Leaf-specific weed control for vegetable crops in the UK

Weed control in field vegetables in the UK is becoming increasingly challenging due to the loss of herbicide actives and demands by policy makers and consumers for lower pesticide use. Research at University of Reading in conjunction with Concurrent Solutions LLC in the USA, is developing a robotic weeder for field vegetables using image analysis to locate weed leaves and a novel Drop-on-Demand (DoD) applicator to apply droplets of herbicides to these leaves. No chemical is applied to the crop and none directly to the soil. Leaf-specific application of herbicide droplets is an alternative to selective chemistry or biotechnology while potentially reducing herbicide use. Although targeted micro-rates of herbicides have been studied, little is known about the exact rates needed to control weeds when microdoses are applied as one droplet to a single leaf or plant. In glasshouse trials, individual weed seedlings were controlled by applying a single droplet of herbicide and dose-response relationships were quantified. As a general recommendation, weeds that are up to the 4-leaf stage can be controlled with a dose of 32 μg of glyphosate and 28 μg of glufosinate-ammonium when they are applied as a single droplet per seedling. In order to answer the question if the efficacy is reproducible in the field, manually applied droplets of glyphosate and glufosinateammonium were made to the naturally occurring weed population in transplanted cabbage and leek crop. Droplet applications made on three and ten occasions after transplanting the cabbages and leeks, respectively reduced residual weed biomass at harvest by over 90% compared to the weedy control. Also, droplet treatments gave a crop yield, which did not differ significantly from the weed-free control. At the same time, the total amount of herbicide active ingredient applied was up to 82% and 94% lower than currents spraying methods for the leeks and cabbages, respectively. Because of the high value of the crop and the higher yields associated with ultraprecise droplet application, it would appear to be economical to apply these droplets using a robotic weeder. The applicator which was developed by Concurrent Solutions LLC in the USA for Drop-on-Demand droplet applications was tested under indoor conditions. The effect of pressure, distance from the target, wind direction and motion of the applicator was tested on the targeting accuracy of the applicator. Recommendations for future field applications suggested that the applicator should operate at 138 kPa pressure and set at 15 cm height from weeds