Page 28 - ALG Issue 3 2014

Regulars Q
ike Thurlow... &MA
I have tried to select questions that may be
topical and cover most aspects of the vegetable garden/allotment. Allotment gardening covers a wide range of interests; if you want to include any other
areas of gardening please send your questions in.
Whitefly issues
QI have a small polytunnel and over the last week it has become infested with whitefly on tomatoes, peppers,
aubergines and all the young plants I
have in there waiting to go outside. I have put up sticky yellow traps and sprayed with organic fatty acids but I still have
a real problem. I have heard that there
is a product called SB plant invigorator
– it’s a plant food but also claims to be effective against whitefly. Have you any experience of using it and what would you recommend that I do? Di, Bristol
ATaking on an allotment for the first time there is always the possibility that you will inherit crops left over by the previous tenant. It can be a pleasant surprise
like a bonus crop of beans, carrots or potatoes but often, as in your case, it is an unpleasant feast of pests but “Don’t panic!” as Corporal Jones would
say. This is a common
occurrence on an allotment
site especially when a plot
has been left unattended
and neglected for some
time. The pests, this time
whitefly, will multiply in
their thousands. The most
usual host plants for most
pests are members of the
brassica (cabbage) family,
so look around the plot,
remove and dispose of
any old plants that are left around. The tops of the plants can go on a compost heap but I prefer to chop off and burn
the roots to reduce the risk of club root infection, another ‘nasty’. Having cleaned up the allotment of old crops and weeds look around the plot to see if there are any trees or hedges overhanging your garden. With the owner’s permission these are best cut back because they could also be harbouring a potential pest problem. We have had terrible problems this year with the low box hedging alongside the paths hosting whitefly colonies.
It does help to understand the life cycle of any pests that you are trying to control
It does help to understand the life cycle of any pests that you are trying to control. Whitefly have a four day egg to emerging cycle so in the early days you will have to
be extra vigilant in whatever method you choose to control them. In the greenhouse whitefly are fairly easy to control using yellow sticky traps and then the biological control encarsia formosa. Outdoors can be more of a challenge. The sticky traps could provide a short term ‘hit’ but the encarsia formosa wouldn’t survive outdoors. I avoid using poisonous insecticides especially in the fruit and vegetable garden. There is a product called ‘Savona’, an insecticidal soap which is a fatty acid. It is used in exactly the same way as a conventional pesticide but instead of poisoning the pest
it dries it out by desiccating its body.
Other crops such as spinach and carrots
can be attacked by whitefly with differing consequences. With the leafy crops you will have to wash the leaves clean before using them; the carrot’s underground roots will
be unaffected. Once you are in control of the plot problems will gradually disappear over time. Work with nature by encouraging ladybirds, hoverflies, lacewings and ground beetles into the allotment. They are major carnivores and will consume thousands
of aphids and whitefly. A predator that I
am always happy to support are wasps; they help to clean up the garden at the
end of summer and early autumn when other predators are less active. One plant that I have found irresistible to hoverflies is beetroot. I always overwinter a few plants letting them run to seed during the summer.
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