The major problem with soil pests is that they work unseen. Most of the ones shown below eat away at roots and by the time the damage becomes obvious the plant may be beyond recovery. There are no all purpose soil-pest killers, the biological ones based on beneficial nematodes will help to control some pests including vine weevil, chafer grubs and cutwrom, but others such as wireworm need a specific insecticide.
The fungus gnat or sciarid is a tiny black fly which is often seen fluttering above the tiny plants in seed trays. It is harmless, but the eggs laid on the compost hatch into minute colourless maggots which eat young roots. In severe attacks the seedlings can be killed. Do not overwater and apply spray strength malathion solution.
The favourite food of these soil-living caterpillars are bulbs, corms and rhizomes, but they will also attack Chrysanthemum, Larkspur, Dahlia and several other plants. Unlike cutworms they move backwards when disturbed and stems are rarely attacked. Use a biological soil-pest killer based on parasitic nematodes - otherwise keep under control by regular hoeing.
These wrinkled white grubs are the larvae of the adult dark brown vine weevil. They are extremely destructive underground both outdoors and under glass, eating the roots of many plants. If a plant suddenly dies, look in the soil for this rolled-up grub. If present pick out and destroy. Use a biological soil-pest killer based on parasitic nematodes.
This serious disease of the vegetable garden can affect Wallflowers and Stocks. Below ground the roots are swollen and distorted and above ground the plants are small and die off earlier than normal. The best precaution is to apply lime to the soil before planting and to avoid growing Wallflowers on the same site year after year.
Cats can be a pest of annual flowers. Their scratching disturbs seed beds and newly transplanted plants. The resulting root damage can lead to the death of seedlings. Protection is not easy if cats have chosen your flowerbed for their toilet, one of the cat deterrent sprays may help.
These hard, shiny insects are a problem in new gardens and in plots adjoining grassland. They are slow moving and not active like the friendly centipede. They eat the roots of most flowering plants and may burrow up the stems of Chrysanthemums. Water the soil with pirimiphos-methyl where they are a problem.
These green, grey or brown soil-living caterpillars may be two inches long. They gnaw both roots and stem, but their telltale effect is to sever seedlings and young plants at ground level. When this happens look for and destroy the cutworms near the attacked plants. Always remove the grubs exposed when digging the soil. Use a biological soil-pest killer.
The fat curved grubs of the chafer beetle feed throughout the year on the roots of garden plants. Plants are occasionally attacked and badly affected plants are killed. If these grubs are found in the soil, or if you intend to plant into newly broken up grassland, use a biological soil-pest killer for prevention or control.
Black Root Rot
This is a common disease, affecting Antirrihinum, Begonia, Sweet pea, Geranium, etc. Above ground the leaves turn yellow and wilt. Below ground the roots are blackened. There is no cure, so avoid the causes - unsterilized compost indoors, uncomposted leaf mould outdoors and replanting the same type of plant in infected soil.
An invasion by moles can cause havoc. The hills thrown up by their tunneling are unsightly and cause severe root damage. Small plants may be uprooted. Eradication is not easy, smokes or sonic deterrents should be tried first. It may be necessary to set traps or to gas them, this work is best done by a professional exterminator.