Bioecology and control of pests of rose

Abstract

The distribution of the major insect and mite pests of rose in Trivandrum taluk and the damages caused by them were studied in a survey . The survey was conducted in six locations in the taluk (Kowdiar, Paruthippara, Karamana, Palkulangara, Vanchiyoor and Vellayani) at monthly intervals for a period of 13 months starting from August 1986, adopting standard sampling techniques . The results of the survey revealed that the major pests of rose in the area were the thrips, R. Syriacus, S. dorsalis, the scale A. aurantii, the leaf feeding beetles Adoretus spp and the mites, T. neocaledonicus and T.cinnabarinus. The mean levels of population /damage found during the period of the survey showed that T.neocaledonicus was the most important pest in all the locations and it caused more than 50 percent of the plants damaged in some locations. It was followed by Adoretus spp, A. aurantii, R. syriacus, S.dorsalis and T.cinnabarinus in a descending order of importance with apparent variations in pest status at different locations. An overall assessment of the seasonal incidence of the pests revealed that the thrips and mites were seen in serious proportions during the months of December to May and the beetles caused heavier damage from November to January whereas the scale insect was seen damaging the plants throughout the year. Between the population of thrips and mites and maximum temperature there was significant positive association. While the relative humidity and number of rainy days showed significant negative correlation. Rainfall also had significant negative correlation with the thrips and mites, but it was statistically insignificant in the case of T.cinnabarinus only. The nature of damage caused by various pests of rose was studied in detail. It was seen that the thrips, mites and the scales were causing serious damage to leaves causing its drying and withering. The other sucking pests and the defoliators noted were of minor importance except the leaf beetles Adoretus spp which was found to cause serious defoliation of the of the plants. The investigation on the biology of R.syriacus on the rose showed that the life cycle was completed in 16.9days. When they were reared on castor and subabul the duration and size of various stages were same as those of rose while those reared on cassava were bigger in size and the life cycle was shorter. The experiments on chemical control of pests of rose showed that monocrotophos, dimethoate or fenthion at 0.05percent spray was effective in controlling the different spices of pests . But in the case of flower bud damage caused by S.dorsalis, a higher concentration of 0.1 per cent of the insecticides was necessary for getting proper control.