Crop Crack

Spring Cereals

Spring crops are looking very well and without the more usual effects of waterlogging seen in other years.  Although weeds are emerging fast as a result of last week’s rain, be sure all are well through before spraying. Also watch the size of the annual meadow grass if this weed is also to be controlled – efficacy falls off rapidly once it begins to tiller. It is important to note that this season aphid numbers are the highest I have seen for a very long time and it would be advisable to apply an aphicide to control the spread of BYDV.

To minimise the effects of competition on the crop and optimise the level of weed control, herbicide application should be carried out once all 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 when they are at the 2-4 leaf stage is much more effective especially on difficult weeds such as fumitory and knotgrass, rather than delaying to coincide with the 1^st fungicide application.

Broad leaved weeds resistant to particular groups of herbicides in NI is not a new problem – chickweed resistant to herbicides such as ALLY has been widespread throughout the province for some years. Sulfonylurea (SU) herbicides such as metsulfuron have a single mode of activity, blocking the production in many BLW of a key enzyme, acetolactate synthase. Products that use this mode of activity are known as ALS inhibiting herbicides and include the SU chemistry. As well as chickweed, mayweed and poppy have also developed widespread ALS resistance. This particular resistance problem has been managed by including herbicides into the tank-mix with different modes of activity to maintain good weed control.

In spring cereals, ZYPAR will give excellent control of a wide range of weeds that will not be controlled by Ally on its own. These include chickweed, fumitory, fat-hen, groundsel, brassica weeds, and cleavers. It’s one relative weakness is redshank. Whilst it will control it to 6-leaf, it should be tank-mixed with another herbicide to ensure redshank right up to flowering is satisfactorily controlled. ALLY MAX and SAXON are excellent tank-mix partners for this purpose.

Winter Cereals

Winter cereals have greened up well and are now racing through the growth stages. Awns are now out on almost all winter barley crops with growth regulator applications complete. The cool nights during April held back the crop response to nitrogen, but this has turned around and all nitrogen applications should be completed in the coming days to maximise green leaf development and crop yield.

Winter wheat crops which have not yet received T2 should be treated as soon as possible along with the growth regulator if required. The cool dry April and well timed T1 treatments have kept Septoria infection low, but it is present in all crops and remains a key focus for T2 treatments planning forward. Yellow Rust has been observed at low levels but perhaps a combination of cold nights and effective varietal resistance has meant that there have been no explosions of infection we were more familiar with other years.

A good start has been made to drilling spring crops, with the earliest drilled now emerging in the more forward areas. After a very mild winter, the colder temperatures during the first half of April slowed development in all winter crops, with many fields actually going backwards. The cold night-time temperatures have been very stressful to winter crops, hampering nutrient uptake causing purpling, yellowing and tipping of some leaves. However warmer temperatures and rain over the last week has improved everything, with all winter crops now looking much better. What is clear given current pricing it is more important than ever to optimise fertiliser applications to maximise the efficiency of utilisation of N, P and K. Soil pH is key – make sure this is above 6.2 for winter and spring crops. Granulated lime at around £125-135/t is excellent value and we should see a lot more of the granulated lime being applied to improve NPK utilisation. Correct use of foliar feeds also has an important role to play, where often it is not the amount of N applied that is the limiting factor, but perhaps sulphur or one of a number of micro-nutrients.

Growth regulation

The size of canopy at GS30-31 is a good indicator of future lodging risk, with larger canopies associated with greater lodging risk. Assess lodging risk on a field-by-field basis, also taking account of the field soil residual N and lodging history, and the varietal lodging resistance score. Numerous other factors contribute to crop lodging including sowing date, early growth over the winter months, and late season extreme weather events.

Against this background, a programmed approach made up of a number of treatments promoting shorter and stronger stems is essential. Plant growth regulator (PGR) choice, timings and rates all impact the outcome achieved. Early sown crops with thick canopies are most at risk of lodging, particularly if of a weaker strawed variety, and will require a more intensive programme to minimise the risk of lodging

Fungicide update

With a better understanding of disease resistance to single-site triazole, SDHI and strobilurin chemistry, maintaining the efficacy of this chemistry is critical to being able to continue to control wheat and barley diseases effectively. Multi-site chemistry is key to prolonging the efficacy of the single-site chemistry. Chlorothalonil (CTL) was the mainstay of multi-site activity for years, but with its loss two seasons ago now, folpet, available from Syngenta as MIRROR is regarded as the most effective replacement.

Folpet is a multi-site active, and all manufacturers are advocating the inclusion of this active into wheat and barley programmes, not only to prolonging the single-site actives, but to improve disease control also. Its inclusion improves Septoria activity in wheat and gives some improvement of Ramularia in barley. Like CTL, folpet is a contact ingredient only with no systemic activity, protecting the surface of the leaf by preventing the fungal spores germinating on the surface of the leaf.

Early weed control – Annual Meadow Grass In Spring Crops

If Annual Meadow Grass (AMG) is to be controlled in spring crops, this must be done as soon as possible. This will be done before the timing for controlling broad-leaved weeds (BLW) in spring cereals. There are a number of product options, but all must be applied either pre-emergent or in the case of one, very early post-emergent of the crop.

Applied pre-emergent, all work by residual activity to control the AMG. Since residual herbicides require sufficient soil moisture to be effective, so their performance will be compromised in drier soils. This is the primary reason for the variable performance of AMG control achieved in the spring. Best control is achieved when applied onto a damp seedbed, keeping the water volume up and travelling slowly. To maximise efficacy and crop safety, ensure the label guidelines are strictly followed.

The last couple of weeks have offered a good opportunity for farmers to get up to date with much needed fieldwork. Grass growth has been slow due to low night time temperatures but chickweed has grown away through the winter and will need controlled especially in autumn reseeds. The presence of broad-leaved weeds will always take away from grass yield and quality. Docks and chickweed are nutrient loving weeds, thriving in nutrient rich regimes, ie more intensively managed swards. Docks have only 65% of the feed value of grass and are unpalatable to stock. Where infested swards are ensiled, their high nitrogen content adversely hampers a good fermentation, so leading to high pH silage that spoils quickly when opened and depresses intake. Dock seeds can also survive in silage and pass through the cow, infesting a field where slurry has been spread. The best defence against perennial broad-leaved weeds is to stop them establishing in the first place. This can be achieved by having a well-managed, dense sward, growing in well-structured non-compacted soil. Over or under-grazed leys that have been poached, offer perfect conditions for weed seeds to germinate. Topping or mowing weed plants provides short-term visual satisfaction but stimulates active regrowth – so the problem gets worse not better. The long-term solution for controlling persistent weeds in grass is to use modern systemic herbicides. A well-timed treatment with an appropriate herbicide can transform a weedy pasture into a productive ley, without the need for costly reseeding. Farmers may have to be more pro-active this year, as weeds have generally survived the mild winter and kind spring, so weed numbers are much higher than usual.

DOCKS

As thoughts turn to silage, treating dock-ridden leys with DOXSTAR PRO or PIVOTAL four weeks before cutting will significantly increase the amount of grass that ends up in the clamp and improve silage quality. Docks have much less feed value than grass and pull down dry matter. FOREFRONT T and HALCYON are the most effective herbicides available to grassland farmers for the control of docks, ragwort, chickweed, thistles, dandelions, nettles and buttercups. Both have long lasting weed control to date with a single well-timed spray giving up to 18 months control so whilst they may appear expensive it really is good value for money. Once the established docks have been controlled it is best to keep the problem under control with follow-up treatments every year. This controls new growth of seedling docks that will reappear because all that is required for dormant seeds to germinate is a gap in the sward caused by poaching or tractor marks.

In fertile soils, the dock root system consists of a large tap root with a highly branched mass of smaller fibrous roots. This means what appears to be a small dock plant above ground may in fact be growing from a large rooting system below ground. In order to achieve effective herbicide application docks should be at the rosette stage, with foliage8-10 inches high or across. If grass has been cut or grazed a period of three weeks must occur to allow sufficient regrowth and a suitable target for spraying. If applying FOREFRONT T, HALCYON, DOXSTAR PRO,PIVOTAL or PAS.TOR, livestock should be kept out of treated areas for 7 days before grazing and until the foliage of any poisonous weeds has died and become unpalatable, where clover is important SQUIRE may be applied in establishes grass.

CHICKWEED

There are 2 types of chickweed, common chickweed which is the most commonly found type, with a smooth leaf and mouse-eared chickweed which has a larger leaf than common, with a very hairy surface on the leaf & stem. Chickweed levels have built up very quickly this spring as this weed grows at lower temperatures than grass, and should be treated as soon as possible to avoid choking out the young grass. Similarly, established swards that have been poached by autumn grazing tend to be very open in the early spring and this allows chickweed a chance to become a problem. Chickweed can mature and produce seed in 5-6 weeks hence there can be several generations in a year. Mouse-eared chickweed is very common on many local farms and it is important to note the distinct differences and treatments. Both ENVY and LEYSTAR will be used widely on new sown leys this season where clover is not important. These will control both strains of chickweed.

To ensure a well fermented silage sufficient fertiliser must be applied at the correct time for intended cutting dates. On average allow one day’s growth for each 2-3 units of nitrogen between application and cutting. The younger the grasses the higher the feed value but the lower its yield. In general aim to cut before 50% of the ears have emerged to gain as much yield as possible. Short chopping speeds up fermentation and aids consolidation ensuring not to cut too short as long fibre is required for rumen function. Where conditions allow fast wilting in good weather will increase the concentration of sugars and reduce effluent production.