Carl White
Botanical Gardens

So what's bugging your houseplants? The following is a list of possible suspects and some ways to curb their influence.

Aphids are 2-3 mm long, soft bodied insects that feed on plant sap and often infect stressed plants. They can be winged or wingless and can be translucent green or black in colour. They congregate in bunches or colonies on the underside of leaves and new shoots. Infested plants become yellow and twisted with curled leaves that eventually fall off. Growth is stunted and, in bad cases, new buds are poorly formed. Control can be achieved in several ways; pick off the adults you can see and spray thoroughly with water to remove the eggs. Safer's Insecticidal Soap at 20 ml/l of water or Pyrethrum 0.2 per cent according to label instructions should give good control. (Editor's note: Pesticides must be used with care; readers should refer to the
How to Spray section below for safety hints.)

Fungus gnats are 3-6 mm flies. The adults are harmless but the young maggots live in the soil and feed on organic matter. They thrive in moist soil and affected plants will be stunted and foliage may fall off. The best control is to remove plants from the soil, wash the roots and repot in sterilized soil. I wouldn't worry about these guys too much, for in all my years dealing with plants I have yet to see damage caused by fungus gnat maggots.

Mealy bugs are tiny, white insects that look like tufts of lint. They are another of the ‘sap suckers' and bad infestations will cause stunted growth and eventually kill the plant. You will find them on the underside of leaves and where the leaves branch off from the main stem of the plant. Use the same controls as for aphids.

Mites are generally too small to be seen without a magnifying glass. They are brownish in colour  and look like dust. Mites suck plant juices and leave foliage speckled and yellow. If not controlled the leaves will turn brown and fall off, and new growth will be stunted with deformed buds. Spider mites produce webs on the leaves to hide and feed under. Plants growing in hot, dry locations are most susceptible to mite attack. Take control measures as soon as you notice these pests because mites multiply very rapidly. Try Safer's Insecticidal Soap at 20 ml/l of water or two treatments of  Malathion 50 per cent at 2 ml/l of water, 10 days apart.

Scale insects are oval bugs up to 4 mm in diameter that don't resemble any other pest. When I first encountered them I thought they were a fungus of some sort. Nope, they are bugs all right, with a brown shell-like covering. They can be found on stems and leaves and suck juices from the plant causing poor, stunted growth. They attach themselves to the plant and move very slowly. This means you can scrub them off  with a toothbrush dipped in rubbing alcohol or dab them with alcohol using a Q-tip and pick them off by hand.

Springtails are the little, white bugs that you see hopping around the soil surface after you water. They range in size from microscopic to about 5 mm. They love wet soil and feed on decayed organic matter in the soil. They may attack tender new growth but prefer material that is already dead. If you have them you could be overwatering. They are not a big threat but since nobody likes bugs in the house try treating the soil with Pyrethrum or Malathion at the concentrations mentioned earlier. Transplanting to new sterile soil after washing the roots is another way to control them.

Thrips are small, thin pests, the young being yellow and the adults brown or black. The adults are winged and tend to fly around the plant when disturbed. They rasp the plant tissue and suck the juice, leaving silver specks on the surface. Their black droppings are small but you can still see them on a badly infested plant. Females leave a small scar on the tissue where they deposit their eggs. Decent control can be achieved with the same materials used on aphids.

Whiteflies are small pests that hide and feed on the undersides of leaves. They suck the plant juices, leaving foliage pale or discoloured. These little guys are hard to get rid of because they fly around and seem to built up immunity to insecticide as fast as you can apply it. You have to trick them by spraying Malathion 50 per cent at 2 ml/l of water, then about five days later apply Pyrethrum 0.2 per cent (follow label) then a week later hit them with the Malathion again. Goodbye whitefly.

How to Spray
Don't "spray and pray". Pesticide applications, especially indoors should be a last resort. Remember that these substances are poisons and treat them as such. Whenever you apply a insecticide you must follow the directions on the label.

Read the full label as many products list the plants that it is safe to use the product on. Ferns and cacti are two groups that can suffer from certain chemical treatments. If your plant is not listed, you can try a little of the chemical on a few leaves and wait a couple of days to see if any damage occurs. If the instructions say "2 ml/l of water" then you must use that formulation; 4 ml/l is not twice as good or twice as fast. Don't set the infested plant on the kitchen table and spray. Never apply chemicals around fish tanks, pet dishes or food preparation areas. Treat the plants outside if possible and if it is too cold, use the basement or the garage. Another trick you might want to try is using a spray booth to treat your houseplants. Place a large cardboard box on its end, put the plant inside and tape the lid flaps shut. Cut a small (2 inch) U-shaped slit on two sides
of the box. This will create two flaps you can fold up to apply the insecticide. You can now place the nozzle of your sprayer in the open flaps and spray, containing all the spray in the box. Plants should be sprayed until they just start to drip. Leave plant in the box until it is dry.

Never place a plant that has just been sprayed in direct sunlight. Sadly, the best control method for a severely-infested houseplant is to throw it out. You can always take a cutting, clean all the critters off it, and start a new plant. Many insecticides now have formulations for houseplants
and some like Safer's Insecticidal Soap and Pyrethrum come in their own sprayer bottles. This is handy for the occasional user and eliminates mixing and cleaning the spray equipment. So don't be bugged. Next issue we will look at some houseplant diseases and control measures.