Although most cactus have tough thorns, certain pests are just too small to be repelled through this defense. Have you ever had an encounter with small white insects on your cactus? Are you fed up with treating them because they keep on coming back? Here’s the solution (hint: some products you have at home can save your cactus).
Scale insects can be removed from a cactus through 1) Biological, 2) Mechanical, and 3) Chemical approaches. The best way to completely and safely eliminate scale insects is by using both mechanical and chemical (organic) approaches.
Scales are so tiny that you can’t tell if there is an infestation until one day, your cactus is covered in an unusual clump. However, don’t fret at the sight of it because you can eliminate them as I do. Read on and know more.
Scales insects are parasites that attach to the plant’s epidermis and feed on their vascular tissues. If left unchecked, they can damage and kill the plant.
Their name is derived from the waxy shell-like structure that covers their body. The wax cover protects the insect itself and its eggs. The majority of scale insects are small, and they form clusters as they multiply.
Scale insects use their needle-like mouth to pierce and suck the juice off the plants’ tissues.
Some scales can cause significant damage to the plant, whereas others do not appear to harm plants even when the infestation is widespread. Scales are sometimes unnoticeable because they don’t seem like most other insects.
Scale insects’ color, texture, shape, and other characteristics differ depending on the species. Some scale insect species are flat circular with brown midpoint and gray edges that appear like bumps on the plant’s epidermis. Scale insects range in size from 0.1 to 1.2 centimeters.
Some are flat, while others are elevated and wart-like; some are hidden on their hosts, while others are obvious.
Some scales have a complex lifecycle, while some have a simple metamorphosis that starts in an egg laid inside the protective coat. Other species gave birth to live progeny.
When the eggs hatch, nymphs called crawlers come out. They start to seek feeding sites to settle and where to extract the plant’s sap.
Nymphs are extremely small (0.9-1mm approx.), and it is usually tough to spot them at this early stage.
Shortly afterward, the nymphs begin to molt and become immobile. They begin to produce their protective covering and soon after becoming mature adults. In some species, female adults do not move, while males have a single pair of wings.
Scale insects have 21 families with over 6000 species. The most known scales are armored scales and soft scales. These scales, along with mealybugs, are common parasites that attack the cactus.
Armored Scale Insects
The family of armored scales (Diaspididae species) is the largest species of scale insect.
They are the tiniest scales, ranging from 0.1 to 0.3 centimeters. They have a rigid white/brown waxy coating that acts as armor for the insect. Armored scales secret a wax and shed skin and use it as a shell to hide their yellow bodies and protect their eggs. This species does not excrete honeydew.
The waxy armor is not attached to the body of the insect. Males and females have different shell covering. Males appear to be elongated and smaller, while females are oyster-shaped. Armored scale insects reproduce sexually. They feed directly on the tissues of the plant and cause slow deterioration.
Soft Scale Insects
Soft scale insects (Coccidae species) have a brown, thin waxy outer covering attached to the body. They secrete honeydew that causes molds to form.
They have a size that ranges from 0.25 to 0.6 centimeters. Adult females have waxy coats that protrude from the plant’s surface and may have a spherical or flat elongated form. Species of soft scales insects differ in color- reddish, brown, or black.
The soft scale insects usually found on the plant are females that produce thousands of eggs twice a year. Females can either reproduce sexually or parthenogenically (clonal asexual reproduction by a female without the need for male fertilization). During a single growing season, massive populations can develop.
Scales aren’t one of those insect pests that will go away on their own if left alone. Almost often, they need to be removed.
The various covering of a scale insect acts as a barrier to standard contact pesticides, making them difficult to eradicate. Most scales can be controlled effectively using a pest management technique, including cultural, biological, mechanical, and chemical measures.
Several insects feed on the scales and may help curb the population.
Parasitic wasp, ladybugs, ladybird beetles, and lace-wings flies effectively control scales, including mealybugs. Encourage the presence of these insects as they help keep scale populations low. Monitor scales infestation regularly. However, heavy infestation should be treated accordingly, as described below.
In the case of small infestations, manual removal of the scales may be feasible. This is achieved by uprooting the plant, disposing of its soil, and brushing off the scales under running water with the help of a gentle bristle.
This method will just be effective if the scales are already in their adult stage when they are immobile. The disadvantage of this strategy is that if the scales have crawlers among them, they will crawl to another plant. Since most species have waxy coatings, they will just float on the water.
Another manual method is to prune and discard the heavily infested part of the cactus. This method is only applicable to cacti species like Opuntia, Cereus, and other long-stemmed cactus.
Although a good pest control strategy should begin with prevention and other non-chemical techniques, these are not always enough. A pesticide could be used in this situation. Be mindful, if possible, always choose the least hazardous pesticide that will do the job successfully.
Chemical treatment of scale on cactus can either be contact or systemic.
Organic contact insecticides are those organic compounds that damage and kill the target insect through contact.
This technique gives its best only when used in conjunction with the manual approach to remove the infestation effectively. Approaches of this kind are regarded as a beneficial pest management method.
These organic contact insecticides are non-residual, meaning they are only effective during the treatment period and gone on for a short time. These pesticides are low in toxicity to humans and pets and have a minimal impact on pollinators. Find some examples of organic chemicals that can kill scale insects and their applications below:
Alcohol is an organic compound used as a primary insecticide alternative. Isopropyl and ethyl alcohol are the usual types of alcohol used by most gardeners to get rid of scale insects and other soft-bodied pests.
Spraying alcohol and smothering the scale insects is an effective way to kill them. The alcohol below is a good ally against scale insects.
For sprays, the alcohol-water proportion should be 50/50 when using 70% ethanol. If you use 95% alcohol, the ratio should be 1 ½ parts water to 1 part alcohol. Do not spray during the heat of the day as it may cause burns on the cactus. Always label spray bottles.
I always recommend brushing off the scales after spraying alcohol to contact the pest’s body and directly kill them.
2. Botanical Insecticides
There are some naturally occurring insecticides derived from plants called botanical insecticides. Botanical pesticides have various advantages over synthetic insecticides.
Insecticides extracted from plants degrade rapidly in the environment, posing a low risk of residues on food crops and beneficial insects. Botanical insecticides work when sprayed directly onto the scale insects, clogging their breathing tubes and disrupting their cell membranes.
One example of botanical insecticide is neem oil. It is a natural insecticide found in the seeds of the neem tree. According to the University of Nevada, neem oil has several components, but azadirachtin is the most potent element. It is most effective on eggs and nymphs of scale insects and other pests.
Be sure to read the label as neem oil is an extract and should be diluted with water. Neem oils are applied at a 1 to 2% solution to water. Dissolve thoroughly and shake well before spraying. I recommend using neem oil with high azadirachtin content like the one below.
Always check for phytotoxicity before application. Remember that neem oil can also cause burns if used during daytime with temperatures 30 centigrade (90 F) above. For this reason, it is recommended to apply neem oil at night.
Insecticidal soaps have several advantages in pest control. They are formulated solely to control pests like soft-scale insects. They are not toxic to humans and pets and are safe to beneficial insects as well.
Scale insects, mealybugs, whiteflies, mites, and aphids are just a few of the common soft-bodied pests that will die upon contact with insecticidal soaps. These pests cannot resist soaps, which leads to damage to their protective coatings.
There are several ready-to-use insecticidal soaps available in store. One example is the insect control oil-based soap solution found below. Since it contains oil, it is advisable to apply it during the nighttime to avoid sunburn.
Most contact pesticide sprays do not penetrate the scales’ protective coating. As a result, the most effective pesticide treatments are given during crawler emergence, which occurs shortly after egg hatch.
Here is a video showing how to remove scale insects on a cactus.
Systemic insecticides are absorbed by plants through the roots and circulate throughout the entire plant system. You can use it by spraying directly to the cactus or drenching the potting mix with an insecticide solution. It can control both crawlers and adult scale insects.
However, most systemic pesticides contain residues that are highly toxic to nature. When handling broad-spectrum systemic insecticides, it is recommended to use proper protective equipment as these chemicals are hazardous when inhaled and get in contact with the skin.
Prevention is sometimes better than cure. Provide your cactus a favorable growing environment and proper cultural care so it can resist scale damage.
Check your plants regularly and examine whether the cactus have female scales (those do not have wings), crawlers, honeydew, sooty mold, ants, or other pests. If you purchase new cacti, do not mix them with the rest of your healthy plants. Isolate and check for possible insects and fungi. If necessary, treat a sick plant before mixing it with the rest because one sick plant can affect all healthy other plants.
Consider the environmental setup of your plants. The more moist the area is, the more likely it is to develop scales. Add in a warm setting, and the odds will be double. Poor air circulation can also contribute to the problem. Sometimes, the more crowded the area is, the more likely it is to have scales that can spread quickly.
Discovering scales in your healthy-looking cactus makes you wonder where on earth did they came from. Remember, scale insects are tricky little creatures that exist everywhere and spread rapidly. Both indoor and outdoor plants can get scale insects.
The 5 most common reasons for having scale insects on cactus are: :
- Using scale infested potting mix
- Reusing dirty, contaminated pots
- Bringing in new plants infested with scale insects
- Other insects/animals that feed on scales can transfer the eggs to your cactus
- Outdoor, natural winds can disperse the crawlers from one plant to another
Scale insects, if left untreated, can cause irreversible damage to plants and cactus in particular.
The outbreak may not be fatal and seem to occur quickly, but it can still look bad. Cacti infested with scales will have stunted growth. Wilting, yellowing, and eventually death can happen if the infestation is heavy due to excessive sap loss.
Species that secrete honeydew attract other insect scavengers like ants that dwell under the roots and lay eggs beneath. It will disturb the roots of your cactus and may cause root rot. Honeydews will also cause the formation of sooty molds and breeds fungus on the plant.
Scales can be hard to detect due to their size. Many gardeners are unaware that they have a problem until the plant has been extensively infested and has suffered harm.
Some mistakenly diagnose a scale insect as a bug because of its outer shell. Species with white fuzzy covering are sometimes recognized as fungus attacks. Below are the signs that indicate scale insects outbreak.
1. Presence Of Honeydew
Some scale insect species that feed on the sap of a plant excretes sugary liquid called honeydew. These secretions cause the plant to look shiny and sticky.
2. Presence Of Ants
Insects like ants are attracted to honeydew droplets. They feed on the sweet secretion of the scale insect. In exchange, ants protect the scales from other predators. Sometimes, they transport the scale insects to another area, increasing the chance of infestation to other plants.
3. Presence Of Sooty Molds
Sooty molds are black stuff on the cactus due to the growth of fungal organisms from honeydew. Sooty molds are not harmful to the cactus, but it has an ugly appearance.
Be aware that other insects like aphids and whiteflies also excrete honeydew that leads to sooty molds.
1) Scale insects are parasites that feed on cactus sap. They may not be fatal, but they will cause severe damage to the cactus if left untreated.
2) Cactus can get infested with scales by using infected soils or mixing in newly bought plants with scale infections.
3) The best way to remove scale insects is by using a mechanical approach coupled with an organic chemical approach.
“Scale Insects,” Iowa State University
“Introduction to Scale Insects,” University of Minnesota
Lawrence, Cera R., “Charles Bonnet (1720-1793)”. Embryo Project Encyclopedia (2009-06-10). ISSN: 1940-5030 https://hpsrepository.asu.edu/handle/10776/1745
“Insecticides for Indoor Use,” Iowa State University
“Horticultural Oils, What a Gardener Should Know,” University of Nevada
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