Broad mite being early should be a worrying sign for all blackberry growers in the
Midsouth region. First, when pests like broad mite blow up early it could mean that
infestations may be more widespread than normal. Blackberry fields will still be at
risk for infestations through September meaning there is a much wider window for infestations
to occur and ramp-up in places we don’t normally see them hit threshold. Additionally,
some growers often need two miticide applications, with the first being in Mid-July
then another in late August. It’s possible that some fields could warrant additional
miticide applications. What we do know is that agents and growers need to be on the
lookout for this pest in plantings across the state (Picture 1). Outlined below is information about the biology of broad mite, how to monitor it
in your plantings, and what you can do to control it, which should lead to successful
management of this pest.
Picture 1. Broad mite damage observed on blackberry in 2024 in Northeast Arkansas. Broad mite
damage can easily be identified by inward rolling of leaves, leaving a spade-like
appearance, along with shortened internodes.
What is Broad Mite? Broad mite, Polyphagotarsonemus latus (Banks), is a tarsonemid mite that feeds on new leaf material, flowers, and fruit.
Unlike other mite pest species, such as the two-spotted spider mite (tetranychid mite),
broad mite is microscopic (0.1-0.2 mm) (Picture 2) and generally goes unnoticed until injury on new growth and reproductive structures
is observed. Broad mite is distributed throughout much of the world and occurs as
a pest mainly in tropical or subtropical regions such as the Southeastern United States.
Broad mite has a large host-range and is most notably a pest in greenhouse production
of food and ornamental crops.
Picture 2 . Ambered-colored broad mite adult observed using a dissecting microscope.
Broad Mite in Blackberry
Broad mite was first reported as a pest of blackberry in the United States in 2007
and was further realized as a serious threat to commercial blackberry production in
2014 (Vincent et al. 2010; Johnson & Garcia 2015). Commercial plantings in Northeast
Arkansas exhibited large levels of estimated yield loss ($15,000 to $20,000), and
infestations were observed in many states across the Southeastern region. Broad mite
was initially found to infest greenhouse propagation of blackberry plants, and later
infestations of established plants were observed during the early summer months. Over
the last 5 years, economically significant populations of broad mite have been observed
on multiple blackberry plantings in Arkansas each year. Severity can differ from year
to year, but it appears this pest is here to stay and may be exacerbated by climate
change.
Broad mite is a subtropical pest species that does not emerge until the summer in
climates with cold winters. We usually begin to see a few mites in late-May, and we
don’t generally observe injury or significant infestations until mid-late July. This
varies from year-to-year and sometimes we don’t see any injury until August. A good
rule of thumb is to begin scouting primocanes when harvest starts on floricanes, and
don’t let up until it starts to cool down in the fall.
Broad Mite Injury in Blackberry Broad mite feeding on blackberry is often reminiscent of injury from auxin herbicides
and stunts plants in a similar manner. Malformation of plants is due to the toxic
nature of the mite’s saliva. Feeding leads to stiff, curled leaves with cupped margins,
a decrease in internode length, and potentially leaf death and tip dieback in serious
infestations (Picture 3, Picture 4) . Broad mite will also feed on and damage the fruit and flowers of primocane-fruiting
cultivars (Picture 5) . Significant yield loss has been observed to primocane crops through a direct effect
on developing flowers and fruit. A rating scale has been developed by Jared Linn (Graduate
Student - UARK Hort IPM) that helps to identify broad mite damage and judge the potential
impact to next years’ floricanes (Picture 6) . We expect yield loss when canes reach a rating of 4 and especially 5, but excessive
stunting could ultimately lead to yield loss depending on when damage is first observed
and whether this stunting ultimately leads to unacceptable canopy-fill.
Picture 3 . Early signs of broad mite damage to primocanes terminals. Injury is characterized
by the bronzed coloration and upturned nature of new leaves, along with twisted and
cupped leaves on older nodes.
Picture 4 . Severe injury from broad mite infestations. This primocane was severely stunted,
leaves began to be necrotic, and the tip was completely killed back.
Picture 5 . Broad mite damaged (left) and normal (right) blackberry flowers and leaves. Photo
credit Vincent et al. 2010.
Picture 6 . (1-5) Rating scale for broad mite damage. A rating of 1 has no shortened internodes
or leaf cupping. A 2 rating indicates leaf bronzing, reduced internode length and
the beginning of leaf cupping or upturned leaves. A rating of “3” exhibits excessive
leaf cupping and a rating of 4 indicates that leaves are beginning to become necrotic.
A rating of 5 indicates tip-dieback and excessive necrosis of new leaves. Photos by
Ryan Keiffer, Jared Linn, and Aaron Cato.
Broad Mite Management in Blackberry Scouting is key to broad mite management. Any miticide that is applied before broad
mite is present is likely to have no positive effect and could potentially lead to
increased issues in the future. It’s likely that pyrethroids or other broad-spectrum
insecticides used to control insect pests such as spotted-wing drosophila promote
broad mite issues, as they kill predatory mites. Growers should scout for signs of
injury in their plantings throughout the year, especially once harvest begins on the
floricane crop. Damage often emerges on field edges before it spreads throughout plantings.
It presents first as tightening of the internode and leaves will begin to roll or
cup before it begins to look serious (Picture 6 ). Once any suspected broad mite injury is observed, pull 10 unfurling leaflets (third
node from the top, leaves should be just starting to lay flat) from surrounding primocanes.
Ambered-colored adult broad mites can be seen at about 30x-60x magnification, which
is usually available at your local extension office. Also be on the lookout for their
distinctly polka-dotted eggs, which indicates that it is time to spray (Picture 7) .
Picture 7 . Broad mite egg on the underside of a blackberry leaflet as viewed through a dissecting
microscope. These eggs are distinctly polka-dotted and a sign of a rapidly increasing
broad mite infestation.
Broad mite numbers often build very rapidly and work by Dr. Donn Johnson has indicated
that reaching between 1-5 mites per leaflet is the sweet spot for control (Johnson
and Garcia 2015). Once mites exceed an average of 10 per leaflet, damage is usually
widespread and populations can be difficult to effectively manage. Finding eggs in
samples along with adult mites is also a good indication that it is time to apply
a miticide for control.
Ultimately the largest issue with using broad mite numbers to indicate the need for
a miticide is the microscopic nature of this pest. Our observations and current work
from Jared Linn indicate that our visual rating scale (Picture 6 ) of plant injury may be used to make miticide applications. Broad mite generally
hits threshold when canes can be observed at an injury rating of 2-3. When any canes
can be found at an injury rating of 4-5, especially interspersed with lower levels
of broad mite injury, populations are usually raging and likely to be 2-3 times threshold.
We recommend sending in leaves for ID if small amounts of suspected damage are observed,
and miticide applications are necessary if damage (rating of 2-3, picture 6 ) is widespread. After applying any miticide for broad mite, continue scouting to
assure effectiveness and for the potential of new infestations. Farms in Arkansas
that have major broad mite issues often necessitate two applications a year, especially
in years when the first infestations begin early.
Broad Mite Control Options Currently there are many options to control broad mite, but only a few that can safely
be used in the heat of the summer (above 80-90°F). Products such as Mpede (potassium
salts of fatty acids), Microthiol (sulfur), JMS Stylet Oil (paraffinic oil), or Neem
Oil all offered sufficient suppression of broad mite (Lefors et al 2017). These products
can be risky to use in the heat of the summer and can damage blackberry plants if
applied when it is too hot. It is important to note that these products were not always
found to be effective in efficacy trials (Johnson and Garcia 2015).
Agri-Mek and Magister continue to provide excellent control with great residual, but
a 7-day preharvest interval (PHI) hampers their usefulness (Figures 1-4) . Portal (1-day PHI) is a good option for growers that are either looking to finish
out floricane harvest or need to protect developing fruit while harvesting primocane
fruiting varieties. Results from our trials indicate that Portal will knock back damaging
broad mite populations and limit the amount of plant injury that is observed, while
offering a 1-day preharvest interval. However, any grower that uses Portal should
continue to scout for damage and mites. A second portal application of Portal should
only be considered 14 days (label restriction) after the first if harvest is ongoing,
and either Agri-Mek or Magister should be prioritized for a second application to
help reduce the likelihood of resistance.
Effective Management Plan for Broad Mite Broad mite has not been found to affect the floricane crop, but it can start to feed
on primocane growth prior to the end of floricane harvest. Control efforts generally
need to be focused on limiting damage to this year’s primocanes, which could translate
to yield loss in primocane fruiting cultivars and lowered yield potential in next
year’s floricane production. Scout for leaf injury and confirm that it is broad mite
damage by sending in samples to your local extension service. If you are observing
damage and there is more than 1 broad mite per leaflet across a significant portion
of a plant, Agri-Mek + NIS is a good first option. If you are still harvesting late
varieties such as Navaho or Von, or have primocane fruiters, consider using Portal.
Save Magister to use as a rotation tool if necessary. You will need thorough coverage
(60-100 GPA is preferable) to get acceptable control, as broad mite is often feeding
deep inside terminal leaf material.
Give me a call at 479-249-7352 if you have any questions.
Aaron Cato
Figure 1. Broad mite adults and immatures observed per leaflet in Trial 1 across 5 miticide
treatments in blackberry compared to an untreated check (UTC) observed 0-21 days after
the first miticide application (DAA) and 3-7 days after the second miticide application
(DA2A) on a grower field in White County, AR. *indicates significant difference from
Untreated Check.
Figure 2. Broad mite damage ratings (1-5) in Trial 1 across 5 miticide treatments compared
to an untreated check observed 0-21 days after the first miticide application (DAA)
and 3-7 days after the second miticide application (DA2A) on a grower field in White
County, AR.. *indicates significant difference from Untreated Check.
Figure 3. Broad mite adult and immatures observed per leaflet in Trial 2 across 3 miticide
treatments in Blackberry compared to an untreated check observed 0-13 days after application
(DAA) on a grower field in White County. *indicates significant difference from Untreated
Check.
Figure 4. Broad mite damage ratings (1-5) in Trial 2 in blackberry across 3 miticide treatments
compared to an untreated check observed 0-13 days after application (DAA). *indicates
significant difference from Untreated Check.
References Johnson & Garcia. (2015). Broad mite biology and management on blackberry. SRSFC Report.
https://smallfruits.org/files/2019/07/2015-06.pdf .
LeFors, J. A., D. T. Johnson, and T. Woodruff. 2017. Acaricidal Control of Broad Mites
in Blackberry, 2016. Arthropod Management Tests, 2017: 1-2.
Vincent, C. I., M. García, D. T. Johnson, and C. R. Rom. 2010. Broad Mite on Primocane-fruiting
Blackberry in Organic Production in Arkansas. Hort. Tech. 20: 718-723.
