Farm Ireland
Independent.ie

Thursday 8 December 2016

Create an efficient chemical strategy to increase returns

Extensive homework on fungicide timings and prices will help to achieve better yields and income

Michael Hennessy

Published 13/04/2010 | 05:00

Physical pain is often associated with running a marathon. Getting through the pain barrier is necessary for most novice marathon runners in order to complete the run.

  • Go To

It may not be quite the same thing but fungicides are the last input to be applied to cereals, and growers can often feel some psychological pain when loading the car/jeep with fungicides for the final time. But, in the same manner, the application of this input is necessary to get over the finish line -- hopefully with some profit.

The return from fungicides can vary quite wildly from year to year. However, in trials and in the field, an average return of at least two to two-and-a-half times the cost of the fungicide can be expected. So a well-timed and priced fungicide programme will pay handsomely.

Tillage growers are locked in a battle with various diseases to keep them from destroying yields. These diseases are a moving target in terms of their genetic makeup.

When a grower goes to a field to apply a broad-range fungicide, not only is the fungicide trying to control three or four diseases, it is also trying to control a range of genetically different fungi within each disease species. Fungi produce numerous cycles of spores during a season and this allows mutations to occur and multiply. This enables the organism to continually evolve to the challenges put in front of it. For our part, repeated applications of fungicides will continually control fungi, which are easily killed (very sensitive) but will also select for fungi which are not so easily killed (insensitive). Different groups of fungicides have different modes of action, or the fungicide targets different processes in the fungi to prevent growth/multiplication. This is why the use of different modes of action is important so that the fungus is hit from several different angles to prevent resistance -- or to at least slow the build-up of resistance as much as possible.

Changes in the septoria population have been tracked by Teagasc in Oak Park and by other organisations throughout Europe. Similar septoria strains have been found across Europe but the frequency of individual strains is different from one country to the next. Triazoles (eg, Opus and Proline) are our main defence against septoria. These chemicals work by interrupting the production of the fungal-cell membrane. The target-site protein involved is controlled by a gene called CYP51, and this has various mutations or slight changes which are influencing the effectiveness of triazoles on septoria. This gradual process of increased insensitivity (or septoria being harder to control) has been ongoing since the introduction of triazoles.

Teagasc researchers found a new strain of septoria in 2008, which had reduced sensitivity in laboratory tests to prothioconazole (Proline) and to a lesser extent epoxiconazole (eg Opus Max). More laboratory tests and field trials last year confirmed that this strain was increasing in frequency at some sites, but information is limited due to the recent development of the new strains.

However, initial results indicate that field performance of prothioconazole and epoxiconazole appear to have been affected where this new septoria strain is prevalent in terms of immediate disease control and also persistence of disease control. The new strain of septoria is sensitive to tebuconazole (eg Folicur) and metconazole (Caramba) so these actives may have a role in reducing the selection pressure for this new strain as well as ensuring good levels of disease control.

Also Read


Generally speaking, metconazole is seen as a stronger septoria product than tebuconazole. Therefore, Teagasc believes that high levels of disease control can still be achieved through the use of sequences of different triazoles applied with a suitable mixer partner (eg, Bravo or Boscalid) or mixes of two different triazoles applied as pre- formulated products (eg, Gleam or Prosaro). Spray timing and intervals between timings will be critical to ensuring maximum efficacy from products selected.

There was limited barley disease sampling in Ireland over the past two years. The results have shown a small shift in net blotch populations, but this shift is expected to have a negligible effect on the effectiveness of strobs this year. Researchers in Scotland have also found a shift in rhynchosporium populations, which may also be an issue in Ireland in the future.

Up to now we thought we had the upper hand in the challenge with cereal diseases but, as we can see, the goal posts are continually shifting. The next part of the jigsaw is how much can we afford to spend on fungicides while achieving good disease control and also making a good return on the fungicide spend?

Most growers last year probably just broke even, while those renting land incurred a significant loss. Apart from an increased value for straw last year, the entire industry was in trouble. This year's margins are probably even tighter then last year and high yields must be achieved just to break even.

Increasing yields or decreasing costs -- or a combination of both -- is necessary to maintain any sort of margin. Fungicides have a part to play in this mix. Targeting an overall fungicide spend per crop, restricting applications to only where necessary and shopping around for the best price should be employed by all growers.

Set yourself a challenging target spend for fungicides this year. In unusually wet years, programmes may have to change but this should not stop the construction of a challenging budget based on a normal weather year.

Teagasc produces figures on the cost of fungicides for all major cereals, which many growers take as benchmark costs. However, there is plenty of insurance built into these figures and growers should be capable of cutting total costs by 10-15pc (see Table A).

Yield responses from fungicides are generally quite good, with the average yield response in winter wheat at 4t/ha. Yield responses at individual timings can vary and responses over untreated crops in winter wheat range from 13pc at T1 to 20pc at T2 and 7pc at T3 timings. In general terms, the higher the disease challenge the higher the yield response.

As you can see from tables 1 and 2 (left) and 3 (right) there is an impressive array of chemicals that can be bought this year. Granted, not all of these chemicals are available in the merchant as distributors have successfully implemented market segmentation. This is not restrictive in terms of access to the important active ingredients at local level, but it makes price comparisons difficult.

Mixtures of different chemical groups can be keenly priced if compared to buying either product on its own, but beware that the additional chemical(s) included in the mixture may not always be needed for the fungicide programme.

The cornerstone of any cereal disease programme will contain triazoles. Triazoles which feature in most programmes are epoxiconazole (Opus Max, Rubric etc.), proline (prothioconazole), Punch C (flusiazole), etc. Other products such as mildewcides (Tern, etc), contacts (Bravo), or strobs (Amistar) will be needed, depending on the timing or disease threat.

Timing of a fungicide programme should not be completed according to calendar date but according to the development stage of the crop. The key thing to remember about controlling disease in cereals is to use a programme approach, rather than relying on a single application for the killer punch.

The length of time a fungicide can adequately do its job in the plant is limited and is rate dependent. In this context, do not plan to get any more than three and a half weeks from a fungicide applied at reasonably high rates.

Dissect

All growers should be familiar with plant growth stages and be prepared to dissect plants to determine which leaf is coming through so that fungicides are applied at the correct timing. Once plants move towards first node it is possible to carefully peel away all the leaves down to the developing head. Count the leaves in reverse order from the developing head: the one nearest the head is the flag leaf, the next leaf is leaf two, etc. You can then determine where leaf three is or how long it will be before it is fully emerged. Protecting leaf three and all foliage above this leaf is the target.

Winter wheat acreage has increased slightly compared to last year but the late spring has restricted growth of early- and late-sown crops. Crops won't have as much time to develop leaves as normal and will shoot through the growth stages more like spring wheat than winter wheat this year.

In general, winter wheat will receive three main fungicides, plus or minus an early season T0 application. With margins tight this year, the T0 should only be used on the earliest sown crops which have the highest yield potential. Many use this T0 as an aid to correctly time the T1 fungicide. Bravo (chlorothalonil) will suffice at this timing and avoid the inclusion of a triazole -- unless other diseases (yellow rust) are very active.

Table 2 (left) highlights the best way to protect yields and minimise the build up of insensitive strains of septoria through the season in your crops.

The main fungicide programme really starts with the T1, which aims to protect leaves two and three, both of which will contribute to final yield. Get the timing of the T1 application wrong and you will struggle to control disease all season.

Apply the T1 when the majority of third leaves have emerged. This is not necessarily at GS 31 or GS 32 but can be anywhere in between.

The target diseases at the T1 timing in winter wheat are septoria, eyespot (in continuous tillage ground) and, to a lesser extent, mildew. Growers in the northeast should also look out for yellow rust in varieties such as Oakley. Include chlorothalonil (Bravo) in all T1 applications. Use a high rate (80pc or more) of a triazole/ triazoles mix at the T1 timing -- Venture Extra, Tocata, or Proline should be used (and will also control eyespot). Cheaper products, such as epoxiconazole, could be used on their own where eyespot is not expected to be a problem.

The T2 or second main fungicide timing should be targeted at the flag leaf emerges. This will comprise of a high rate triazole (80pc +) and chlorothalonil. Triazole loading, or the application of more than a full rate of an individual triazole in a mixed product, such as Prosaro, Gleam or Venture Jewel, will feature heavily at this timing. These products have out-yielded straight products again in last year's trials.

If you have to leave out chlorothalonil in the T2, due to a delayed T2 timing or disease pressure is very high at the time of application, then switch to a product with good contact action, eg Venture Extra etc.

The final application (T3) will again consist of a triazole mix of products (Gleam, Prosaro, etc). Both of these products have good protection from all strains of fusarium (50pc control is regarded as good control) and the addition of a strobilurin may not always be beneficial, but a strobilurin may be justified in high-yielding situations.

Above all, growers should recognise the potential of the variety to contribute towards disease control, as varieties such as Alchemy and Lion have high ratings for resistance to septoria. Blanket treatment across varieties will drive up costs for little extra benefit.

Planning your barley fungicide strategies should start early so that products can be bought on time and at a lower cost. Generally, two fungicide applications are needed to keep disease at bay. Varieties with good disease resistance, such as Quench or Magaly, can lend themselves to a low fungicide strategy -- ie reduced rates at both timings. Keep a close eye on Azalea and Cocktail for net blotch at an early stage.

The first fungicide can be applied from mid to late tillering but should be applied before the first node detectable stage. Half rates are sufficient. Products such as Proline (prothioconazole), Punch C, Lyric and Stereo will all do an excellent job at this stage. Where rhyncho is an early problem, use Proline at a higher rate (40-50pc rate of prothioconazole) as it has the best activity of the products mentioned. Likewise, where net blotch is a problem use higher rates of Proline. The addition of strobilurins (Modem, Galileo, etc) may also be justified.

The second fungicide application (T2) will coincide with the flag leaf emerged to visible awns. Triazoles form the cornerstone of disease control at the T2 timing, with products containing prothioconazole featuring strongly.

Finally, shop around for bargains and be prepared to take your calculator out to work out which fungicide product represents real value.

Irish Independent