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Posts Tagged ‘pests and diseases’

Garden pests and diseases

The euphoria of the first time veg grower is often punctured by their first experience of a pest infestation or the loss of a crop to disease. Whilst you will never mange to completely avoid such experiences there is a lot you can do to minimise any pest or disease problems.

 This series of seven articles aims to give you the knowledge to prevent problems in the first place as much as possible and, manage any outbreaks in a planned and effective way, ideally with limited use of pesticides and chemical controls.

Scroll down the page to get to the first article or click on the links.

Part 1 http://www.hootershall.co.uk/2010/11/12/pests-and-diseases-1/

Part 2 http://www.hootershall.co.uk/2010/11/15/pests-and-diseases-2/

Part 3 http://www.hootershall.co.uk/2010/11/17/pests-and-diseases-part-3/

Part 4 http://www.hootershall.co.uk/2010/11/18/pests-and-diseases-part-4/

Part 5 http://www.hootershall.co.uk/2010/11/19/pests-and-diseases-part-5/

Part 6 http://www.hootershall.co.uk/2010/11/22/pests-and-diseases-part-6/

Part 7 http://www.hootershall.co.uk/2010/11/24/pests-and-diseases-part-7/

Pests and diseases part 7

I’ve always preferred to stick to organic methods in our garden. Although using chemical insecticides and fungicides on the face of it can seem the easier option if you’re doing it properly and safely there is a lot more to it than just spraying. Another difficulty with chemical insecticides and fungicides is choosing which one is most suitable for your garden and its pest and disease problem.

As a start it’s important to understand how chemical insecticides and fungicides work. Most have a contact action. This means that they must cover the plant surface so that the pest is either hit directly or picks up the pesticide from the treated surface. Fungicides too will kill fungal spores when they germinate providing coverage of the plant is adequete.

The alternative mode of action for pesticides is systemic. These are absorbed into the plant and may be transferred to parts which have not been directly treated. Systemic insecticides move upwards to the shoot tips or within the leaves. They do not move down to the roots. Systemic fungicides generally move only with a single leaf and are curative rather than preventative. Systemic insecticides can be useful in killing sap feeding insects, including those concealed in distorted leaves that cannot be reached by a contact spray.

Most pesticides that are available to amateur gardeners have a broad spectrum of action and will affect beneficial insects as well as pests. One way to reduce the effect on beneficial insects is to limit the time period over which the pesticide is effective. Organic insecticides such as pyrethrum, fatty acids and plant oil,s are broad spectrum but are only effective on the plant for less than 24 hours. This means that their impact on beneficial insects is minimised.

The timing of application of pesticides can be critical and many will require more than one application. Non organic pesticides remain active for less than two or three weeks after application. The application of pesticides to fruit, vegetables and culinary herbs will require consideration of the harvest time as it will often be necessary to have a significant interval between application and harvest.

There are several methods of application for pesticides, each with its advantages and disadvantages.

  1. Liquid spray: available for contact and systemic types and is inexpensive. Does require accurate measuring of concentrate and special equipment for application.
  2. Liquid drench: available for contact and systemic types and is inexpensive. Accurate measurement of concentrate required and it can be difficult to calculate precise amounts.
  3. Dust: used direct from packet and is easy to apply. Only contact types available and may leave an unsightly deposit on the plant.
  4. Ready to use sprays and pump guns: no need to measure concentrate out so quick and simple to use. Expensive and only suitable for treatment of small areas.
  5. Pellets: in measured doses so easy to apply correct quantity. May be eaten by pets, children or wildlife. Can become less active after rain.
  6. Aerosols: quick and simple to use. propellant may be flammable, may prove phytotoxic to plants and is expensive.

The most important thing to remember when using pesticides is READ THE LABEL and then follow the instructions to the letter.

Here’s a link to the RHS advice on pesticides and understanding the labels.


Pests and diseases part 6

The next weapon in the organic gardener’s chemical free arsenal against pests and diseases is a physical one. Specifically traps and barriers. At a more basic level physical pest control can simply mean removing the pests by hand. In some cases this can be very sucessful but on a large plot or smallholding isn’t really practical. Traps and barriers work in a number of ways; they can prevent pests reaching your crop, draw them to a more tempting location, some eliminate the pest and others are used to give an indication of when other controls e.g. biological controls might be most effective.

Grease bands are essentially a sticky barrier applied to the trunks of fruit trees to trap winter moths and other related species that have wingless females. Grease bands can also deter earwigs, ants and adult vine weevils. Grease bands can be applied to containers as well as trees. It is also possible to smear grease on the stems of some plants e.g. chrysanthemums and dahlias to stop earwigs climbing up into flowers. Pests such as flea beetles can also be made to jump onto a piece of wood or card covered in grease and drawn grease side down along the top of plants. If the plants are agitated by hand or a stick the flea beetles are disturbed and so jump onto the greased card trap.

Sticky traps are also useful in greenhouses. It’s best to use yellow plastic strips covered in a non drying glue. The traps are hung above the plants and will catch any flying insects. Whilst these traps alone may not control an infestation they provide an early warning system, allowing the gardener to implement other measures such as biological controls before the infestation becomes unmanageable.

Grapefruit and beer traps are useful in the never ending battle against slugs and snails. Hollowed out grapefruit halves can be propped up on stones on the ground in flower beds. The slugs and snails are attracted by the smell, crawl in and stay there. In the morning you can simply remove the grapefruit complete with slugs and snails. A jar half full of beer or milk, almost buried in the ground will also attract slugs and snails which fall in and drown. The addition of porridge oats makes it an even more effective bait.

Earwigs can be trapped by using an inverted flower pot filled with dry grass and placed over a cane among susceptible plants. Earwigs feed at night and will crawl into the trap to shelter from the daylight. Once they have crawled in you can remove the pot complete with earwigs.

Damage from wireworms can be limited by fixing a potato on a stick and burying it. Wireworms prefer potato over plant roots so will preferentially inhabit the potato which can be regularly removed and replaced.   

Pheromone traps use synthetic pheromones of a pest species such as the codling moth to attract male moths into a trap where they are caught on sticky paper. The main purpose of such traps is to record the moth’s main flight and egg laying period accurately so that, if necessary, insecticides can be applied at the appropriate time to control the newly hatched larvae. On an isolated apple or plum tree however the pheromone trap may catch sufficient male moths to limit the mating success of females and so limit the number of fertile eggs produced.

Barriers in the garden can come in a variety of sizes. Fruit cages are one of the largest barriers you can use and will protect your soft fruits from a variety of pests including birds.  On a smaller scale cloches can be used to protect individual plants and can be easily made from lemonade bottles cut in half. Horticultural fleece also provide a relatively inexpensive and flexible barrier method of pest protection as well as protecting against frost.

In the greenhouse putting legs of tables or staging in saucers or pots of water will stop insects climbing up the legs of the table or staging and prevent them reaching your plants. 

Brassica collars can be purchased ready made or you can make your own from carpet, underlay or cardboard. The collar is essentially a circular piece of appropriate material with a cut in it so it can be place around the young plant. The collar lies flat on the soil and prevents the female cabbage root fly from laying its eggs in the soil. instead the eggs are laid on the collar where they will dry up before hatching.

Copper tape is also said to make a useful barrier against slugs and snails when wrapped around containers or raised beds. However, this is relatively expensive compared with the cheap and effective beer/ milk trap described above.