Factors affecting the uptake of chlormequat into cereal leaves

The effects of site of application, growth environment, droplet size, and formulation adjuvants on the retention and uptake of ¹⁴C-chlormequat by wheat cv. Avalon and barley cv. Sonja have been examined using solutions applied by a micro-sprayer. Wheat plants retained a higher proportion of droplets on initial impaction than barley irrespective of growth stage, site of application or formulation. Leaf retention increased approximately two-fold with increase in surfactant concentration (0·03·0–3% w/v) or decrease in droplet size (200-125 μm) but declined markedly with age of leaf. Uptake, which was greater into wheat than barley, increased with increase in surfactant concentration, growth temperature and droplet size, with a combination of decrease in irradiance plus a rise in soil moisture, and after exposure to simulated dew. Droplet reflection increased and chlormequat uptake declined when the fungicide preparations Bavistin and Radar replaced Agral 90 in the spray mixtures. Droplets impacted more readily and spread more extensively over the damaged surfaces of field grown leaves. Both tissue combustion and autoradiography showed that chlormequat translocated readily only in immature tissues.