- Author: Help Desk Team
Spider mites are very common pests found on many of our landscape and vegetable garden plants. They are tiny and difficult to see but once you learn about them, you might start seeing evidence of infestation on a wide variety of plants.
Spider mites live in colonies, mostly on the back side of leaves. They are less than 1/20 of an inch long, have eight legs, and if you look carefully, you can see two red eyespots. When their population is high, you might see dense webbing covering the leaves, twigs, or fruit.
Spider mites use piercing mouthparts to suck cell contents from leaves. Damage appears first as a stippling of light dots on the top of the leaves. Evidence of their presence can be seen or felt on some leaves—fecal matter, cast off exoskeletons of young mites, dead mites, and fine webbing becomes more obvious with heavy infestations. With heavier infestations, leaves can turn yellow and fall off.
Spider mite activity is most severe and damaging during hot, dusty conditions, and when plants are water-stressed. June through October are prime months for these little pests. In Contra Costa's relatively mild climate, spider mites can feed and reproduce year-round on evergreen plants. On deciduous plants, they can spend the winter under rough bark or on the ground.
To control spider mites, make sure your plants are not drought stressed. Dusty conditions often encourage spider mite outbreaks. Regular, forceful spraying of your plants with water, especially the undersides of the leaves, will often reduce their numbers and the damage they do.
Spider mites have many natural enemies that help control them, including lacewings, predatory thrips, and predatory mites. Maintaining a diverse garden habitat can encourage these predatory mites and insects to stay in your garden, waiting to assist with pest control.
If more control is needed, consider using an insecticidal soap or an insecticidal oil such as Neem oil in your sprayer and make sure you spray enough to fully cover both tops and bottoms of leaves. You'll need to spray soap again two or three days later to cover any newly hatched spider mites, because soap doesn't have residual action.
If you choose to spray insecticidal soap or insecticidal oil, don't spray if temperatures are over 90 degrees F and make sure to follow the label instructions. Before spraying it on the whole plant, test it on a few leaves to make sure it doesn't damage them. Using broad spectrum insecticides is not recommended as these can kill the natural enemies of spider mites, which may result in an increase in the spider mite population
How to prevent spider mites
Scout plants for their presence anytime hot and dry conditions occur. If you catch spider mites early, you may be able to prevent a large infestation just by removing a part of a plant or a single plant. Watering down dusty walkways and misting plants when it's hot and dry can make it less attractive to spider mites. If a plant becomes too infested and treatments are not working, consider removing that plant to reduce the chance of the spider mites traveling to other nearby plants.
For more information on managing spider mites, see this Pest Note: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html
Help Desk of the UC Master Gardeners of Contra Costa County (SEH)
- Author: Ben Faber
Key to the Phytoseiid Predatory Mites Found on California Crops
Key to the Phytoseiid Predatory Mites Found on California Crops
Predatory mites in the family Phytoseiidae are known throughout the world in agricultural crops as important predators of pest mites, especially the spider mites (Tetranychidae), as well as small insects such as thrips, psyllids, scales, aphids, and whiteflies.
Detailed line drawings illustrate descriptions of each mite species, and a separate appendix included in the download contains photos of key characteristics of slide-mounted mites taken through a compound microscope. The interactive appendix, includes photos of forty-five of the forty-six mite species found in the key.
For the majority of mite species, photos of the dorsum, venter, ventrianal shield, spermatheca, and chelicera are provided. For some species, additional photos are included for structures that are especially important for confirming identification, such as the peritreme, macrosetae, pores, and dorsal shield indentations.
This free publication is available by download. The publication and the appendix are included in a zip file. Please note this is a large, 36MB file
This publication is best viewed using the free Adobe® Acrobat® Reader. You can download a free copy of the Acrobat Reader from Adobe Systems Incorporated.
- Author: Ben Faber
TYPES OF NATURAL ENEMIES
Parasites, pathogens, and predators are the primary groups used in biological control of insects and mites (Table 1). Most parasites and pathogens, and many predators, are highly specialized and attack a limited number of closely related pest species. Learn how to recognize natural enemies by consulting resources such as the Natural Enemies Handbook and the Natural Enemies Gallery.
Parasites
A parasite is an organism that lives and feeds in or on a host. Insect parasites can develop on the inside or outside of the host's body. Often only the immature stage of the parasite feeds on the host. However, adult females of certain parasites (such as many wasps that attack scales and whiteflies) feed on and kill their hosts, providing an easily overlooked but important source of biological control in addition to the host mortality caused by parasitism.
Although the term “parasite” is used here, true parasites (e.g., fleas and ticks) do not typically kill their hosts. Species useful in biological control, and discussed here, kill their hosts; they are more precisely called “parasitoids.”
Most parasitic insects are either flies (Order Diptera) or wasps (Order Hymenoptera). Parasitic wasps occur in over three dozen Hymenoptera families. For example, Aphidiinae (a subfamily of Braconidae) attack aphids. Trichogrammatidae parasitize insect eggs. Aphelinidae, Encyrtidae, Eulophidae, and Ichneumonidae are other groups that parasitize insect pests. It's important to note that these tiny to medium-sized wasps are incapable of stinging people. The most common parasitic flies are the typically hairy Tachinidae. Adult tachinids often resemble house flies. Their larvae are maggots that feed inside the host.
Pathogens
Natural enemy pathogens are microorganisms including certain bacteria, fungi, nematodes, protozoa, and viruses that can infect and kill the host. Populations of some aphids, caterpillars, mites, and other invertebrates are sometimes drastically reduced by naturally occurring pathogens, usually under conditions such as prolonged high humidity or dense pest populations. In addition to a naturally occurring disease outbreak (epizootic), some beneficial pathogens are commercially available as biological or microbial pesticides. These include Bacillus thuringiensis or Bt, entomopathogenic nematodes, and granulosis viruses. Additionally, some microorganism by-products, such as avermectins and spinosyns are used in certain insecticides; but applying these products is not considered to be biological control.
Predators
Predators kill and feed on several to many individual prey during their lifetimes. Many species of amphibians, birds, mammals, and reptiles prey extensively on insects. Predatory beetles, flies, lacewings, true bugs (Order Hemiptera), and wasps feed on various pest insects or mites. Most spiders feed entirely on insects. Predatory mites that feed primarily on pest spider mites include Amblyseius spp., Neoseiulus spp., and the western predatory mite, Galendromus occidentalis.
AUGMENTATION
When resident natural enemies are insufficient, their populations can sometimes be increased (augmented) through the purchase and release of commercially available beneficial species. However, there has been relatively little research on releasing natural enemies in gardens and landscapes. Releases are unlikely to provide satisfactory pest control in most situations. Some marketed natural enemies are not effective. Many natural enemies are generalist predators and are cannibalistic and feed indiscriminately on pest and beneficial species, thereby reducing their effectiveness.
Only a few natural enemies can be effectively augmented in gardens and landscapes. For example, entomopathogenic nematodes can be applied to control certain tree-boring and lawn-feeding insects. Convergent lady beetles (Hippodamia convergens) purchased in bulk through mail order, stored in a refrigerator, and released in very large numbers at intervals can temporarily control aphids; however, lady beetles purchased through retail outlets are unlikely to be sufficient in numbers and quality to provide control.
Successful augmentation generally requires advanced planning, biological expertise, careful monitoring, optimal release timing, patience, and situations where certain levels of pests and damage can be tolerated. Situations where pests or damage are already abundant are not good opportunities for augmentation.
A classic example of poor timing for augmentative release of predatory mites for control of broad mite in coastal lemon or persea mite in avocado is right now. Pest populations for the most part have soared and releasing predatory mites is little help. Predatory mites need to be releases into a small growing population, so in both of these cases it would have been better to start small, frequent releases early and throughout the spring to knock their populations back.
Adult predatory mite, Euseius tularensis, and citrus red mite.
/h4>- Author: Mark Bolda
Users of predatory mites in berries really should take a look at this link, which covers the feeding habits of the various predatory mites in use:
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=14065