Finland
January 22, 2008
A doctoral dissertation produced
at MMTT Agrifood Research Finland
reveals that early sowing of carrots is the most effective way
to prevent the damage caused by carrot psyllids. If the carrot’s
number one enemy gets at the seedlings at the cotyledon stage,
it can rapidly destroy up to 35% of the crop.
In her dissertation, Research Scientist Anne Nissinen examined
ecological methods of fighting carrot psyllids. The study was
conducted in a greenhouse where the pests were allowed to feed
and lay eggs on 15 different carrot varieties and a wild carrot
in cages.
Nissinen examined the carrot psyllid host plant selection and
the severity of the damage caused by the pest at different
stages of root and shoot growth. She also assessed the
possibility to utilize the push-pull strategy in management
carrot psyllids.
Small, Ugly And Bearded Carrots
Carrot psyllids are a major problem in Finland’s most important
carrot production regions. The psyllids overwinter in spruce
trees and fly to carrot fields from early June onwards. They
instantly begin to suck nutrients from carrot leaves, which
quickly renders the shoots damaged.
Carrot psyllid attacks usually peak either a week before or a
week after the summer solstice. In terms of the crop, it is
critical that the shoots have grown enough by that time to
survive the pest attack.
If the carrots have only been sown in the end of May, the pests
may catch the shoots at the cotyledon stage when the carrots are
most vulnerable to damage. After a pesticide treatments, the
shoots may recover and look fine on the surface, but reveal
small, ugly and bearded carrots at harvest, Nissinen describes.
More Research Needed Into Lure Plants
Nissinen also examined whether a particular carrot variety was
more attractive to psyllids than others, which would allow it to
be used as a trap crop to keep the pests from attacking the
cultivated variety. Of the varieties studied, an old non-hybrid
variety, which can still be found on a Swedish seed list, turned
out to be the most attractive.
Nissinen believes that the use of a trap crop could be an
efficient way of reducing the numbers of psyllids on carrot
crops. She does, however, concede that she dare not recommend
the use of trap crop in practice based on this study alone.
The effectiveness of a trap crop should always be tested in
comparison to the cultivated variety in question, Nissinen
concludes.
Psyllids Unfazed By “Bad Smell”
The study also included an experiment where carrot psyllids were
exposed to a volatile compound: limonene. Limonene can be found
both in carrots and in the psyllids’ winter host, the spruce.
A study conducted in Sweden during the last decade found that
limonene repelled carrot psyllids in the field. In Nissinen’s
greenhouse experiments, however, limonene failed to shoo
psyllids away. neither when sprayed directly onto the carrot
crop nor when released from a carrier substance.
The contradiction between the research findings may be because
greenhouse conditions differ from field conditions and the
psyllids are unable to carry out the change of host plant as
they would in the course of their normal live cycle. Nissinen
explains.
She adds that in her opinion it is important that future
experiments involving potential repellents or attractants should
take place in field conditions.
The dissertation of Anne Nissinen, M.Sc. (Agriculture and
Forestry), is in the field of environmental science and is
titled “Towards ecological control of carrot psyllid (Trioza
apicalis)”. The dissertation will be reviewed on 25 January 2008
at the University of Kuopio, Finland. Nissinen’s opponent will
be Doctor Robert Glinwood from the Swedish University of
Agricultural Sciences, and Professor Jarmo Holopainen from the
University of Kuopio will be acting as her supervisor. |
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