Weeds, worms and geostatistics

Weeds and plant-parasitic nematodes occur in patches in agricultural fields. Farmers can control them with chemicals. They can do so precisely and prevent competition (from weeds) and predation (by nematodes) provided they know where the pests are early in the lives of their crops or before sowing or planting them. Standard geostatistical methods have been used successfully to analyse counts of both weed seedlings and nematodes in the soil and to map their distributions from kriged estimates. The application is technologically sound. The most serious obstacle to its application in farming is that sampling must be intense, with spacings between sampling points of 20–40 m. This means that the cost of sampling and counting the pests is greater than the savings from not applying herbicides or nematicides. Only for potatoes is the effort and cost of estimating the burdens of the parasitic cyst nematodes of the genusGlobodera justified economically. For precise control of weeds proximal sensing at the seedling stage seems more promising.