Pests

Pests of cactus can weaken, disfigure, and possbily kill plants. Following is a list of pests and possible solutions on how to get rid of them.

1. Ants
Ants can cause a number of problems ranging from being a nuisance to being an accomplice

in damaging plants. One nuisance activity of theirs is to set up home in the soil of a potted plant. When weather turns cool and/or damp, ants tend to seek out drier, warmer environs and they may find it in the soil of a potted plant. When they do move in, it seems as if they like to rearrange things. One of the things I've seen them do is place soil on top of a rock dressing around a plant base. Once, a nest of ants placed bits of potting soil on top of a cactus!

Of deeper concern is the damage the some species of ants can cause as the result of their love for sweets. Honeydew is a sugar-like substance that some ants species love. So much so, that they'll harvest the source as well as protect it. Unfortunately for the grower, the source is any number of insects that suck the life out of plants, namely mealybugs (discussed next), aphids, and scale (discussed below). All have been witnessed in the greenhouse, but by far the worst outbreaks have been because of mealybugs.

Ants can be dislodged simply by watering the infested pot, but if they are back in the same pot the next day, then it's time to mix in a little chemical in with the water and try again. A very, very small amount of malithion, cyfluthrin, or Isotox mixed in with water and poured in the soil is often enough motivation for them to leave. They don't like to be wet and they don't like stinky chemicals.

2. Mealybugs
Mealybugs are soft bodied insects that attack plants above and below ground by sucking plant sap. They're typically are white with a cotton-like texture and are easy to spot when the infestation is above ground, but much harder to detect when they are below ground. About the only way to see if there's a problem down below is pop plants out of their pots every so often and look for the cottony clad bugs. That's not practical in many cases, so a preventative approach may help stave off infestations and that's described in the next paragraph. If an infestation goes unchecked, plants may stop growing and in some cases may start to die. And if one plant is infested with them, it is likely neighboring plants have them as well. One method of killing mealy bugs above the soil line is by using isopropyl (rubbing) alcohol. The alcohol can be applied either by spray (asperator) or direct contact (cotton swab dipped in rubbing alcohol then dabbed on the mealybugs). The alcohol acts to suffocate the bugs and is non-toxic to and does not stain plants. After the bugs are dead, they will have to be physically removed from the plant with a pair of tweezers, a small nail, or a small pair of needle nose pliers. Use any of these instruments to gently rub off the dead bugs. Another method of removal is to blast them off with water. This method helps clean the plant of the bugs, but it can leave water spots.

Rubbing alcohol will not help with a root mealy bug problem since the alcohol can damage roots. One way to rid plants of root mealy bugs is to water, wait a day, and then water with a dilute solution of malithion (chemical name), Isotox (brand name), or cyfluthrin (chemical name) and water. The purpose of the first watering is to wet the soil and increase of the soils capacity to hold more water with a subsequent watering. Also, and maybe more importantly, the plant will soak up water from the initial watering and will be less likely to soak up much chemical in the second watering. I had the awful experience of not doing the first watering and went right to water and Diazanon (no longer on the market) on plants with dry soil. I ended up with some plants discolored and disfigured because they soaked in too much diazinon and reacted badly to it. A good mixture to use is two teaspoons of chemical to 1 gallon of water. If mealy bugs reoccur often, try and switch between chemical treatments. If malithion is used too often, then mealy bugs may become resistant to it. At that point, try Isotox or cyfluthrin and see if that helps get rid of them. Please note that malithion and cyfluthrin are contact insecticides meaning that insects are killed when they come in contact with the chemical. Isotox is a systemic insecticide meaning that the plant soaks in the chemical and the bugs ingest the chemical while they're sucking on the plant.

3. Scale
Scale are insects that have a hard "shell". The shell provides protection from predators while they suck a plant's sap. Given their darker color, they are less apparent than mealy bugs and thus a scale problem may go undetected. One bit of good news about scale is that they don't live below the soil line. Once found though, the treatment for scale is the same as it is for mealy bugs that live above the soil line(see above). Since scale tends to stick to a plant, once they're dead they need to be scraped off gently. A pair of tweezers, a small nail, or a small pair of needle nose pliers can be used to scrape of the bug casings. Scale tend to exude more honeydew than other pests, so after treatment, a spray of water may be needed to remove the sugary substance. If you want to avoid possible water damage or water spots, then a cotton swab dipped in water and rubbed on the honeydew should do the trick.

4. Snails
Snails can be a problem by leaving snail trails across plants and/or by nibbling on them. They are best treated by physical removal or by using a snail bait placed around the base of a pot.

5. Spider mites
Spider mites are teeny tiny little creatures that tend to be a problem on leafy succulents, but they do occasionally attack cactus.

Much like mealybugs and scale, they suck the sap of plants they live on. Left unchecked, they can multiply rapidly and do quite a bit of damage. The tell tale sign of a spider mite infestation is the web-like threads they make on plants. Another sign of spider mites are the very small white or tan dots that move when you blow gently on them. Click on the photo to the right to see what an infestation can look like. This plant came from a grower in Florida and thank goodness I set it and the rest of the order in an area of low light AWAY from the greenhouse plants. I figured I'd start out the plants in an area of less sunlight so that they could reacclimate after being in a box. A week passed when I walked in and noticed the problem. Removal is also attained by spraying with plain water or water mixed with rubbing alcohol. Spider mites set up home on plants that don't get a lot of water on the body or leaves, thus an occasional overhead watering may be in order for plants that are prone to this pest.

6. Spiders
Spiders leave webs on plants that can make a plant look unkempt more than anything else. Spider webs can be removed by spraying water, using a vaccuum, or by using a small paint brush.

7. Aphids
These tend to be more a pest on succulents than on cactus. When discovered, the best possible method of removal is probably water. It'll knock the bugs off, get rid of the sticky honeydew, and the old "skins" (I don't really know what else to call them) that aphids leave behind as they age. Chemical control can include malithion and water mixed and sprayed with a spray bottle, but a chemical treatment will likely need to be followed by a water spray anyway, since the bugs, honeydew, and old "skins" will stick to the plant.