Aphids & Spider Mites on Desert Roses

Desert roses (Adenium obesum) are flowering tropical plants that grow well outdoors in U.S. Department of Agriculture hardiness zones 11 to 12. Gardeners can also cultivate them indoors in other regions. These plants are related to oleanders and release a toxic sap that is actually used as an arrow poison in Africa. Keep desert rose plants away from small children and pets. Spider mites and aphids occasionally feed on desert rose plants.

Spider mites (Tetranychidae) are closely related to ticks, spiders and scorpions. They are microscopic in size and can vary in color from green to brown or red.

Desert roses that are infested with spider mites often have unsightly webs on the foliage. Their leaves may appear scorched or bronzed. Severely infested plants may lose their leaves or even die.

Spider mites are the most problematic during periods of hot, dry, windy weather. One spider mite can reproduce within a week of hatching from the egg, so their populations can grow rapidly.

Drought-stressed plants are more prone to spider mite attacks, so it's important to keep a close eye on the soil moisture. The soil needs to be nearly dry between waterings, but should not remain dry for extended periods during the growing season. Use your finger to check 1 or 2 inches down into the soil. If the soil feels almost dry, water your desert roses thoroughly. If your plant is in a container, add water until the excess liquid drains from the holes at the bottom of the planter. Don't add water again until the soil dries.

Control minor infestations by spraying plants with a forceful stream of water. This will dislodge and kill a large number of mites. It will also damage their webbing, which will keep the pests from laying eggs until they can create new webs.

Use horticultural oil for more serious infestations. Mix about 2 to 5 tablespoons of horticultural oil into a gallon of water -- but follow specific label recommendations. Spray plants as needed to control mite infestations. Avoid getting this product in your eyes, on your clothing or on your skin.

Spider mite infestations are notoriously difficult to treat. If your plant is too heavily infested to save, seal it in a bag and discard it far from the rest of your plants.

Aphids have oval-shaped bodies and vary in color from light yellow to almost black. They rarely grow larger than 1/8 inch, and most are much smaller. These insects drain sap from the leaves. Severely infested desert roses may experience dieback, wilt or leaf curling. Aphids also excrete a sticky-sweet liquid called honeydew. This substance can build up on the foliage or on surfaces around the plant. Since honeydew is sweet, it attracts undesirable insects such as flies, ants and wasps. An unattractive fungus called sooty mold may form on the honeydew deposits, detracting from your desert rose plant's beauty.

Spraying desert roses with a steady stream of water will control most minor infestations by dislodging aphids from the plant. Repeat the treatment for several consecutive days.

If you continue to have aphid problems, spray plants with a ready-to-use insecticidal soap every seven to 10 days or as needed. Thoroughly coat both the tops and bottoms of the leaves as well as all other plant surfaces. Do not apply insecticidal soap when temperatures are above 90 degrees Fahrenheit.