Crop Crack

T3 Fungicides – Potato Blight – Grassland Weed Control

After another mixed bag this week conditions remain ideal for many diseases. Blight pressure remains high with the first outbreak of the season confirmed by AFBI earlier this week.Where potato crops are at the main canopy development it is essential the product being used is fully systemic to properly protect the new leaves being put on between applications. Later planted crops are higher risk as they produce more new growth between applications than earlier planted crops, at a time when the level of inoculum in the air is progressively increasing.
During the main canopy development phase the rate of new growth is extremely rapid. This places a huge uptake demand on the uptake of all nutrients, and in conditions of such rapid growth any nutrient that is limited in availability will suppress haulm growth, and as tuber initiation begins, tell the plant to form fewer tubers also. Manganese, sulphur and magnesium are three of the potentially most limiting trace elements, and timely application of these nutrients in an immediately available foliar formulation will offset this yield limiting effect. So that the crop is not adversely affected, it is essential to apply 2-3 maintenance applications of Mn,S & Mg along with N before symptoms are seen, the first going on at the onset of tuber initiation, which normally coincides with about 30-50% ground cover.
Aphid’s damage potato plants directly through feeding damage and indirectly by transmission of several viral diseases, of particular importance in seed crops – aphid control is necessary on seed crops to prevent the spread of potato leaf-roll, mild and severe mosaic viruses. Aphids are the vectors for these viruses i.e. it is the aphids by their feeding action which pass the virus on from one plant to the next.
A number of different species of aphids are responsible for viral spread. When checking plants for aphids, look at both sides of leaves at all levels of the canopy, and monitor the whole crop, not just the headlands. The crop is most vulnerable to virus transmission at the early growth stages, so it is vital to control once aphids are seen – the early sprays are much more important than later treatments in limiting virus spread.
BISCAYA controls all important aphids, including MACE resistant species, by both its contact and systemic modes of action. Central to its efficacy is its penetrant which greatly improves retention on the leaf. The oil forms a film after the water has evaporated, enhancing penetration of the active ingredient, thiacloprid, into the leaf, thereby speeding and prolonging activity. BISCAYA provides the same degree of efficacy in the mid-canopy leaves of the potato plant as on the upper leaves, still providing over 90% control 14 days after application. As a resistance management strategy its label allows only one application in ware crops and two in seed. In order to minimise the possibility of resistance developing, other aphicides with different modes of activity should be included. BISCAYA should be used first in the control programme to take out any aphids resistant to other approved aphicides.

Spring Barley

Ramularia (also known as leaf spot) is widespread in spring barley with the newer barley varieties showing more sensitivity to this late developing disease. It shows itself late on in the season (usually after booting), symptoms are very similar to manganese deficiency appearing as brown necrotic speckling on the upper leaves. Symptoms appear where crops are subjected to stress from alternating periods of wet weather & sunshine, or man-made as a result of scorching. Chlorothalonil (BRAVO) is very effective when used preventatively, helping to maintain green leaf area when used along with a triazole/strob mixture.

T3 Wheat

With ripening still approx 6 weeks away, the T3 treatment has to persist for all of this duration to prevent infection from a range of diseases such as SeptoriaNodorum (glume blotch), as well as Tritici, late season ear moulds and Fusarium. The cornerstone for the head spray fungicide is a strong triazole, giving strong curative activity to control any disease already on the plant as well as good persistence to prevent re-infection right up to ripening. Prothioconazole & epoxiconazole remain the most effective products to give ongoing Septoria protection as well as controlling fusariums and microdochiums on the ear. Prothioconazole (PROSARO) is the highest rated triazole for this range of diseases. The addition of a strobilurin is also essential to extend the persistence of the triazole and improve activity on Yellow Rust. Good grain fill is totally dependent on retaining green leaf area for as long as possible, and the addition of the strobilurin extends the retention of green leaf tissue.

Aphids in cereals

Aphids are now appearing in crops and as the grains begin to fill they feed at its base, drawing off the sugars that should be filling the grain if left unchecked.
Growers need to continue checking crops for aphid’s right up to milky ripe stage (GS73), and spray if present in numbers.

Grassland

Grassland herbicides use growth function to kill weeds, therefore peak growth periods should be used for herbicide application. There must be sufficient growth to allow herbicides to be effective and vegetive growth is the key time to apply, as the chemical then gets drawn down into the roots. Herbicides are less successful once plants have progressed to the reproductive stage and have thrown a stem or began to seed. Once weeds are beyond the ideal growth stage for spraying they should be mown or topped and allowed to regrow again, and a herbicide applied to the fresh young growth.
To optimise efficacy of any herbicide, recommended water volumes should be observed, even when it means more time spent spraying. It is important to note ragwort plants in their second year are now coming close to flower and should be sprayed immediately as flowering ragwort is poorly controlled. The routine herbicide treatments for this weed are full rate MCPA or 2, 4-D, and they are most active on growing rosettes with reduced activity as the stem starts to extend. They are not clover safe. You can use a mixture of both these products as Nufarm Lupo which allows an increased dose herbicide compared with either alone, with a consequent activity benefit. Stock must be kept of until the weeds have rotted away, which can take up to six weeks.

Grain Store Hygiene

Ensuring stores are clean and pest free is essential to prevent any problems after all the hard work of growing and harvesting the crop. Now is the time to make grain stores ready for the coming harvest. Pest problems in stored grain arise from within the store itself, so a good clean-out is essential to minimise the carry-over of grain beetles, weevils and mites. The store should be empty and thoroughly cleaned before any treatment is carried out, removing all traces of grain and dust that might harbor insects or mites. Apply using an applicator to spray all surfaces including underside of roof and floor, concentrating especially on areas where dust can collect – cracks, light fittings, around equipment etc. RELDAN can be applied up to one month before filling the store and has no with- holding period when applied to the fabric of the store.

Horticulture

Carrot willow aphid is now flying into crops and they carry several virus diseases that affect both carrots and parsnips. They may cause leaf distortion and stunting if they infest plants at the seedling stage. Crops should be checked for aphids and an aphicide such as APHOX used if present. Where couch grass is a problem in carrots ARAMO can be used and has annual meadow grass as a label weed.

 

T2 on Winter Cereals – Dock Control in Grassland

All weed control should now be almost complete on spring cereal crops. There was certainly plenty of opportunity to catch up on spray programmes over the last couple of weeks. Crops are moving through the growth stages very quickly this week with the damper conditions. Some spring barley in parts of North Down are already at flag leaf and East Down have crops with awns appearing. Wild oats may be controlled now as long as a period of three weeks has occurred from the weed spray application. Axial and Adigor may be used on both spring barley and spring wheat up to flag leaf. It is certainly a season where growth regulator will be required in abundance. As most crops are now past 2nd node growth regulation products are limited to Cerone for barley up to first awns visible and Adjust and Cerone on to spring wheat up until flag leaf sheath opening. Fungicide application is priority now as rynchosporium is spread by rain splash. This disease has been present in low levels up until now with netblotch being the most dominant disease in spring barley. Whatever the fungicide choice for spring wheat it is critical to include something to cover mildew as most varieties have mildew present on them.

Winter Cereals

Protecting the top three leaves at T2 is critical to yield and profit – up to 80% of the yield is generated from these leaves. Foliar disease not controlled effectively at this time will hasten the senescence of these leaves during grain filling, and therefore affecting yield and grain quality. Yet there is little point in applying any input if it does not give a financial return. To get the best return on fungicides, applying them at the correct timing is critical. Trial work in UK & ROI has consistently shown even in a low disease pressure year, a well-timed application will give returns of 2-4 times their cost and in high pressure situations 5-6 times their cost. In winter barley this should be applied from the end of booting through to awns fully emerged, GS45-59, and be robust enough to protect the upper leaves and ear through to the end of the season. Awns also contribute to yield and it is important to keep them free of disease also.
For winter wheat the T2 should ideally be applied between mid flag leaf to mid-booting, GS38-45 along with the growth regulator. The T3 treatment is then applied post ear emergence to mid flowering, GS59-65, targeting ear diseases and prolonging control of foliar disease on the top two leaves, especially important in wetter seasons and on susceptible varieties.Sumi-alpha should be applied along with the fungicide.

Potatoes

Much of the potato crop this season has gone into cold soils and therefore drills are only warming up now. Both weeds and potatoes have been slow to emerge to date. Most weed control programmes are based on residual products ie products that are taken up through the soil, and are therefore very dependent on sufficient soil moisture to work effectively. Soil conditions are ideal therefore at the moment, moist enough on the tops of the drills to allow the herbicide be taken into the soil and taken up by the germinating weeds.
A huge amount of SAC work suggests that growers should spray before crop emergence to moist clod-free ridges. Holding off until crop emergence will set the potatoes back significantly reducing final canopy cover, and compromise weed control especially if weather delays the application further. The weeds are best treated pre or very early post emergent, especially important on the difficult weeds; fumitory, knotgrass, bindweed, annual meadow grass.
The key message is to apply the herbicide combination before crop emergence, therefore avoiding any check to the crop once emerged and maximising range of weeds controlled.
It is Tuesday today as I write this article and the steam is rising up from the road as I look outside. This certainly has been the first day since potato planting I could say there is a risk of blight. During the early canopy development phase, emergence to rosette products that have zoospore activity are the most effective 1st spray. RANMAN, SHIRLAN or TIZCA will control any zoospores that may be in the soil (either from ground-keepers or infected seed) and provide good protection of the new plant.

Grassland

With farms being short of grazing because of the cold conditions it is important to minimize the effects of encroaching perennial weeds. When targeting nuisance perennial weeds such as docks, nettles and thistles it is important to apply herbicides when the plants are actively growing and at the correct growth stage.
Most herbicide applications to silage ground occur prior to or just after first-cut. Depending on cutting date, the quality and quantity of silage taken will vary, placing greater importance on achieving the best second-cut possible.
Perennial weeds such as docks can significantly affect both the quantity and quality of grass harvested, so well-timed herbicide applications after first cut can reap rewards for the rest of the season and even into the next spring. This is likely to be particularly so this year with recent rainfall in helping to stimulate weed growth. To optimize results, wait for 2-3 weeks after cutting for docks to regrow to the rosette stage, and then apply DOXSTAR to actively growing plants. Doxstar has been developed to deliver the highest levels of dock control. The formulation and the presence of two actives; fluroxypyr and triclopyr, delivers a significantly higher level of control than straight fluroxypyr.

Good levels of weed control can also be achieved in grazing leys at this time of year. Where mixed weed populations are present, including docks, nettles and thistles, PASTOR is the most appropriate product to use. With the dry spring limiting grass growth, stock will have to graze closer to thistles leaving sheep vulnerable to orf. Getting rid of thistles in sheep pasture with THISTLEX significantly reduces the spread of orf while increasing grassland productivity.

FOREFRONT may be applied onto grazing ground giving excellent weed control with no effect on the grass. FOREFRONT contains Fluroxypyr and aminopyralid. As well as controlling docks it will control chickweed, buttercup, dandelion, nettle and thistle.
Treat weeds at the rosette stage, when they are actively growing. If stem extension is already occurring, use a mechanical topper first, and then treat regrowth when it reaches the correct stage.

 

T1 Fungicides on Winter Crops – Weed Control in Spring Barley

The prolonged period of cold weather over recent weeks had restricted growth of all spring crops sown in late March. Whilst all germinated well, growth of most crops had been particularly slow. Rainfall has been adequate, enough to maintain good soil moisture ensuring even germination of crop and weeds, and not too much to cause any transient yellowing associated with plants struggling to take up nutrients in waterlogged soils.

The problem was very much the lack of heat, restricting nutrient availability and therefore growth and development. The pleasant rise in temperature this week has encouraged both weeds and crops to move rapidly. To date aphids have been discouraged from flying due to cool conditions but this will have changed this week with the sudden increase in temperature.

The well below average air temperatures up until now mean soil temperatures have also been well below average for the time of year. The Nitrogen mineralisation process in the soil where fertiliser nitrogen is converted to a form that can be taken up by the crop is a soil microbe process and therefore dependant on soil temperature. Hence colder soil has slowed the availability of nitrogen to the crop, and many other nutrients also, particularly manganese. Many crops are beginning to show nutrient deficiencies as a result.

The application of a broad-spectrum trace-element mix along with key macronutrients at this time is a very useful and beneficial way to supplement the plant’s nutrient requirements during periods of restricted availability, especially when coinciding with phases of rapid growth ie. during tillering and as stem extension begins. An application of a balanced and readily available source of macro & micronutrients that is not dependant on soil availability at this key time will minimise the adverse effects of restricted soil nutrient uptake.

Spring Cereals

To minimise the effects of competition on the crop and optimise the level of weed-control, the herbicide application should be carried out sooner rather than later, once all the weeds have emerged but are still small, and before they begin to compete with the crop for nutrients and light. Carrying out the weed control at the 2-4 leaf stage will lower rates of herbicide and give a much more effective result than delaying to coincide with the 1st fungicide application.

Product choice depends on the weed type and size present and crop growth stage.

Broad leaved wise, Sulfonyl-urea (SU) herbicides will likely be the starting point, controlling a wide range of weeds and are very safe to the crop.

Where the range of BLWs present are limited to chickweed, redshank, fat hen, fumitory & day nettle, the hormone mixture products will work well without the need to tank-mix, but must be applied by GS31. Where the likes of field pansy, forget-me-not, speedwells & corn-marigold are also present however, sulphonyl-ureas products will improve control. Conditions over the last week have been ideal for hormone products with consistent day and night temperatures. Compitox, Minstrel and Oxytril are the most widely used tank mix partners with SU’s.

Grass weeds are commonplace this season especially on head rigs, HUSSAR is the only product now available to treat AMG in spring crops, controlling it up to the end of tillering. It also gives very useful suppression of wild oats that are emerged at the time of application (further plants are likely to emerge later). It also controls a range of BLW very similar to the other SU’s.

If clover is part of the mixture, a clover safe product must be used. TRIAD is a new clover-safe herbicide available for the first time last season. Whilst currently labelled for use in ‘Spring Barley undersown with IRG’ only, a new wider label is currently going through the approval process reading ‘Spring Barley undersown with grass, and grassland’. If seedling docks, thistles and buttercup are also problem weeds, SPRUCE must be added to the TRIAD to improve control of these also. SPRUCE is 2,4DB, a clover safe hormone type herbicide.

Winter Barley

Rhyncho is present in most crops at various levels depending on the disease control already applied. The cool and damp weather pattern over the last month has been ideal for this disease, and without a robust and properly timed fungicide application this disease will move rapidly up the plant onto the upper leaves, awns and heads. Mildew is also present at varying levels. Ramularia is also beginning to show, with newer varieties showing greater sensitivity to this late developing disease. It tends to show late in the season usually after booting, symptoms are very similar to manganese deficiency.

The SDHI chemistry now available have a good position at T2 on winter barley crops where they retain green leaf and are very active against Ramularia. However whilst Bixafen (Bayer) and xemium (BASF) have curative activity, triazoles are still essential to the core of the T2 fungicide mix, with prothio, epoxi and flusilazole being the most robust for Rhyncho, both preventative & curative The SDHI actives are more long lasting than other chemistry groups, providing enhanced disease control and extending the protection period by up to 3 weeks. They also give consistent increases in green leaf area in the field, delay senescence and improve drought tolerance, all components that build yield.

Bixafen, available in mixture with prothioconazole as SILTRA for barley is particularly strong on Rhyncho. Xemium is also very strong but its partner triazole in ADEXAR, epoxiconazole is not as strong as the Bayer triazole. BASF also have boscalid, another SDHI active available in mixture with epoxiconazole as CHORD. Whilst the boscalid is not as curative as xemium, CHORD is very strong on Rhyncho and also has excellent activity on Ramularia at T2. Isopyrazam (Syngenta), in mixture with cyprodinil as BONTIMA for barley is particularly strong on rusts. None are particularly strong on Mildew or Fusarium.

Chlorothalonil is still an option when used preventatively to improve Ramularia activity but only when an SDHI is not being used at T2. (It has no activity on any other barley diseases.) FIELDER is an ideal triazole partner, combining both TALIUS and chlorothalonil in the one pack to control both  Ramularia and Mildew Where the SDHI chemistry is not being used, strobs also have a very important role in the T2 fungicide programme in those crops with good potential, improving control of Brown Rust, Net Blotch & Rhyncho. With a different mode of activity to the triazoles, it is an excellent partner in resistance management.

Winter Wheat

Most crops have now moved through the stages of stem elongation.Septoria tritici is present in all crops at variable levels depending on T1 timing. Mildew is also present in all varieties depending on whether TALIUS has already been applied.

The flag leaf will be emerging in most crops within the next week or two, and this is the key time to apply the T2 treatment. Of all fungicide treatments, T2 gives the greatest response in terms of grain yield and quality, keeping the top three leaves clean and the ear as it emerges. For this reason the manufacturers are targeting their new SDHI chemistry at this timing when the big spend will give the greatest return. Trial work on both sides of the Irish Sea last year showed consistently higher yields when these products were applied at this time.

While not as curative as the triazoles, each manufacturer claims extended persistency against Septoria for their SDHI actives. Co-formulated with triazoles, they all show excellent Septoria activity as well as extended activity on rusts and in the absence of disease enhance green leaf retention (similar to strob activity), so boosting grain-fill. Whilst their disease performance is not enhanced by the addition of a strob or chlorothalonil at this timing, from a disease resistance management point of view chlorothalonil should continue to be added.

Epoxiconazole and prothioconazole remain the key triazoles for controlling Septoria. However the difficulty in controlling this disease should not be underestimated. Part of any pathogen’s survival mechanism is to change in response to outside influences that adversely affect its development, and the Septoria pathogen is continuously modifying itself in response to a fungicides’ mode of action, developing ways around it. Population strains of the Septoria pathogen continue to change. New genetic variants are more able to tolerate particular fungicides, becoming harder to kill with epoxi and prothio (Group 1 triazoles). However these same strains are easily controlled with certain older triazoles including tebuconazole and metconazole (Group 2 triazoles). Hence the rationale for the best performing triazole products in recent years to be co-form triazole mixtures. In PROSARO, Bayer have demonstrated over the last 3 years that the effect of two triazoles mixed together is greater than the sum of both when used separately, the tebuconazole improving the product performance on Septoria over straight prothioconazole. BASF have identified a similar effect with BRUTUS, a mixture of epoxiconazole and metconazole. This product consistently outperforms straight OPUS, gram for gram and produces results in the field similar to PROSARO.

 
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