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PEST AND DISEASE CONTROL IN U.K. NARCISSUS GROWING: SOME ASPECTS OF RECENT RESEARCH
Applications were in the hot-water treatment (HWT) tank, as a post-HWT cold dip, or as a spray over the bulbs at planting.
Before HWT, bulbs were stored at ambient temperatures, or at 18°C for 2 weeks or 30°C for 1 week to reduce the phytotoxic effects of both the HWT and the chlorpyrifos.
Using chlorpyrifos in HWT reduced the number of bulbs with larvae after the first growing year to nearly zero, in the worst cases from control levels of 12 per cent.
Cold dip and spray treatments were ineffective.
The control due to using chlorpyrifos in HWT did not persist to the second growing year.
Bulb yields at the end of the first growing year were reduced following treatment with chlorpyrifos in HWT, unless pre-warming at 30°C was used; however, crop growth in the second growing year compensated for losses in the first.
A peroxyacetic acid-based disinfectant was evaluated as a replacement for formaldehyde in HWT. Using a healthy bulb stock, crop growth with peroxyacetic acid was at least as good as using formaldehyde, with no phytotoxicity.
When used with a bulb stock infested with both basal rot (Fusarium oxysporum f.sp. narcissi) and stem nematode (Ditylenchus dipsaci), lowest nematode damage and highest yields resulted from using formaldehyde (tested at the standard rate of 0.5% commercial formalin) or peroxyacetic acid (at rates of 1 or 1.5% ‘Jet 5’) in combination with thiabendazole fungicide.
Three biocontrol agents for basal rot were tested on three narcissus cultivars which had received a full fungicide treatment (thiabendazole as a post-lifting dip and in HWT), a reduced fungicide treatment (thiabendazole as a post-lifting spray only), or no thiabendazole treatment.
Basal rot inoculator bulbs were planted evenly among the plots.
The basal rot-resistant cultivar St Keverne did not become infected with basal rot, while cv Yellow Sun showed some basal rot but crop performance was unaffected by the treatments.
In the susceptible cv Golden Harvest one antagonist, coded 089, a Trichoderma spp., increased bulb yields slightly in the first year when no thiabendazole had been used previously.