Identifying and Controlling Garden Pests

Watch out for these pesky garden pests, and learn how to control them.

From: DK Books - Learn to Garden
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Leaf Eaters

Leaf Eaters

©2008, Dorling Kindersley Limited

2008, Dorling Kindersley Limited

Lily beetles are bright red with black heads. Both adults and young grubs eat leaves, flowers and seed pods, and may kill plants unless removed or treated.

Step 1: Watch Out for Picky Eaters

Aphids

Aphids

©2008, Dorling Kindersley Limited

2008, Dorling Kindersley Limited

Green aphids or greenflies, secrete sticky honeydew on leaves and stems providing an ideal growing medium for black fungus known as sooty mold.

Most beetles and caterpillars are picky about what they will eat. Viburnum and lily beetles, for instance, stick to their respective hosts. Greenfly and blackfly, officially called aphids, also have a limited range of host species. The trouble is that there are so many different kinds that aphids of one sort or another will attack most plants at some time. These insects obtain nutrients by sucking plant sap through their thin, hollow mouthparts. Other sap-suckers include thrips, scale insects and capsid bugs. To aid feeding, some sap-sucking insects inject materials that regulate plant growth, and induce severe distortion and curled foliage that hides and shelters the insects. Their hollow mouthparts may also spread viruses.

Step 2: Keep an Eye Out for Garden Gluttons

Vine Weevil Invasion

Vine Weevil Invasion

©2008, Dorling Kindersley Limited

2008, Dorling Kindersley Limited

Vine weevils can be introduced into your garden in the roots or top growth of newly-bought plants. Always check plants and root balls before planting.

Slugs and snails eat most plants; seedlings, herbaceous plants and climbers are worst affected. Holes appear at the edges of and in the middle of leaves, and you may notice slime trails. Slugs and snails also bore into bulbs and tubers. They feed in mild, humid weather, mainly at night. When slugs and snails damage soft growth, other problems often follow. 

Vine weevils attack a wide range of plants. The adult insects, all female, cannot fly; they crawl around the garden from mid-spring to mid-fall, usually after dark, laying eggs. They feed on leaves, mainly of herbaceous plants and shrubs (especially evergreens), notching the leaf edges only, as their mode of feeding is not adapted to making holes in leaves. The eggs, too small to be easily seen without a microscope, hatch into grubs, which feed on roots. The grubs start to cause damage in late summer and early fall, which is when you should apply controls.

Step 3: Control Pests Once and For All

Acting swiftly when problems arise eases their control, so watch for signs of trouble. Often, pruning out diseased shoots or removing cover for harmful pests will put a stop to damage. At other times, pesticides may be needed; you will only need a small amount if a problem is dealt with quickly. Ready-to-use packs are useful for small infestations—they save the chore of making up a small quantity of the solution. 

Organic gardeners will only use pesticides that are derived from natural sources, such as pyrethrum. Although they may be less effective than synthetic products, they are good enough for most small insect pests. In fact, when used in the early stages of a pest or disease problem, they are usually all you need to stop the trouble before it gets out of hand. If you want an organic approach, it’s also worth considering biological controls. 

Pest controls work in a variety of ways:

  • Systemic controls are absorbed into the plant’s sap, killing fungi and sap-sucking insects as they feed. Thorough coverage with a spray is less important with these pesticides than with contact-action controls.
  • Contact insecticides include the naturally derived materials, as well as some synthetic pesticides. The chemical has to touch the pest to do its job, so you must cover the upper and lower leaf surfaces. Act quickly: once foliage becomes distorted and curled, it is difficult to get contact materials where they are needed.
  • Dusts are contact materials and must be applied early. Puffer packs are not very satisfactory applicators and sprays are usually preferable to dusts.
  • Pellets and baits, such as slug pellets, have gotten bad press and are certainly harmful if misused. If you follow the instructions, though, and store them safely and securely, they are a useful and safe treatment.

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