Decorative plants are grown for their appearance, and pests should not be allowed to spoil this. However, many ornamentals are prone to disease..
Pests and diseases of ornamental plants.
Bulbs and roots
- Plants affected: Most types of bulbs including crocus, iris, tulips.
- Treatment: Dust bulbs with sulphur as a preventive measure, then store in a dry, well-aired place that will not be affected by frost. Destroy bulbs as soon as the first symptoms appear.
CABBAGE MOTH: The caterpillar of this moth particularly attacks the roots of China aster, French marigold (Tagetes) and pelargonium.
HONEY FUNGUS: Caused by the Armillaria mellea fungus, this disease attacks the roots of trees, shrubs and flowering plants, such as the abutilon and the peony.
- Symptoms: Bulbs rot in the ground, or produce twisted leaves with no flowers. This is caused by the larvae of narcissus flies, which lay their eggs in the soil around dying leaves in spring. The larvae hatch and burrow down into bulbs to feed for a year or two. Adult flies look like bees and are seen around bulb foliage.
- Plants affected: Narcissus, amaryllis, snowdrop, snow flake.
- Treatment: Avoid this pest by planting firm, healthy bulbs at the correct depth. Dispose of soft bulbs. Feed bulbs after flowering with a fertiliser high in phosphate and potash. Sprinkle crushed garlic around dying foliage as a deterrent.
NECK AND ROOT ROT
- Symptoms: The stem goes soft and the rest of the plant withers and dries up. When violets are affected, purplish spores grow on their roots, which then rot and crumble. This rot is caused by a variety of fungi including Pythium and Verticillium, which grow vigorously in wet weather.
- Plants affected: Sweet alyssum, busy lizzy, lobelia, lupin, carnation, French marigold (Tagetes), pelargonium. pansy, petunia, sweet pea, sage (Salvia), verbena, violet.
- Treatment: Remove and destroy affected plants. Replant with non-susceptible types and change the planting scheme every two years. Apply sulphur dust around the roots when planting, or at the base of the stems of healthy plants in infected areas. In bygone days, gardeners treated plants with horsetail decoction and stinging nettle extract to protect plants at risk.
This little weevil, whose larvae are more harmful than the adult insect, attacks a large number of flowering plants, such as begonia, fuchsia, busy lizzy ( impatiens), pelargonium and primula. The natural control is a parasitic eelworm (nematode) which is drenched onto the soil and plant roots. The nematodes parasitise the weevils.
- Symptoms: On bulbous plants, white rot appears first at the base of the bulb, and then the leaves turn yellow. On ornamental plants with roots, oily traces appear on the leaves followed by a white, downy layer. The plant rots and dies. This rot is caused by the Sclerotinia sclerotinium fungus.
- Plants affected: Many types of flowering plants, but most commonly antirrhinum, China aster (Callistephus), cornflower (Centaurea), crocus, delphinium, gladiolus, iris, lupin, sweet alyssum.
- Treatment: Remove and destroy affected plants and disinfect the soil. The disease can be active for up to four years in the soil, so do not replant with susceptible species. Dust the roots with sulphur when planting and feed with liquid nettle manure to toughen the growth and increase resistance to the disease.
As the saying goes, prevention is always better than cure. By keeping the garden clean and tidy as well as ensuring that plants are healthy, there is less chance of pests and diseases causing much harm. A watchful eye can also alert you to problems early, so inspect plants regularly.
However, no matter how careful we try to be it is inevitable that some problems will occur through the growing season. If you do not garden organically and feel you must spray, please do follow the instructions on the packaging of the chemical to the letter. Always try and spray when the weather is still, and in the evenings when there are less bees and hoverflies about.
If you prefer to garden organically, then no spraying should be done at all. Rely on building up a wide diversity of plants in the garden, especially those which will encourage wildlife. Leave the odd corner here and there, undisturbed where beneficial creatures like hedgehogs and toads can shelter. It can take a few years to build up the natural balance between pests and predators which keep problems under control, but be patient it is a much healthier way of gardening.
Here are a few attractive plants to attract beneficial insects into your garden. They are easy to grow and ideal choices even for new gardeners. As an added bonus many of these insects will also pollinate your fruit and vegetable crops, increasing the yield..
1. Cornflower(Centaurea cyanus)
This beautiful flower has extra floral nectaries. The plant's leaves release nectar even when the flowers are not blooming. This nectar is highly attractive to flower flies, ladybugs, lacewings, and beneficial wasps.
2. Sweet Alyssum (Lobularia maritima)
A lovely white, scented annual, which attracts aphid eating flower flies. Useful as an edging plant for borders or as a ground cover plant.
3. Borage (Borago officinalis)
This annual herb has bright blue clusters of edible, cucumber-flavoured flowers. Borage is exceptionally attractive to beneficial insects. Common green lacewings have a very strong preference for laying their eggs on borage.
4. Golden Marguerite (Anthemis tinctoria)
A long flowering perennial with bright yellow blooms that are highly attractive to ladybirds, lacewings, flower flies, tachinid flies and mini-wasps.