ISHS Acta Horticulturae 109: III International Symposium on Flower Bulbs
CONTROL OF NEMATODES IN BULBS AND CORMS |
| Author: | W.A. Windrich |
| Abstract:
Rates of nematode infestation in lots of bulbs are generally expressed as percentages of bulbs containing nematodes or showing symptoms. However, the number of nematodes differs between bulbs. Therefore, the number of bulbs freed from nematodes by a given treatment depends on the frequency distribution of nematode numbers per bulb. These distributions were similar in several lots of infested tulips, daffodils, and crocuses at different average numbers per bulb. The percentage infested bulbs after treatment is determined by the average number of nematodes per bulb before treatment and the nematode mortality due to the treatment. Therefore, only the mortality should be taken into consideration where the efficacy of treatments (hot water or chemical) is to be compared. To prevent an increase in percentages of infested bulbs, control measures must balance between the multiplication and spread of nematodes. Hot water treatment and chemical dips achieve a reduction of the number of nematodes per bulb, which results in a reduction of the percentage of infested bulbs at planting time. A field treatment with systemic nematicides prevents the spread of nematodes to newly formed bulbs. This spread too is a function of nematode numbers in the planted bulbs, but for the tulip stem nematode its magnitude appeared to be very variable and reductions in the number of infested bulbs occurred even without treatment. Effects of aldicarb treatment on the spread of the tulip stem nematodes were also highly variable, and therefore a general measure of control could only be derived from the results of experiments in several years and with bulbs of which the degree of infestation is known. | |
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