One area where greenhouses are having an impact is the citrus industry. Citrus nurseries are facing more and more problems from the Asian citrus psyllid. This bug can carry a bacterial plant disease that slowly kills citrus trees. The bugs are very hard to keep out of orchards and once one tree is infected all nearby trees may also become infected, until the whole orchard or nursery is affected. Thus, growers have been turning to growing citrus nursery stock in greenhouses and screenhouses. Citrus trees require precise humidification and temperature control, so a high pressure fogging system and fans are a perfect way to keep the trees healthy and growing at an optimal rate as long as the system can be automatically triggered when humidity and temperature are no longer at proper levels.