Most studies on weed population dynamics in farming systems have focused on the effects of different weed control strategies. Those studies usually assume that farmers, operating within a particular system, have a uniform management style. However, it is likely that weed management decision making also varies between farmers that operate within a system. In this study, the relationship between weed management behavior and the outcome of that behavior within an organic farming system is studied. It is hypothesized that differences in weed pressure between organic farms can be related to differences in farmers' weed management behavior. We explore which weed and general management factors are of main influence on the weed pressure, and investigate the influence of farmer's beliefs and knowledge on weed control techniques and the observed weed pressure. Preventive measures and timing of main soil tillage operation were identified as the weed management factors most influential for weed pressure. With the increasing number of preventive measures applied, weed pressure decreased, with a stale seedbed being the most important preventive measure. The weed pressure increased with the number of days after September 1st on which the main tillage operation was carried out. Because of this postponement of the tillage treatments, the growing season of weeds was extended and more species were able to reproduce before winter, thereby enhancing weed pressure. Field size, rather than weed pressure, determined the number of hand-weeding hours per ha; with increasing field size the amount of hand weeding per surface area was reduced. On farms with lower weed pressures a higher percentage of competitive crops were grown than on farms with higher weed pressures. The farmer's beliefs and knowledge on weed control techniques differed between farmers with different weed pressures. Market-oriented growers had a higher on-farm weed pressure than crop-growth–oriented growers. It was concluded that studies on weed management behavior and the effect of that behavior can lead to a better understanding of farming systems and to more effective weed management in those systems.

Leaf-beet is a typical and very important protected cultivation crop in central Italy. In leaf-beet protected cultivation, weed control is one of the most important problems because of its fairly long crop cycle (approximately 4–5 months). The aim of this research was to set up an efficient non chemical weed control strategy performed with innovative machines built and set up by the University of Pisa. A two-year (2006–2007) ‘on-farm’ experimental trial was carried out in Crespina (PI). A conventional weed management technique (consisting of one pre-transplanting chemical treatment) was compared with an innovative physical weed control strategy in an organic production system (consisting of using a stale seedbed technique, in several post-emergence precision hoeing and in-row hand-weeding treatments). In the conventional technique, leaf-beet was manually transplanted, while it was sown with a precision pneumatic planter in the organic system. All innovative machines for physical weed control were adjusted and set up for the protected cultivation. Similar yields were recorded for the two systems in this two-year trial. Total labor time (for weed management and crop planting) was appreciably lower in the conventional system in the first year of the experiment (−67%), while in the second year, some improvement in the physical weed control techniques decreased labor needs with respect to the conventional technique (−40%). Weed dry biomass at harvest was significantly lower in the organic cropping system (on average −50%).