Common Pests, Diseases and Problems
You!
OK, the first thing I’m going to say here is that You (and I) are the biggest problem! Well, your watering regime is, to be more precise. Over-watering is the biggest killer of many Tropical Plants. Remember this and you won’t go far wrong:
Watering Hoyas
‘You can water a dry plant but you can’t dry out a rotten one!’
Many plants, particularly Cacti and Succulents, are specifically adapted through millions of years of natural selection to exist with very little water. The root systems have developed to enjoy good drainage, with no water-logging. They have the ability to conserve water extremely efficiently, as have many plants.
Too Wet – If you allow your soil to become wet and water-logged, you will be starving the roots of the air they need to grow healthily. Before long, root rot will set in and your plant will die. You won’t see the rot at first, as it is below soil level, but it will happen and your plant will die, especially if ventilation is poor and temperatures are low. When the leaves start to drop, it’s probably too late to do anything about it.
Too Dry - On the other hand, if you keep your plant on the dry side, you will allow air to the roots, promoting health, and if you go a little too dry, you will soon see minor signs like slight leaf wilting. These should prompt you to water that plant you’ve been neglecting!
Panic over – Just err on the dry side and you shouldn’t have a problem. Obviously, different plants have different needs, so pay attention to specific care guidelines and ask questions to make sure you get it right!
Scale Insects
There are thousands of species of scale insects, most of whom feed on the sap of plants. They pierce the plants vascular tissue with their sharp mouthparts and suck away. Crawlers run amok all over your plant, while the females find a spot to stay in, covering herself up with a waxy layer, before feeding on the plant sap and producing thousands of eggs. Some Scale Insects are hermaphrodites, which means they can produce offspring without the need for a mate. In fact males can be very rare in infestations.
Effectively, Scale Insects will bleed your plant to death if you let them. Whilst they are a terrible pest if left untreated, in my experience they are relatively easy to treat. Traditional pesticides may not be effective at adult stage, as the waxy layer can repel most liquids , but other controls are available.
Biological controls can involve Ladybirds, who will happily munch on them, but many prefer to use horticultural oils and soaps to smother and suffocate them.
Considering what I’ve heard and read, a combination of handpicking the scale insects, spotting them with a little methylated spirits or similar on a cotton bud, and the application of oils and soaps will control, if not eradicate your infestation, whilst avoiding the use of chemical pesticides.
Spider Mites
Spider mites are a classic greenhouse problem. Anyone that has grown tomatoes over the years will have encountered a spider mite. They are tiny mites that feed on the sap of your plant by piercing the vascular tissue with their mouthparts. Unlike Scale, they do not have a waxy layer to protect themselves, but they do spin fine webs that can form liquid-repellent micro-habitats for them.
They prefer warm, dry conditions and will reproduce extremely quickly if given the chance. They are almost invisible to the naked eye, but the use of a hand held lens will soon allow you to identify these little bugs. The first thing you’ll probably notice is a fine web over your plant, especially on the underside of the leaves. If you allow this to go unchecked, the web can entomb your entire plant, with the thousands of mites causing serious damage.
If you are unlucky enough to have an infestation, your immediate action should be to isolate the infested plant, or plants. Unless there are serious reasons not to, raise the humidity by placing trays of wet gravel in your greenhouse, or make your own humidifier (ask me how).
Biological control is the preferred action here. You can buy predatory mites that will eat all the troublesome mites, then just die off when their job is done. Be careful with timing, though, as they are only effective in long daylight hours.
Pesticide treatment can be effective, but at least 2 applications will be needed at 10-14 days apart. This further treatment is required because there may be unhatched eggs that avoid the first wave of insecticide treatment. If you don’t have another go and get these newly hatched mites, your first attempt would have been a waste of time.
Oils and soaps can be used too – many people state that this is the only way to control spider mites.
I’ve even heard of someone vacuum-cleaning their plant to remove the majority of webs before treating with soap. Apparently, it worked!
Mealy Bug
There are many different types of Mealy Bug, all favouring the warm, humid conditions that you want to provide your Tropical Plants with. Similarly to Scale Insects, they use a waxy layer to protect themselves and their newly hatched offspring, whilst feeding on your plant. The appearance is of ‘cotton wool’ growths near leaf axils.
Mealy bugs can be a pain – rubbing alcohol or similar can be effective when applied directly. Change the compost and look out for any woolly nests hiding in the soil or near the roots. They can hide in pot rims & saucers too, so a thorough inspection and a few shots of alcohol on offenders will be needed. Regular ongoing checks will need to be done too, and you may have to revert to pesticides if you have an infestation.
Prevention invovles a close eye on your new additions, some regular TLC for your plants and the provision of a healthy, well-balanced environment. Healthy plants are not usually as succeptible to infestations.
Sooty Mould
Sooty mould is a common ‘problem’ with Hoya collectors. Sooty mold grows on sweet, sappy residues that are left on your plants. They can be a result of your sweet Hoya nectar dripping on the leaves, or a more serious indication of infestation by a sap-sucking bug.
However it comes about, treatment is very simple. All I do is wipe it off with a damp cloth, before spraying with a weak Seaweed Extract Fertiliser. This seems to keep it in check and I’ve never had a serious problem. I recently unwound a very old Hoya carnosa and found sooty mould on the inner leaves. It must have been there for some time and was eradicated by a quick wipe and spray. I think the generally fleshy nature of Hoya leaves allows them to withstand a good rub down. This method may not apply to thinner, more delicately-leaved varieties, as the mould can get quite thick and needs a good rub, so make sure you take care.
Keep on top of your husbandry and attend to any areas that receive regular nectar drips, and you shouldn’t ever have a problem.
Aphids
Aphids can be a real problem, especially as they are know carriers of many plant viruses. With the recent decline in Ladybird numbers, they are becoming an ever-increasing problem. They reproduce extremely quickly and as such, numbers can grow dramatically if unchecked.
Everyone will be familiar with Greenfly and Blackfly, and will have their own methods of controlling them, but this is what I do.
I always attack them by hand first. The beauty of aphids is that they are usually visible to the naked eye. Just ‘rub’ them off to keep numbers down. My fish enjoy them as a snack, so I often shake them into a bucket and drop them in my aquarium – there’s nothing wrong with free food!
If you find that you just can’t keep on top of them, just use a weak soap solution in a spray. Apply to the infected areas and you should see a reduction within a day or two. The soap will be washed away once it has done its job, so this is a very low-impact method of control that is very effective.
Pesticides can be used in serious infestations, but there should not be a need to if you keep on top of them with other methods.
Also, consider companion planting to help deter pests.
Other Pests
Whilst diseases are pretty rare in well-maintained indoor tropical plant collections, there are many other pests that you may encounter.
Whitefly, Catterpillars, Thrips, Fungus Gnats and many many more can cause problems, but I’ve concentrated on the most commonly requested pests.
I will add more detail to this factsheet as time goes by, but please visit ‘About Molly’ and contact me if you need any advice in the meantime.
Fortunately, I haven’t had any problems with anything listed on this page. In fact, these are the only photos I’ve used on my site that I haven’t taken as you can’t take a picture of something you don’t have!
However, I have received plants that had a few bugs on them, but a period of quarantine and a close eye made sure there were no serious problems.