Threshold‐based spraying decision programmes for the red spider mite Tetranychus marianae on eggplant

Abstract

The red spider mite, Tetranychus marianae McGregor (Acari: Tetranychidae), has been an important pest of eggplant Solanum melongena L. (Solanaceae) and other vegetables in the Mariana Islands. The damage due to T. marianae has been severe and caused huge economic losses. Because no threshold levels are available for T. marianae, many growers are applying up to 12 chemical applications per eggplant cropping period. This is not only expensive, but also results in lower yields because of extensive foliar damage and development of resistance in mites to chemicals. To diminish the calendar‐based chemical applications and to preclude damage to foliage and fruit quality, this study was undertaken for the development of a threshold level for optimum timing of chemical applications for T. marianae. In the direction of this aim, an attempt was made to generate different threshold levels by applying chemical spray (Sun‐spray 6E, 5 ml/l) within 12 h after reaching the threshold levels at 2, 4, 6, 8 and 10 mites/leaf, as well as current recommended calendar‐based sprays and non‐sprayed control in a replicated block design for the dry and wet seasons of 2010 at two locations (Yigo and Inaranjan) in Guam (USA). Based on T. marianae‐infested leaves, incidence of T. marianae and yield levels, the plots sprayed at 2 or 4 mites/leaf in the dry season and 2–8 mites/leaf during the wet season had significantly lower leaf damage and incidence of T. marianae compared with a greater number of mites/leaf in calendar‐based sprays and control plots. At the greater threshold levels, the mean yield was significantly reduced in comparison with the mean yield obtained when plots were sprayed at a threshold of 2–8 mites/leaf. Therefore, it is concluded that the optimum threshold chemical spray for T. marianae on eggplant is 4 mites/leaf during the dry season and 8 mites/leaf in the wet season.

Density threshold‐based acaricide application for the two‐spotted spider mite Tetranychus urticae on cassava: from laboratory to the field

“…The determination of these thresholds requires yield tests for one growing season or more. There are several studies regarding the economic injury level, economic threshold, action threshold, damage threshold and control decision threshold of T. urticae in different plants, such as corn, strawberry, Bartlett pear, ivy geranium, hop, cabbage and eggplant . To the best of our knowledge, there are only a few studies about these ‘thresholds’ in cassava green mite (CGM) Mononychellus tanajoa , which is the only mite species studied on cassava.…”

Action Threshold Treatment Regimens for Red Spider Mite (Acari: Tetranychidae) and Tomato Fruitworm (Lepidoptera: Noctuidae) on Tomato

“…Growers should be recommended to follow the practice of action thresholdbased chemical sprays in managing major pests for tomatoes and avoid the traditional regular The action threshold-based chemical spray has been used to control T. marianae with Sunspray 6E on other crops such as eggplant, with the optimum threshold of 4 mites per leaf during the dry season and 8 mites per leaf in the wet season (Reddy et al 2013). For our present study, the same Sun-spray 6E was used and resulted in the mean number of T. marianae and infested leaves of tomato plants being significantly fewer in threshold-based chemical spray treatments than in regular spray treatments.…”

“…In fact this species was described first from specimens collected in Tinian, Mariana Islands (McGregor 1950). Tetranychus marianae is also a pest of several annual crops and certain perennials (Reddy et al 2013). This mite could also become important in pasturelands and rangeland .…”

Field Evaluation of Petroleum Spray Oil and Carbaryl AgainstTetranychus marianae(Acari: Tetranichidae) on Eggplant

“…The present study extends this work by developing an integrated approach to T. marianae control. Reddy et al (2013) reported that eggplant plots sprayed with petroleum spray oil (PSO) at a threshold of 2 or 4 mites/leaf in the dry season and at 2-8 mites/leaf during the wet season experienced significantly less leaf damage. Similarly on tomato, based on T. marianae infested leaves, the population density of and degree of plant damage caused by T. marianae on tomato was significantly reduced when experimental plots were sprayed at a threshold of 8-12 mites/leaf in the dry season and at 8-14 mites/leaf during the wet season (Reddy & Tangtrakulwanich 2013).…”

“…The red spider mite, Tetranychus marianae McGregor (Acari: Tetranychidae), is a severe pest on vegetables and ornamental plants in the Mariana Islands (Reddy et al 2011) where it feeds and reproduces year round (Moraes et al 1987;Reddy et al 2013). The climate of the Mariana Islands is hot and humid year round, resulting in high mite populations and severe damage to eggplant (Solanum melongena L.; Solanales: Solanaceae) and tomato (Solanum lycopersicum L.; Solanales: Solanaceae) (Reddy & Tangtrakulwanich 2013).…”