Glyphosate applied to genetically modified herbicide-tolerant sugar beet and 'volunteer' potatoes reduces populations of potato cyst nematodes and the number and size of daughter tubers

Glyphosate, applied early or later or twice to genetically modified glyphos ate-tolerant sugar beet, gave excellent control of planted 'volunteer' pota toes growing within the crop compared to conventional herbicide programmes with or without clopyralid. In three out of four trials, this resulted in s ignificant reductions in the numbers of eggs and cysts of potato cyst nemat odes (Globodera rostochiensis and G: pallida) where infestations were moder ate (23-89 eggs g(-1) soil). In the fourth trial, which had very high initi al populations (130 eggs g(-1) soil), none of the herbicide treatments had any significant effect on numbers of nematode eggs or cysts. This was proba bly due to competition for feeding sites, and the early death of the potato es in all treatments caused by feeding damage by the nematodes and infectio n by blight, which prevented the nematodes from completing their life cycle . Glyphosate also significantly reduced the number and size of daughter tub ers produced, thus helping to prevent a further volunteer problem in the ne xt crop in the rotation. This was achieved by one or two applications of on e chemical compared to 2-5 applications of cocktails of conventional herbic ides.