What is Scale on Plants?
Although the word “scale” sounds like a disease, plant scale is actually an infestation of over 7,000 different species of extremely small, insects. Scale cling to the branches and stems of plants and can also be found on the underside of leaves and hiding in the internodes. Scale sucks the sap from plants.
Plant scale is frequently mistaken for a bacterial or fungal disease due to the bumpy, shell-like appearance. Knowing the difference between scale and a bacterial or fungal disease is important because the treatments are completely different. Due to the wide variety of species and characteristics, plant scale can be difficult to detect and treat.
What Does Scale Look Like on Plants?
Anyone with either houseplants or a garden is most likely to encounter scale at some point in time. This is because there are a tremendous number of species. There are large differences in the size, shape and color of each species. Some are orange, black or white. Others camouflage themselves by blending into the color of the plant. Most plant scale are extremely small.
The average length is between 1/16th and 1/8 of an inch. There is no such thing as one scale on any plant. This pest always invades in a cluster. The biggest difference between plant scale and other pests is once they have locked themselves in place, they become immobile. These insects feed on sap by piercing the plant. The best indication your plant has scale is there will be a cluster of tiny bumps like shells.
These clusters form all over the branches and stems of the plants. There are two basic groups of these insects: armored or hard scale, and soft scale. Soft scale is covered with a waxy substance providing them with protection. The hard scale variety have a hard shell, capable of protecting them from predators. Pesticides are not recommended because they are not effective against this type of invasion.
Anyone wondering what scale looks like must realize the answer is dependent on the specific type of scale. Tea scale are a variety with a fuzzy brown and white coating. Scale is found on the underside of leaves. Camellias and certain hollies are most susceptible to tea scale. Each species prefers different plants.
The plants most often infested include fruit trees, Euonymus, shrubs and magnolia. Mealybugs are included in the unarmored or soft scale family. The difference is this pest is larger than most of the other species, making the identification of the insects much easier. Mealybugs do not generally look like a fungus or disease. There are approximately 8,000 different types of these insects.
Plant Scale Identifications
All plant scale are a part of the Coccoidea superfamily. There are subdivisions for the smaller groups. Some are more prominent than others, with both differences and similarities. The Pink Wax Scale or Coccidae usually secretes a white coating like wax. This covering is protection from insecticides, making them all but useless.
The most well-known pest in this family is called Coccus viridis, frequently referred to as either green scale or coffee scale. One of the worst and most often seen pests in agricultural coffee crops is the Coccus viridis. Tree dwellers are another insect included in the wax scale family. This family also includes the calico scale and the maple scale. Scale feed by flattening their scales on tree branches.
Many gardeners are unaware one of the most common types of scale are mealybugs. This variety is different from most scale because although there are legs, they are rarely used. This is because once a good feeding spot has been located, these insects rarely move. Scale is quite a common pest in greenhouses. Mealybugs are often found attacking crops in agricultural areas.
There are more than 2,650 species of armored scale. Unfortunately, this type of pest often thrives because they are immune to may predators. This is because of the armor-like scales. One of the hardest pests in this classification to kill is the San Jose scale. This is an agricultural pest frequently found all over the United States. Documentation for this insect has been traced back to San Jose during the late 1800s.
Despite this, the San Jose scale originally came from China. In 1914, this was the first pest in this species to become resistant to insecticides. The California Red Scale is another agricultural insect. Although citrus trees are the preferred target, this pest will also feed on other fruit trees, olive trees, and specific vegetables including pumpkin.
The Cottony cushioned scale or Icerya purchasi is one of the oddest appearing insects currently in existence. It is also one of the largest species of scale. The size is mostly due to the cottony exterior. One of the rarer species of scale is the Armenian cochineal. The color and shape resemble a berry.
The wooly beech scale is the best example of the Eriococcidae family. The appearance of the scales are like a bump or lump found on the branches or twigs of the plant. This species is frequently mistaken for tree buds. This family is at risk due to numerous predators including birds and ladybugs.
What Causes Scale on Plants?
What causes scale on plants is a question that has many answers. In general, most pests can be introduced to your growing environment in several ways including:
- A new plant that was not thoroughly inspected or quarantined
- Contaminated soil
- Fresh produce or cut flowers
Another issue, for outdoor plants and crops can be climate change, resulting in periods of both drought and excessive heat. This results in stress to the plants, providing a much better food source for sucking pests, including scale.
Life Cycle of Plant Scale
The life of scale is simple. The eggs are laid beneath the adult female’s covering. Once the eggs have hatched, nymphs are born. The babies have antennae and legs and walk away to find new places to feed. For many scales, this stage is the only one where the insects are crawling on the plant. Once a desirable location is found, the mouthparts are inserted into the plant to feed on the sap.
The characteristics of the insects are developed quickly once they begin feeding. As the growth of the nymphs occur, most species lose both their antennae and legs. Both adult females and nymphs for most of species spend their entire life in the same location. The adult males are like gnats and fly to the females to mate.
What Does Plant Scale Damage Look Like?
The type of plant scale damage depends on the severity of the infestation. The most common damage includes:
- Yellowing leaves
- Decreased plant or tree vigor
- Premature dropping of leaves
- Black sooty mold due to honeydew excretion
- Fruit, twigs or leaves with discolored blemishes
- Dying branches or twigs due to heavy or recurring infestations
- Attraction of ants
How to Get Rid of Scale on Plants Naturally
The best way to get rid of scale on plants includes:
- Apply Trifecta Crop Control
- Lady beetles and parasitic wasps
- Closely observing the infestation
- Manually removing the insects
- Discarding or pruning the plant or tree
- Using double-sided tape on infected branches and twigs
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Predators including lady beetles and parasitic wasps can effectively decrease the colonies of scale. The progress of the infestation should be observed closely. In some instances, adverse weather will get rid of or kill smaller infestations, so treatment is not required. If there is a small infestation on small shrubs and trees, houseplants or non-cannabis, scale can be removed manually by hand or spraying the infected areas with water. The pests can often be removed with nothing more than fingers and water.
PHOTO CREDIT Charles Olsen, USDA APHIS PPQ, USDA APHIS PPQ, Bugwood.org
All heavily infested branches should be either pruned or destroyed. If only one or two branches of a bush or tree are infested, they can be pruned carefully and removed to prevent the infestation from spreading. For non-cannabis and sturdy plants, thoroughly spray the entire plant or tree with water. Sometimes, the infestation can be controlled simply by washing the branches, stems or leaves with water.
Double-sided tape can be effectively used on the branches and twigs in any affected areas. Tape is also useful in the areas most susceptible to scale. The bodies of the insects are so small, they will become trapped within the adhesive of the tape.
Beneficial insects (biological pest control) are recommended for eating the insects. The best options are lacewings and ladybugs since these insects are the natural enemy of scales.
Do not be surprised if the old scales remain on the plants once they have been killed by these natural predators. The above treatments will become more effective by moving a thumb over the groupings of scales. Dead scales are hollow, and this movement will remove them easily. If the insects are alive, a wet, colorful residue will be left behind on the thumbnail.
How to Prevent Scale on Plants Naturally
There are several effective methods of prevention including:
- Apply Trifecta Crop Control
- Extreme weather
- Watering plants frequently to ensure the soil remains moist
- Diverse flowering plants
- Avoiding the use of pesticides
In general, many unwanted trouble insects and pests are discouraged by the essential oils contained in our unique formula. Apply Trifecta Crop Control as a preventative to keep most pests off your plants so you never have to worry about an infestation. Apply as follows or click here to view and/or download our complete application guidelines.
- .5oz per gallon applied once per week during veg
- 1oz per gallon applied once per week during flower up to 2 weeks before harvest for cannabis plants. Crop Control can be applied up to the day of harvest for fruits and vegetables. Please wash your produce before consuming to remove any residual product.
Plant scale are often killed by extreme weather. Unfortunately, the weather also kills the predators and parasites responsible for keeping them under control by attacking the plant scales.
Watering plants during a drought is critical for decreasing the plant stress often resulting in an infestation. The insects feeding on scale are nourished through flowering plants.
Planting a good diversity of plants can also discourage the attraction of scale to your crops.
Soft Scale Management in Greenhouse Using Biocontrols
Cryptolaemus Montrouzieri
Soft scale can be managed with a predatory ladybird beetle called Cryptolaemus montrouzieri. You can find them hiding in plant crevices and beneath leaves where scales generally feed. Once the eggs have hatched, they become voracious larvae with waxy, white and long projections like mealybugs. Cryptolaemus thrive with relative humidity levels of 70 to 80 percent.
The ideal temperature is between 72- and 77-degrees Fahrenheit. You can have them shipped in plastic tubes as adults. Depending on the severity of your infestation, introduce two to five adults for every infected plant. Each square yard will require two or three adults. For the most effective results, use the following tips.
- Adult beetles can be stored in containers for a maximum of 18 hours
- Before releasing, mist the area with water
- Predators should be released the day they are received during the evening
- When releasing, do not wear white clothes or you will attract the beetles
- If the temperature is under 56 degrees Fahrenheit, Cryptolaemus will not fly
- Keep vents and windows closed the day you release the beetles to prevent dispersion
- If present, control ants or they will protect pests
- Tap the beetles from the container gently, onto the infested plant’s foliage
- When released, keep your humidity level between 70 and 80 percent
- Put three by five-inch white cards by the hot spots to help the beetle locate prey
Metaphycus Helvolus
Metaphycus helvolus are small parasitic wasps you can use as an effective preventative shipped during the pupae stage. Adult wasps can become trapped in heavy honeydew due to their tiny size. If excessive honeydew is present, use predators as an alternative or rinse the honeydew from your plants. One egg is laid inside of the scale, with the scale consumed from inside by the larvae once hatched.
Approximately 42 days are required for the emergence of the parasitoid from the scale cadaver. The average lifespan of the adult is two months. The ideal environmental condition is a relative humidity level of about 50 percent and a temperature between 73- and 87-degrees Fahrenheit. You need to release between five and ten pupae for each plant. The best way to use Metaphycus includes:
- Metaphycus should be used for a preventative treatment
- Biocontrols should be released as soon as delivered for prevention and management
- Adhere to the biocontrol suppliers’ recommendations for release
- All infested plant material needs to be removed immediately
- Do not overfertilize
- Humidity levels should be about 50 percent
- To determine effectiveness, inspect plant leaves and stems once each week
- Temperature should be between 73- and 90-degrees Fahrenheit
- Remove honeydew and scales from plants with a gentle water spray
- Heavily infested plants should be pruned to prevent the spreading of scales
- Yellow sticky traps attract these parasitoids, so only hang them two to three times each week
