2020 – The Year of the MITES!

The UN-ENDING HEAT and SUN of the 2020 growing season has supported high populations of spider mites. Be on the lookout for spider mites with this informative post on the detection and management of spider mites!
Spider mites are very TINY, sometimes it is easier to detect them with vigorous branch shaking over a white surface. Blow debris lightly from the white surface and use your hand lens to identify and count plant feeding mites.
Oligonychus ununguis | Guide to Nursery and Landscape Arthropod ...

Spider mites have needle-like, piercing sucking mouthparts and they are very tiny. They feed sucking plant sap by piercing the leaf epidermis, feeding from the cells below. Their feeding damage causes very tiny yellow spots, which then turn brown. After a few weeks, the tiny necrotic spots look like stippling or bronzing, especially when viewed with the naked eye, like this photo of spruce spider mite damage on eastern white cedar (photo above: David Cheung, DKB Digital Designs).

SSm Dave Cheung Monitor for nymphs and adults of spruce spider mite on conifers with a history of mite damage (Photo: Dave Cheung).  They can be found in blocks of Thuja, Picea and Abies and are more common in evergreens receiving regular irrigation.  Spruce spider mite nymphs and adults are brown with black backs and found on new foliage this time of year.  Click HERE for a short video.  Miticides registered for SSM include Floramite and Shuttle/Kanemite, Vendex.  Miticides may be required where pest pressure is moderate to heavy (container grown conifers with overhead or drip irrigation). 

Enlarged (200x) photo of spruce spider mite (Photo: Dave Cheung, DKB Digital Designs)

Spruce Spider Mite populations in field production and in the landscape can really explode with the cooler nights of August/September so be on the lookout for these tiny mites on your evergreens once this heat subsides!

Oak English spider mite
Oak spider mite damage as viewed from upper leaf surface (photo: L. Stitt)
Oak spider mite
Oak spider mites viewed from lower leaf surface on white oak photo: L. Stitt

You might notice some bronzing and yellowing on the foliage of white oak species, caused by the Oak spider mite (Oligonychus bicolor).  This mite becomes active in mid summer and feeds for a good 6 weeks before populations start to die down. It rarely causes significant damage to host trees unless infested trees are very juvenile.  (Notice how they look a lot like spruce spider mites?  They are of the same genus).

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Maple spider mite damage as viewed from upper leaf surface

If you see bronzing and flecking on red-silver hybrids and red maple, it is likely the Maple Spider Mite (Oligonychus aceris). Yes, this is another cousin of the spruce spider mite and looks identical to oak spider mite. As with Oak spider mite and spruce spider mite, eggs overwinter near buds for next year’s growth. Where you see a high infestation, mark your calendar for mid-October…once leaves have dropped, dormant oil applications work well at smothering the overwinter egg stage before freezing temperatures start.

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Maple spider mites as viewed under dissecting microscope on leaf undersides (Photo: Kendra Thurston)

Yes, the Maple Spider Mite is another cousin of the spruce spider mite and looks identical to oak spider mites and can be managed similarly.

Two-spotted spider mite damage viewed from upper leaf surface
Two-spotted spider mites as they feed from lower leaf surface, they resemble debris to the naked eye….

Two-spotted spider mites (Tetranychus urticae) are feeding  on several types of deciduous woody (Viburnum and Hydrangea in container production) and herbaceous perennials. Look for chlorotic leaves with stippled appearance.  The leaf undersides will have a “dirty” appearance. Use your hand lens to see tiny, clear bodied two-spotted spider mites with dark regions (may be faint black) on their backs.

Apollo is registered in outdoor nursery crops to target the egg stage and newly hatched nymphs (Nealta, Floramite, Kanemite, Dyno-mite, Vendex).  Dormant oil is not effective for TSSM since they mites overwinter as adults in leaf litter (NOT as eggs on the plant).

In the greenhouse, biocontrol agents should be brought in to coincide with the first sign of TSSM.  Phytoseiulus persimilis is a predatory mite that feeds on TSSM when temperatures are below 26oC and it is a good choice when TSSM populations are low-moderate.  Amblyseius californicus is a predatory mite that can be brought in ahead of TSSM appearance (because it can find other sources of food).  Stethorus punctillium is a new beetle that is a good predator of TSSM.




About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
This entry was posted in Weekly Nursery Landscape Report and tagged , , , , , . Bookmark the permalink.

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