Facebook Q&A Session 19th August 2014

Controlling Nuisances, Diseases and Pests
- your horticultural questions answered.

View the answers to our previous sessions.

"Is there a way I can get rid of wireworm?"

Sue - T&M
Horticultural Expert

"Hi Bryn. Wireworm can be a real nuisance and there are no quick fixes I'm afraid. The eggs are laid in early summer below the soil surface and once hatched; the larvae will feed on plant roots, potato tubers etc. The bad news is that this larval stage can last for up to 4 years! Eventually they will pupate and the adults overwinter in the soil before emerging in early summer to mate.

There are no chemicals currently available for use against Agriotes spp. However, the problem should be quickly reduced in soils that are regularly cultivated. Thoroughly turn the soil in autumn and dig it over again in spring. This will expose wireworms to predators such as birds. It is well worth encouraging birds in your garden all year round as they will definitely help to limit this pest.

While the weather is warm I would also suggest that you apply some nematodes of Heterorhabditis megadis. There are a number of suppliers online. They can be watered into the soil and will kill any wireworms that they find. Given that wireworm lifecycles are so long then it will probably be necessary to make a number of applications over several years.

If you make your own compost then its worth checking to see whether there are wireworm present. If so, then dispose of the compost off site. Don't be tempted to spread it anywhere in the garden.

It goes without saying that it is best not to grow susceptible crops such as potatoes in infested soil. You could try to reduce the damage to any current crops by lifting them early, but this will obviously reduce your potential yields. It's a difficult problem to control. I hope that you are able to limit it successfully."

"How do you get rid of the horrible vine like weed please? It's driving me mental thanks."

Sue - T&M
Horticultural Expert

"Hello Leeanne. I'm guessing that you are probably referring to Bindweed which is a rhizomatous perennial. The rhizomes (underground stems) spread deeply and in all directions. They can reproduce from just a small fragment of stem or rhizome which makes them difficult to get rid of. It's a good idea to try and gently fork out as many rhizomes as you can before collecting them and disposing of them in household waste - don't compost the pieces as they will quickly regrow all over your compost heap! They are easy to spot as the rhizomes are white.

Any further growth can then be treated with a weed killer that contains glyphosate, which is carried through the plant to its roots, causing death of the entire plant. This is a non-selective chemical and will kill your garden plants too if you are not careful so make sure you cover the plants you want to keep before spraying! To get the best results spray the weeds on a still, overcast, dry day. If the Bindweed is growing among established borders then you may prefer to use this chemical in gel form. It can be painted directly on to the leaves of the weed, thereby minimising the risk of killing your surrounding plants by accident. In severe cases you may need to reapply the herbicide. I hope that helps Leeanne."

"Can you give me any advice on getting rid of fairy rings on our lawn, they are spreading out in ever increasing circles?"

Sue - T&M
Horticultural Expert

"Hello Elizabeth. Fairy rings are quite interesting things really. They are caused by a fungus such as Marasmius oreades which grows within the roots of the grass. The fungus causes characteristic circles of toadstools in autumn, but are visible throughout the year as circular areas where the grass dies back. The spores are airborne so there is little that you can do to stop a colony forming in the first instance. Once a colony forms it begins to spread gradually outwards, dying back from the centre and so takes on a ring like appearance. Incredibly, a colony may spread up to 30cm a year! Fairy rings are not particularly harmful in any way.

In terms of control, I'm afraid that there is little that you can do. There are no chemical controls available. Given that the mycelium grows outwards through the soil then in minor instances you could dig out that area of soil (from beyond the outside of the ring, and to a depth of around 30cm) and replace it with fresh topsoil and turf. However, if you have lots of rings then this would be very expensive and make a horrible mess of your lawn. Being realistic, you may have to learn to live with them, as a colony can survive for up to 100 years! Sorry Elizabeth, that's not the answer you were hoping for, is it?"

"Every year we have more and more ants in our garden - the lawn has more and more nests. I use ant powder but it doesn't seem to work. Any ideas? Ants are generally quite beneficial in the garden as they feed on sap sucking aphids and the honeydew that they produce. But I can appreciate why you wouldn't want them living in your lawn."

Sue - T&M
Horticultural Expert

"There are numerous products on the market from powders to gels that can be used to kill a nest. I believe that the gels are often found to be slightly more effective so it might be worth trying one of them during a period of drier weather. You can also buy nematodes that are watered onto the area and these are found to be very effective too. You could try the old fashioned remedy of pouring boiling water over the nest - this will certainly upset them but also tends to kill the grass leaving unsightly bare patches!

The other option is to find a way to live with them. You can reduce the mess made when mowing by raking over and excavated soil mounds on a dry day prior to mowing. If you can encourage birds into your garden then they will readily dispose of any ants and eggs that are brought to the surface by this process. I hope that one of these suggestions works for you Ray. If all else fails, try watching them for a while - they are fascinating insects and you may even grow to like them!"

"Hi Sue. Helppppp! My year old Rosa Garden Party plants were fine and healthy last autumn but have developed dreadful powdery mildew after our wet winter. I was hoping that drier weather coupled with new fresh growth would overcome this problem but they are still looking very sad. I try to garden organically where possible, but would consider anything to save them!"

Sue - T&M
Horticultural Expert

"Hi Jane, you're absolutely right – this fungus thrives in moist and humid conditions. Soft new growth can be prone to attack so it is recommended to use a low nitrogen fertiliser if you're feeding your roses. Luckily rose powdery mildew mainly grows on the surface of leaves and stems so there are a number of organic substances you can use to control it such as those based on natural plant or fish oils. You'll see these sprays labelled as 'organic', such as Vitax Organic 2 in 1, and they will list on the back whether they control powdery mildews. You'll probably need to spray several times throughout the growing season to maintain control. Make sure you spray plants in early autumn too as this may help control the amount of overwintering spores. If you feel the need to use chemicals then try sprays which contain difenoconazole or myclobutanil, such as Westland Plant Rescue Fungus Control or Bayer Garden Systhane Fungus Fighter. They are systemic (enter the vascular system of the plant) so will provide 2 or 3 weeks protection per treatment. I hope this helps Jane, best of luck."

"Hi Sue, I have grown the Cup and Saucer Vine from seed every year with no problems but this year the seedlings come through and just as the second leaves grow they wither and die. I have sown a second lot in new compost and sterilised pots but the same is happening again. All the rest of my plants are perfectly fine .Thanks x"

Sue - T&M
Horticultural Expert

"Hi Jane, this sounds most like damping off, although it's strange that no other plants have been affected. Damping off is a fungal disease caused by a variety of water moulds that flourish in wet compost and need water to spread from plant to plant. They penetrate the plant cells and cause plant collapse which looks like wilting. These fungal diseases can easily be introduced in compost or rainwater and take hold when presented with moist and humid conditions. Try watering the compost sparingly after sowing the seeds and allow the compost to dry out slightly between watering to reduce the risk of damping off. Take care to keep them away from cold chills too as they are tropical plants. If you think there may be an issue with the seed please contact our customer care team by emailing ccare@thompson-morgan.com or phoning 0844 573 1818 and they will be able to arrange a replacement for you. I hope this helps Jane, let us know how you get on."

"I emptied a large compost bin which had top soil - however I did not find any worms. Does this mean the soil is unhealthy?"

Sue - T&M
Horticultural Expert

"Hi Santosh, this is nothing to worry about. Worms will only be present in soil if there is a supply of organic matter for them to eat, such as dead leaves, decaying plant material or manure. I'm also not sure if your compost bin is sitting on the ground with easy access for worms or whether it is raised up on feet. The soil in the compost bin could have lacked organic matter or it may have become too saturated with water or too dry for worms to be happy. Also if it has been in there for a while there could be a lack of oxygen in the soil. Once the topsoil is spread back out in the open many creatures should start to inhabit it again. You can help improve your soil by digging in lots of organic matter such as well rotted manure or compost. I hope this helps."

"Hello sue, we have a plum tree which is only three years old. Last year we saw our first sight of a plum (only two) but they shrivelled up and dropped off. We had some terrible leaf curl last year which seemed to be aphids. The same thing has happened already this year complete leaf curl with aphids in the curled leaf. There are also ladybirds on the tree but they can't keep up with the extent of the problem. Please help thank you."

Sue - T&M
Horticultural Expert

"Hi Tracey, this does sound like plum leaf-curling aphids which are most active in mid to late spring. In summer they can also be followed by mealy plum aphid. The stress of heavy infestation by these aphids could be causing the tree to abort fruit so it's best you tackle the problem to ensure good crops. The best way to control leaf-curling and mealy aphids is by using a systemic insecticide containing thiacloprid, such as Bayer Provado Ultimate Bug Killer. This spray is safe to use on edible crops and fruit trees, although never spray while the tree is flowering - wait until afterwards. For heavy infestations, spray several times throughout the growing season, at the recommended intervals and take care to stop spraying a number of weeks or days before picking the fruit (check the label for further advice). Mealy plum aphid (pale greenish-white in colour) can also be treated with sprays containing lambda-cyhalothrin or pyrethrum such as Westland Plant Rescue Fruit & Vegetable Bug Killer. You can also tackle the overwintering eggs by applying a winter tree wash on a dry day in winter – they're available in all good garden centres. This dual approach should help to bring the problem back under control. I hope this helps Tracey, let us know how you get on."

Sue Sanderson T&M horticulturalist

About Sue Sanderson

Plants and gardens have always been a big part of my life. I can remember helping my Dad to prick out seedlings, even before I could see over the top of the potting bench. As an adult, I trained at Writtle College where I received my degree, BSc. (Hons) Horticulture. After working in a specialist plantsman's nursery, and later, as a consulting arboriculturalist, I joined Thompson & Morgan in 2008. Initially looking after the grounds and coordinating the plant trials, I now support the web team offering horticultural advice online.


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