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Pests - We receive an increasing number of calls about pest problems on tropical plants and for us to formulate a better response to your questions we have put together this page to help you manage the inevitable infestations that will arise from warm conditions. Pest management is important for both plant health and the prevention of spreading diseases, basically you have the choice of Biological or Chemical control but not a mixture of the two methods. I do not cover control of grasshoppers as in the one in the picture above but be aware they love to eat many plants and this one was munching through one of my Citrus Trees - probably a manual control needed here!

Your Growing Environment

The location of your plants may also have a big impact on the particular type of pest problem. In particular a dry conservatory with a solid, perhaps tiled floor, used as an outdoor room with a few plants grown in pots, is a haven for Spider Mite and White fly. Particularly susceptible are the passion flowers, brugmansia, bananas aroids and many other large leaved plants. Some control may be effected by wiping down the leaves of these plants in a weak washing up liquid water solution using a damp cloth, paying particular attention to the reverse of the leaves. Spider mite on house plants or dry conservatory plants gives rise to most of our problem calls plus damage or plant death resulting from using the wrong insecticide.

This site http://www.greengardener.co.uk seems to carry many of the Biological Control Products if that helps?

 

Insecticide Control

Often a quick and easy method of controlling pests on a manageable area as long as you use the correct insecticides. Many tropical plants are intolerant of the typical pest management products that you can purchase in garden centres. The product range has also been significantly reduced as the EU recently put restrictions on any chemical that may prove harmful to the environment or potentially be a health hazard. The following controls are based on our own experience but we do not take any responsibility for their use.

Biological Control

The green and safe alternative to pest control by introducing predatory insects that will eat their insect prey. An excellent choice given the right environment and the correct temperature and of course an enclosed space to contain the predatory insects from flying away. Several points to bear in mind though. You cannot use any insecticides at the same time as these may kill the introduced control insects. You will need to introduce different predatory insects for each type of pest that you are trying to control - and they do come at a high price!

  Ants

Ants are a nuisance in that they "milk" aphids and other pests for food and in the process spread and farm the insects. Any resulting nests in the pots also disturb the roots. On top of that I can't stand ants!

A conventional ant powder will usually work sprinkled around the base of the infected plant but "Provado" will also kill any ants directly sprayed.

Ants

No known biological control apart from an "Ant Eaters" which are somewhat impractical!

  Aphids

Aphids are soft bodied insects which live on the sap of a wide number of plants. They are generally green but can also be black, orange, or shades of brown. Some have wings to fly in from outside and set up new colonies at any time. They multiply extremely fast during warm weather by producing live young which already have the next generation developing inside them when they are 'born'. Aphids suck the sap out of the leaves and stems of the host plants, weakening them and causing distortion to emerging flowers and leaves. Bad infestations are very debilitating. They excrete a sticky honeydew which attracts ants and turns black in damp conditions, resulting in sooty mould. This is not damaging in itself, but should be wiped off to allow more light to the leaves. Young Canna shoots are particularly prone and these spread the Canna Virus so must be controlled.

"Chess" is a useful spray that does not seem to damage delicate Tropical Plants. However this is a professional pesticide not normally available to the Retail sector. Most other aphid pesticides I find can burn the leaves of bananas etc.

Aphids

Aphidius & Aphidoletes  - Aphidius is a small, highly effective midge which lays its eggs inside Aphids, parasitising them to produce new generations of Aphidius to gain continuing control. This beneficial insect is a native insect to the UK, so it also works outside, but is best in a glasshouse or conservatory where it will stay until there are no more Aphid to parasitism. This is best introduced early when temperatures are regularly above 10C.

Aphidoletes is a small midge, 2mm long and slender with long legs, males have long grey antennae and those of the females are darker and shorter. Most often seen are the larvae which are maggot-like grubs, narrowing at both ends, and up to 3mm long when fully grown. The larvae are orange or orange-red in colour. They can be seen amongst aphid colonies. Excellent for larger infestations but needs a higher temperature 15Cto be effective.

 

  Mealybug

Mealybugs look like small woodlice, leaving fluffy cotton-wool like egg masses in cracks and crevices on and around the plants. They can multiply very quickly in warm weather and make the plant very sickly and unsightly. They occur in conservatories and greenhouses, as they are killed by frost outside. They attack the plant by feeding on the sap and weakening it. They also drop sticky secretions onto the leaves below, which may develop sooty mould in damp weather. It should be wiped off to allow more light to the leaf. This is a very difficult pest to completely eradicate!

"Provado" ultimate bug killer from Pbi (Bio) is effective in killing Mealybug but repeat applications may be needed as the tiny young hatch out at a later date from the cotton wool like nests. Adults lay up to 300 young.

Mealybug

Cryptolaemus montrouzieri - This brown Australian ladybird eats all stages of Mealybug (under glass only) in the UK. It needs high warmth and light levels to work efficiently, so it is best introduced in June to give a good 3 months of the summer before the cooler weather sets in. Cryptolaemus settle best when there are quite a large number of Mealybugs to attract them. Cryptolaemus larvae look similar to mealybugs so be careful not to squash them.

 

  Scale

Scale insects are brown wart-like creatures that tend to congregate on the underside of leaves and suck sap. Over a period of time they debilitate the plant and are not easy to control. Citrus and many other woody type plants are very prone to attack. The sticky excretion is unsightly and attracts ants and a black mold.

"Provado" ultimate bug killer from Pbi (Bio) is effective in killing Scale and gives a lasting control through a systemic action.

Scale

A mixture of Soft Scale controls give maximum control: Metaphycus helvolus, Encarsia citrina and Encyrtus infelix. These are all very small flying insects which target scale insects, sucking the juices out of some and laying their eggs in others. They each live about a month and lay approximately 6 eggs a day, the young of which emerge through a small hole after 3 or 4 weeks. They work best between 20-30C, so are best introduced from May when temperatures and light levels are at their highest. None of them will be easily noticeable flying around the conservatory and, as with other biological pest controls, they are not interested in humans or pets!

  Sciarid Fly

These are the small black midges about 2-3mm long living on and around the compost surface of pots, generally under glass. Their small white larvae like tiny maggots live in the compost and feed on plants and cuttings. Although unsightly and irritating, they do not cause large-scale damage but can be disruptive to seedling germination.

Provado "Vine Weevil Killer" will control Sciarid fly and Vine weevil for up to 6 months when watered into the soil.

 

 

 

Sciarid Fly

Hypoaspis miles  - Tiny brownish crawling beneficial mites which eat egg and adult Sciarid Flies. They lay their own eggs in the compost and their larvae will eat up to 7 developing Sciarid a day each, gaining effective control over a few weeks. The soil temperature needs to be above 12C to be effective.

 

  Slugs & Snails

Slugs and snails come in many shapes and sizes and are commonplace around the garden, particularly in damp conditions. In the Tropical Greenhouse infestations become serious because of the constant warm damp conditions. Large slugs have the potential to produce 90,000 grandchildren and has approximately 27,000 teeth! Slugs and snails eat leaves, stems and roots of plants, weakening them and often causing them to die. They leave slimy trails over plants and soil, and are particularly devastating to seedlings and cuttings. The unsightly holes all over lush clean foliage is one that really upsets me.

The use of a slug pellet control is not so serious in a greenhouse where our wild bird population do not have access to eat the poisoned slugs and snails.

 

Slugs & Snails

Phasmarhabditis (nematodes) Are microscopic beneficial nematodes (eel worms) which are watered into pots or open ground with a watering can, indoors or outdoors, when temperatures are above 5C. They enter the slug through a hole in its back while it is underground and poison it so that it will die within a few days underground, out of sight. They can be applied at any time of the year when the temperatures are suitable, and they remain in sufficient concentration to give good effectiveness for about 6 weeks, if the soil is moist.

 

  Spider Mite

Most Spider Mites are actually Two Spotted Mites: pale greeny-brown in colour with 2 dark dots on their backs. Red Spider Mites are very tiny and generally live underneath leaves, getting worse in hot conditions. They suck the plant juices resulting in mottling of the leaves and sickly looking growth. When the infestation becomes advanced, fine webbing appears on new growth. Eventually leaves turn brown and drop off. They are generally found indoors, particularly in warm dry conditions like a conservatory room or indoors on house plants, but may damage plants outdoors in hot weather during July and August. You will have to look hard to see these mites without a good lens or a microscope (or young eyes!)

The best insecticide control we have found to work is "Dynamec" derived from a soil born fungus that suffocates pests. Very effective against Spider Mite and Thrips but only available commercially. We also now offer a product from Growth Technology called "Spidermite Control" that has good reviews on the Web and is claimed to be 100% organic, 100% safe and 100% effective. We will be undergoing some trials this summer to test effectiveness and plant tolerance. The only alternative is to wipe down the large leaves of plants like Musa in a weak washing up liquid water solution using a damp cloth, paying particular attention to the reverse of the leaves.

Spider Mite

Phytoseiulus persimilis - Tiny predatory beneficial mites, shiny orange and relatively fast moving. It eats both adult and eggs of the Two Spotted mite giving excellent control. These predator mites work best when temperatures are regularly above 22C over 12 hours day length. This generally means application end April until September indoors, or June and July outdoors. They work very effectively and can achieve a complete clean up in several weeks.

 

  Thrips

Thrips or "Thunder Flies" are brown or yellowy 2mm long narrow insects which fly about in summer and burrow into plant tissue or developing leaves and buds. They tend to cause most damage from June to September by sucking juices out of leaves and emerging flowers, resulting in distortion of shape and colour. Leaves may be crooked and flowers have a 'rasped' look about them. They do not generally kill plants, but make them look tired and unsightly. Western flower thrips a particular problem for the horticultural indistry, are slender, very small insects, about 0.03 inch long when mature. Adults have 4 feathery wings and vary in colour from yellow to dark brown; nymphs are white or pale with small dark eyes. There can be numerous generations each year. Adults become active in early spring and deposit their eggs into plant tissues. Full development from egg to adult takes place in approximately 2 weeks.

"Dynamec" is very effective against Thrips and Spider Mite but only available commercially, you may be able to obtain some through your local horticultural or allotment society though.

Thrips

Amblyseius cucumeris - These are tiny pale beneficial mites which seek out and eat the developing stages of Thrips while they are in compost and on the plants. They can find their prey deep inside buds where chemical sprays have difficulty reaching. Amblyseius are suitable for glasshouses and conservatories, as well as outside during the Summer. They need to a temperature of at least 15C to be most effective.

 

  Vine Weevil

Vine Weevils are black beetles about 8mm long with the front part narrower than the back. Eggs are laid near the plant stems from which hatch 8-12mm long, white, horseshoe shaped grubs which stay in the pots or soil between August and early June before hatching into adults. The adult feeds at night on leaves, making unsightly notches around the edges, hiding during the day. It is the grubs which cause most damage, by feeding on the plant roots over Winter, often completely severing them from the upper stems. "Provado" vine weevil killer from Pbi (Bio) is effective in killing off the grubs by watering a solution into the pots, it is a systemic giving a lasting control up to 6 months - useful in that it also controls aphids and whitefly at the same time.

Vine Weevil

Steinernema kraussei - These are tiny beneficial nematodes (eel worms) which are watered into pots or open ground with a watering can, indoors or outdoors, when the soil temperatures are above 5C. This generally means application times of August to early November, or March to end of May. The nematodes enter the grub, poisoning it and then feeding off it to increase their numbers. Vine Weevils live outside in the UK, so if you have had a problem before, then it would be wise to assume it will happen again and use a drench twice a year.

 

  White Fly

One of the biggest problems for greenhouse growers. They are small white flies which live and lay eggs on the undersides of the plant leaves in glasshouses. They fly about at the slightest disturbance and are resistant to most chemicals. They are fairly inactive in cool temperatures over Winter, but multiply very quickly in warm Spring and Summer weather. Whiteflies suck sap from their host plant and drop sticky secretions onto leaves below. Left uncontrolled they overwhelm the plant, weakening it and flying around in huge numbers. Undersides of leaves become populated with adults and white eggs (scales). Yellow glue traps help but again we find that "Provado" ultimate bug killer from Pbi (Bio) is very effective giving a lasting control without damage to the delicate tropical plants.

White Fly

Encarsia formosa - These are tiny midge-like insects which lay their eggs in the white scales, turning them black as the new Encarsia develop inside. They eventually kill all the whiteflies by reproducing quicker and parasitising all their eggs. They are supplied as unhatched scales on hanging cards. They will multiply in the area in which they are settled, until there are no more whitefly scales to parasitise or cold weather sets in. Encarsia work best with temperatures above 21C with 12hr+ daylight hours. Generally, this means introducing Encarsia from mid April to August, although it can be earlier or later with extra heat and light.