Dendrometer Stem Monitoring of Tomato Plants Attacked by Whiteflies in Greenhouses

Abstract

Mexico is one of the largest producers of tomato and the first exporter in North America and greenhouse tomatoes have to be grown without pesticides. Tomato plants are severely attacked by whiteflies that suck their leaves for sap and transmit viruses. An experiment was carried out in a greenhouse at the University campus and an insect net protected half of the transplanted tomatoes from insects. Whiteflies (Trialeurodes vaporariorum) were identified in the other tomato plants grown in tezontle substrate pots. Whitefly population was obtained by counting flies in upper leaves and with the use of a custom made vibrator. Plastic covered plates only indicated whitefly presence, but 10-minute vibration and leaf counting were similar. As the vibration increased to 15 minutes the number of flies sticked into the plastic doubled. Point dendrometers were fixed to the stem of two healthy and two infested plants to determine daily growth during the entire season. Plants infested with a population count of 50 whiteflies in the superior eight leaves showed limited growth and a lower shrinkage of 0.5mm was encountered after midday. As fly density increased to 20 whiteflies per leaf, transpiration decreased and plant stress increased, ending in a thinner stem.