An integrated approach to the management and reduction of volunteer potatoes is particularly important where less competitive crops, such as sugar beet, are part of the rotation.
Potato tubers left in the field at harvest lead to problems in following crops from volunteer potatoes. These volunteers compete with the crop for light, space and nutrients leading to reduced yields and quality. They are often also the source of potato blight infection. The problem can be particularly troublesome in crops such as sugar beet, where the crop is relatively uncompetitive during early stages of establishment and growth.
In general, potatoes reproduce both vegetatively and by true seed. The latter, though viable at an early stage of berry development, is generally a less extensive source of weed potato infestation. The greatest increase in volunteer potato problems arises as a consequence of vegetative reproduction. Varieties such as Cara and Maris Piper are renowned for their capacity to produce large numbers of small tubers.
The sugar beet crop, with its slow development and low competitiveness is the crop most likely to allow volunteer potato numbers to flourish. In the UK, there is a significant geographic overlap between the major potato and sugar beet growing areas, confirming the extent of the potential volunteer potato problem in these shared cropping regions. Volunteer potatoes can only be controlled successfully by complete integration of agrochemical and husbandry techniques.
In the sugar beet crop the single most important product to use in controlling volunteer potatoes is Dow Shield 400 (active ingredient clopyralid). Dow Shield 400 is selective to many arable and horticultural crops, whilst causing distortion of stems and foliage of potato plants. Efficient translocation to the daughter tubers results in reduced weight, number and viability.
Dow Shield 400, applied in tank mixture with ethofumesate containing products, is the very best treatment against volunteer potatoes in sugar beet. The effect on progeny tubers is carried through to succeeding generations, thus reducing the threat from volunteers in the second year after treatment. The extent of haulm control from Dow Shield 400 varies with variety, as shown below.
Potato control is consistently enhanced by tank mixing with ethofumesate or products formulated with ethofumesate. To increase flexibility, Dow Shield 400 has recommendations for tank mixing with many ethofumesate containing products.
The first application of Dow Shield 400 at 0.25 litres per hectare should be made when the volunteer potato shoots are between 5 cm and 10 cm tall, providing the sugar beet crop is at the correct growth stage. The second application, again 0.25 litres per hectare, should be made when volunteer potatoes are between 10 cm and 20 cm tall. This is the size of an untreated potato so, for an accurate guide to when this stage is reached; it is advisable to leave a small area of untreated volunteer potatoes in the field. Typically the second application is made 7 to 14 days after the first.