Crop Clinic

Potato volunteers  are a problem as they result in non-certification of a seed crop & difficulties in producing a uniform ware sample. They also sustain soil-borne pests and diseases between crops such as powdery scab and potato cyst nematode.

Control of volunteers is not easy and relies on an integrated approach utilising cultural and chemical methods.

Potato volunteers in cereals (May)

For those that have crops infested with groundkeeper or seedling potatoes there may still be time to undertake a treatment, although the crops are getting very close to ear emergence in some cases.  The next week or so is a good time because potato seedlings are still emerging.  Up to GS39 (flag-leaf emergence) a tank-mix of 100g/ha Harmony M SX (metsulfuron + thifensulfuron) or similar mix  and 1 litre Starane 2 (fluxoxypr) hectare is most effective, if no sulfonyl-urea has been used previously except for Eagle or Pursuit. Starane 2 can be used alone up to GS45 (boot swollen stage) at 2 litres per hectare, which allows for a more flexibility.  These treatments do not give complete control of groundkeepers, but reduce the number of tubers produced and their ability to survive and produce strong plants next season.

If you miss these growth stages, a pre-harvest glyphosate treatment is effective, but the potato plants should still be green at treatment. Do not use pre-harvest glyphosate in seed crops, and check with your merchant if it is bound for distilling.

Volunteer potatoes in set-aside (July)
Mid-July is often the best timing for tackling volunteer potatoes with glyphosate in set-aside land and it is best to treat the plants at or around flowering. Do not attempt to reduce doses; SAC trials show that the full recommended dose of glyphosate gives the most consistent results.

Timing can be a problem when considering control of volunteer potatoes in set-aside. In order to get good control of newly produced tubers from this season’s volunteers, there needs to be plenty of potato foliage present in July to be treated with glyphosate. Ideally the volunteers should be at or post-flowering for best effect. The volunteer problem is such that this treatment will be of considerable importance on many farms. So, where possible, do not treat the volunteer potatoes until flowering or beyond, and make sure that you maintain the best blight programs for your crop.

Failure to control the volunteer potatoes will give you problems for many years, and this must be seen as a priority.

Volunteer potato control in stubbles (cereals harvest)
There is an opportunity to control volunteer potatoes in stubbles using glyphosate products. In general, a high rate is recommended, and the best results are obtained when new tubers have started to be formed after there has been haulm re-growth after harvest. The spraying should be done before autumn cold starts natural die-back. There are suggestions that lower rates plus adjuvants can be used, but higher rates are preferred as conditions deteriorate. 

Volunteers from lifted potato crops
If you are aware that you may have a volunteer potato problem following difficult conditions at lifting, avoid ploughing until the spring so that tubers near the surface get a chance to be frosted. Shallow cultivations that bring any tubers near the surface will be of benefit.

Failure to control the volunteer potatoes will give you problems for many years, and this must be seen as a priority. It will be even more important than usual, meanwhile, to use the best programmes for blight control in your crops, and SAC advisers can help you develop such programmes.