Pests and Diseases Affecting Flower Bulbs

The aim should be to prevent rather than cure pests and diseases and this means that a high standard of cleanliness in garden, frame, greenhouse and storage place must always be maintained. Partly diseased bulbs and bulb remains should always be burned and steps should be taken against slugs, snails and aphids, for often even slight damage by pests opens the way for disease spores.

Occasionally the lower parts of bulbs are damaged by boring pests such as wireworms, and where they are suspected one of the good soil fumigants should be worked into the ground..

Of the larger pests, mice are perhaps the most troublesome both when bulbs are in store and when growing. Traps or one of the baits available on the market are reliable ways of getting rid of them, although the instructions given for the use of the bait should be rigidly followed. This ensures that no harm is done to domestic animals and birds.

In woodland areas, rabbits and hares may eat the young growths and some method must be devised to keep them away. Aphids of various kinds are harmful to growing plants since they suck the sap from the foliage causing the leaves to become twisted, malformed and discoloured. They also transmit virus troubles and the honeydew they secrete encourages ants. A good derris-based insecticide applied at frequent intervals where aphids are seen or suspected should soon eradicate the pests.

If when lifted a bulb is found to be infested, it should be destroyed by burning and apparently healthy bulbs lifted in the same batch should be dipped in a good insecticide.

Narcissus flies can be destructive. There is a type sometimes identified as the merodon or eumerus fly which has a grub-like larva and this burrows into bulbs which then become soft and decay from the base. If leaves develop they are twisted and stunted. Affected plants are best burned although commercial growers have had success in immersing them in water at a temperature of 45°C. Since this kills the grubs without harming the bulbs. The same pests also attack some other bulbs.

Stem and bulb eelworms are extremely small and only visible under a microscope. They are usually first noticed when the leaves become malformed and sometimes streaked. If a bulb is cut, it will show brown patches or lines. This pest is liable to attack not only narcissi, but tulips, iris and hyacinths. The same treatment is needed as for narcissus fly although most gardeners decide to burn affected bulbs.

Thrips are very minute pests which cause silvery markings on the leaves and often on the flowers. Although gladioli are the most commonly attacked, they will affect various other bulbs such as cyclamen and hippeastrums. If nothing is done to destroy the pests, they will crawl down the stems in the autumn and hide under the dry skins of the new corms and reappear the following season. Many gardeners destroy the growths as soon as the silvery markings are seen. Lindex, or one of the other modern systemic sprays, is effective or a nicotine-based spray can be used. When the corms are stored they should be dusted with whizzed naphthalene which will help to destroy the pests.

There are few diseases which trouble bulbs grown under ordinary good conditions.

Botrytis is one of the most serious problems, particularly affecting liliums and tulips. It is generally to be seen as brown spots or markings on the leaves and stems and is more likely to appear in a damp season. It first shows itself as brownish markings which later turn a greyish colour and the leaves drop and the stems may collapse. A simple remedy is to spray the entire batch of plants with Bordeaux Mixture.

Tulips are affected by a related form of botrytis, the disease in this case being referred to as tulip fire. The plants become stunted and the foliage withers and turns greyish brown. It spreads rapidly, particularly in damp weather. Where the disease occurs, it is best not to grow liliums or tulips on the same site for two or three years.

Occasionally bulbs are affected by a basal rot which is a form of fusarium. It is often first noticed when the bulbs are stored and they become soft. Such specimens should not be planted but destroyed.

Occasionally the bulbs of Iris reticulate become spotted with ink-like markings. This causes the bulb to rot and all bulbs however slightly affected should be burned since there is no cure.

Virus troubles are only likely to occur when aphids are not dealt with. When they do appear they cause distinct yellow stripes on the foliage and the bulbs become weakened, but it does not mean that every bulb showing foliage with yellow stripes is affected by virus. This may simply be due to local — soil or climatic — conditions.

09. July 2011 by admin
Categories: Pest and Disease Control | Tags: , , , | Comments Off on Pests and Diseases Affecting Flower Bulbs


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