Now Is the Time to Start Scouting for Rust Mites

Josh McGillPests, Tip of the Week

By Xavier Martini

Rust mites are recurrent pests in Florida that pose problems mostly in fresh citrus production. While severe infestations can lead to fruit drop, leaf injury and abscission, rust mites cause aesthetic damage in the form of sharkskin or bronzing on the skin of fresh fruit (Figure 1A). Fresh fruit requires clean and undamaged skin, and any abrasions or visible damage can tremendously reduce fruit grade and marketability.

Rust Mites
Figure 1. A: Rust mite feeding can result in sharkskin damage (photo by Danielle Sprague). B: Rust mites can be observed on fruit skin with magnification (photo by Emilie Demard).

Rust mite damage is often visible as the fruit gets close to its final size. However, at this stage, damage has already occurred, and it is too late to act. Early scouting and timing for mite control are key to preventing major damage to fresh fruit.

Rust mites are in the Eriophyidae family and are characterized by an elongated body, four legs and a very small size that makes them impossible to observe without magnification (Figure 1B). There are two main species of concern: the pink citrus rust mite (PCRM) and the citrus rust mite (CRM). PCRM populations begin to increase in April to early May on new foliage, reaching a peak in mid-June to mid-July. CRM population densities increase in May–July.

For best results, it is recommended to scout 20 trees per 10 acres, with four fruit per tree taken midway in the canopy. Trees should be randomly selected and not adjacent, and fruits should be sampled at random with a 10X or 14X hand lens in each of the four quadrants of the tree. A hand lens view is approximately 1 cm2,and the number of rust mites should be counted to determine if the density has reached the action threshold. The number of rust mites per cm2 should be averaged for the 10 acres. For fresh fruit production, an average of two rust mites per cm2 is considered the action threshold. The action threshold is six rust mites/cm2 for processing fruit.

Xavier Martini is an assistant professor at the University of Florida Institute of Food and Agricultural Sciences North Florida Research and Education Center in Quincy.

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