Relationship between weedy rice (Oryza sativa) infestation level and agronomic practices in Italian rice farms

Weedy rice (Oryza sativaL.) is a troublesome rice (Oryza sativaL.) weed in Italy and in many other rice areas. The objective of this study was to correlate theO. sativainfestation level in northern Italy, the main European rice-growing area, with agricultural practices adopted by farmers by using data obtained from a farmer survey. In 2018 to 2019, a survey was carried out on 98 rice farms chosen to ensure different sizes, different cultivation practices, and variable degrees ofO. sativainfestation. The following information was acquired: farm size; area cultivated with Clearfield® varieties; the most-adopted agronomic practices (type of tillage, crop rotation, type of sowing, water management, origin of seeds, adoption of stale seedbed, use of imazamox, presence ofO. sativaresistant to imazamox); and level ofO. sativainfestation: low (≤5 plants m−2), medium (>5 to 20 plants m−2), and high (>20 plants m−2). The data were analyzed through descriptive statistics and ordinal logistic regression to determine which agronomic practices influenced the level ofO. sativainfestation. Farm clustering was also determined through two-step cluster analysis. Rice was cultivated as a monocrop and mainly sown in water, using purchased seeds, in plowed fields. More than half of the farms used the stale seedbed practice, and 63% adopted Clearfield® varieties, while about 45% of the farms reported imazamox-resistantO. sativa. The ordinal logistic regression underlined that use of a stale seedbed was correlated with the infestation level ofO. sativa, and the two-step cluster analysis showed that the farms were mainly grouped based on the use of this technique. Most of the farms that used a stale seedbed had higherO. sativainfestation than those that did not use it, meaning that this practice was mainly applied in zones whereO. sativainfestations were more serious.