From BASF: The Chemical Company Website
By Paul Pilon
Mites are not the first pest that comes to mind when growers think about poinsettias. However, mites are occasionally found feeding on them. The two most common mite species which infest poinsettias are Lewis mites (Eotetranychus lewisi) and the two-spotted spider mite (Tetranychus urticae). Mites have become more problematic for growers in recent years since many of the pesticides on the market today are more targeted with each product controlling a specific type of pest or a relatively small number of pests compared to past products which tended to offer broader spectrum control of a number of various pests simultaneously.
Most growers are familiar with two spotted spider mites which are have small oval shaped bodies (1/50 inch or less), usually appear light yellow to green in color, and have two large dark green spots on either side of their body. The other mites occasionally observed on poinsettias are Lewis mites (also commonly called the Lewis spider mite). Lewis mites are even smaller, measuring only 0.5 millimeters which is about half the size of the more common two-spotted spider mite. These tiny mites have slender, straw-colored to greenish-yellow bodies and DO NOT have the two distinguishing spots on each side of the body as observed on the two-spotted spider mite, but do have four tiny spots on their abdomen that can be seen best using magnification.
Both types of mites can be difficult to detect, especially when their populations are low, as they are so small and most commonly feed on the undersides of plant leaves. The two spotted spider mite can be seen with the naked eye, but many growers verify their presence by viewing them with a 10 to 20X hand lens. The smaller Lewis mite usually requires using a dissecting microscope with higher magnification to properly view and identify them. As the mite populations increase, they can be observed on most above ground plant parts. Under severe infestations, both of these mites produce webbing (which is why they are referred to as spider mites) that covers plant leaves and stems.
The injury symptoms observed on poinsettias is best described as stippling, or the presence of numerous small pinpoint spots, creating a mottled or speckled appearance on upper leaf surfaces. Severe infestations often cause the leaves to turn yellow (chlorotic) or bronze and may cause leaf drop. From a distance, growers often describe Lewis mite injury as looking similar to micronutrient deficiencies; closer examination will reveal the fine stippling of the leaf surface.
Early detection of mites is essential and allows growers to treat isolated areas before they spread throughout an entire crop and cause significant economic losses. As the crop canopy closes in, it becomes increasingly difficult for growers to control mites using miticides since they are located almost exclusively on the undersides of the leaves where it is hard for spray applications to make good contact with them.
Predatory mites (Amblyseius californicus, A. cucumeris, A. fallacies, and Phytoseiulus persimilis) can be used to control two spotted spider mites. The predatory mite Phytoseiulus persimilis and a small midge Feltiella acarigusa are both predators commonly used for controlling Lewis mites. When using predators, it is best to release them before the mite population climbs too high and to make multiple releases throughout the production cycle. When done properly, controlling spider mites biologically can be just as effective as using chemical strategies.
There are numerous miticides available for controlling two spotted spider and Lewis mites. Ovicides (clofentezine and hexythiazox) primarily act on mite eggs and very young larvae and are best used when mite populations are low. Several products containing the active ingredients abamectin, bifenazate, chlorfenapyr, etoxazole, fenpyroximate, and spiromesifen are effective at controlling various life stages of these mites. Refer to each products label to determine which mite and life stages they control.
It is particularly important to rotate the chemical families of the miticides being applied to prevent resistance to these chemistries. Several miticides have minimal impact on predators (check the label of each product) which allows growers to combine both biological and chemical control strategies. To obtain effective control of mites using miticides, it is very important to ensure good coverage of the upper and lower leaf surfaces. In most instances, it will be necessary to make multiple spray applications to obtain adequate control of mite populations.
The mention of specific active ingredients does not constitute an endorsement or recommendation of, or discrimination against similar products not mentioned. ALWAYS READ PRODUCT LABELS AND USE THEM AS DIRECTED ON THE LABEL.