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Crops notes June 04

Potatoes

Blight Control

It is time to plan this year’s blight control programme. Key elements are the removal of infection sources and a spray programme timed to have maximum impact.

Hygiene

Minimise problems later by eliminating infection sources now. Growers should:
  • Plant healthy seed;
  • estroy potato dumps;
  • Eradicate volunteer potatoes in cereal and vegetable crops.

Targeting fungicide use

Blight is encouraged by warm, humid conditions but since weather varies across Northern Ireland blight risk is also variable. It is important that growers know the risk in their own area so that fungicides can be targeted properly and disease controlled effectively with the minimum amount of fungicide used. Targeting can be achieved by using Smith Periods, which use temperature and humidity data to predict the risk of blight outbreaks.

Blight-Net

DARD Blight-Net 2004, which is available from Tuesday 1 June, will provide potato growers with information on blight in their local area through the Internet at the Blight Net page on RuralNi. Upon entering Blight-Net growers can select the Blight-Net weather station nearest to them and see twice weekly updates on the incidence of Smith periods and "risk hours". Also included is an analysis of the blight risk, specific advice for that area, and links to DARD’s recommended blight control strategy for 2004. Armed with this information growers will be able to judge the best time to start their blight control programme and adjust spray intervals according to current local blight risk.
This season weather data will be collected from Newtownstewart, Limavady, Antrim, Belfast, Dervock, Ardglass, Moyallen and Magherafelt.
Blight Warnings are also available via the Blightline 24 hour telephone service on (028) 9038 2372 from 1 June. Warnings will also be broadcast on local radio including Farmgate on Radio Ulster and can be issued via text messaging.

Fungicide programme 2004

Growers are reminded that the use of products containing fentin (tin) fungicides is now illegal and all stocks should have been disposed of safely by 31 March 2004.
Two types of systemic fungicides are approved for blight control, phenylamides (e.g. metalaxyl-M in ‘Epok’, ‘Fubol Gold’) and propamocarb (in ‘Merlin’, ‘Tattoo’). Systemics are most useful early in the season when crops are growing rapidly.
Strains of blight resistant to phenylamides (but not propamocarb) occur in Northern Ireland and reduce the benefit of using phenylamide products. To help limit the incidence of phenylamide resistance growers who opt to use phenylamides should apply no more than two phenylamide-based sprays and avoid their use after mid-July. This strategy has resulted in a reduction from 76 percent of blight samples containing phenylamide-resistant strains in 2001, to 60 percent and 59 percent in 2002 and 2003, respectively.
Following consultation with Dr. Louise Cooke and George Little, Applied Plant Science Division, DARD the following fungicide programme is suggested for 2004:
  • Start the fungicide spray programme as soon as a blight warning is issued or when the crop meets within the drills (whichever is earlier)
  • Start with a product containing a systemic, either propamocarb (e.g. ‘Merlin’ or ‘Tattoo’) or a phenylamide (e.g. ‘Epok’, ‘Fubol Gold’). If a phenylamide is used, do not exceed 2 sprays and switch to another product no later than 15 July
  • Continue with either a protectant (e.g. ‘Electis’, ‘Ranman’, ‘Shirlan’) or translaminar (e.g. ‘Curzate’, ‘Invader’, ‘Sonata’)
  • Complete the programme with at least 3 sprays of a protectant such as ‘Shirlan’, or ‘Ranman’ to help prevent tuber infection
  • Ensure protection is maintained by regular spraying until the haulm is dead
Appropriate spray intervals and complete coverage of the crop are the key to successful blight control. In humid, wet weather favourable to blight, use shorter intervals as recommended on the product label for high risk conditions. Nozzle selection can influence the efficiency of application and the volume of water used. Angled jets give better canopy cover at all stages of growth but particularly up to and including full canopy cover from which point the crop starts opening up allowing easier canopy penetration.
At the end of the season, if there is blight in the crop, destroy the haulm as soon as possible to reduce the risk of tuber blight and wait at least 3 weeks before lifting.

Spring Barley

Nitrogen top dressing
The optimum timing for a nitrogen top dressing in spring cereals is up to mid tillering (GS 25). Avoid excessive applications of nitrogen by fully taking into account any organic manure applications or nitrogen contribution from previous cropping.
Weed Control
Aim to apply a broad-spectrum herbicide whenever most of the weeds are at the two – four leaf stages. This will ensure that weed competition is removed at an early stage of crop development. The mixing of two herbicides from ‘different families’ should be considered as a precaution against herbicide resistance.
Fungicide Programme
For spring barley crops with high yield potential, a two-spray fungicide programme can be justified. This is based on the use of reduced rate fungicide applications. The first application should be applied from late tillering to the start of stem extension. The second fungicide application should be made three to four weeks after the first at around GS 39 – 49 (flag leaf emergence – first awns visible).
Mixtures of triazole, for example, Opus (epoxiconazole) or Punch C (flusilazole), at a rate appropriate to the level of disease infection and a strobilurin, for example, Acanto (picoxystrobin) or Twist (trifloxystrobin), or a strobilurin/triazole product such as Landmark (epoxiconazole + kresoxim- methyl), are appropriate for both first and second treatments.
For growers adopting a single fungicide approach this single application should be made at the earlier timing as this usually gives the best financial return.

Environmental Issues

Insects are a vital food source for wild-bird chicks in June. Insecticides used after mid-March have a severe effect on June insect populations in crops. Countryside Management Scheme participants must not treat any fields entered into the Conservation Cereal option with an aphicide (or any other insecticides) after 15 March. Growers not in the option should consider whether an aphicide is needed. The Home Grown Cereals Authority (HGCA) guidelines are that the treatment threshold with an aphicide only occurs when more than 66% of the ears are infested and not to treat if more than 5% of aphids are mummified. If an aphicide is needed choose a selective product and consider using a reduced rate.
DARD Farm Management Notes for June 2004 have been prepared by Greenmount Campus, College of Agriculture, Food and Rural Enterprise - Tel: 028 9442 6771.