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Bugs That Damage Plants

Posted by Darlene Caviness

2-spotted Spider Mites

What Are Spider Mites?

Let’s get this straight - mites are not insects, rather they are related to spiders and ticks.  They possess eight legs (with a few exceptions) and are mostly microscopic in size. 

Spider mites, spruce mites, European red mites, carmine mites, broad mites, Eriophyid mites, rust mites, gall mites, Cyclamen mites, predatory mites – there are literally hundreds of different kinds of mites.  Fortunately, many of those that cause problems in our industry can be grouped into three general categories: spider mites, Tarsonemid mites and Eriophyid mites. 

Spider Mites:

Most spider mites are members of the Tetranychidae family of the Arachnida.  This family includes genera such as Tetranychus, Panonychus and Oligonychus.  Common names include two-spotted spider mites, carmine mites, spruce mites, and European red mites.  While newly hatched larvae have only three pairs of legs, later instars and adults have a full complement of 4 pairs of legs.  While all mites feed by inserting their stylus mouthpart into a single plant cell and sucking out its contents, spider mite feeding causes a characteristic leaf stippling.  And even though you still need magnification to see them, spider mites are the largest members of our three groups.

One thing that sets spider mites apart from other mites is that like their more noticeable cousins the spiders, spider mites produce webbing.  They use their webbing for protection instead of capturing prey because spider mites are essentially “herbivores.”  They spin it on the underside of the leaf, which is where you usually find the mites.  Large colonies can cover the plant’s twigs and main stem, providing shelter for eggs and nymphs and providing a super highway system for adults.

spider mite damage Spider mites should be suspected whenever your plants develop stippling on the leaves. When scouting plants for spider mites, take a sheet of white paper and strike the plant over it.  Mites show up as tiny moving dots on the paper.  You can use a magnifier to take a closer look at them.

 Fortunately, we have several control options available for when mites attack.  Products like insecticidal soaps, neem and horticultural oils offer soft options for control of both mites and insects.  However, good control requires good coverage.  These products will not work if the mites (which are on the undersides of the leaves) are not well coated. 

A common misconception is that insecticides control mites.  After all, they’re kinda like insects, right?  Wrong.  Miticides are specific for control of mites and very few insecticides have any effect on mites.  And even among miticides, you need to know what specific mites and life stages they control.  Some miticides control spider mites but do not touch the Tarsonemid or Eriophyid mites.  So once again I say, “Read the label.” 

Types of Mites

Tarsonemid Mites:

broad mitesThis group includes the broad and Cyclamen mites.  Did you think that spider mites were small?  Prepare to squint because members of this group are even smaller.   Members of this group are pale and translucent, with eight legs and oval bodies.  They feed like other mites, by inserting their stylus into the plant cell.  The difference is that they are very small and can only pierce cells with thin membranes, such as found in new growth.  The broad and Cyclamen mites also inject a toxin when feeding.  This causes the plant cells to thin, making it easier for the mites to feed, but also causing the new growth to distort. 

Tarsonemid mite damageLook for this distortion when scouting.  I suspect broad mites whenever I find a deformed group of plants that have new leaves with rolled-under margins.  Since these mites are microscopic, the suspected infestation must be examined under magnification.

As with the spider mites, several options exist for control of Tarsonemid mites.  However, you must check the label to make sure your chosen product actually controls these pests.

 Eriophyid Mites:

Eriophyid mites on evergreen needleNow we come to the exception.  Eriophyid mites include the rust, bud, blister and gall mites.  However, they look nothing like the Spider and Tarsonemid mites.  Instead of having oval bodies and eight legs, Eriophyid mites have spindle-shaped bodies with four legs clustered at the larger end (the head).  In fact, the first time I saw an Eriophyid mite it reminded me of a carrot.  Like the Tarsonemid mites, they are microscopic in size and inject toxins as they feed. 

The range of plant responses to those toxins is enormously varied.  The rust mites cause a bronzing effect on the leaves or fruit of plants such as Hemlock and pear.  Gall mites cause a variety of distorted growths on the leaves of plants such as maple and oak.  Eriophyid mites are responsible for Echinacea rosetting, Juniper bud deformation, flower galls and many other plant reactions.  They are even linked to the spread of rose rosette virus.Linden leaf galls

As with the Tarsonemid mites, scouts must look for plant responses instead of the mites themselves.  Preemptive examinations of susceptible varieties can let you take action before the damage expresses itself, but you have to know where to look.  Miticide labels state whether or not the product controls Eriophyid mites.  Be sure to use the correct miticide.

 A Final Word…

 …About product labels.  Some labels list the mites they control by common name while others list them by Latin name.  Make sure you have at least a general knowledge about what kind of mite you are trying to control.  This helps you design your mite control program more effectively.

Tags: Pests/Disease