New fungicides and new opportunities

The introduction of two new strobilurin fungicides for 2002 broadens the choice of products but does not change the approach to cereals disease control. While both Acanto and F500 raise overall disease control expectations, they should not radically alter the approach to disease prevention and control. There seems little doubt that growers will benefit from this new chemistry, but it comes at a cost, and it is important to remember that the older strobilurins have not lost their effectiveness or benefits. However, they have been surpassed to some degree. In this article, Dr Tom McCabe, of UCD, Lyons Estate, outlines his experiences with the different products and where they fit into good farm practice.

In recent years, new fungicide introductions have contributed to very significant advancements in yield and quality in cereal production in Ireland. They have resulted in practical and tangible benefits for cereal farmers. They have also increased the consistency of high yielding wheat and barley crops and have contributed to higher profitability.

The introduction of these new fungicides has generally been well anticipated in advance of their commercial launch. While Opus was not available commercially until 1996, its arrival was heralded by its stunning performance in winter wheat trials in 1993.

Similarly, the introduction of the first strobilurin fungicide, Amistar, in 1997, indicated that a new era in cereal fungicide use and performance was emerging. Growers looked forward enthusiastically and were innovative in the use of these new products.

The subsequent introduction of both Allegro and Twist have made available to farmers a range of fungicides that offer excellent strob-based fungicide treatments at each of the key application timings on cereal crops.

There can be little doubt that the changes in recent years have been very significant in terms of their effect on cereal disease control capability in this industry. In this context, it is perhaps understandable if farmers view the introduction of two more new strobilurin fungicides this year with somewhat less anticipation than seen on previous occasions.

Acanto and F500 mixes - new standards

These two new strobilurin actives bring new standards in the efficacy of control of some key cereal diseases. Picoxystrobin (Acanto) provides a new standard for net blotch control in barley while the pyraclostrobin (F500) products provide a new standard for Septoria tritici control in wheat.

Another big consideration with these two new actives  often referred to as second-generation strobilurins ö is that they offer both curative as well as protectant control properties against these two key diseases. Hence, these products will bring more choice into the strobilurin fungicide market whilst also offering more flexibility in the use of fungicides over the season. This is especially true with regard to application timing and the intervals between applications.

Both of these products have been very well tested under Irish conditions. Acanto has been in UCD trials for five seasons (1997-2001) and F500 products in UCD trials for the past four years. Over this time, the performance of these two fungicide actives has been impressive.

Picoxy

Acanto contains straight picoxystrobin, a new strobilurin fungicide with some interesting properties. Amongst these are its excellent movement and redistribution characteristics within the plant. It is being marketed by Syngenta as is Amistar  but Acanto is a big step forward in that it has very useful curative properties. It has an excellent profile for control of a range of key barley diseases and has performed very well from both early-season and late-season applications, indicating its flexibility and versatility. Acanto gave excellent performance on spring barley at Lyons in 1997 and 1998 under very high disease pressure.

It also gave a useful reduction in necrotic blotching on the extremely blotching-prone variety, Cooper. In these early trials, Acanto seemed to be the first strobilurin fungicide that had enough activity and a sufficiently broad spectrum of disease control to be used alone. But experiences over the past three seasons indicate that it will perform much better in combination with other fungicide products, specifically with key triazole fungicides.

Acanto provides a new standard for net blotch control on barley. This is done through its excellent curative and protectant activity. Over the last two seasons, in both winter and spring barley trials, it is obvious that crop performance has been consistently enhanced from Acanto-based programmes, where highly active triazole fungicides were used as partner products. The most consistent treatment in this regard has been Acanto plus Opus. But, on barley, rhynchosporium remains a key disease, and control capability has not been significantly enhanced. So where either Acanto-based treatments or F500-based treatments are being used for rhyncosporium control, application timing is of critical importance. The strobilurin component of the mixture is much more effective when used preventatively, with the triazole partner providing the key curative control properties.

On winter wheat, Acanto offers effective early season disease control, with septoria tritici control being a notable strength of the product.

But mixing with a suitable triazole fungicide is critical at this timing. In the field, excellent lower canopy green leaf retention has been a notable feature of the product for applications up to GS 33. It is also important to be aware of the fact that rhynchosporium control capability with the best chemistry is lower than with most other diseases. In fact, potential control of rhynchosporium from current fungicides is in the 70 to 80 per cent range, while most other disease are in the 90 per cent plus bracket.

Another point to remember is that the duration of this control is in the three to four-week range for all product combinations (strobilurins and triazoles) under high disease pressure. So, when rhynchosporium pressure is high, the chemistry needs to be worked hard.

F500 or Modem

The F500 chemistry comes from the new strobilurin active, pyraclostrobin, and is being offered in three separate products. These are Modem (F500 alone), Opera (F500 plus Opus) and Covershield (F500 plus Allegro). As with Acanto, F500 is also characterised by its combined curative as well as protectant activity against specific diseases.

In barley, this product range offers an excellent control spectrum of key diseases and is a significant advance on Allegro, especially for net blotch control. However, the F500 products receive most attention in relation to their efficacy on key wheat diseases, specifically Septoria tritici.

Trial studies at UCD in 2000 showed excellent control of Septoria tritici from Opera and Covershield under high disease pressure. These trials were conducted on both Consort and Savannah and they also indicated that there is more rate flexibility in disease control from these new fungicides than with Allegro. Results show excellent S. tritici control from a two-spray programme comparison of Opera and Allegro. Here, 50 per cent (0.75 l/ha) and 75 per cent (1,125 l/ha) rates of Opera were compared with equivalent rates of Allegro (0.5 l/ha and 0.75 l/ha, respectively). Where Opera was used, septoria tritici levels were substantially lower.

The experience has been that the F500 products are most effective at the mid-season or flag leaf timing. This is in terms of disease control, green leaf retention and overall grain yield response.

The trials at UCD indicate that this chemistry offers an enhanced strobilurin yield response effect of up to 0.5 t/ha over an Allegro standard. A key winter wheat trial in north Dublin in 2001 provided evidence of the high yield response effects that the F500 products can deliver.

Straight strobilurins or triazole mixes?

The introduction of Modem (pyraclostrobin) is an interesting move by BASF as it is the first strobilurin product offered commercially by the company without a triazole/morpholine partner in the mixture.

It is also of interest technically as the product has very good curative control of Septoria tritici and, therefore, it begs the question: Does the product need a triazole partner? The answer is clearly yes, since the use of two chemistries, strobilurin and triazole, gives much more consistent and robust control of Septoria tritici.

Control of other key diseases, such as Yellow Rust, will be greatly enhanced by tank mixing.

With regard to Septoria tritici control, the benefit of a tank mix will be most evident under a high disease pressure situation.

Trials at UCD in 1998, in a very wet summer with conditions very conducive to the spread of Septoria, showed that the triazole fungicides were critical to achieving high levels of disease control on a consistent basis. This is because successful Septoria tritici control necessitates curative fungicide effects as well as duration of control; i.e. the persistence of the fungicidal effect is all important.

Trials have shown that appropriate strobilurin plus triazole mixtures offer much more persistence than either chemical applied alone. Mixes also help prevent resistance development.

Is there room for the 'old' and the 'new' strobs?

The introduction of these two new strobilurin fungicide actives brings the total number of strobilurin fungicides commercially available to five.

This offers a lot of choice to farmers and advisers with regard to choosing the best product for any situation. Twist (trifloxystrobin) is the currently available strobilurin that will most challenge the two new products for the key early and mid-season fungicide treatments.

Twist has shown very consistent trial performance over the last two seasons. It has proven itself as a strong contender for the control of key wet weather diseases such as Septoria tritici and net blotch. But, as is the case for the new strobilurins, the triazole partner product is very important.

Where a suitable partner is used with Twist it has provided excellent disease control and yield response effects on winter wheat and spring barley.

Allegro and Amistar still have clear strengths and niches for usage in the future. Allegro is an excellent and very cost effective early-season product on wheat, delivering strobilurin effects at minimum cost. But, its flag leaf timing strength over the past few seasons is now clearly superseded by the introduction of Opera.

On barley, Allegro will continue to be a key product option, specifically with regard to dose and timing flexibility. It also offers as high an efficacy on mildew as any of the other strobilurin fungicides, and at a lower cost.

Amistar is still an excellent product for late-season use on both wheat and barley crops. On wheat, the product combines excellent protectant activity against S. tritici with sooty mould control and crop colour effects. These are comparable/superior to any other strobilurin fungicide. It also provides very good control of Microdochium nivale but needs to be mixed with tebuconazole or metconazole for activity against fusarium species.

On barley, Amistar combines excellent net blotch control with sooty mould control, which is better than most other strobilurins.

Home | About | Search | Help | Contact Us