Broad Mites
Species described by scientists have a Latinized name used in scientific disciplines, often called a, “binomial name” which is agreed upon to minimize confusion and miscommunication and to show relatedness. Many times this name is highly descriptive as in the case of the Broad Mite, Polyphagotarsonemus latus. “Poly-” means “multiple”, “phago-” refers to eating, and “-tarsonemus” refers to the larger family name, Tarsonemidae, the Thread-footed Mites.
The “Multi-eater Mite” eats hundreds of different plant species which is peculiar since many of its relatives can only pierce thin cells from algae and some fungi. Broad Mites and some of their closer relatives developed toxic substances in their saliva that gnarl and corrugate plant tissues, puckering them to provide shelter as well as more accessible cell structure for feeding.
Although not very closely related, a similar process developed in some russet mites, such as the Hemp Russet Mite, while other russet mites cause minute damage to their hosts. Since both Broad Mite and Hemp Russet Mite colonize Cannabis with similar damage it is important to be able to tell the difference for short- and long-term management decisions.
Like many mites, Broad Mites have a haplodiploid reproduction style: a female will produce males from unfertilized eggs, and females from fertilized eggs, and so only one female on a suitable host is necessary for a colony to establish near or on a crop. Infamously, Broad Mites have a symbiotic, perhaps parasitic, relationship with the Silverleaf Whitefly Bemisia tabaci.
Individuals are attracted to the waxes produced by adults of this species and not any other whitefly. Perception of the wax induces grasping behavior that adheres them to the whiteflies, themselves pests of Cannabis and myriad other plants, allowing them to move with the winged vector. This behavior when one organism aids in the dispersal of another is called phoresy and it is pretty common among insects and mites. Unfortunately for the whitefly this behavior can weigh them down and interrupt their ability to feed with terminal results.
Detection
The Broad Mite is tiny, ~200 micrometers (0.2 millimeters) in length and under magnification, prolate in shape as the front and back taper to a point, somewhat shaped like an American football. Eight legs emerge near the front in adults, and individuals move rather fast for their size. Their eggs have small structures called tubercles which give them a distinctive dotted appearance and is a great way to confirm their presence.
Observation of individual mites is possible unaided with good vision, but their damage from feeding is much more noticeable and indicative of presence. Because many plants can host Broad Mites it is likely that some nearby vegetation can harbor them.
It may be prudent to control such plant life, especially close to structures and equipment associated with the crop. For example, the noxious invasive Castor Bean can house many common generalists including like Broad Mites.
Treatment
There are several species of predatory mites, like Neoseiulus cucumeris and Amblyseius swirskii, which are highly effective against Broad Mite in many crops including Cannabis. They can be applied reactionarily though they perform the best when established preventatively in the crop as a sufficient population of predators will extinguish a small colony before it grows too large.
Many times pollen such as that from cattail is sold as a supplemental food source that can increase and sustain populations when applied to foliage particularly if prey levels are low. Combining Cannabis plants with other pollen-producing banker plants like ornamental peppers can help sustain omnivorous Type III predatory mites like Swirskii and Cucumeris already mentioned.
However, not all mites benefit; Type I specialists like Phytoseiulus persimilis feed exclusively on spider mites and will not feed on pollen as an alternative food source.
Additionally, broad mites are susceptible to several substances. Like many insects and mites, they are vulnerable to micronized sulfur applied to the foliage. However, this is not suitable when flowering and will decimate beneficial insect, mite, and fungus populations where applicable.
Horticultural oils are also an option though their primary mode of action occurs by suffocating the mites, rather than having a toxic effect. Using these as a knockdown and waiting an appropriate amount of time before applying biocontrols or waiting to apply biocontrols after eradication are popular ways to integrate these two techniques synergistically.
Depending on how the mites establish, sometimes a few plants will be much more infested than those surrounding them. Especially when logistics requires staff movement through affected plants, it can be viable to cull the greatest source of mites carefully by fully encasing in a bag and securely disposing/destroying the contents to quickly decrease the population.
It should be noted that some plants will still be colonized and may have mild symptoms during the very beginning of Broad Mite presence, so combining multiple treatment techniques in tandem is most efficient.
Twisted foliage does not recover after Broad Mite eradication. Some cultivators elect to cull damaged leaves as they may shelter future Broad Mites and other pests or simply as an eyesore, but it is not strictly necessary.
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One Response
As always, it’s a pleasure to learn from someone like Matthew who has such a perspicacious perspective on Entomology. Cheers