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Crop Crack 25.04.09
By Wendy Fearon
Spring has arrived at last, and the sound of sprayers, the sight of ploughs and planters throughout the countryside are a very welcome sight on this pleasant Monday morning, but I will not get carried away as I know this can quickly change.
The remainder of winter crops received their nitrogen top dressing and the T1 will now be completed on winter barley and winter wheat. Potato and vegetable planting have begun and most of the grassland acreage has received fertiliser over the past few weeks. Leatherjackets have not been a problem in winter cereal crops but they are certainly showing signs of damage in spring sown crops. Spring cereal crops should be inspected now for leatherjackets. Where numbers are found to be above the threshold limits, of 0.3-0.5 million Larva per ha the best control is achieved by applying Dursban WG. Highest risk situations are fields coming out of long term ley or stubble fields with good grass cover.
Potatoes
Last spring was exceptionally dry and as a result in many cases weed control was very poor.
Where the contacts were used late and weeds had size, they did not do as good a job as PDQ would have done, especially on grass weeds, fat-hen and polygonums. All residuals need adequate soil moisture to work effectively. With soils being so dry for much of last spring, the residual partners performed particularly poorly.
All herbicides should be applied early to be effective as none of the alternative contact products will control the same size or range of weeds as paraquat. This will mean a greater reliance on the residual products therefore to maintain clean drills. With a year’s experience gained, we are more knowledgeable as to the strengths and weaknesses of each of the alternatives.
This year also sees changes to the LINURON label that now limits its use to 1.2lt/ha. 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.
Grassland
It is important to allow one days growth for each 2-3 units of nitrogen between application and cutting to achieve good quality feed. 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. 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. 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. Spot control of Nettles, Thistles and Docks can be achieved using Grazon 90 or Nushot.
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