Controlling weeds in potatoes is a problem for many farmers. Paraquat is a very useful herbicide for potatoes because it can be used to burndown weeds from before planting right up to the point at which the potato sprouts start to emerge from the soil1. This allows for weed control measures to be tailored to the weeds present. As potatoes may take up to four weeks to emerge, significant weed growth may have occurred after planting. Weeds can quickly overrun potato crops if they are allowed to grow unchecked before the crop leaf canopy closes.
They compete with potato plants for light, water and nutrients, so if they are not controlled weeds reduce yield and quality. In addition, large weeds entangle the crop and interfere with harvesting. Weeds may also encourage pests and diseases. Filling the crop canopy, they restrict air flow, increasing humidity under which fungal diseases, especially potato blight (Phytophthora infestans) thrive. Blight can devastate potato crops so intensive use of fungicides is needed to achieve control.
Paraquat is inactivated and immobilised immediately on contact with the soil, so cannot affect the seed potatoes, or later, the developing crop of tubers.
Over the past 20 years potato production has doubled in developing countries.