Scotland: How to manage OSR disease and grassweeds this month
James Howat provides advice on oilseed rape disease management and looks at how best to control troublesome grassweeds in wheat crops across southern Scotland
At a glance
This month’s key messages
- Use the Bayer/ADAS SpotCheck initiative to monitor OSR disease risk
- Apply a fungicide to untreated crops at risk from light leaf spot and phoma
- Do not apply prothioconazole with OSR herbicide carbetamide
- Metconazole provides the best PGR partner for prothioconazole
- Minimise pigeon grazing in OSR crops
- Apply a contact and residual herbicide spray where grassweeds are present in wheat
Crop progress
Winter cereals have all been drilled and are growing away well, except for the last remaining winter wheat crops after potatoes. With the relatively dry autumn so far, these late crops should go in to good soil conditions when planted. Where pre-emergence herbicides have been applied, growers have been happy with performance and there shouldn’t be any further issues with annual meadow grass.
Oilseed rape has established well, with very little cabbage stem flea beetle damage in the region when compared to further south. Growth stages range from about 5 true leaves up to 10 true leaves.
James’s agronomy tips for November
- Use the SpotCheck service to uncover any latent OSR disease
It is important to use decision support tools where possible and the Bayer and ADAS SpotCheck service is something growers and agronomists should be taking advantage of. Sampling kits are available on request from ADAS Rosemaund and will provide a picture of any latent disease problems in the crop and help inform of the need for fungicide treatment.
- Apply any outstanding OSR fungicides during November
Most growers will have already applied an autumn fungicide to control light leaf spot and phoma, but where that might have been delayed, it will be worth considering a treatment based on current risk and a variety’s resistance score. Where disease is present or a variety has a score of below a 7 for light leaf spot or below 6 for phoma, a 0.32L/ha or 0.46L/ha application of prothioconazole will help protect the crop against both diseases.
- Be aware of suitable tank mix partners for late prothioconazole sprays
Where growers have outstanding OSR fungicide applications, there will be a temptation to apply them with the grassweed herbicide to save an extra pass of the sprayer. If using prothioconazole, it is compatible in a tank mix with Kerb Flo 500 (propyzamide) and Astrokerb (propyzamide + aminopyralid), but make sure soil conditions are suitable for the herbicide to work effectively (soil temperature of 10C or below at 30cm). It should be noted that prothioconazole is not compatible with carbetamide products, such as Crawler.
- Use a suitable PGR in big OSR crops
Prothioconazole will give the best broad-spectrum disease control, but it has no PGR effect, so a suitable partner is required where shortening required. Tebuconazole is an option, but requires about 25g per true leaf to have any meaningful effect. As there is a limit of 250g/ha for each crop, it will only be effective up to 10 true leaves. Metconazole has stronger PGR activity, but remember that it is weak on disease.
- Monitor pigeons and keep them on the move
As temperatures drop, pest pressure will fall away, but the threat from pigeons remains. Growers should monitor high-risk areas, such as field edges around woodland or in thin crops. Keep them off crops with strategically-placed rockets or gas guns to minimise grazing damage.
- Take grassweeds out of wheat with post-emergence herbicides
Where grassweeds have escaped the pre-emergence herbicide in wheat crops, a follow spray containing a contact and residual should be applied. Options include Atlantis OD (iodosulfuron + mesosulfuron) and Hamlet (diflufenican + iodosulfuron + mesosulfuron). These should always be applied with Biopower and pendimethalin is the ideal option for an additional residual partner. Othello (diflufenican + iodosulfuron + mesosulfuron) is also available in the autumn, but some growers favour its use for annual meadow grass control in the spring where that is their main target.
