Tag Archive: diseases

pest controlPests and diseases-

Buy varieties of plants that are restistant to pests and diseases. If you want to grow vegetables, choose modern varieties that are easier to grow and protect them with crop covers such as insect-proof mesh or garden fleece. Encourage natural predators to take up residence in your garden by growing nectar-rich flowers, providing nesting and overwintering sites, and by feeding birds in winter. Use bilogical controls in the greenhouse.

Further information:

Natural pest and disease control

Biological Pest control- RHS

Source: ‘Short Cuts to Great Gardens’ (Reader’s Digest 1999)

Old School Gardener


greenflyA few more clippings from a book I bought in a charity shop last summer ….

Altruism Truism:

A garden is an area of land devoted to growing fruit, flowers and vegetables, which in turn are dedicated to insect rearing.


1. The earth is alive to the sound of mastication.

2. Healthy plants breed healthy bugs.

Law of the vegetable patch:

A dose of insecticide whch would wipe out a medium-size town will do no more than temporarily stun a cabbage white. You can fool all of the people some of the time, but you can’t fool the caterpillars.

Law of Killing Generosity:

Don’t look a gift horse in the mouth, but if it comes from a garden centre, do check for trojan aphids somewhere in its anatomy.

A Winning Aside:

In the fight between you, the world and blight, back the blight.

PotatoLateCycleFrom : ‘Mrs. Murphy’s Laws of Gardening’ – Faith Hines (Temple House books, 1992)

Old School Gardener


I recently had a ‘tweet’ from fellow Norfolk resident, Claire in Thetford. She was wondering what the growths on these leaves were.

I must admit to being a bit puzzled at first, but some further research suggested that they are some sort of Gall, which Wikipedia describes as:

‘…abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites. Plant galls are often highly organized structures and because of this the cause of the gall can often be determined without the actual agent being identified. This applies particularly to some insect and mite plant galls.’

My guess from the pictures was that these were galls possibly created by some sort of parasitic wasp (in this case on the leaves of a Lime Tree). Claire’s own research came up with a more precise description: a ‘Nail Gall’ formed by a small mite Eriophyes tiliae. These microscopic mites overwinter in the bark of lime trees and crawl on to the underside of the foliage in spring to feed. The mites secrete chemicals into the leaves causing them to produce the unusual projections into which the mites move to continue feeding during the summer. Infestations of mites and the nail galls they induce don’t appear to affect the health of the trees and there’s no way of controlling or preventing them. The galls caused by this mite are said to be yellow-green or red in colour (see picture below). It may be that the whitish nails in Claire’s picture have been be caused by another mite (Aceria lateannulatus), which affects both the small-leaved lime (Tilia cordata) and the Common Lime (Tilia x europaeus), but not the large-leaved lime (Tilia platyphyllos).

Nail Galls cauised by Eriophyes tiliae

Nail Galls cauised by Eriophyes tiliae

Galls are fascinating phenomena. As Wikipedia continues, those created by insects are:

‘…highly distinctive plant structures formed by some herbivorous insects as their own microhabitats. They are plant tissue which is controlled by the insect. Galls act as both the habitat and food source for the maker of the gall. The interior of a gall can contain edible nutritious starch and other tissues. Some galls act as “physiologic sinks”, concentrating resources in the gall from the surrounding plant parts. Galls may also provide the insect with physical protection from predators.

Insect galls are usually induced by chemicals injected by the larvae or the adults of the insects into the plants, and possibly mechanical damage. After the galls are formed, the larvae develop inside until fully grown, when they leave. In order to form galls, the insects must seize the time when plant cell division occurs quickly: the growing season, usually spring in temperate climates, but which is extended in the tropics.

The meristems, where plant cell division occurs, are the usual sites of galls, though insect galls can be found on other parts of the plant, such as the leaves, stalks,branches, buds, roots and even flowers and fruits. Gall-inducing insects are usually species-specific and sometimes tissue-specific on the plants they gall.’

Galls are also caused by fungi, bacteria, viruses and nematodes. It seems that in many instances these growths do not cause any significant harm to the plants they infest, though in some cases long term harm can be caused to some species, for example by affecting their overall shape and vigour.

Crown Gall on apple- RHS

Crown Gall on apple- RHS

Crown gall affects a wide array of plants and roses are definitely one of them. It is a plant disorder caused by the bacterium Agrobacterium tumefaciens, that interferes with the plants ability to take up water and nutrients. This results in poor growth and weak plants that are easily stressed and injured- the only remedy in this case is to dig up the plant and dispose of it.

The study of plant galls is called cecidology. While these weird structures have intrigued humans for many years, there is still much that we don’t know about them.

Wiches Broom Gall - picture Rosser1954

Wiches Broom Gall – picture Rosser1954

While some galls are well hidden and hard to spot, others are much more conspicuous. Have you ever looked up into a birch tree (Betula spp.) and noticed what looked like large, dense birds’ nests? In some cases these may well be nests, but very often they are actually galls called ‘witches’ brooms’. These are caused by a fungus (Taphrina betulina), which stimulates the tree to produce numerous extra shoots, resulting in a dense nest-like cluster. The fungus can then feed on the shoots. It was once believed that they were caused by witches flying over the tree!

If you spot an odd-looking growth on a dog rose (Rosa canina) it could well be a Robin’s pincushion gall, caused by a wasp (Diplolepis rosae). There was once a belief in England that these were caused by the woodland sprite, Robin Goodfellow or Puck. It is hardly surprising that people ascribed supernatural causes to some galls – they look pretty strange, and their causes aren’t exactly obvious.

'Robins Pincushion' gall on a Wild rose

‘Robins Pincushion’ gall on a Wild rose

The real gall specialists include gall midges, gall flies and gall wasps. Perhaps one of the most familiar galls is the oak apple, caused by a tiny wasp (Biorhiza pallida).

Oak apples

Oak apples

There are actually hundreds of species of oak gall wasps and they cause a fantastic variety of galls on oaks (Quercus spp.). A single oak tree may support many thousands of galls. Each gall wasp species creates its own unique and outlandish structure: some resemble cotton wool or marbles, pineapples or tiny UFOs!

Here’s a gallery of some of the other amazing galls to be found.

This slideshow requires JavaScript.

Sources and further information:

Galls- Wikipedia

Eriphyes tiliae- Wikipedia

British Plant Gall Society

Trees for Life- Galls

RHS- Crown Gall

Old School Gardener

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dying dahlias 4This week’s question concerns some rather sad looking Dahlias (see picture), and comes from Jen Reteaj of Loughton, Essex. The plants are flowering, but the leaves have yellowed and then turned brown. It appears that some other nearby plants are also affected. Jen says:

‘It’s got quite serious as you can see from the pictures. I have sprayed, fed and watered them but still they die! Is it a virus?’

Dahlias can be prone to a number of diseases (and that’s what this is, I think). The pictures you’ve sent suggest that the stems are still green and looking healthy, so I’d rule out over – watering and consequently rot setting in. As you say you’ve been watering and feeding them so we can also probably rule out mineral deficiency of some sort. The browning of the leaves (if it’s occurred from the bottom and moved up the plant) sounds like a disease, probably fungal. The recent hot, and sometimes humid weather we’ve had is perfect for such problems. The only safe remedy is to remove the affected leaves for burning or disposal (not to compost). If there are some uninfected leaves left you might try to save the plant by watering only in the morning, so leaving the leaves dry into the night time. If the disease has spread throughout the plant (and your pictures suggest it has), I’d remove everything (including the tuberous roots and stems) and dispose as above.

The Dahlia was named after Anders Dahl (a swedish botanist), born on 17th March, 1751

For the future you might like to be aware of some common Dahlia disease and pest problems:

Ringspot- large, yellow circles appear on the leaves. This viral disease is transmitted by insects called thrips. it infects the dahlia’s roots and spreads throughout the plant. Gradually the rings on the leaves grow larger and brown spots may develop in the middle of each ring. It is not usually possible to treat the sick plant.

Dahlia Mosaic- this is another root-based viral disease. It gets its name from the alternating light and dark green patches that appear on leaves. These appear because the virus causes an imbalance in the plant’s chlorophyll. Yellow leaf spots and veining are also symptoms. The infection is usually spread by aphids and once infected it is usually very difficult to treat, so once gain you need to remove the plant and burn it.

Powdery Mildew – grey, fuzzy leaves that fall off is the symptom of powdery mildew. This is a fungal disease that infects dahlias when it is very humid, but it may also strike in dry weather. It is also more common in plants that are planted close together (restricting airflow). The disease can be treated with wettable sulphur once a week.

Insects- thrips are small flying insects that can destroy dahlia flowers by sucking out their juice as well as brining Ringspot. They can be controlled by placing sticky traps around the plant and spraying the plant with insecticidal soap (this also works well on controlling aphids). Leaf borers can also be a problem for dahlias. These tiny worms burrow into the stem and this kills the plant. The problem can be dealt with through applying a bacteria called Bacillus thuringiensis when watering – this kills the borers, but is safe for the plant.

‘The Dahlia you brought to our isle

Your praises forever shall speak

‘Mid gardens as sweet as your smile

And colour as bright as your cheek.’

            Lord Holland (1773–1840)


Further information:

Dahlia diseases

Dahlia Care

Old School Gardener

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Water Lily Beetle- image from Donsgarden.com

Today’s GQT comes from Adele Inwood from the lsle of Wight:

‘I have a new pool in my garden and I want to know how to deal with the main pests and diseases of pool plants please.’

Adele, the worst pest of pool plants is the Water Lily beetle- it’s larvae are like small slugs, dark on top and pale underneath. They feed on the leaves of water lilies.

The small brown beetles hibernate in the hollow stems of other aquatic plants, which should therefore be cut down in the autumn and burnt. You can control the larvae by laying a double thickness of newspaper over all the foliage from the first appearance of the pest (indicated by holes chewed through the foliage). If this is done in the evening and the papers removed in the morning, and the process is repeated at weekly intervals for at least four weeks, you should find that the beetle larvae will have been eaten by other water life.

Remove the worst damaged leaves. This method of control is also good for the reddish-black aphids which can seriously damage the leaves. Hosing off the aphids and beetles is also effective – but be careful not to add too much new water to the pool.

You might also see a thick green scum appearing on the surface of the pool. If the pool hasn’t been filled for a matter of only a few days or weeks, remove the worst of the scum with a fine mesh net. The scum – really an algae – appears after you change the water, before it settles down again. The presence of foliage on the surface will help to speed up the process by preventing light from getting to all of the water, stopping the formation of the algal ‘bloom’. So perhaps look at trying to cover more of your water surface with plants – about a third coverage is a good target.

Pond algae can be reduced by increasing leaf cover on the water surface

Pond algae can be reduced by increasing leaf cover on the water surface

Further information:

Water Lily Pests

Old School Gardener

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'Friend or foe?'

‘Friend or foe?’

‘Prevention is better than cure’ applies to many situations in  life and controlling the pests and diseases in your garden is one of them.

As part of the ‘Master Composter’ project providing advice to families and groups about using green waste to make compost and enrich their soil, I’ve recently been sent a useful factsheet about organic pest and disease control. And pest control – specifically pigeons and blackbirds – is presently keeping me well exercised in the garden! More positively, I don’t seem to have had much of a problem with either slugs and snails, aphids or caterpillars – so far. A harsh winter and dry spell may be part of the answer. Anyway, I thought I’d share the basics of this factsheet with you (plus a few thoughts of my own).

Here are 7 tips for effective action to prevent your crops and plants being trashed by those not – so – welcome forces of nature!

1. Healthy soil

Too much fertiliser and your plants will be soft and sappy – providing a lovely lunch for pests and encouraging you to spray to deal with them. Not good practice. Better to feed your soil with a ‘wholefood’ diet of garden compost and leaf mould rather than those ‘fast food’ fertilisers designed to feed the plant and not the soil.

2. Resistant plants

Choose varieties of plant that can withstand the attack of pests and disease; e.g. blight resistant potatoes such as ‘Remarka’ and Sarpo’ and root aphid resistant lettuces like ‘Milan’.

Leaf mould - a great way to improve your soil

Leaf mould – a great way to improve your soil

3. Rotate your crops

Focusing on the veggy garden, crop rotation is an essential technique to build soil fertility and controlling the build up of pests and diseases.  Divide your veg into at least four groups (those in the same or similar families and having similar feeding habits) that stay together each year, but move onto another part of the garden  every spring.

4. Barriers and scarers

Keeping pests out of your crops and off your choice plants is probably the most effective way of reducing if not preventing damage. There is a range of different barriers and scarers suited to different types of crop or plant:

  • Fine mesh netting  – works well for carrot root fly and pea moth as well as pretty well most pests that attack cabbages (flea beetles, cabbage white butterfly, leaf weevils, birds and white fly).
  • Other Netting – useful for preventing birds eating/ damaging fruit and vegetables, but remember it should be tightly drawn to the ground to avoid any gaps – my own experience is that pigeons and blackbirds are past masters at finding the smallest of holes and working their way in! Netting can also prevent cabbage white butterflies from laying their eggs on Brassicas, but the gauge of the net needs to be fine enough to stop them. Also, having used hard plastic mesh netting for a while, I’d suggest investing in those made of softer, string -like material (nylon?), as this will drape more easily over crops.
  • Cabbage collars  – a collar of carpet underlay around the neck of  a young cabbage will prevent cabbage root fly from laying its eggs at the base of the cabbage.
  • Bottle cloches – made out of plastic bottles (tops and bottoms cut off) and placed over newly planted vegetables will prevent them being eaten by slugs or anything else that takes a fancy to them.
  • Small gauge chicken wire – always useful, this can be placed over newly sown peas to stop them being eaten by mice while germinating or being scratched up by cats. Wrapped around flowering bulbs, it can prevent them being dug up by squirrels.
  • Bird scarers – a ‘humming line’ (sometimes called buzzwire) criss – crossed over veg and which vibrates in the slightest of breezes will help scare off birds. You can come up with any number of other devices that use the wind to create noises or flashes of light and colour that will put off the birds, but move them around, as birds get used to things being in the same place and will eventually ignore them. I’ve just bought (for the princely sum of £2.50) a colourful windmill that I’ve stuck atop a cane and put over a spot where pigeons come to pinch my raspberries – we’ll see how effective that is! Another method is to tie up old CDs/DVDs to lines between canes to let them flash and move in the breeze. I’ve also seen some pretty realistic models of Owls and other birds of prey and a host of other devices that you can set up to ward off other birds – I’m not sure if they are effective, though.
A beer trap will entice slugs

A beer trap will entice slugs

5. Traps

Beers traps for slugs do work. Codling and Plum moth traps hung from apple trees and other ‘sticky’ traps can also be effective, using  a pheromone stuck to a sticky base which attracts male insects and gets them stuck in the glue. Greasebands painted around the trunks of apple trees in autumn will prevent the wingless female winter moth from climbing up the tree to mate. Sticky glue is also useful for glasshouse staging if you have a problem with ants. Sticky yellow bits of card hung up in greenhouses can help reduce the white fly population.

6. Beneficial bugs

These are your best friends when it comes to controlling pests in your garden. Planting simple annuals among the veg (e.g. Marigolds, Californian poppies), will attract  a wealth of beneficial insects  like ladybirds and hoverflies which will gobble up your aphids. I’ve put some marigolds alongside my tomatoes in the greenhouse for this reason and also planted Nasturtiums which can attract cabbage white butterflies as a diversion away from my Brassicas.You can also plant a few native shrubs and herbaceous perennials (e.g. hazel and hardy geraniums), create a pond, leave a small pile of logs in the corner of the garden or create a ‘bug hotel’  and feed the birds throughout the winter. There are other ‘biological controls’  that you can buy to deal w ith specific problems- little packets of some of the bugs for use in the greenhouse as well as nematodes that can attack some of the more troublesome pests.  Any or all of these will keep enough wildlife in your garden to eat literally thousands of pests and their eggs!

'Bishybarnabee' - or a ladybird- will eat loads of aphids at one sitting

‘Bishybarnabee’ – or a ladybird- will eat loads of aphids at one sitting

7. Keep it clean

Think ‘clean cut’. If you’re removing a dead or diseased branch from a tree (e.g one with coral spot), make sure you cut into healthy wood and always wash your tools in boiling water or wipe them with surgical spirit afterwards. Scrub out pots and give your greenhouse a good scrub every winter to get rid of over wintering pests. Maximise air circulation by correct pruning of plants and leaving  just a little more space between plants will help control fungal diseases, though his needs to be balanced of course against closer planting to keep weeds under control! Controlling powdery mildew in Roses is something that benefits from greater air circulation, for instance. Finally, and most importantly, be vigilant and check your plants regularly so that any pests and diseases don’t get a foothold. For example, start checking the centre of any Gooseberry bushes in April for Sawfly eggs and larvae. Also be wary of accepting gifts of onion and cabbage plants, as they may well carry onion white rot or clubroot respectively!

So, not a spray in sight – rather planning, forethought, observation and simple control measures can help you beat those garden pests and diseases!

Source: Master Composter Manual Factsheet 4, Jojo Norris, Garden Organic 2013

Old School Gardener

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