Remote sensing using unmanned aerial vehicles (UAVs) can obtain high-resolution surface data of weed communities over time and is expected to be useful for monitoring their dynamics. In this study, we estimated the leaf area index (LAI) of a community dominated by kudzu (Pueraria lobata (Willd.) Ohwi) and evaluated its growth and spatial distribution based on the spectral reflectance measured by the UAV. The multispectral images of the riverbank (40 m × 30 m) were obtained from a 50 m altitude five times from June to October 2018. The orthomosaic images were then generated and divided into 3221 grids (50 cm × 50 cm). The multiple regression models, used to estimate LAI from three vegetation indices, were acquired on each observation date (adjusted R² = 0.42–0.57) except for October 2 (adjusted R² < 0.2). The LAI estimated from the regression models were found to decline in the center of the kudzu community from July to August 2018, as the clusters of high LAIs moved from the center to the outer margins of the community. This change is seemingly due to the spread of leaves on higher-order branches, which occurs in the renewal process of leaves during the summer. Time-series spectral reflectance measured by UAVs is considered to be useful in evaluating the spatial growth and distribution of weed communities.

Wild oat (Avena fatua L.) is a problematic weed in small grain crops. I evaluated the effects of lime-nitrogen (LN) fertilizer application on seed reduction during the non-crop season, which might be used as part of the integrated control of this weed. The LN was applied in summer and autumn, after wild oat seed shedding and before emergence. I conducted field pot experiments to investigate the effects of commercial granular LN fertilizer application rate, application timing, wild oat seed density, seed over-summering conditions (buried in soil versus surface-sown), and differences among populations on emergence patterns. The application of LN equivalent to 60 kg/10 a of commercial fertilizer between July and September, with 4,000 seeds/m² in the soil, promoted early, uniform emergence in mid-September and reduced emergence in the winter and the following year. To simulate no-till conditions in summer, I left the weed seeds on the soil surface over the summer. Under these conditions, the total number of emerging seedlings was reduced when compared with the number that emerged after the seeds were incorporated into the soil. The application of LN under these no-till conditions had an additive effect on the inhibition of germination and mortality of the wild oat soil surface seeds. When I compared five wild oat populations with different germination characteristics, LN application tended to advance the uniform emergence of the seedlings, but the peak emergence period differed according to the germination characteristics of each population.