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CROP CRACK - 26-04-08
By WENDY FEARON
Clarendon Agricare - Get on Top Of Disease
It is important to inspect all winter cereal crops for signs of disease with recent showery conditions. All T1 fungicide treatments should now be complete on winter cereals. Many factors influence the types and severity of diseases, which affect your crops including variety, weather conditions, crop rotation, cultivation, sowing date and fungicide treatments. Weather still remains the biggest factor in disease management to Northern Ireland cereal growers.
The most common disease to us is rhynchosporium on barley and septoria on wheat.Septoria tritici requires wet conditions for the spores to spread from one plant to another or from one leaf to newly emerged leaves higher up the canopy. It can also spread through the crop if it is wet from dew and there is a light breeze. It will also develop faster inside the leaf during warm weather whilst septoria nodorum requires wet weather to infect a plant but will develop even faster at higher temperatures than septoria tritici. Septoria nodorum may become a problem in the height of the summer (if it comes).
Rhynchosporium poses a greater risk to crops in high rainfall areas and this provides optimum conditions for spores to develop and spread from stubble to the crops for subsequent infection. A long period of dry weather will slow down the disease, but in high risk crops, early protection is essential to manage the disease.
Brown rust and powdery mildew both prefer warm and humid conditions and many brown rust incidences have been observed on the variety Alchemy this season.
Yellow rust prefers wet and cool weather to develop although due to last years weather there was a lot of yellow rust during the summer months.
Conditions to date have been ideal for the spread of eyespot especially in early drilled second wheat’s. Common eyespot prefers mild winters and wet, cool conditions around stem extension that favour the retention of lower leaves around the stem base and give time for lesions to penetrate the stem. Dry weather at this timing allows older leaves to senesce and fall away, reducing the risk. Eyespot is usually present in trash from previous cereal crops but there are airborne spores of the fungus as well which can blow into a crop hence infecting it.
Much late sown second wheat was not treated for take-all in the autumn due to seed scarcity. Take-all levels are more severe in light soils, whilst well structured heavy clay soils can be affected to a lesser extent. Factors such as compaction or acidity that restrict root growth will increase the effects of take-all.
Winter barley achieves a greater yield response from an early fungicide treatment applied at GS30 and GS32 than from later fungicide applications at GS45.Around 60% of yield benefit from fungicides comes from early treatments with the additional 40% benefit at (GS45-49).Spring barley crops differ in that the early fungicide probably provides 40% of yield benefit with the 60% yield at the later timing. Winter wheat crops typically require three sprays in the program but some early drilled wheat crops have already received two fungicide treatments.
Most early drilled winter barley crops are showing signs of manganese deficiency and the frost seen a couple of weeks ago has enhanced these symptoms.Maxman manganese should be applied as soon as symptoms appear. Manganese is an essential plant nutrient and is important for the synthesis of chlorophyll and the metabolism of nitrogen, phosphates and potassium.
Plant Growth Regulation
It is critical at this time to monitor growth stages of both winter wheat and winter barley. In winter wheat the weakest part of the stem tends to be the lowest internodes, whilst in barley it is the higher internodes. It is during the later stem extension stages and early flag leaf emergence that the maximum straw strengthening effect will be achieved. The flag leaf has appeared on most winter barley and stronger crops should receive Cerone and Adjust immediately.
Spring Barley
Quite a bit of spring cereal has emerged this week. Weed control should be planned now with the aim of applying a herbicide as soon as possible. If applied before first node (GS 31) hormone weed killers such as Foundation, Dockmaster, Compitox plus or Oxytril CM can be used alone to provide a cheaper option or in tank mix with Ally Max or Harmony-M to provide better weed control. It is essential to include either Compitox or Starane in the mix if chickweed is a problem. Hussar now has a label use for spring barley and spring wheat. It may be applied from the three leaf stage of the crop controlling annual meadow grass, some broad leaved weeds and also suppressing cleavers and wild oats. Adjust may be used on spring cereals. Adjust applied early will maximize the suppression of the main stem development, and therefore divert nutrients and growth to promote secondary tiller development. This will help boost yield and reduce lodging.
Spring Wheat
Spring wheat’s are emerging well and similar weed control options are available as for spring barley.
Adjust can be used to increase tiller survival and reduce lodging. Applications made before or during tillering will have the biggest yield benefit.
Grassland
Fertiliser applications were applied late and it is important to allow one days growth for each 2-3 units of nitrogen between application and cutting. Failure to use up the fertiliser applied may result in poor fermentation due to high levels of non-protein nitrogen in the crop.
Docks are the most damaging weed which infests Northern Ireland farms. Part of the reason for the success of docks is that they will germinate and grow in almost any situation, and can then multiply by seed production or from underground roots. Seeds can be spread by a variety of means such as wind, water stock and machinery. More recently the spread of seed through slurry has become one the most common mechanisms of seed spread.
In most grassland fields there are approximately 12.5 million dock seeds per hectare in the top 15cm of soil and these can remain viable for up to 80 years. This seed bank provides an enormous reserve for reinfestation and reinforces the message that weed control is an ongoing battle not a one-off measure.
It is important to remember that grassland herbicides are only effective when grass and weeds are growing actively and should not be used when there is a risk of low night temperatures.
The ideal time to spray docks is when they are in full leaf at the rosette stage just before the flowering stalk appears. Use plenty of water, about 30-40 gallons per acre, and do not spray in strong sunlight. Products containing straight CMPP whilst effective on chickweed give only leaf control on docks. For effective root kill it is necessary to use translocated herbicides such as dicamba, Fluroxypyr and triclopyr to allow sufficient time for them to move from the leaves down into the root system. This is usually 3-4 weeks. Examples of products, which contain dicamba, are Grassland herbicide, Foundation and Dockmaster. Doxstar and Pastor contain both Fluroxypyr and triclopyr and are preferred on silage ground as they have little or no effect on the growth of grass. Forefront has proven to be the most successful grassland herbicide available for quite some time. Forefront may be applied giving excellent weed control with no effect on the grass. Forefront contains fluroxypyr and aminopyralid, a completely new active, which is rapidly absorbed by the plant and may be grazed or cut 7 days after application. As well as controlling docks it will control chickweed, buttercup, dandelion, nettle and thistle.
Spot control of Nettles, Thistles and Docks can be achieved using Banish, Grazon 90 or Nushot.
Potatoes
With planting well under way consideration should now be given to weed control. Products containing Linuron should be used pre emergence of the crop and have residual activity. Performance of the residual herbicides is very dependant on soil moisture. Any ridging up should be done before application of a residual herbicide, as any soil disturbance after application will adversely affect performance. Emerged weeds will be controlled when application of the residual is delayed as late as its label allows, and a contact herbicide added. This also benefits the residual performance by allowing it to persist later into the season up to the point where the crop canopy will cover the drills and prevent further germination. Retro can be applied up to 10%emergence on seed crops and 40% on ware but has no residual activity. RETRO replaces PDQ for this season. A non ionic wetter such as Activator should be added when applying RETRO .Sencorex which is both contact and residual may be applied on specified varieties pre emergence up to when stems are 15cms in height. Alternatively Sencorex and Titus may be used up until the main stem is 25cm and an adjuvant such as Libsorb must be added.
Defy is a residual with pre-emergent activity controlling a wide range of broad-leaved weeds and some grasses, with no varietal restrictions and safe on all soil types. It will be used as an alternative to Linuron in combination with Retro at early crop emergence. It does however have some important gaps in its weed spectrum including redshank, fat-hen and knotgrass, requiring the inclusion of AFALON (Linuron) or SENCOREX to provide residual control of these weeds also. It has no post-emergent activity. Where scutch is a problem in ware Falcon may be used.
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