Crop Crack

Welcome to the first crop crack of the season. As I write this article on this fine spring morning I have momentarily forgotten the difficult and challenging times with regards to weather and markets we have experienced over recent months. Wind and rain have been the main features of the winter with most fields still remaining quite wet. Despite this, the mild conditions have meant crops and grass continue to grow. Crops that were early sown are surviving well apart from parts of fields where the water has remained on the surface for an extended period. Disease is certainly present in crops in varying levels. As ground conditions improve spring fieldwork can commence and fertiliser and spray applications can get underway.

Autumn 2015 was again kind to us, allowing much of the winter barley and some winter wheat to receive a herbicide treatment during October and November. Mixtures of CRYSTAL and SEMPRA were widely used and by and large, performance has been excellent.

Control of Annual Meadow Grass (AMG) is the first priority in all crops if not already done with an autumn treatment. OTHELLO is an excellent contact solution for AMG in wheat in the spring, however there is no similar contact option for barley. None of the autumn products will control AMG beyond the mid tillering stage, yet they are the only AMG options for barley. Note that the actives in OTHELLO that control AMG (iodosulfuron and mesosulfuron) will only control AMG that has already emerged; unlike the autumn actives these are not residual and have no pre-emergent activity. In addition they require the weeds to be growing actively so delay its use until all grasses have emerged and temperatures have risen to allow growth to have resumed.

OTHELLO will also control a wide range of pre or early post emerged broad leaved weeds, but where these weeds have size then a contact product needs to be added to ensure larger overwintered BLW are controlled effectively. The cheapest option is DUPLOSAN, improving control of chickweed, fumitory and cleavers, but is temperature sensitive, therefore needs a milder spell to work properly.

Where the AMG has been controlled in the autumn but for example over-wintered chickweed, cleavers or groundsel are problems weeds now, SPITFIRE is a more effective option controlling these and most other emerged BLW. It also works best when the weeds are growing actively and has post em activity only, therefore delay use until all cleavershave germinated and temperatures have risen to encourage growth.

Brome grass and wild oats

Brome grass infestations are becoming more prevalent right across the province. Last season in particular saw a significant increase in the numbers of infested fields, with rye brome appearing in quite a number of winter barley crops where it was not previously present.

Effective control can only be achieved using a combination of cultural and chemical control methods. Cultural control methods (break crops, stale seedbeds).Chemical control then is a sequenced approach of an autumn treatment followed up with a spring treatment. CRYSTAL at 4lt/ha in the autumn was the first part, and should have been applied to wheat and barley. The follow-up then in the spring is BROADWAY STAR but note this product can only be used on wheat. There is no follow-up brome product available for barley and therefore in a severe infestation situation, only wheat allows effective control.

To avoid crop damage, do not spray any crop under stress. Note that performance of some wild oat/brome herbicides can be adversely affected by other herbicides used on the crop. To avoid these antagonisms, a minimum time interval must elapse between applications of the various herbicides.

The need T0 treatment?

Rhynchosporium and Septoria are the two most damaging cereal diseases in NI. Both have always been more effectively controlled protectantly, but in previous times where the curative properties of the azoles were able to rescue a bad situation later, particularly in wheat this is no longer the case. Growers must now change their approach, looking to keep ahead of both diseases by starting earlier than before and maximising the protectant activity of the chemistry available then right through to crop senescence.

In barley the lower leaves contribute more to grain fill than the upper leaves. Therefore, particularly in a year like this where crop was drilled early last autumn, plants are forward and disease is already present, so a relatively cheap T0 applied now will reduce the level of inoculum present keeping the newly emerging leaves clean and allow the T1 be better timed and protectant focused. Most of the azoles still have good curative activity on Rhyncho and the addition of morpholine will strengthen this as well as control Mildew.

With virtually no curative activity available in wheat, maximising protectant activity is paramount. Multiple modes of action in the tank is also essential, ensuring control of all strains of Septoria. Whilst only ever having had protectant activity, chlorothalonil has multiple modes of activity and as a result still controls all strains of Septoria including those now resistant to the various azoles. This makes it an essential partner at all timings, supporting the azole and SDHI chemistry to control all strains and help slow the build-up of resistance. Application of a T0 introduces Septoria and rust protection early, allowing the T1 be better timed and still targeted at protectant activity. For most situations a triazole/chlorothalonil mix will work well.

Growth regulation – managing thin crops

When applied before 1^st node, GS31, application of certain chlormequat growth regulators can significantly increase tiller numbers. Chlormequat works by suppressing apical dominance, ie main stem development. In doing so it diverts the plant’s resources into producing and supporting more tillers. Particularly in wheat but in barley also, more tillers will go a long way towards compensating for low plant counts, ultimately increasing yield.

Correct timing is critical to maximise this effect. The earlier it is applied during tillering the greater the tiller effect, but note early application to increase tiller numbers will also reduce its effect on lodging. Application of a chlormequat based growth regulator often goes on with a T1 fungicide application sometime around 1^st-2^nd node, GS31-32. At this timing it is too late to affect tiller numbers and survival but will maximise the stem stiffening effect.

Early application will also increase root growth and so reduce stem-base lodging. Stem-base lodging is where the plant folds over at the soil surface as a result of poor anchorage in the soil, and is caused by poor root ball development, more likely when the seedling develops in wet soils that limit root development. All winter crops have rooted very shallow this season as a result of the persistently wet conditions and therefore stem-base lodging is likely to be a significant problem later this season.

Only chlormequat works by suppressing apical dominance, but the active itself does not work effectively at temperatures below 8°C. ADJUST, a more consistent chlormequat formulation was widely used here in NI for some years, subsequently replaced a number of seasons ago with a newer formulation known as SELON. The manufacturer Taminco further developed the formulation and adjuvant partner to enhance the uptake in marginal conditions and therefore improve the reliability of performance, consistently working right down to 1°C. The new adjuvant mix also works as a crop safener, particularly when applied in tank-mixes with other pesticides. The rates of use, label timings and tank-mix flexibility for SELON are identical to ADJUST.

Manganese deficiency in winter barley

A combination of waterlogged soils, plants already suffering from restricted nutrient uptake and plants trying to grow will lead to Mn deficiency appearing in many barley crops. Continuous cereal ground and ground recently limed is most prone to deficiency. Symptoms begin with small pale green speckles appearing throughout the leaf and these will progress to turn brown unless treated.

As soon as the ground allows, Mn deficiency should be addressed as soon as possible along with the SELON application to increase tiller numbers.

Copper deficiency often accompanies Mn deficiency – its symptoms are complete browning of the leaf tip especially the youngest leaves, and apparent wilting of the plant. Treatment will be most effective if treated immediately symptoms are seen.

Sulphur deficiency in winter wheat and winter barley

With air quality significantly improving over the last two decades, the most important source of sulphur to the soil coming from the pollutant gas sulphur dioxide has also reduced significantly. Its deficiency is now being recognised and corrected on grassland through the application of high sulphur compound fertilisers, however in cereal crops its impact in NI has by and large been not been recognised or misidentified. After nitrogen, phosphate and potash, sulphur is the next most important element required by all crops, used to make essential sulphur containing amino acids and proteins in all plants. Deficiency causes paling in the cereal plant, caused by a reduction in chlorophyll production and decreased uptake and efficiency of nitrogen utilisation. Though often mistaken for lack of nitrogen, sulphur is not very mobile within the crop and therefore deficiency is most pronounced on the younger leaves; the opposite to nitrogen deficiency which affects the oldest leaves first.

Crops of both wheat and barley with high yield potential are particularly responsive to one to two applications of foliar sulphur at the timings of rapid growth.

Winter Wheat

All T3 fungicide applications onto winter wheat should now be planned for application over the next couple of weeks. Winter wheat crops have moved at exceptional pace during the dry warm period over the last couple of weeks. The cornerstone for the T3 head spray fungicide is a strong triazole that as well as being effective on Septoria is also effective on Fusarium.  Prothioconazole & epoxiconazole remain the most effective products to give ongoing Septoria protection. Tebuconazole and metconazole are very strong triazoles for Fusarium and an important contributor at this time. The addition of a strobilurin is also essential to maximise the persistence of the triazole and strengthen 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. Pyraclostrobin (COMET) is still the highest rated strob for use in wheat being the strongest performer on Yellow rust and the late ear disease. I have seen a lot of physiological tipping on winter wheat and there are a lot of theories as to what may have caused this but most noticeably it seems to be specific to certain varieties. Mildew has been present on most cereal crops this season where the variety has low resistance a mildewicide must be included in the fungicide program.

Spring Barley

It is fair to say that most spring crops have made a remarkable recovery over the last couple of weeks. All weed control should now have been carried out on spring barley crops and the T1 fungicide application must be planned as rhyncho is now showing on varieties Concerto and Waggon. The two most dominant diseases in our climate are powdery mildew and rhynchosporium with ramularia becoming an increasing problem over recent years. Ramularia can be difficult to identify but unlike most other physiological leaf spots which are only visible on the upper side of the leaf ramularia is easily seen both on the upper and lower surface of the leaf and the longitudinal edges of the brown lesions remain enclosed by the leaf ridges. 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.

All weed and disease control should now be complete on both spring wheat and oats.

Grassland

Attention must now be given to those grass fields which were not sprayed prior to first cut. 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. Forefront is the most effective herbicide on ragwort.

Stock must be kept off until the weeds have rotted away, which can take up to six weeks.

The prolonged period of cold wet 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. Most crops appear to have recovered from the transient yellowing associated with plants struggling to take up nutrients in waterlogged soils this past week.

The problem was very much the lack of heat, restricting nutrient availability and therefore growth and development. The slight rise in temperature this week has encouraged both weeds and crops to move steadily. To date aphids have been discouraged from flying due to cool conditions and aphicides at present may not be required. It is important to remember the work of the beneficial insects on crops.

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.

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. For winter wheat the T2 should ideally be applied between mid-flag leaf to mid-booting, GS38-45 along with the growth regulator. Most winter barley crops are looking exceptionally clean and should  have good yield potential if the weather works in our favour . I think we are well overdue a spell of decent weather, although predicted prices would not excite any of us!

Potatoes

The protracted planting this spring has meant most potato crops have yet to receive weed control. This task must take priority as to delay until after crop emergence will set the crop back even further in an already late season. Conditions have been ideal for the use of residual products (Afalon,Linurex,Sencorex).Where broad –leaved weed control has yet to be completed and the crop has passed the latest timing for Sencorex a reduced rate of Sencorex tank-mixed with Titus will provide a wider weed spectrum of weed control than Titus used alone and can be used on emerged crops up to 25cm high where the label allows .Scutch, other grasses or volunteer cereals are not controlled by the Titus/Sencorex mix. Where these weeds become a problem in coming weeks the graminicide Shogun can be applied. Shogun can cause transient yellowing and is therefore not approved for use on seed crops.

As canopies close, the soil surface will tend to remain damper, encouraging slugs. Timing is critical for effective control, just before the crop meets across the rows. Take advantage of any rainfall by applying pellets just afterwards, as this rain will encourage slugs up onto the soil surface. Potato varieties particularly susceptible to slug damage include Maris Piper ,Desiree and Kerrs Pinks.

Blight fungicides move through the plant in three different ways contact, translaminar and systemic.Dithane,Ranman Top, Shirlan and Tizca are all contact fungicides. These Products protect only the outer surface of the leaf onto which they are deposited.Translaminar products such as Curzate M, Invader, Resplend and Revus move into the leaf and redistribute throughout the leaf tissue as it increases in size whilst systemic products such as Consento and infinito move in through the leaf surface and upwards into the new growth protecting this from infection also. Products that have zoospore activity are the most effective 1^st spray, applied at the rosette stage prior to rapid haulm growth. Shirlan or Tizca will control any zoospores that may be in the soil and provide good protection of the new plant. During the main canopy development phase with the considerable amount of new growth 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 drilled crops, at a time when the level of inoculum in the air is progressively increasing. If spraying during periods of unsettled weather, rainfastness of all products will be further improved with the addition of a sticker to the spray solution. Guard is a latex sticker and will improve the retention of the fungicide onto leaf surface, so improving both adhesions onto the leaf immediately post application and over the following days should rainfall levels remain high. The way the blight product is applied is as important as the product choice. Make sure nozzle type used is correct to ensure sprayer pressure; droplet size and water applied is as directed on the label. Inspect and calibrate nozzles regularly to maintain performance. Never use any blight product at reduced rates. Do not spray when the leaves are wet as this will significantly increase the likelihood of runoff