Organic conversion – keeping a clean site
When it comes to using chemicals in organic vineyards, it is commonly thought that farming organically involves no pesticides. Others often assume that we are allowed to spray with copper, sulphur and Bordeaux mixture only, and that we can drench the vines with these chemicals as much and as often as we like. Both of these views are inaccurate, and so I want to use this issue to give a true picture of organic disease control in vineyards. This is particularly relevant as I am writing this in mid-harvest 2001 (the press is running as I write), and we have seen grapes with heavy botrytis and powdery mildew infections. I should point out that the organically grown grapes have not been the worst, and our own crop has been among the cleanest grapes crushed this year.
The Soil Association standards state that the following pesticides (and nothing else) are allowed for use on organic vines:
- Sulphur permitted for use on vines, with no restrictions beyond those applied to any UK vineyard.
- Copper oxychloride & copper sulphate - Copper is a restricted product, therefore permission must be sought for its use from SA Certification. The EU are due to review the use of copper in organic systems in the spring of 2002 and it is important that we are aware of the quantities and frequency with which it is used on Soil Association registered holdings. Where copper is used on top fruit and vines it is important to be aware of residual copper levels in the soil. These must not exceed 50 mg/kg of total copper in top soil on a dry matter basis. Following a soil analysis we were given permission to spray copper oxychloride up to 3 times this year at 0.6 kg per hectare. We have been asked to keep weather records to justify each occasion.
- Foliar feeds - Several seaweed derived nutrients
From the above list it is immediately obvious that there is no chemical defence against botrytis. Dr. Uwe Hoffman explained to me that in an organically healthy balanced vineyard botrytis is not really a problem - the challenge is to achieve healthy balanced soil and vines.
This year is our first under full organic management. We have sprayed on 5 occasions over the summer, and I include my spray record sheet for the Horsmonden vineyard site below:
- Biomax GP is a natural growth promoter. We are trialling this product for the manufacturer (with Soil Association approval) to assess its effect on a vines resistance to downy mildew.
- Comfrey solution is a foliar feed containing moderate levels of nitrogen and high levels of potassium. This is made at Davenport Vineyards using home-grown comfrey leaves.
Time is spent to getting the spray application right – correct application rate, good coverage, and correct weather conditions – the stuff that all vineyard managers already know about.
Our Horsmonden vineyard was completely disease-free throughout the summer, while our Rotherfield site saw some powdery mildew in June followed by a downy mildew outbreak in August. These were brought under control with heavy applications of sulphur and Biomax GP. By the end of September there was no significant active disease seen in the vineyard, a slight botrytis presence was seen, although at very low levels. Leaf stripping helped to improve air flow, and infected bunches were removed when seen. Early grape samples indicated that harvest was likely to be 1 to 2 weeks late, meaning that we still had up to a month to cross our fingers. The vines were netted against birds on 23rd September, after which we were unable to spray. Little more could be done to help. It is.