by Courtney Llewellyn

For such a small pest, mites can be mighty frustrating. And there is no one best way to handle them. That’s why Rick Fletcher, technical services manager for turf and ornamentals of NuFarm, preached the power of mite management rotations at Cultivate’21.

Mites feed on leaves, berries and various tissue of nearly all species of ornamental plants. An egg-laying mite can lay several hundred eggs. They can have very short lifecycles (as fast as four days) so their populations can build rapidly. Under their ideal environmental conditions – often the same ones that exist in greenhouses – mite populations can explode.

Unfortunately, mites are not usually detected until plants are already damaged. The damage seen is often yellow- or gray-striped webbing of leaves and other tissue, because the mites are sucking nutrients out of the plants.

Tenuipalpid mites, also known as false spider mites. Photo courtesy of Rayanne Lehman, PA Department of Agriculture, Bugwood.org

Management is a simple process, though, according to Fletcher. “Scouting leads to management,” he said. “Think ahead about what you’re fighting.” He noted that in monitoring, some growers are using drones inside their greenhouses to look for damage. Others use more basic tools, such as a hand lens or even the old white paper trick (gently tapping or shaking a plant to see what falls on to a sheet of white paper). Growers should monitor regularly, every seven to 10 days, and remember that mites can overwinter, so vigilance is key.

In scouting, growers need to determine what pest mite they have, what lifecycle stage it’s in (since some pesticides target different parts of a lifecycle) and where it’s located. The three mite types Fletcher mentioned to be especially aware of are the following:

  • Eriophyid mites – These are microscopic and often go undetected. They’re usually quite host-specific, but as there are hundreds of species of them, a lot of plants are at risk. According to the Missouri Botanical Garden, most Eriophyid mites make their homes on leaf surfaces where their feeding can cause bronzing or reddening (or possibly galls on flower buds). These mites can transmit some plant diseases. Plants affected by Eriophyid mites includes honey locust, tomato, lilac, cherry, apple, citrus and eastern white pine. Plants that may see blisters or galls on leaves or buds include maple, ash, aspen, plum, elm, cottonwood, birch, hackberry, pear, apple and all conifers.
  • Tarsonemid mites – Fletcher said these are becoming more common in greenhouses. Many Tarsonemid species are fungivores, algivores and herbivores; others are predators of other mites, parasites of insects and possibly symbionts of insects. Their feeding damage is easily recognized on all hosts because affected leaves become cupped, dwarfed and thickened, and the internodes are greatly shortened. Damage from mites feeding in developing shoots can cause longitudinal bronze streaks of discoloration, horizontal cracks, distortion and death of leaves and flowers, according to University of California Agriculture & Natural Resources.
  • Tenuipalpid mites – Also known as false spider mites, these pests are very host-specific. The mites are reddish in color and slow-moving. They normally feed near the midrib or veins on the undersides of leaves. They inject toxic saliva into fruits, leaves, stems, twigs and bud tissues of numerous plant species. Feeding injury symptoms on plants can include chlorosis, blistering, bronzing or necrotic areas on leaves, according to the University of Florida.

Once the mites have been identified, growers need to find which products are labeled for their mite and site. They need to consider the mode of action, plant movement and the efficacy of the product. They also need to take into account the environmental side effects of their product choices.

“The development and the introduction of new materials for controlling mites on ornamental plants continues,” Fletcher said. “Ten years ago, the choices were limited and even further aggravated by the loss of older products through the re-registration process.”

Additionally, most of the new active ingredients in pesticides have unique modes of action. Therefore, successful insect management comes from developing an integrated pest management program that includes a resistance management program. “To do so, you need to understand the mode of action of the products available and the biology of your target pest,” Fletched stated.

“Deposition is critical,” he continued. “You can have a great spray but if it’s not placed properly, it’s useless – and since space is money, you squeeze in as much as possible. You have to make sure everything gets wet.”

Product rotations are key for dealing with different mite lifecycles as well, Fletcher concluded.