A case of weather permitting

editorial image

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 problem 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 cleavers have 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 or not for a 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 and 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 to 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 1st 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 1st-2nd 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 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.