How to recognise it
Growth is stunted and distorted and leaves have serrated, brown scars along the leaf margins. If you cut open an infested narcissus (daffodil) bulb you will see brown marks on the bulb scales where the mite colonies have developed, although these can be confused with similar markings caused by stem eelworms. On hippeastrums red streaks may appear on the leaves and stems, although these could also be caused by other conditions, while yellow streaking may appear on narcissi leaves. Where flower buds have been damaged the resulting flowers may be distorted.
The mites themselves are very small (up to 0.25mm long). They have oval bodies with light brown colouring.
Reproduction may involve males but is often parthenogenetic. The females lay about 50 eggs each, which hatch after a few days. The larvae feed for a week or so before entering their ‘quiescent’ stage, or resting, pre-adult stage. The length of time to develop into adult mites depends on the temperature, but can be as little as one week in higher temperatures. Breeding continues year round, but at a slower pace in the winter. The females crawl onto new plants to find new feeding and breeding sites, sometimes assisted by males who carry larvae in the quiescent stage on their backs to the new sites.
Why it’s a problem
Affected bulbs tend to be smaller and can go soft and rot when stored. Flowers and leaves may be distorted by damage to the bulb and also direct damage by feeding mites.
Where you are likely to find it
Mainly affects narcissi (daffodils), hippeastrums and other members of the Amaryllidaceae family. It’s particularly likely to be a problem where bulbs have been forced at high temperatures (eg in greenhouses or houses) as this increases the activity and reproduction of the mites.
How to deter it
Maintain good hygiene, particularly in glasshouses. Hold any suspect plants in quarantine conditions until you are happy they are not affected. If they are affected, isolate or destroy them as soon as you notice the infestation, being careful not to drop any mites onto other plants.
The risk of infestation can be reduced by growing the bulbs outside for at least one year before you start to force them.
How to get rid of it
While chemical controls (eg organophosphorus pesticides) are available, these can actually be counterproductive as they may kill predators of the mites, causing a net increase in the mite population. Narcissus bulbs can be cold treated to eliminate mites by putting them outside on a couple of frosty nights about a week after forcing has started. Alternatively, hot water treatment of dormant bulbs is effective – immerse the bulbs in water heated to 43.3°C for 4 hours, or at 44.4°C for 3 hours. This treatment may be repeated every 2 years. However, the hot water treatment may cause flowers and foliage to be distorted the following year (though they should be fine after that).
Research is ongoing to find a biological control for this mite.
Is it good for anything?!
Other useful information
Bulb mites are often a secondary problem in bulbs which were already weakened by another pest, disease or physical damage.