Scout from the start

Photos courtesy of SePRO

Poinsettia season is well underway and that means battling and preparing for the major pest outbreaks that come with it. Whiteflies, mites, fungus gnat larvae, thrips, and mealybugs are among the most common pests and can attack the crop all season long. Poinsettias originate from southern Mexico in a mild climate where temperatures range from the mid-50s to the mid-80s year-round. If the growing conditions are not ideal, pest pressure due to plant stress will be a recurring problem. Starting with clean plants and providing conditions for them to thrive is the key to success for poinsettias.

The foundation of an effective pest management program should start with routine scouting and accurate pest identification. It’s critical for growers to consider the potential for introducing pests anytime they accept new plant material. It makes no difference the time of year (when plants are in greenhouses) or where the operation is located, as most of these pests are capable of surviving for several weeks even without a host. If the plants survive the trip, it’s highly likely the pests will, too. It is important to effectively manage pests early in the crop and especially before bract formation, as the insecticides and miticides labeled for application on bracts are more limited.

Whiteflies continue to be the major insect pest on poinsettias. These tiny, sap-sucking insects can cause a lot of damage. They are most common during poinsettia production and can build up to extremely high populations in greenhouses. When actively feeding, whiteflies cause leaves to turn yellow and eventually brown as the leaf tissue dies. Large colonies typically develop on the undersides of leaves where they normally lay tiny oblong eggs that range from yellow to white in color.

After the eggs hatch, the young whiteflies go through four nymphal stages called instars. Winged adults emerge from the last nymphal stage. All stages feed by sucking plant juices from leaves and excreting excess liquid as drops of honeydew when they feed. In addition to the destructive feeding damage whiteflies cause on the poinsettia, the honeydew excreted on the affected leaves provides a source of nutrition for sooty mold fungi. Additionally, growers need to account for whitefly biotypes that have developed over the last decade or have the potential to develop insecticide resistance (i.e., Mediterranean whitefly).

Mealybugs (Pseudococcidae) are insects that are notorious for attacking all types of ornamental plants, which includes poinsettias. Mealybugs are difficult to detect and even more difficult to control. Once the young crawler stage becomes established on the plant, they may no longer move or move so slowly that they appear dead. Sometimes, they may even be confused as part of the plant. They are often located in hard to see areas such as roots, lower stems below the canopy, the underside of leaves, or bracts where they remain hiding in the nooks and crannies. Light infestations can easily be overlooked, allowing the population to build to damaging levels before detection is finally made. Mealybugs feed by inserting their mouthparts into plant tissue and sucking out sap. There may be no symptoms when just a few individuals or a small population are present, but larger populations can cause plant stunting and the leaves may develop yellow spots. Branches can often die back and sometimes plants completely defoliate as a result.

Although mites are often grouped with insects, they are arachnids and more closely related to ticks and spiders. The two most common mites on poinsettia include broad mites and Lewis mites. Broad mites are only 1/100 of an inch long and require a dissecting microscope to be seen on the leaves. Broad mite feeding causes distortion and deformation of the terminal leaves of poinsettias. Lewis mites continue to become more of a problem on poinsettias and can be mistaken for two-spotted spider mites, but they are smaller. Lewis mites feed on the underside of leaves and cause damage that is often mistaken for a nutritional deficiency.

Fungus gnats have a wide host range, they can be a nuisance to people and can be mistaken for mosquitoes. Fungus gnats are small flies that develop in the growing medium and are a common problem in the production of poinsettias. The larvae feed on algae, fungi, and plant roots, but the adults do not feed or bite. Fungus gnat larvae are typically found within the top few inches of growing media, especially under wet conditions. Fungus gnat adults are highly attracted to moist growing media, so watering practices should account for changes in temperature and day length, such as fall and winter months when plant growth and water usage slows down.

Poinsettias are not a preferred host for thrips, but the larvae and adult stages of Western flower thrips can cause direct damage to the leaves and bracts of poinsettia plants. The feeding damage causes leaf scarring and distortion in addition to black spots, or excrement may be visible on plant leaves. Large populations can cause extensive plant damage in short periods of time. Use yellow sticky cards to capture adult thrips, which will help detect early infestations.

When it comes to effective pest management for poinsettias, be sure to check out the latest poinsettia guide from SePRO, as you go the extra mile to deliver extraordinary poinsettias this season. The guide includes detailed product recommendations with multiple solutions for all the major pests that attack poinsettias including whiteflies, mites, fungus gnats, thrips, and mealybugs. Remember effective pest management requires a preventative approach, so be sure to routinely scout the poinsettia crop and avoid situations that lead to high pest populations.