The distinction is not usually necessary for pest management decisions. The viruses and thrips frequently enter the greenhouse with vegetatively propagated plant material. For example, hanging baskets with vegetatively grown crops should not be placed over susceptible seedlings, if possible, since most young plants are susceptible to both thrips injury and virus infection. Plants that appear healthy prior to transplanting may die or show low yields later in the field. Insist on good thrips control from your plant suppliers.
Information is available for retrofitting active or passive ventilation-type houses.
Count and change cards weekly, noting upward population trends that signal the need for treatment. More than 10 WFT per card per week is a threshold value some growers have found useful. To monitor plants directly, tap flowers or portions of plants over a white paper or board to dislodge thrips. Although still quite small, the background makes them much easier to see. A hand lens may be helpful to see the nymphs.