COMMON INSECT PESTS OF TOMATO PLANTS





Because of its origins in South America, the tomato plant has very few natural pests here in Great Britain, although it will suffer the scourge of common glasshouse pests if they are grown under protection. In fact, you are far more likely to experience problems when growing under glass or in a grow bag than you will ever get when growing directly into well prepared soil.

Although the list below is certainly not exhaustive, it will cover the most common problems you are likely to come across.

APHIDS

Cause: Aphids are a well known pest insect that can quickly colonise the soft tissue parts of your plant. They damage and weaken the plant by sucking the sap out of pressurised parenchyma cells just below the leaf cuticle.
Symptoms: Clusters of these small insects are readily identifiable, normally at the plants tips or on the underside of their leaves. In severe cases, the infected parts can begin to wither due to the quantity of sap being removed from that area. The foliage can become sticky and may show signs of a harmless black mould called sooty mildew.
Control: There are many chemical treatments available including a number of organic, but all of these must be applied at the first signs of infection to achieve the best results. Try applying contact insecticides such as pyrethrum, derris or soft soap solutions as these are the best option for organic gardeners.

BLACKFLY

Cause: Blackfly are a well known pest insect that can quickly colonise the soft tissue parts of your plant. They damage and weaken the plant by sucking the sap out of pressurised parenchyma cells just below the leave cuticle.
Symptoms: Clusters of these small insects are readily identifiable, normally at the plants tips or on the underside of their leaves. In severe cases, the infected parts can begin to wither due to the quantity of sap being removed from that area. The foliage can become sticky and may show signs of a harmless, black mould called sooty mould.
Treatment: There are many chemical treatments available including a number of organic, but all of these must be applied at the first signs of infection to achieve the best results. Try applying contact insecticides such as pyrethrum, derris or soft soap solutions as these are the best option for organic gardeners.

FLEA BEETLES

Cause: Even though these tiny, fast moving insects are difficult to spot, there are perhaps the most easily recognised pest of tomato plants due to the characteristic damage that these beetles cause.
Symptoms: These beetles can cause significant damage by leaving copious amounts of small holes in the leaves. As the leaves grow, the holes become larger and end up looking as though they have been hit by a shotgun blast. This infestation is usually experienced at two distinct times of the year, usually in April and July.
Control: Flea beetles are difficult to control as they have a habit of ‘hopping’ away if disturbed, making contact insecticides a bit 'hit and miss' in their application. However, you can also consider “trap crops” such as radish which may help lure the flea beetles away from your treasured tomatoes. So long as the radish is not in flower (as the applied insecticide will then harm beneficial pollinating insects) you may wish to use a systemic insecticide, however this will make the radish crop inedible. With this in mind, remember to label it clearly to prevent human ingestion.

GREENHOUSE WHITEFLY
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Cause: Greenhouse whiteflies are a well known pest insect on protected crops and can quickly colonise the soft tissue parts of your plant. They damage and weaken the plant by sucking the sap out of pressurised parenchyma cells just below the leave cuticle.
Symptoms: Like aphids, whiteflies have piercing-sucking mouthparts so the damage caused is very similar to that of aphids. Direct damage to tomato plants can cause deformed new growth and wilting, chlorotic leaves. Whiteflies can also transmit some plant viruses, so if your plant becomes infected, immediately remove and destroy. Also like aphids, whiteflies secrete honeydew, upon which an unsightly, yet harmless sooty mould will grow on. Feeding by whiteflies can also cause deformed fruit and discoloration of your tomatoes.
Treatment: There are many chemical treatments available including a number of organic, but all of these must be applied at the first signs of infection to achieve the best results. Try applying contact insecticides such as pyrethrum, derris or soft soap solutions as these are the best option for organic gardeners.

LEAF MINER

Cause: Leaf miners are small larvae which burrow in-between the leaf layers. You may also come across small puncture marks on new leaves caused by the adult females during the feeding and oviposition processes. Sometimes this can also result in a stippled appearance on foliage.
Symptoms: Typically the first signs you will come across are white ‘wiggle’ marks in the leaves which is the major form of damage by the larvae, and will result in the destruction of the internal leaf mesophyll. The mine becomes noticeable after about three or four days after oviposition and becomes larger in size as the larva matures. Both leaf mining and the stippling caused by the female adult can greatly reduce the leafs ability to photosynthesise. Extensive mining can also cause premature leaf drop.
Control: Leaf miner are difficult to control using a contact insecticides as they are pretty much out of reach, protected by the leaf membrane. They can be controlled though by a systemic insecticide but then you probably wouldn’t want to risk eating the crop afterwards. This is one of those cases where it may be best to leave them alone - other than picking off and destroying the worst affected parts of the plant. In fact, your tomato plants can have as much as 60% of its foliage affected with leaf miner without affecting the fruit or its growth. After harvesting your crop, you can try double digging the soil where the tomatoes grew as the adult leaf miners experience difficulty in emerging if they are buried. You can try repeating this several times over the winter before re-planting your crops in the late spring

RED SPIDER MITE (also known as two spotted Spider Mite)

Causes: Like the whitefly this is another fast-colonising pest usually found on protected crops. The red spider mite is a tiny wingless insects with eight legs and a one-piece body. Red spider mites (Tetranychus urticae) are also known as two-spotted spider mite or greenhouse spider mites. The first sign of a red spider mite infestation are either small spider webs - often high up on the plant - or white speckling on the upper surface of the leaves.
Symptoms: Red spider mite causes the leaves of affected plants to initially show a fine speckling. As the attack progresses, they take on a bronzed appearance and may wither and die. A fine webbing is produced, strung between parts of the plant or under the leaves. Using a magnifying glass the red spider mites and their eggs can be seen on the undersides of the leaves. In an unheated greenhouse the worst attacks occur from June to September, but red spider mites can be active year round.
Control: Spray plants with a fine mist of water, twice daily, as the spider mite can only thrive in hot dry conditions. Also try applying contact insecticides such as pyrethrum, derris or soft soap solutions as these are the best option for organic gardeners. They will need to be applied every 5-7 days during the summer on both the upper and lower sides of the leaves. Biological controls can be used safely 1-2 weeks after spraying with Derris, 4 days after pyrethrum and 1 day after soft soap sprays. For an effective home-made solution try making a rhubarb spray. It contains the toxin ‘oxalic acid’ which appears to suck the moisture out of them!
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