Crops Notes May 2010
A long winter and cool April has meant that winter cereals are less developed than we might have expected. This has given cereal growers a chance to apply nitrogen top dressings in good time, but it will mean that much of the winter wheat will receive its first two fungicide treatments in May, which is very unusual. Spring barley plantings have been completed in good time and this must lead to the potential for high barley yields providing we get a decent summer this year. With this in mind, agronomy seems more important than ever if spring barley is to make a profit.
Spring barley
The most profitable growers time their nitrogen top dressing at the two to three leaf stage (GS 12 to 13). Later applications than this may green the crop but add little yield. Aim to apply a mixture of at least two broad-spectrum herbicides when most of the weeds are at the two to four leaf stages. This will ensure that weed competition is removed at an early stage of crop development, and may allow a reduced rate of product to be used. I believe it is also good practice to prevent disease becoming established at this stage by tank-mixing a fungicide with your herbicide.
Winter cereals
All crops should have received their main nitrogen top dressing – applying this up to second node detectable (GS 32) is likely to result in the highest yields. Ensure that all wheat crops have received their T1 fungicide application by GS 32. Target the T2 fungicide application for winter barley at early awn emergence (GS 49).
Winter barley in Co Down last May
Potatoes
New developments in weed control
The withdrawal of paraquat (Gramoxone), two years ago, has forced us to be more creative in selecting herbicides for our potato crops. Last year the closest replacements were Basta and Retro, which had disadvantages compared to Gramoxone. This year Basta will not be available, while Retro can now be used at a more effective four litres per hectare rate. A major addition to the weed armoury for 2010 is the clearance for use of some of the Roundup family of products, which, for the first time, have approvals for use pre-emergence on potatoes. This will make for a very cheap and effective treatment and can be mixed with our most common residual herbicides to extend the duration of weed control.
Other factors to consider when controlling weeds in potato crops are:
- Stage of crop growth - There are few herbicides that can be used safely once the crop is fully emerged but a number of treatments can be applied at 10 to 40 percent emergence or before the crop is 15 cm (6 inches) tall.
- Variety grown - Some treatments should not be used on specific varieties, whilst other treatments have restricted use with some varieties. Growers should carefully check the product information before using a herbicide.
- Seed or ware crops - Herbicides which affect the crop foliage may render a crop liable to be rejected for seed classification. If a seed crop is to be treated make sure the product has approval for use on seed crops.
- Soil type - Lighter soils usually require lower doses of residual herbicides. Over-dosing can result in damage to the crop. Conversely, on soils with high organic matter levels some residual herbicides are ineffective or a higher dose rate may be recommended
Planting potatoes at Limavady
- Soil condition - Residual herbicides require moist soils to work well. Heavy rainfall following application on light or stony soils can move some herbicides down to the seed and may adversely affect the following crop. Residual herbicides usually perform poorly on cloddy tilths - often a problem on heavier soils.
Prevent blight infection from potato dumps
Dumps of last season’s potatoes are a major source of blight infection and their management should be incorporated into the potato production cycle.
We should examine potato dumps regularly for signs of sprout growth and take action to destroy all green material by spraying with glyphosate.
In the past, the residual herbicide Casaron G would have been used extensively to control regrowth on dumps. However, this is no longer available.
A substitute would be to completely cover and seal the dumped potatoes with black plastic, so as to isolate any possible source of infection.
