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ARS Home » Pacific West Area » Wapato, Washington » Temperate Tree Fruit and Vegetable Research » Research » Publications at this Location » Publication #377129

Research Project: New Technologies and Strategies to Manage the Changing Pest Complex on Temperate Fruit Trees

Location: Temperate Tree Fruit and Vegetable Research

Title: Residual activity of Acaricides for controlling spider mites in watermelon and their impacts on resident predatory mites

item Schmidt, Rebecca
item COFFEY, JOHN - Clemson University
item MILLER, GILBERT - Clemson University
item MONICA, FARFAN - Colorado State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2020
Publication Date: 1/27/2021
Citation: Schmidt-Jeffris, R.A., Coffey, J.L., Miller, G., Monica, F. 2021. Residual activity of Acaricides for controlling spider mites in watermelon and their impacts on resident predatory mites. Journal of Economic Entomology. 114(2):818-827.

Interpretive Summary: Twospotted spider mite is an international pest of watermelon. Feeding by spider mites removes chlorophyll and other cell contents from leaves, resulting in decreased plant vigor, which decreases fruit production. This pest is managed solely with pesticides, but is notorious for rapidly developing pesticide resistance. In some crops, outbreaks of this pest can be avoided by conserving predatory mites, which feed on the pest spider mites. Identifying pesticides that quickly control twospotted spider mite, require few applications, and cause minimal harm to predatory mites will greatly improve pest management in watermelon by reducing the risk of pesticide resistance development and allowing for increased use of natural biological control by growers. Researchers at the USDA-ARS in Wapato, WA in collaboration with scientists at Clemson University and Colorado State University, conducted two field trials and two laboratory studies to determine which pesticides were most effective at controlling twospotted spider mite on watermelon but did not reduce predatory mite abundance. In the field trials, all pesticides except tolfenpyrad reduced pest mite populations, but all products also reduced abundance of a key predatory mite. In the laboratory experiments, abamectin and bifenazate caused the highest mortality of spider mite adults, whereas etoxazole had the longest lasting residues and prevented egg hatch. A combination of an adult-killing with an egg-killing pesticide may be the most effective for control. However, new pesticides that are more selective for predatory mites need to be developed and registered on watermelon to preserve biological control

Technical Abstract: Twospotted spider mite, Tetranychus urticae Koch (Trombidiformes: Tetranychidae) is an important, worldwide pest of watermelon, Citrullus lanatus L. (Thunb.) Matsum. & Nakai (Cucurbitales: Cucurbitaceae). Feeding results in chlorotic spots and leaf necrosis, which can substantially reduce yields. In watermelon, T. urticae is managed solely with acaricides. Issues with acaricide resistance and pesticide label restrictions on number of applications per season require research-based recommendations on products with effective, long-lasting residues. To improve recommendations for T. urticae management in watermelon and to measure possible effects on non-target beneficial mites, we conducted acaricide efficacy trials in two locations in South Carolina, USA. The adulticidal products abamectin, bifenazate, fenpyroximate, and tolfenpyrad and the ovicidal products spiromesifen and etoxazole were tested. We also conducted two bioassays to better determine duration of acaricide residues. In the field trials, all acaricides except tolfenpyrad reduced T. urticae abundance, but all acaricides also reduced abundance of the most common predatory mite, Neoseiulus fallacis (Garmin) (Mesostigmata: Phytoseiidae). In the bioassays, abamectin and bifenazate residues caused high adult T. urticae mortality at up to 21 d after treatment, performing better than fenpyroximate and tolfenpyrad. Etoxazole and spiromesifen were longer-lasting, with <1 offspring per treated female in the etoxazole treatment at 28 d after treatment. Based on efficacy, abamectin or bifenazate should be rotated with etoxazole for fast knockdown of active stages while reducing reproduction, respectively. However, development and registration of more selective acaricides in watermelon is needed to preserve biological control of T. urticae by predatory mites