Problem Identifier / How to Identify and Get Rid of Spider Mites

Despite their tiny size, spider mites can do a lot of damage. They are one of the most common outdoor pests, with over 1,200 different species. Spider mites feed on an extremely large variety of plants. It is nearly impossible to see spider mites with the human eye. This is the reason they are generally not identified until after damage to the plants has been done.

Spider mites are a part of the Tetranychidae family, and frequently seen throughout North America attacking both outdoor and indoor plants. Significant damage is common in greenhouses. Spider mites are not an insect, but a type of arachnid. The spider mite is related to spiders, scorpions and ticks. The arachnids live in colonies, most often found on the underside of leaves.

Spider Mite Infestation
Spider mite infestation.

Feeding occurs by piercing the tissue of the leaves and sucking out the fluids in the plant. Spider mites are commonly found when the conditions are dry, or insecticides have been used because chemicals kill many of their natural enemies. Most of the species is made up of plant-feeding mites. Due to the fertility of the species, once you see spider mites on plants, there is a good chance there is already an infestation.

Red spider mites attack a wide range of plants in the garden, but camellias and azaleas are attacked more often. There are two different types of red spider mites: The Southern red spider mite and the European red spider mite with the Southern red being more common. The European species is generally found only on apple trees. Learning how to identify and get rid of spider mites is critical because every species can cause severe damage or killing the plant.

What do Spider Mites Look Like?

Spider mites are so tiny, the only way to accurately identify them is with a 10x magnifying glass. The best way to find spider mites is by examining the leaves for damage. The shape of the body is oval, with slight bristling. The juveniles are pale green, with darker green spots developing with maturity.

The green dots are the contents of the guts of the spider mites, and how the two-spotted mite was named. The red spider mite is completely red, where many of the other species are partially red. Red spider mites are approximately 1/50th of an inch in length.

If the underside of the leaves looks dusty, there is a good chance these pests are the culprits. Look at the leaves closely, the dust will move because it is mites. Another telltale sign of spider mites is webbing on the plant’s branches or the underside of the leaves.

What Does Spider Mite Damage Look Like?

Spider Mites cause the following damage:

  • Webbing
  • Whitish-yellow or tan spots on the needles and leaves
  • Yellowish discoloration with a bronzed cast
  • Distortion of the leaves and flowers
  • Tiny red or white spots moving on the leaves
  • Random white specks on the leaves
  • Leaves appear sunburned

Spider mites have piercing mouthparts they use to suck on the underside of the needles and leaves resulting in a yellowed discoloration. If there is webbing on the plants, there is an infestation. To learn how to get rid of spider mites, understanding the difference between an attack and drought stress is important.

White, tan or yellow spots appear on the leaves. Tiny moving red or white spots are the mites. Look for cottony white webbing on the underside of the leaves. A large infestation on bedding plants or vegetables often results in the death of the plants.

The damage initially seen are white specks on the top of the leaves. The specks are so small, they do not draw the eye. This often causes the damage to go unnoticed. With the right environment, the damage can quickly turn into an infestation. When spider mites feed, the entire contents of the plant cells are eliminated.

The life of the plant is drained, resulting in dryness and discoloration. The leaves will eventually fall, leaving the plant significantly weakened. If you do not take immediate action to combat and kill the spider mites, your plants will eventually die. The most common damage for vegetables including watermelons, melons and squash includes falling leaves resulting in sunburning and smaller yields.

Spider mites on plants including beans and sugar peas result in direct damage. Unless there is an infestation, the damage on ornamental plants is minimal. Spider mites also attack roses.

How to Get Rid of and Kill Spider Mites Naturally

When spider mites are found early, preventing an infestation is simple. All the methods below are good options for getting rid of and killing spider mites.

  • Trifecta Crop Control to kill spider mites
  • Diatomaceous earth (for outdoor application only)
  •  Natural predators
  • Spray the plant with pressurized water (for sturdy, non-cannabis plants only)
  • Discard the plant

Essential oils are frequently used to prevent mites but if mites are already present, the oils attack the spider mites’ central nervous system, killing them. Once you have a spider mite infestation, you must be diligent in your application of Trifecta Crop Control! It can take several weeks for all the mites to die and to completely break their life cycle. Apply as instructed below or click here to view/download our full application guidelines.

Spider Mite Infestation Cannabis
Spider mite infestation cannabis. PHOTO CREDIT: Whitney Cranshaw, Colorado State University, Bugwood.org

The infestation protocol is 2oz of Crop Control Super Concentrate per gallon applied every 72hrs until the infestation is under control. From there, you can switch to once weekly at preventative dose of 1oz per gallon. Spider mites can be tricky, especially if they are well established. Their webbing acts like a canopy and protects them from the spray. We recommend vacuuming the webs off before spraying for best results.

Diatomaceous earth can be used to slow down an infestation. Dust the leaves with diatomaceous earth labeled food grade as opposed to pool grade because handling this type is safe. The mites dry out and die.

Natural predators are another good option. Make certain the predators you select are the right ones for the specific season. Parasitic mites can be purchased from a local nursery including ladybugs, six-spotted thrips, bogeyed bugs, Western flower thrips and minute pirate bugs.

For non-cannabis and sturdy plants, a faucet or hose can be used to spray the stems and leaves of the plant using pressurized water. Start by isolating the infected plant, then spray everything possible for effectiveness. This process will need to be repeated a few times.

Any leaves showing the signs of a heavy infestation need to be removed. Put the leaves into a plastic bag with a good seal, then dispose of the bag. If a houseplant or an entire plant becomes infested, throwing out the plant is the best course of action since this will prevent the infestation from spreading to other plants.

How to Prevent Spider Mites Naturally

Spider Mite Damage Cucumber Plant
Spider mite damage on a cucumber plant.

The best options to prevent spider mites naturally include:

  • Apply Trifecta Crop Control as a preventative
  • Quarantine new plants
  • Beneficial bugs
  • Minimize plant stress
  • Regulate the humidity and temperature

By applying Trifecta Crop Control as a preventative, you can ensure you never have to deal with a nasty spider mite infestation. Apply as follows or click here to view and/or download our Application Guidelines.

  • .5oz per gallon applied once per week during veg
  • 1oz per gallon applied once per week during flower up to 2 weeks before harvest

Always be sure to quarantine new plants. Spider mites are so small and could go unnoticed even with a quick inspection. If introducing new plants, be sure to keep them isolated for at least 2 weeks.

Beneficial bugs such as the minute pirate bug, ladybug, assassin bug, green lacewing will help ensure spider mites don’t become an issue during flower. Be sure to make sure your growing conditions match with the spider mite predator’s optimal conditions.

Make certain the plants have all the necessary nutrients and are well watered to reduce any stress on the plant. If the plants are indoors or in a greenhouse, spider mites can be discouraged by regulating both the relative humidity and the temperature. Spider mites love the heat, so decreasing the temperature and adjusting the RH between 55% and 65% can help keep your plants free from these pests.

Life Cycle of the Spider Mite

Spider Mites Hatching
Spider mites hatching.

The lifecycle of the spider mite changes according to the environment. For the ideal conditions, the humidity must be lower than 50 percent, with temperatures at 80 degrees Fahrenheit or above. In this environment, only five to seven days are necessary for the egg to mature into an adult. This process usually takes place from June until September.

When the process takes place during the spring or fall, the life cycle increases to about 19 days. The population of spider mites can be decreased when the humidity and temperature in the growing area are regulated. This is the best option if spider mites are identified on plants in a greenhouse. When food sources are scarce due to shortened sunlight hours, the females go into a stage called diapause.

During this stage, the color of the spider mite changes from green to orange. Spider mites will not lay eggs or eat during this period.

 

Spider Mite Management in Greenhouses Using Biocontrol

The first greenhouse pests controlled with an application of predators were spider mites. Biocontrol suppliers offer numerous predators feeding on different groups of mites. Biocontrols are usually ineffective for eriophyid or cyclamen mites. Your best solution for the management of these pests is the removal and destruction of infected plants when spider mites are detected.

Phytoseiulus persimilis is an important predator for controlling spider mite populations on numerous crops. These mites are active throughout the year, feeding on spider mite adults, nymphs, larvae and eggs. You can increase the rate of reproduction with a minimum temperature of 82 degrees Fahrenheit. You should flag all active colonies of spider mites when scouting to introduce predators on delivery.

Look for dead spider mites appearing on your plants as small black dots to determine effectiveness. Also, look for adult predator mites and their oval-shaped eggs. Phytoseiulus is an orangish-red, with a lot more mobility than spider mites. Phytoseiulus should be introduced every week until you achieve control or for a total of three weeks.

If the infestation is light, one predator is necessary for each square foot in addition to 10 more for every infested leaf. If your infestation is heavy, release between 10 and 100 predators for each plant. Tips for Phytoseiulus use:

  • Begin early to achieve control over populations of spider mites
  • Without spider mites for prey, Phytoseiulus will starve or disperse
  • If you do not achieve control, the predatory rate must be increased
  • You should be able to decrease your spider mite colonies in two or three weeks
  • Predators should be poured over plant hangers or placed right on infested leaves
  • If your mite population decreases then increases, you must reintroduce new Phytoseiulus

Neoseiulus californicus is a predatory mite effective as a biocontrol option when greenhouse humidity is less than 60 percent. You can introduce this mite as a preventative measure when having difficulty finding populations of spider mites in your crops because prey is not required for survival. You need to release the predators early for controlling the populations of spider mites due to their fast reproduction with low humidity and high temperatures.

 

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