Leek Moth

Can't identify that mould? Got a great tip for keeping slugs at bay? Suggestions for organic weed control? Post them here...

Moderators: KG Steve, Chantal, Tigger, peter

Claire Wheat

We have been growing leeks for years and years but for the first time ever, our plants have been badly attacked by leek moth.

The earlier plantings (planted out as small plants on 5 June) were more badly affected than the later batch (planted out on 18 June) but there is not really a lot in it. Some of the leeks keeled over completely but others have been just about salvagable, once we have picked out the little chrysalises.

Has anyone suffered from this and found a solution (barrier or organic)? I am afraid that there will be chrysallises that overwinter and the cycle will start all over again next year, even if we move the leeks as far a way from this year's position as possible.

Thanks
User avatar
John
KG Regular
Posts: 1608
Joined: Fri Nov 25, 2005 10:52 am
Location: West Glos

This pest is becoming a real problem now. It seems to be worse in some years. I grow my leeks under environmesh and this has worked well. As there's not so much space when growing under mesh I grow them close together as finger-sized leeks.
I seem to remember that on the old forum Beryl (from Saunders Allotments?) made some really good postings on sorting this little pest out. With any luck she might notice your post and put something up for us. I think one piece of advice given was to have a really good clear up over the winter and not to compost leeks so as to prevent a carry over of the pest from one season to the next.

John

PS I'll see if I can find anything on the old forum.
John & Beryl

Hi,Yes, the leek moth is a very big problem here in the south and I also believe it is now spreading across the country.
There is no known insecticide that will kill the devils off the only way is to adhere to strict hygiene on your plot, use what ever barrier method you can, fleece, mesh etc. also I have found that by planting later and setting out strong plants that have been potted on seem to survive better. Plants do tend to look very tatty but if you can bear to leave them in I find most will recover sufficiently to give you a good crop. Of the 2 seasons when the moth is most active I think August is the worst time - when it is very dry.
Obviously any plants that have gone wet and slimey - remove but do not compost. I have been told that by dusting plants with yellow sulphur will help but I have not tried it as yet.

Hope you have better luck this year.

Here is a letter received in 2002 from RHS Wisley you may find helpful also an atricle by a John Trim.

The Royal Horticultural Society Garden,
Wisley, Woking, Surrey. GU23 6QB.
18th September 2002

The damage that you have noticed on your leek plants has been caused by the caterpillars of a pest commonly known as the leek moth. This is a local occurrence in Britain, being mainly found along the east and south coast of England, although it does sometimes occur further inland. Where it is found it can sometimes be very troublesome and make the growing of leeks and onions difficult. It has two generations during the summer with the larvae being active during May and June and again between August and October. The larvae feed initially as leaf miners in the foliage but as they grow larger they bore into the stems of leeks and into the bulbs of onions. Once the caterpillars have penetrated the deeper tissues of their host plants it is very difficult to reach them with insecticides. When the larvae have finished feeding they emerge from the plant and spin net-like silk cocoons, usually on the foliage. Pupae of the late summer generation are present during September to October and the adult moths emerge during the latter month. This pest overwinters as adult months which seek sheltered places during the autumn.
It is worthwhile examining the foliage on your leeks to try and detect these pupae which can be destroyed by hand removal before the adult months emerge. Next year you should watch out for signs of leaf mining beginning on your plants during May and August. There is currently no pesticide available to amateur gardeners for use against pest on leeks. In the absence of pesticides, gardeners now have to either tolerate the damage cause by the leek moth or they can try and protect the plants by growing them under the cover of as horticultural fleece. This is a finely woven material which allows light and water through but will exclude most pest, including the egg laying females of the leek moth.
The only pesticide which is currently approved for the use on leeks for leaf miner control is nicotine. This is not sold in small amateur packs and is only available to professional growers. If nicotine is to be effective it needs to be applied when signs of leaf mining are first seen. There would be no point in spraying your plants now as we are at the end of the larval feeding period and they will be currently emerging from the foliage in order to pupate.

LEEK MOTH.
The following article was written by John Trim in the National Vegetable Society Quarterly Bulletin. Vol.10 part 4.
The Leek moth is becoming increasingly frequent problem in Southern England and it can also attack onions. This moth is of local occurrence in Britain, being mainly found along the east and south coasts, although it does
sometimes occur, further inland. Those of us who have been troubled by this pest have found that the growing
of leeks has become exceedingly difficult. The moth produces two generations during the summer. The larvae are active during May and June and again between August and October. They feed initially as leaf miners in the foliage but as they grow they bore into the stems of the leeks and into the bulbs of onions. Once the caterpillars have penetrated deep into the tissue of the plants it is nigh on impossible to reach them with pesticides. When the larvae have finished feeding they emerge from the plant and spin net like silk cocoons, usually on the foliage. Pupae of the late summer generation are present during September to October and the adults emerge during the latter month. This pest then over-winters as an adult moth in sheltered places. Control - Examine the foliage of the plants regularly, and if you spot damage on the leaf you can usually track down the larvae and destroy them. Pay special attention to your plants from May onwards. There is currently no pesticide effective against the moth that is available to amateur gardeners. An alternative, and very effective, way to protect your crop is to grow under fleece or, even better Enviromesh. The latter is more expensive but will last many years and has the advantage of allowing air circulation and natural rainfall through to the crop. It will exclude most pests, including the egg laying females of the leek moth. I have known some exhibition growers who have installed ultra violet lights that electrocute the moths when they attempt to land. If all else fails and your crop has been badly infected you can always cut the foliage off your leeks and they will re-grow, albeit somewhat smaller. But do not try this with onions. But, realistically, if you live in an area where leek moth is prevalent the only way forward is to provide some form of physical barrier to prevent the female moth reaching the crop.

If you have managed to read all this you will probably find some more on my web site in the Diary pages.
www.saundersallotment.co.uk
User avatar
oldherbaceous
KG Regular
Posts: 13925
Joined: Tue Jan 24, 2006 1:52 pm
Location: Beautiful Bedfordshire
Has thanked: 335 times
Been thanked: 357 times

Thought I would bring this topic up again, as it is Beryl’s Birthday…..
Kind Regards, Old Herbaceous.

There's no fool like an old fool.
Post Reply Previous topicNext topic