Tuesday, April 22, 2014

Honeydew Isn't Always a Melon

Honeydew dripping from a Schefflera
I can spot a houseplant problem "a mile away". It's true. Of course, the whole girl scout troop had head lice in 2nd grade, (19 years ago), and I can still spot them "a mile away", too. Lol!
 I'm going to do a couple of posts about different insect pests of houseplants. So many people aren't sure what is bothering their houseplants. I'd like to help  identify the problems and the ways to solve them. I'm going to start with the insect and mite problems and then will attempt to tackle the diseases and other disorders. So, here we go.
When you have shiny, sticky leaves on your houseplants, it usually means you have a pest problem, unless someone has recently spilled honey or some such substance on your plant. Let me expound on this. 
On the following plants you will notice a shiny substance. If you touched it, you would find it is sticky, as well. This is the excretion (yes, it is what you are thinking) from certain insects. It comes from scale, mealybugs, and aphids. The first is a soft scale which are the brown spots you see in the following pictures. There are insects living under the brown covering and  they are sucking the juices from your plants and slowly killing them. They then excrete the leftovers and it is deposited on your plants and if the infestation is large enough, on your floors and carpeting. Yuck!

Sticky honeydew on scale infested staghorn fern.

Scale on Schefflera arbicola

Hemispherical scale and honeydew on a bird's nest fern

As you can see from these pictures, these scale like ferns and schefflera, but also love ficus, palms, and many other plants. Scale are very hard to get under control. We will talk about control after we talk about the next insect.

My brother sent me the picture below, asking if there was any hope for this palm. I told him it was pretty bad. Not only does it have scale, it has spider mites, which most people usually miss. Unfortunately, they are quite obvious on this plant, but we will talk about them later. The spots on the stem are the scale insects.

Scale as well as spider mites on a palm plant (Photo by Keith Eldred)
The second pest is mealybugs. They are extremely slow moving insects which like to hide in crevices and under leaves. When it gets as bad as the pictures below, it is VERY hard to eradicate them. In fact, in my experience, mealybugs are the hardest pest to control in the indoor garden.The plant pictured is a jade plant and it would seem that they are mealybug magnets. Actually, they love all succulents. The pictures aren't showing them hiding, as these plants have very large infestations. They were hiding, but now have revealed themselves in a big way. 

Mealybugs on jade plant

Notice the large mealybug near the top of the picture.

Mealybugs and cryptolaemus on strelitzia

Honeydew on heliconia

 How do you eradicate these plant juice sucking insects? One way is to get some cotton swabs, dip them in rubbing alcohol, and touch each one of the insects. The alcohol dries them out and removes their protective coating. Another solution and it can be used in combination with the alcohol, is neem oil. I use a product called Rose Rx which is neem oil and it seems to help keep them under control. The oil smothers the insects. If these remedies do not work, a systemic insecticide may be your next step. I use Bonide Houseplant insecticide which has a very low percentage of the insecticide imidicloprid. The product, placed in the soil, moves through the plant when it is watered. The insects then chew on the plant and they die. I wouldn't recommend using this on plants your cats or dogs would chew on or where children are present.
Cryptolaemus destroying mealybugs

If you would like to use a biological control, there are a few different choices. Cryptolaemus, the mealybug destroyer, is an insect that eat the mealybugs in the immature and mature stages of their lives. They are black/tan lady beetles, but I only have pictures of the larval stage. They were imported from Australia in 1891 to control citrus mealybugs in California. They control citrus and long tailed mealybugs and some scale. I have only ever seen these in greenhouse settings, never in a home, but I'm sure they would work anywhere. The only downside to this, is that this control measure involves more insects. I'm sure some people would rather not introduce more insects into their homes. Another biological is the parasitic wasp, Leptomastix dactylopii. They attack citrus mealybug and do not usually control the other varieties of mealybug. They are native to Brazil and were introduced to America in 1934-35. These are good at finding low populations of mealybugs, so if you have a small problem, these are a good control measure. 
If it is scale you are fighting, the red scale exterminator, Aphytis melinus are parasites of California red scale, San Jose scale, and oleander scale. The purple scale parasite, Rhizobius lophanthae, is a small black lady beetle which will eat both the larvae and adult scales. They also will eat mealybugs. You can find these predators at biological control mail order sources. 

Cryptolemus larvae or mealybug killer
Lets try to use the least toxic control for the insects on our houseplants. We want to definitely be conscious of the products we use in our homes and on our plants. Yet, we also don't want to lose our fern from great-grandma that is irreplaceable. Try the least toxic control, and if that isn't working, try something else. If you don't want to use chemicals, then you have to decide whether the plant is important enough keep fighting the insects or just throw the plant away and call it a day.


  1. Excellent blog and great photos. Over time you find some house plants are just prone to certain insect problems. So, you either don't grow those, or keep them under close surveillance. Again, great article.

    1. Thanks so much Bob! I appreciate it!