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1. Introduction
Sinapis spp and Diplotaxis spp are cruciferous weeds very abundant and competitive in temperate areas worldwide that reduce yield in winter cereal crops, such as wheat (Triticum durum L.) [1–3] and in legume crops such as lentil (Lens culinaris L.) [4, 5], broad bean (Vicia faba L.) [6], and pea (Pisum sativum L.) [7]. Although wheat sunflower is one of the main crop rotations in Spain, winter legume crops for human or animal consumption are also usually introduced into the crop rotations. The results of field surveys conducted recently on 30,000 ha near Córdoba and Seville in Andalusia, southern Spain, indicated that more than 65% of winter crops were infested with cruciferous weeds, including Diplotaxis spp. (generally D. virgata Cav. DC. and D. muralis L. DC) and Sinapis spp. (generally S. arvensis L. and S. alba) [8]. Winter crop weeds in cereals are often controlled by presowing herbicides (e.g., glyphosate) and applying preemergence herbicides to legumes (e.g., linuron in broad bean and pendimethalin in pea). However, these herbicides cannot adequately control cruciferous weeds and specific herbicides, such as triasulfuron, and can be applied to postemergence cereals at weed flowering stage, although postemergence herbicides for legume crops have not yet been developed, and thus tillage or hand weeding is frequently used to reduce cruciferous infestations. Moreover, most winter crops in Mediterranean conditions are produced with nontillage or minimal tillage techniques to reduce the impact of soil erosion. Consequently, weeds such as cruciferous have become more problematic because they cannot be reduced by repeated tillage or cultivation.
Despite the usual uniform management of fields, patchy distribution of cruciferous and other weed species, as well as the potential herbicide savings from treating only infested areas, has already been assessed using geostatistical approaches [9, 10]. However, herbicides are usually broadcast over entire fields, and there are evident economic and environmental risks from overapplication. To overcome this situation, patch spraying (in cereals) or hand weeding (in legumes) of cruciferous weeds has supported the feasibility of using site-specific weed management (SSWM) for control of these worldwide weeds. A key component of SSWM is precise and timely weed maps, and one of the crucial steps for weed mapping is weed monitoring, either by ground sampling or...