Redberry mite

The Acalitus essigi, commonly referred to as the redberry mite, is a microscopic pest belonging to the family Eriophyidae within the order Trombidiformes. Because of their minute size and hidden life cycle within plant structures, these mites often go undetected until significant damage to the crop has already occurred.

This pest specifically targets cultivated and wild blackberries. The mites feed primarily on the drupelets of developing fruit, injecting enzymes that prevent the berries from ripening normally. This specialized feeding habit causes distinct physiological issues that affect the entire yield of the plant if left unmanaged.

The biological cycle of Acalitus essigi is synchronized with the phenology of the host plant. Adult females overwinter under bud scales or within crevices on the canes. As temperatures rise in spring, they move to the emerging flower buds to begin feeding and reproduction. The mite completes multiple generations per season, with its reproductive rate heavily influenced by warm, stable weather conditions.

The primary symptom of infestation is known as the "redberry disease." Fruits affected by the mite fail to ripen into their characteristic black color, remaining hard, sour, and partially red or green. These deformed berries are commercially worthless, leading to severe economic losses for growers who fail to implement preventive measures early in the season.

Management strategies focus on reducing the mite population before they infest the fruit clusters:

• Sourcing certified, mite-free propagation material to prevent initial introduction.
• Sanitation practices, including the removal and destruction of infested canes and old leaves where mites overwinter.
• Application of specialized acaricides during the dormant bud stage and early pre-bloom periods.
• Frequent field scouting during the fruit development stage to identify and prune out heavily infested clusters.