury November 2016.

Now is the important time to apply a fungicide to spring barley as the open nature of the crop means the lower leaves are important for yield production. As the target at this time is largely scald and net blotch, an application of Delaro® will fit the bill.

This should then be followed with an application of Aviator Xpro at GS37-39.

Last edition's mystery photo:
In the last edition, the Bayer team was puzzling over a disease that was difficult to identify. Before sending it away for testing, we predicted that it might be a mixture of net blotch and physiological leaf spotting.

The lab results are in and the mystery has been solved. If you suspected it was the spot form of net blotch, you'd be right.

Let us know what you think this edition's mystery photograph might be.

Image: Last edition's mystery photo.

Image below: this week’s mystery photograph. Is it Ramularia leaf spot? We will know soon as it is being identified.

Net blotch - spot form
mystery disease

Southland scald

Wheat and Barley - Southland

Like other parts of the South Island, scald is developing rapidly in both wheat and barley throughout Central Otago and Southland.

Treatment options are outlined throughout this Disease watch update, just make sure that the growth stage of the crop matches the treatment plan.

Image: Very aggressive scald attack on an untreated barley crop in Southland.


Wheat - Mid-South Canterbury

Septoria leaf blotch is present in many crops but at present is mainly on the lower leaves. However, the prevailing changeable weather is ideal for disease transfer and development so growers will need to remain vigilant.

Now is the time to ensure you do not let Septoria develop from the bottom of your crops. If you do, yields will suffer as there is a very long time between now and harvest.

Image below: While Septoria leaf spot can easily be seen in the crop, at the moment it is confined to the lower leaves. Without adequate control now, it is poised to spread quickly.

Septoria leaf blotch in lower leaves

Image below (left): Now an uncommon disease to find, stripe rust is still present in Canterbury and will continue to attack if left unprotected. Image below (right): An impressive infection by powdery mildew.

Stripe rust Powdery Mildew

Images below: Take-all symptoms, characterised by blackened stem bases and roots and stunted patches in the crop are now starting to show. (These photos were actually taken on the lower North Island 9-11-16).

Blackened stem bases

Image below (left): Sharp eyespot is a stem base disease caused a soil dwelling fungus. Unless the infection level is very high sharp eyespot doesn’t result in dramatic yield losses Image below (right): Stem base browning, caused by the pathogen Monographella nivalis, can be difficult to conclusively identify without microscopic identification.

Stem base browning