Plum Bud Gall Mite discovered at UCSC Farm

January 31, 2020

By Sky DeMuro and Erin Foley 

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Plum Bud Gall Mite damage manifests as small round bumps at the base of pointy fruit bud.
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The Plum Bud Gall Mite (Acalitus phloeocoptes (Nalepa)) has recently been discovered at the UCSC Farm, and has the potential to infect economically important stone fruit crops.

The pest was discovered by a volunteer and positively identified by the Santa Cruz County Department of Agriculture earlier this month. The affected trees at the UCSC Farm included a Satsuma plum, a Golden Nectar plum, and a pluot of unknown cultivar. The discovery of the mite at the UCSC Farm marks the first positive identification in Santa Cruz County.

Native to Europe and the Middle East, the Plum Bud Gall Mite was first discovered in California in early 2019. The mites can affect all trees in the Prunus genus (plums, pluots, apricots, almonds, cherries, peaches, and nectarines) and have been reported to cause severe damage to almond trees in Turkey, resulting in tree deaths within three to six years. The pest can spread via wind, bird, insect, and by moving affected wood.

While no damage has yet to be reported on almonds in California, the crop is California's third most economically significant crop. The state produces 82% of the world's almonds and leads the nation in apricot, peach, and nectarine production. The Plum Bud Gall Mite is currently an "A" rated pest in California. According to the CDFA, an "A" rated pest is defined as, "an organism of known economic importance subject to state enforced action."

What you can do

By learning how to identify the pest, you can help control the spread of Plum Bud Gall Mites. Adult female mites overwinter in galls before emerging in spring when galls crack open. They then migrate toward new buds and begin to feed. Plum Bud Gall Mite damage manifests as small round bumps at the base of pointy fruit bud (see photos). 

If you suspect the presence of the mite, report it immediately to the California Department of Food and Agriculture (CDFA) Pest Hotline at 1-800-491-1899 or by completing the CDFA "Report a Pest Sighting Form" or by emailing the CDFA Pest Hotline at reportapest@cdfa.ca.gov.

Because this pest is so new to the area, true risk and correct treatment is unknown at this time, but if Plum Bud Gall Mites are discovered in your Prunus species, it is recommended that you prune the affected areas of the tree, double-bag them in garbage bags, and solarize them by leaving them out in the sun for as long as possible. After several weeks of hot weather, the bagged prunings should be disposed of in the garbage. Wettable sulfur can be applied to the tree as an organically approved method of pest and disease control. 

We ask that any visitors to the UCSC Farm and Garden please do not move any wood, buds, or propagative material of Prunus species from the sites. Until more is known about the pest, we also recommend refraining from moving, selling, trading, or purchasing Prunus scion wood at this time.