Imidacloprid is a systemic insecticide that is applied to the soil through irrigation systems. Imidacloprid follows the water-conducting channels (xylem) within the tree and is thus easily distributed to all tissues. Many insects, including the Asian citrus psyllid (ACP), feed from the vascular system. Systemic pesticides like imidacloprid are, therefore, ideal against such pests since they directly target the insects during feeding. One of the attractive features of imidacloprid is its persistence. A good application can result in several months of protection. And, because of its systemic properties, imidacloprid will move from older tissues into developing leaf tissues during flushes. In our research we are studying the conditions within citrus groves that are conducive to better imidacloprid uptake. At a commercial grapefruit grove in Riverside County, we evaluated 2 application rates (1X label rate and an experimental 2X label rate) of imidacloprid in 50-year old trees growing on sandy soil. Late Summer/early Fall applications of imidacloprid were very effective with rapid uptake and persistence through the winter months to the following Spring. At the higher experimental 2X rate, the imidacloprid concentrations in young flush recovered to levels that would be toxic to ACP. With early Spring applications, there was a long delay before the appearance of imidacloprid within the leaf tissue at ACP target threshold levels. The experimental 2X rate was noticeably more effective than the 1X rate, providing good protection to trees at a time that is likely to be critical for ACP control should the insect establish on commercial citrus in California. The delay in uptake observed with the Spring applications may be linked to poor root development at that time of year. Applications later in the year occur at a time when root activity is well established, thereby allowing for a more rapid rate of uptake. At a second site in Ventura County, 24-year old lemon trees growing on a heavy clay soil were treated with the label rate of imidacloprid. Treatments between June and August resulted in very poor uptake and on no occasion during the season did imidacloprid concentrations reach the ACP threshold level. Interestingly, imidacloprid levels within the trees appeared to spike at several times during the season, albeit at low levels. This pattern is likely due to the irrigation schedule used at this site, which is on a 3-week cycle. However, with long periods between irrigations, imidacloprid uptake was less effective. The impact of irrigation frequency on imidacloprid uptake was compounded by the heavy soil conditions at the lemon grove. Imidacloprid can become bound up in heavy clay soils, particularly when water is not available to keep the imidacloprid solubilized. With no water to release it from the binding sites on soil particles, imidacloprid uptake may be compromised. At the grapefruit grove, irrigations were more frequent (weekly) and, combined with the sandier soil conditions, there was less opportunity for imidacloprid to become bound up and unavailable for uptake. Comparisons of imidacloprid behavior in citrus groves are critical to our understanding of the role that imidacloprid will play in the management of ACP.