How We Grow

2019 July/Aug How We Grow

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6 A L M O N D O R C H A R D 2 0 2 5 G O A L S PEST MANAGEMENT Managing Late- Season Mites As almond trees become more stressed due to heat or the implementation of strategic deficit irrigation, almond growers in the Central Valley should turn their attention to mites. It is important to monitor for and manage mites throughout the summer and into harvest, as after August mites begin to overwinter and monitoring and treatment are no longer necessary. According to Kern County UC integrated pest management (IPM) farm advisor David Haviland, this means that before harvest begins it's important to get in the orchard and begin monitoring (and treating, if needed) to ensure dust during harvest doesn't exacerbate mite problems and lead to defoliation. While it may be difficult for growers to tolerate tree defoliation or webbing and browning leaves, it's recommended that they avoid preventive mite treatments and instead rely on sound IPM methods to keep mites in check throughout the season. Let natural enemies roam Almond Board of California (ABC)- funded studies show that natural enemies of spider mites, if left to thrive in the orchard, can control both two-spotted spider mites and Pacific spider mites. As a result, an effective mite management strategy should revolve around preserving those beneficial mite predator populations. Six-spotted thrips are the most common and effective natural predator of spider mites. Other beneficial insects include minute pirate bugs, lacewings and predatory mites. Treating prophylactically, or at the first sign of mites, reduces the food supply for natural mite predators and likely causes mite problems to worsen later. Instead, said Jesse Roseman, senior specialist for Environmental and Regulatory Affairs at ABC, growers should preserve beneficials in the orchard by avoiding broad-spectrum insecticides or miticides that can negatively impact beneficial populations, and base treatment decisions on presence/ absence sampling for both mites and beneficials. The University of California recommends weekly monitoring for mites and beneficials through harvest. 1 About 15 leaf samples should be taken from at least five trees in representative areas within the orchards and observed for the presence/absence of both spider mites and predators. Special attention should be paid to previous hot spots or the edges of the orchard. As a general rule demonstrated by ABC-funded research, Haviland recommends growers treat with a selective miticide only if more than one-third of the leaves sampled have mites and some beneficials are found in the orchard. If no predators are found, that threshold should drop to 25% of leaves with mites present. Haviland advises the use of yellow sticky cards to monitor for the presence of six-spotted thrips in the orchard. These cost-effective traps can be hung from the tree near navel orangeworm traps and provide a more accurate picture of the presence of six-spotted thrips. There is a direct correlation between the number of thrips found on the card during weekly monitoring and the number of mites found on leaves, Haviland said. As beneficials increase, mites decrease exponentially, and vice versa. In general, leading up to hullsplit, if there are six thrips present on each card during weekly sampling, mites will almost certainly decrease within Mites damage tree foliage by sucking out the contents of leaves' cells, and in some instances the leaves turn yellow and drop off.

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