Cabbage Caterpillars – There are three types of caterpillars which cause considerable damage to the brassicas. The small white butterfly, the cabbage moth and the cabbage white butterfly.
The small white lays eggs singly on the underside of beans. The cabbage white lays clusters of bright yellow eggs on the underside of the leaves making them difficult to see. The cabbage moth lays clusters of eggs on the underside of leaves and they hatch out into small light green caterpillars. All the caterpillars eat a lot of leaf until they are ready to pupate.
Control – Crush between the fingers any eggs found. Once a week is often enough. Take care not to Mistake the elongated eggs of the ladybird with the bullet shaped eggs of the cabbage white. Use a spray of Bacillus Thurnigiensis which is very effective.
Coddling Moth – Larvae of this moth eat into the flesh of fresh fruit. Eggs are laid later in the season, July/August. Eggs are laid on the fruit near the eye. Once there, the fruit is doomed. No sprays are effective once the grub is inside the fruit. Grease bands around the tree stop the grub reaching the fruit or use the very effective coddling moth trap. Natural pheromones (the attractants given off by the female moths) lure male moths into a sticky trap. If there is no mating there will be no maggots. This pheromone is only attractive to the coddling moth male, therefore harmless to all other beneficial insects and bees.
Vine Weevil – The plump legless white larvae (about 10mm long) feed on the roots, corms and tubers of many plants, particularly in greenhouses and conservatories where pots of cyclamin, begonias, ferns, fuchsias, primulas, gloxinias, orchids and many others can be attacked. The first symptoms are s often the plant wilting or collapsing suddenly, by which time it is too late to control them. The adults, which are seldom seen, vaguely resemble small cockroaches, with two long crooked antennae. They feed at night, eating holes in the leaves of a wide range of plants. The weevils can lay up to 1000 eggs in potting composts and organic matter over a period of 3-4 months. Once there is an infestation they are extremely difficult to control.
Control – There are not safe effective chemical controls available to the gardener. Affected plants should be knocked out of their pots and the roots and compost closely examined, so that the grubs can be collected and destroyed. It is best to stop the adults reaching the plants. Pots on greenhouse benches can be protected with a sticky barrier of Trappit Glue around the bench top and supports. It can be applied to strips of PVC tape so that it can be removed easily. Individual pots or containers of susceptible plants can also be treated. To help prevent vine weevils getting into a greenhouse, the entire base could be treated with a band of Trappit Glue, particularly across the door and other possible entry gaps. Check the sticky band regularly to prevent bridging by debris.
Carrot Fly – In carrot growing areas, such as East Anglia, and on allotments, carrot fly can frequently be a serious pest limiting the growth of carrots. The creamy-white larvae, up to 10mm long, feed on and in the roots often making the crop unusable. Eggs are laid in late May and June, with a second generation in August and September.
Control – Sow thinly to avoid thinning out the young plants as the smell from the damage attracts the fly. Lay Enviromesh netting over the crop from late May onwards. Burying the edges in the soil, or covering the edges with stones, bricks etc. Alternatively, make a tunnel type clothe with wire hoops. The Enviromesh could also be used to form a half metre high barrier around the crop by cutting it into four equal strips lengthwise (sealing the edges with a flame, such as a gas lighter or blow lamp). Posts should be driven in around the plot, which should be about two metres wide and the mesh stapled or nailed onto them. Allow an inch of the net to be buried into the soil. The barrier prevents the carrot flies from ‘homing in’ on the crop as they fly close to the ground causing them to fly up and over the crop. This method is widely recommended by organic growing advisers using polythene, but Enviromesh has the advantage that it can be reused over a period of at least five years and its greater rigidity makes it easier to erect and fix into the posts. Enviromesh is also less vulnerable to wind damage than polythene, particularly in exposed areas. (This cover will also protect against the carrot-willow aphid which spreads a carrot virus.)
If Enviromesh netting is placed over the beds after sowing, soil capping and paddling from heavy rain can be reduced, which can lead to improved germination and crops.
When celery and parsnips are covered with Enviromesh, they will also be protected against celery fly (also known as celery leaf miner). These are small flies, the pupae (maggots) of which tunnel into the leaves.