Plum Bud Gall Mites

 

A Potential Pest of Concern for California Almond Growers

 

Plum bud gall mite (Acalitus phloeocoptes) was first identified and confirmed in Santa Clara county in February 2019. Since then, the pest has been confirmed in Contra Costa, Alameda, Marin, San Mateo, Santa Cruz, and Sonoma counties, and more recently in Western Oregon.

Why is this Pest Important?

In Western Asia plum bud gall mite is also referred to as Almond Bud Gall Mite, because of its impact on almonds. In Europe and the Middle East, where plum bud gall mite is primarily found, it has been reported on almond, apricot, peach, plum trees, and cotoneasters.

So far in California, plum bud gall mite has been found in plum and pluot trees, and further information is needed about the susceptibility of apricots to this pest. So far, other stone fruit trees, especially almonds, that are located nearby plum bud gall mite infected orchards have not been impacted by these mites. Also, so far the impact of this pest has been seen in mostly residential areas and very few commercial orchards have been impacted.

Damage Caused by Plum Bud Gall Mites (PBGM)

Mites are piercing and sucking feeders, and the mites' feeding activity causes the cells to grow and envelop the mites leading to the formation of gall like deformations, which range in diameter from 1.3 to 1.8 mm, around buds on almond, apricot, plum, and peach trees. Mites may also lead to the deformation of fruit spurs (Fig. 5). Reports have found that tree susceptibility to the pest and the severity of infestation is highly variety dependent.

Plum bud gall mite infestations have led to weakened trees, decreased yield (seen in almonds in the Middle East), or, in some cases, the death of the tree. In other instances, trees have recovered from the mite attack, and some cultivars are known to be resistant to the mites.

Infected bud galls in Golden Nectar plum tree

PBGMs with a wormlike body and whitish color

Microscopic view of an eriophyid mite

Key Findings from 2020 Almond Host Range Study

  1. No galls were formed on any of the five almond varieties that were tested.

  2. The study found that almonds do not serve as a host for plum bud gall mites.

  3. No galls were formed on any of the Santa Rosa plum trees that were tested.

  4. In the study of different plum varieties, only Mariposa plum trees formed galls.

  5. In infested Mariposa plum trees, it took around five months for galls to form.

  6. In N. California, emergence of PBGM infested galls was seen from Feb-April.

  7. Steaming kills plum bud gall mites that are located inside infested galls.

  8. Old galls formed during prior years of infestation do not harbor mites.

For more information about plum bud gall mites and the 2020 host range study, download the below publication

Aparna GazulaAlmonds, IPM, insect, pest, mites, Pest Management, Prune, Plum, Apricot, Invasive, Pest Alert, New Pest