Pests & Diseases

Cabbage Root Fly

A serious pest spoiling summer cauliflowers, broccoli, sprouts, spring and autumn cabbages, savoys and kales.

The adult flies are grey, 1cm long in colour and similar to a common house fly.

In spring flies emerge from pupae which have overwintered in the soil. The females will then lay eggs on or just below the surface of the soil close to the main stems of brassica plants. After a week creamy-white maggots emerge and feed on the plant roots and base of the main stem. After a further 3 weeks when the maggot matures it will form a red/brown pupa a short way from the plant. The process will continue producing several generations of fly throughout the summer months.

Plant Symptoms: They will droop and wilt.

Treatment: Beetles are natural enemies of the immature stages, unfortunately conventional insecticides kill many beneficial insects as well as the cabbage root fly. Plants should be removed and burned together with any grubs from the surrounding soil.

Flea Beetle

General feeders affecting a wide range of plants - the small beetles appear early in the growing season and are particularly fond of the squash family, peas, beans, eggplants, beets, spinach, and potatoes.

The creatures life stages are completed underground and only adults are commonly seen by gardeners. Adults overwinter underground and during the spring they mate, and deposit eggs. Some species lay individual eggs while others clusters. Egg sites may be in soil, on leaves, or in holes chewed into stems. Eggs usually hatch in 2 weeks. Adults emerge from the pupae in late summer.

Flea beetles are usually oval in shape, and vary in color, pattern, and size. For instance, potato flea beetles (Epitrix cucumeris) tend to be more oval, blackish, and about 1/16 inch long.

Striped flea beetles (Phyllotreta striolata) are more elongate and dark with yellowish crooked stripes, and measure about 1/12 inch long.

Spinach flea beetles (Disonycha xanthomelaena) are both oval and elongate. They have a black head, antennae and legs. The collar behind the head is yellow to yellowish-orange. Wing covers have blackish-blue luster. They approach 1/5 inch in body length.

Plant Symptoms: Populations of adults can devastate vulnerable seedlings with small circular gouges in the leaf surfaces.

Treatment: Control weeds around plants, depriving larvae of food and remove old crops which the beetles use to over-winter. Insecticides may be required to regulate population levels.

Woolly Aphid

These pests (eriosoma lanigerum) appear on the bark of fruit trees in spring - The aphids are covered in a waxy substance which gives them the appearance of fungus - this coating makes them difficult to treat with sprays.

The pest weakens the tree by feeding on the bark and roots which will prevent wounds from healing, they also transmit perennial apple canker and contribute to the development of black sooty mold on the leaves, which will inhibit photosynthesis and reduce cropping.

The aphid is a small, soft-bodied insect with piercing-sucking mouthparts and is so called because of its fuzzy appearance.

The aphid overwinters in the nymph stages underground on tree roots, in spring, wingless females give birth to live nymphs. The first-stage nymphs are called crawlers because they are the most active of the four nymph stages. Crawlers allow colonies to disperse from roots to above-ground parts of the tree.

These are dispersed by the wind, birds, or other insects from tree to tree within an orchard or nursery.

Treatment: Natural enemies are small parasitic wasps which lay their eggs in aphids. The wasp egg hatches within the aphid, and the young wasp larva consumes the aphid. Unfortunaterly the wasp is susceptible to insecticides.

Other natural enemies of apple aphids include hover fly larvae, lacewing larvae, lady beetle larvae, and lady beetle adults.

Treatment: The removal of suckers will discourage development of woolly apple aphid in early-spring. Pruning cuts should be examined every few weeks throughout the summer for the presence of new colonies of woolly apple aphid which can be squashed.

An insecticide can be applied in late-spring but because of the aphids' waxy covering, high volume application is needed and a second application is recommended two weeks after the first.

Carrot Root Fly (Carrot Rust Fly)

This pest (Psila rosae) is a small fly, approx 8mm long, with a red/brown head - and causes serious damage to carrots, parsnips, parsley and celery.

The female lays eggs in the soil near the carrot and they will usually hatch in about a week depending on temperature. The larvae burrow into the soil and feed on the roots. There are usually two generations of root fly each year, the first in late April/early May with the 2nd egg-laying in late July.

Treatment: Crop rotation.
Practice sound rotation.
Dispose of badly infested crops.
Plant in containers over 24" high or between the two egg laying periods.