'Willpower & sheer idiocy combine in harmony'
Plants keeling over? I'll bet it's these root-muching grubs
I HATE vine weevils. They're underhand and sneaky.
My experiences with them are worst in my mam's back garden, which is full of container-grown plants - the perfect place for adults to lay their eggs (they like non-gritty compost).
The adults are bad enough, but it's the grubs that really get me.
Creamy, fat, C-shaped legless grubs have light brown heads and are up to 10mm (about 3/8in) long.
During autumn and winter, they feed on plant roots, causing wilting, and often plant death.
Last winter, a Heuchera Silver Blush came away in my hand as I was weeding round it - roots severed, with grubs underneath.
Plants grown in open ground are less susceptible, although grubs are partial to strawberries, primulas, polyanthus, Sedum, Heuchera and young yew.
Adult leaf damage
Adult beetles feed on the foliage of herbaceous plants and shrubs, especially Rhododendron, evergreen Euonymus, Hydrangea, Epimedium, Bergenia, Primula and strawberry, causing irregular notches on leaves.
They are about 9mm (about 5/16in) long, dull black beetles with a pear-shaped body when viewed from above.
All adults are female and each can lay many hundreds of eggs from April to September.
The eggs are brown and less than 1mm (about 1/16in) in diameter, making them hard to see.
Larger yellowish-brown spherical objects seen in potting composts are likely to be fertiliser pellets - similar whitish objects are usually gastropod eggs.
Gardening evil of the vine weevil & fungus gnats
Grub nestled into what was the root system of Heuchera Silver Blush; Shasta daisies, with tell-tale notched leaves where adults have fed.
1. On mild spring or summer evenings, inspect plants and walls by torchlight and pick off adult weevils. Shake shrubs over an upturned umbrella to collect more. In greenhouses, look under pots or on the underside of staging where the beetles hide during the day.
2. Trap adults with sticky barriers placed around pots or on greenhouse staging.
3. Encourage natural enemies - birds, frogs, toads, shrews, hedgehogs and predatory ground beetles.
4. Stand potted plants on upturned pots sat in saucers of water - the adults can't swim.
5. Surround pots with Barrier Glue from Agralan - the adults cannot walk across it. Move plants away from walls, as the adults can jump down on to them; they cannot fly.
6. Add a 2cm (0.75in) deep layer of sharp grit or gritty gravel on top of the compost or around the base of the plant to prevent the adults from laying eggs.
7. Adult vine weevils hide in debris around the bases of plants so keep the area free from dead and fallen leaves.
8. Place landscape fabric at the base of plants to prevent newly-hatched larvae from entering the soil.
9. A biological control of the larvae is available as a microscopic pathogenic nematode (Steinernema kraussei). Apply in August or early September when the soil temperature is warm enough for the nematode to be effective (5-20ºC/41-68ºF).
10. Another nematode, Heterorhabditis megidis, is also available but is more temperature-dependent (12-20ºC/ 54-68ºF).
Both nematodes can also be applied to garden soil, but give poor results in dry or heavy soils. They work best in open potting composts, such as peat or coir. Nematodes can be used safely on all edible and ornamental plants.
Vine weevils - top 10 organic controls
Weevil attack
ADULT weevils cause irregular-shaped notches in leaf margins during summer.
Grubs are found among the roots. Plants wilt and die during autumn to spring as they eat roots.
My Heucheras have been hammered - this one (Ebony - or it could be Obsidian - still has the grub in the centre.
Nothing for it but splitting it into plantlets and growing it on.
I have ended up with six bonus plants, though.
STV's Greenhouse insect catcher laid across the top of the tomato ring culture pots - this lot were caught in four days; below, yellow sticky traps all over the conservatory.
Fungus gnats attack
A YEAR-ROUND annoyance for me in the conservatory is a host of tiny black flies on and above the soil surface of tomato gro-bags.
They don't seem to do much damage, but they are annoying!
I was under the impression they were thrips, but further investigation has led me to believe they're sciarid flies, also known as fungus gnats (Bradysia paupera).
The flies are about 2mm long and run over the soil surface or fly slowly around pots. The larvae are the bad guys, small translucent worms, up to 1cm long and very hard to see, living just under the surface. When infestations are heavy, there are shiny silken threads on the top of the soil.
Fungus gnats can breed all year under glass and in house plants. Larvae feed on fungal growth and decaying plant material but some damage the roots of seedlings or soft cuttings. Adults don't cause damage. The life cycle can be completed in a month, speeding up to one-two weeks in hot weather.
Larvae attack the roots of virtually all houseplants, pot and border plants including vegetables, ornamentals, fruits and fungi.
Organic treatment
Place yellow sticky traps between and around the base of plants to catch adults.
Biological control: pathogenic nematodes (Steinernema feltiae), predatory mites (Hypoaspis miles) and a predatory rove beetle (Atheta coriaria) are available. These biocontrols are added to the potting compost where they will help control the eggs, larvae and pupal stages in the fly's life cycle.
Letting the soil dry out partially may help to reduce the larval population in pots.
Prevention
Good hygiene: remove any dead leaves and fungal growth from the top of pots or benches - larvae can survive in patches of mould.
Water plants only when required to prevent the build up of fungal growths.
Cover the surface of pots with sand as a barrier against egg-laying females.
