Scale insects belong to the order Hemiptera, placed in the superfamily Coccoidea under the Class Insecta. They have a significantly variable appearance and reproduction methods. Scale insects resemble herbivores in feeding patterns and pierce plant tissue with their mouthparts. Primarily, they feed on the sap and remain stick to the location. As a result, they secrete honeydew which is the best growing media for inviting sooty mold. Like Aphids, they also have mutualistic affiliation with ants, which feed on the honeydew and safeguard them from predatory insects and birds. Whenever there is scale insects’ infestation, look for ants and blackish sooty mold development on your plants. This multidimensional infestation could lead to significant damages when present in sufficient numbers. Many scale insects are serious crop pests, and only in 1990, together, they instigated about $5 billion of damage in the United States, only.
Scale insects identified in the fossil record were well-preserved in amber from the Early Cretaceous period. Since the Coccomorpha contains nearly 8000 species of scale insects, it is hard to find the lineages of each species. There are several species of scale insects that are considered serious pests of garden plants, angiosperms, and commercial crops. The cottony cushion scale is also one of them that lives on more than 65 species of woody plants including, the Citrus tree, and it originated from Australia. Now, scale insects are found on all angiosperms, fruit plants, and shrubs throughout the US.
The mature females have a shape like a pear, may be circular or elliptical, without wings, no constriction between the body and the head. It could have marginal bristles on the body segments. The majority of the females don't have legs, and when present may have one to five limbs. No compound eyes and mouthparts are shaped to pierce the plant tissues and sap-sucking. Some adult females may not have antennae, and when present, may have 13 segments on them. Mature males are with typical head, thorax, and abdomen. The males often resemble aphids and whiteflies, having a slender body, segmented antennae, compound eyes, and legs with 5-segments. The majority of the males possess wings. A few of them are wingless that die within 2 to 3 days after emerging from the eggs.
A mature female lays up to 2000 eggs, or live young that is dependent on the species reproduction pattern. Both eggs or the live young scales are found under the body of a female. Usually, the eggs could hatch between 7 to 21 days. The newly hatched nymphs are pale that could crawl to find a location where they would spend the rest of their life. The nymphs pass through 3-Instars to become an adult. Meanwhile, a waxy coating appears on their bodies which can't be separated. They could lay eggs in the fall or overwinter as fertilized females. Hatching or giving birth to a live nymph happens in the spring soon after overwintering under plant debris, stubbles, and twigs.
Scale insects suck sap from the leaves, tender shoots, and stems by piercing their mouthparts. Sap sucking may cause leaves yellowing or wilting, plants to look stunted, and death of the plants or tissues occurs when the infestation is too heavy. The plants with stunted growth become susceptible to fungal diseases as honeydew accumulation provides them an excellent environment to thrive. Such plants are also susceptible to severe chill, drought, and other environmental extremes. Honeydew, which was deposited on the surfaces of the leaves, could also attract ants, bees, and flies due to rich-sugary content that passed undigested from scale insects stomachs. Blackish sooty mold appears on the honeydew that could spoil the quality of the fruits, roses, and bushes where it invades.
Scale insects often emerge as crawlers in the spring when the temperature ranges between 45 and 85°F. The crawlers are tiny creatures having legs that could take them to the feeding site. Usually, their presence is often neglected. But, their damages become prevalent, the gardeners look for them around. The best time to monitor and check their reproduction remains in the 50's°F range. Otherwise, they produce most abundantly when it reaches 82.5°F. So, look for them on the upper surfaces of the leaves when the temperature falls in the range mentioned above.
Besides following the preventive measures if, Scale insects’ infestation goes beyond your control, here are the most authentic ways to keep their population suppressed using the biological, organic, and chemical methodologies;
Green Lacewings are from an exceptional class of predatory insects that work efficiently against the crawlers and other sucking insects that harm your garden plants. Chrysoperla rufilabris feed on the scale insects when they emerge in the spring. Release them in combination with Trichogramma species when they see scale insects depositing honeydew on the surfaces of the leaves. Green Lacewing is also friendly with Ladybug and Praying Mantis. 1000 Green Lacewings are enough for 500 square feet when released in the greenhouse, and they could cover up to 2500 square feet when released in the garden.
Their eggs hatch in around 4 to 5 days, and this remains the best time to release them in the garden to live on scale insects.
Adult Trichogramma wasp lays an egg within the host egg, and as the wasp larva develops on the host embryo, causing the egg to turn black. Usually, Trichogramma observes a life span of about 7 or 10 days, and their multiple generations similarly feed on the host eggs. It keeps the scale insects' population pretty checked and never let them damage your precious garden plants. Besides attacking scale insects, they also target bollworms, budworms, cutworms, and caterpillars of several insect species.
Each square contains about 4000 eggs, and a total of 12000 eggs are available in 3-squares. 3-5 five eggs can have applied per square foot of the infected area.
Monterey-Horticultural Oil is OMRI listed and a wise choice for controlling many sucking, chewing and biting insects that damage plants foliage. It contains 80% mineral oil with 20% petroleum distillates. The product may have poor control over worms and caterpillars. But, it destroys the eggs of the listed species on the label. Moreover, it can be used on all edible plants including, fruits, vegetables, and crops irrespective, of the growth stages or the season.
Add 3 to 5 tablespoons of horticultural oil in one gallon of water and apply from the foliage to the stems.
It's also another horticultural oil but, it contains only 2% mineral oil in ready-to-use chemistry. So, the gardeners don't need to calibrate the concentrate dosages and fix water quantities. It is good against the egg and Nymph stages of scale insects and several other damaging pests including, whiteflies, aphids, leaf miners, and thrips in the home garden. No residual effects and toxicity were observed since the product is OMRI listed and allowed in organic gardening. Additionally, it can be sprayed on the day of harvest.
Just point out the spraying end towards the foliage and pull the trigger.
These are the systemic granules that can only be applied to non-edible plants and into the soil. The control could persist for two months if the applied granules are spread, incorporated into the soil, and watered immediately after application. 0.22% Imidacloprid is absorbed by the roots and transported to the other parts of the plants making them poisonous for the invaders. Usually, moderate feeding kills Scale insects besides other sucking pests.
Also, avoid using on indoor plants due to the toxicity associated with Imidacloprid and other systemic insecticides.
Check out our other guides on common garden bugs.
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