Broad Mites in Blackberries— a 2016 update
Posted: July 29, 2016
Leaf distortion and cupping of blackberry leaves infested by broad mites. Photo credit: Donn Johnson, Univ. of Arkansas
There is a window of opportunity to greatly slow the spread of broad mites if symptoms are noticed early and plants are rogued. An article written on this topic last fall for the Fruit Times newsletter provided details on the situation and images to help with diagnosis of damage. Additional newsletter articles can be found in the April 25, 2016 issue, and the July 14, 2016 Alert of the Arkansas Fruit and Nut News.
Syngenta has issued a 2(ee) label for use of Agri-Mek SC for broad mite control on caneberries in 7 states (AR, FL, IL, IN, NC, PA, and SC, effective from July 6, 2016 to July 6, 2020; in addition to a supplemental label that already was issued for spider mites on caneberries. This is a welcome addition, as the number of miticides labeled for use on blackberries is somewhat limited, and none currently are labeled for management of broad mites.
Broad mites are found primarily in the tender terminal growth of blackberries, unlike 2-spotted spider mites which are found on the lower leaves. Because of this fact, materials that have translaminar activity (i.e., can make their way into the plant tissue), which Agri-Mek does have, are needed for effectiveness against broad mites. Agri-Mek is also reported to provide residual control that lasts 21 days. It’s also important to get good coverage of the correct area of the plant.
Agri-Mek SC has a 7-day PHI, so the time to treat is either early before harvest starts (but ONLY if broad mites are present – don’t just spray “in case”), or in the case of floricane-fruiting varieties, after harvest is over. Work conducted at the Univ. of Arkansas showed good efficacy of this material, but it was found that a second application may be needed to control mites that hatched after the first application. Apply Agri-Mek SC at rate of 3.5 fl oz/acre mixed with non-ionic (NIS) activator type wetting, spreading and/or penetrating spray adjuvant (read activator label, usually use 0.5% NIS v/v). Scout weekly using a 20X magnification lens to check for presence of active broad mites: immatures are white and adult females are amber with white hour glass shape on back. The life stage that is the least likely to be confused in appearance with other species, however, is the eggs, which are clear with white dots, and sometimes described as “jeweled” in appearance.
Greatly-magnified young blackberry fruit with broad mite female (right) and eggs (left of center). Photo credit: Sara May, Penn State Univ.
Remove a leaflet from the first expanded terminal leaf from each of several randomly selected primocanes in each planting and inspect for broad mites on the underside of each leaflet. Also, walk your blackberry field looking for the first terminal damage (leaf bronzing or cupping). If this pest is present, it is time to apply a miticide, and reapply 7 days later (if live mites are still present), when there is an average of between one to five active broad mites per leaflet or you first detect terminal leaf damage. Only 2 applications of Agri-Mek SC are allowed in a year, as resistance development to miticides is a serious concern with broad mites as well as other mites.