Vegetable growing advice

This section is about problems and issues most common on allotments..

Info taken from the RHS website

 Tomato and Potato blight

(we now stock a treatment in the shop for blight and other similar problems, see our latest news page)

Potato and tomato blight is a disease caused by a fungus-like organism which spreads rapidly in the foliage and tubers or fruit of potatoes and tomatoes in wet weather, causing collapse and decay.  It is a serious disease for potato and outdoor tomatoes, but not as common on tomatoes grown in greenhouses. 

You may see the following symptoms:


  • The initial symptom of blight on potatoes is a rapidly spreading, watery rot of leaves which soon collapse, shrivel and turn brown. During humid conditions, a fine white fungal growth may be seen around the edge of the lesions on the underside of the leaves
  • Brown lesions may develop on the stems
  • If allowed to spread unchecked, the disease will reach the tubers. Affected tubers have a reddish-brown decay below the skin, firm at first but soon developing into a soft rot as the tissues are invaded by bacteria. Early attacks of blight may not be visible on tubers, but any infected tubers will rot in store


  • The symptoms on tomato leaves and stems are similar to those on potatoes
  • Brown patches may appear on green fruit, while more mature fruits will decay rapidly

Infected material should be buried or burned rather than composted. Earthing up potatoes provides some protection to tubers. Early-harvested potatoes are more likely to escape infection. Operate a rotation to reduce the risk of infection, ideally of at least four years.

Tomatoes are generally very susceptible, but the varieties ‘Ferline’, ‘Legend’ and ‘Fantasio’ are claimed to show some resistance, but will eventually succumb in wet, warm weather. It is probably best not to rely on host resistance for blight control in tomatoes.


At Swiss cottage I haven't been a victim of Potato blight but don't grow tomatoes outdoor anymore because of this disease.  My tomatoes in the greenhouse are fine.


 Allium leaf miner

The allium leaf miner was first detected in Britain in 2002, since when it has spread in the Midlands and has also been found in Surrey. The larvae bore into the stems and bulbs of leeks, onions, chives and garlic with devastating consequences. Affected plants often develop secondary infections and rot.

Allium leaf miner is a pest of many common crops: leeks, onion, chives, shallot and garlic. The initial damage is done by the maggots, but secondary fungal and bacterial infections often cause the most noticeable rotting.

The first sign of an attack from allium leaf miner is the presence of the adult fly:

  • The greyish brown flies are 3mm long
  • Before laying eggs, the female flies feed by making punctures in the leaves and sucking up the exuding sap
  • This causes distinctive lines of white dots on the foliage

Next seen is damage from the maggots:

  • The larvae are white, headless maggots without legs
  • These make tunnels in the stems and bulbs of their host plants
  • Note: Similar damage is caused by caterpillars of the leek moth but that pest has creamy white larvae with brown heads and small legs

But perhaps the most obvious signs of a problem appear when rotting sets in:

  • Plants affected by both allium leaf miner and leek moth tend to rot due to secondary infections from fungi and bacteria that develop in the damaged tissues
  • On closer inspection, cylindrical brown pupae may also be found embedded in the stems and bulbs

Plants can be protected by covering them with horticultural fleece, or an insect-proof mesh such as Ultra-Fine Enviromesh, at times when the adult flies are active and laying eggs (March to April and October to November). Crop rotation must be used, as adult flies might emerge from pupae underneath the fleece covering if susceptible plants are grown in the same piece of ground in successive years.  None of the pesticides currently available to amateur gardeners for use on leeks and onions is likely to give good control of allium leaf miner.

Allium leaf miner has two generations a year:

  • First generation female flies lay eggs on the stems or base of leaves during March to April
  • The second generation repeats the process in October to November

The maggots bore into the stems or bulbs of their host plants and, after a couple of weeks, are fully fed and ready to turn into brown pupae. Pupation takes place mainly within the stems and bulbs during summer and winter but some pupae may end up in the soil, especially where plants have rotted off.

  Onion White Rot 

 White rot is a serious disease of the alliums, especially bulb onions, garlic and leeks, caused by the soil-borne fungus Sclerotium cepivorum which can persist in the soil for many years. Look for symptoms from mid-summer until early autumn.

You may see the following symptoms:

  • Above ground, the first symptom is yellowing and wilting of the foliage, especially in dry weather.
  • Under wetter conditions the plants may not wilt, but will become loose in the soil.
  • Below ground, the pathogen rots the roots and then invades the bulb.
  • White fluffy fungus growth appears on the base of the bulb and later this becomes covered in small, round, black structures.

Onion White Rot is effectively impossible to eliminate once it has been introduced and the long survival period makes crop rotation impractical. It is therefore extremely important to avoid introduction to previously clean sites. It is transported in contaminated soil, for example on tools or on muddy footwear. Take particular care in areas where cross contamination can occur easily, for example on allotments.

It can remain in the soil for at least 15 years, though they will not always live this long. They can only germinate once and the fungus will then die out if it can not infect. Both sclerotia germination and fungal growth are inhibited above 20ºC (68ºF), so in the UK the problem is more severe in cool, wet summers; in warmer climates the disease is only a problem over the winter months.

I have an area of my allotment with White Rot so I know not to put my onions there.....

 GREASEBANDS and how to use them.  Available in the shop

Greasebands are only effective on young trees with smooth bark: if your trees are older & have uneven trunks, you will need to apply tree grease by hand.

Greasebands are pest barriers that are used for two main things:

  1. Trapping a variety of female winter moths. These wingless insects emerge from the soil and climb fruit trees in early winter to lay their eggs. When these hatch, the caterpillars eat leaves and fruit.
  2. Greasebands will also trap earwigs and prevent ants from protecting aphids and scale insects, which they farm.

Using Grease Bands against Winter Moth Caterpillars

Full instructions are included with every pack of Greasebands, but put simply the greaseband is cut to length and wrapped around the trunks of your fruit trees in autumn, with the sticky side outwards. The females of a range of winter moths are wingless and crawl up the trunk to lay their eggs. They get stuck to the greaseband and die.

Greasebands and Earwigs and Ants

To trap earwigs, ants and other crawling pests, you can apply greasebands in exactly the same way, but between May and September.

Each pack of Boltac Greasebands contains enough material for 10-12 average sized trees. In addition to the pack contents you will need a pair of scissors and some garden twine. There is no pesticide involved so our greasebands may be used for organic gardening as well as in combination with other methods of control. 

Club Root

Club root is a fungal infection of the roots of brassicas, such as cabbage, cauliflower, turnip and swede, leading to swollen and distorted roots and stunted growth.  A good treatment for this (and we stock in the shop) is Perlka.  Club root can infect whenever the soil is moist and warm, so most new infections occur from mid-summer until late autumn.  If you have had problems in the past then soil treatment with Perlka is a must.  Digging in Perlka is a preventative measure so this needs to be done if you know Club Root is a problem.