Integrated control of bulb-scale mite in narcissus

Results 1. In field-grown bulbs, adult and egg numbers decreased during late winter 2008-9.  A lower proportion of mites was present on the shoot tips during January and February, possibly an indication that the cold weather during this period had affected survival.  Mite numbers continued to decline during the spring and then increased by a small amount in May-June, before decreasing again in late summer.  2. Trials showed that mites can move between plants when the foliage is touching. There was no evidence that damage was greater or less at the edges of the fields than towards the centre, but there were patches of infestation in the field. There is no evidence to date that weeds are a source of bulb scale mites, but in the South-West naturalised narcissus (e.g. in field margins or dumps) are a potential source of bulb scale mite and bulb mite.  3. In experimental situations, hot water treatment at all tested temperatures and durations killed bulb-scale mites, but warm-storage treatments were ineffective, as were frosting treatments.  None of the acaricides tested were very effective when applied to narcissus foliage.

Action points for growers:

• Growers should be aware that the debris accumulating in bulb handling and storage facilities may provide a source of mite infestation and that they should implement appropriate hygiene measures, by keeping these areas as free of dust and debris as possible.

• HWT procedures should be carefully maintained, and treatment monitored.

• Any mite-controlling effects of a dry heat or frosting treatment are unreliable.

• In the South-West, growers should remove volunteer narcissus growing in field margins or close to newly planted crops.

• Further recommendations must await the completion of the project.

Bulb-scale mite was once regarded as a sporadic pest, but for the last 10 years there has been a need for more effective control measures.  While bulb-scale mite symptoms rarely cause concern in field-grown bulbs or in storage, temperatures in glasshouses, where bulbs are forced for cut-flowers and grown as pot-plants (an increasingly popular product), favour rapid multiplication of the pest, resulting in seriously damaged, distorted leaves and stems, with rejections and serious losses to producers. The aim of this project is to develop an integrated control strategy for bulb-scale mite based on an understanding of its biology and ecology. Objective 1: Define the relationship between temperature and bulb-scale mite development, Objective 2: Discover when, where and how bulb-scale mite originates and spreads in field crops and in bulb storage, Objective 3:  Design optimal high or low temperature and/or chemical treatments to control bulb-scale mite in bulbs for replanting and for forcing and ensure all stages in its life-history are killed and that crop quality is unaffected.