CROP PROTECTION

PESTS AND DISEASES

Plants may suffer all sorts of indignities. Pests diseases,

nutritional disorders, physiological problems like cold,

competition for space with other crop plants and weeds.

Large birds may pull them up – peas and crows;

Small animals may eat them – broad beans and mice;

Adult insects may devour them – Colorado beetle – potato;

Insect larvae may devour them – Colorado beetle – potato.

All living organisms have a life cycle. Usually there is a weak point somewhere within it, where the grower can influence the pest population numbers. There is no absolute need to use only chemical pesticides or only biological methods for control; so far as written answers go, well-presented arguments from either camp could score full marks. For the present, however, biological control methods do not provide a complete answer to all pest-related difficulties.

There are some ways of avoiding use of pesticides where biological control is not effective, including the acceptance of lower crop yields and/or quality, or even giving up that particular crop altogether, but these-may not be viable choices in a society needing that crop.

The bulk of biological control methods consist of:-

Rotational techniques – to starve out a life cycle stage.

Cultiyational and

cultural regimes – to bury the pests or starve them

out via varietal selection, sowing dates/harvesting dates.

Physical systems – Heat/cold/electrical deaths for

the organism concerned.

Hence the Colorado beetle is such a serious pest (insect pupae and eggs are rarely a problem in themselves, as they do not specifically damage the crop. The presence of insects in a salad or a tin of vegetables, however, would be unacceptable to many – hence their control is desirable. There are other non-insect pests such as slugs and snails, woodlice and millipedes, red spider mite and eelworm).

Biological systems

Predation by natural and imported beneficial insects, fungi or bacteria.

Control of bacteria can be aided by some pesticides (all garden chemicals other than fertilisers would properly be defined as pesticides under the latest Food and Environmental Protection Act) but bacterial problems tend to be difficult to control, e.g. bacterial canker of cherry.

The methods of applying a pesticide vary – one of the most economical (and environmentally kind) is:-

A seed dressing

usually a dust which clings to the roughness of the seed coat.

A dust

less environmentally sound, but dusts are useful – they will stick to onions, for instance, when coated with dew -few other treatments do as well.

A wettable powder

mixed with water and applied as a protective spray.

Liquid formulations

these are easy to mix with water and are helpful in that wetting the plant thoroughly is relatively easy. A wetting agent may be incorporated to enable it to be spread more effectively.

Granules

may be placed at the base of the plant, for example, to reduce the successful egg hatch and establishment of, for instance, cabbage root fly larvae.

Gas (and atomisable

fluids) – penetrate all parts of a building or

store – very helpful in the case of some pests and diseases under glass.

Extracts from plants have shown remarkable properties including the natural control of some disease organisms and some pests. Studies of these naturally occurring organic compounds have enabled the laboratory synthesis of very closely related compounds – available as Benomyl and Permethrin.

Plant breeders are working to reduce plant problems by breeding-in resistance to:-

Weather damage e.g. Petunia Resisto hybrids. Eelworm attack e.g. the potato ‘Pentland Javelin’. Tomato leafmould e.g. the tomato beefsteak variety Dombito’.

In the longer term, plant breeders will contribute enormously to the economics of agriculture by reducing the need for pesticides (and fertilisers).

Good cultural management, together with careful soil husbandry – ample soil depth, good humus levels, and good drainage – help crops to grow well without the need for extra irrigation and without the stress caused by low soil nutrient levels. Sufficient shelter and environmental care also help plants to thrive, and in healthy crops, most pests and diseases remain at a manageable level without necessitating the massive overkill attendant upon a full pesticide regime.

Note: Cabbage root fly, carrot fly, onion fly, and celery fly obviously can arrive in the garden from elsewhere, but clearly if large numbers of them are already breeding at home, the problem is likely to escalate.

WEEDS

Different tillages aid the containment of weeds. For example, in an overwintering crop of leeks or spring cabbage, chickweed and annual meadow grass could become a nuisance, whereas a good digging or ploughing after potatoes would reduce this potential problem to very small proportions. Similarly, an organic gardener using an overwintering catch green manure crop of winter tares or rye would find that competition from the tares would control weeds. An additional benefit of this system is the reduction in the leaching of nutrients by winter rains.

CROP LIST

THE BRASSICA FAMILY

1. Brussels sprouts

2. Cabbage

3. Cauliflower

4. Broccoli

5. Calabrese

THE LEGUMES

6. Broad Bean

7. French Bean

8. Runner Bean

9. Peas

THE ALLIUMS

10. Onion

11. Leek

ROOT CROPS

12. Beetroot

13. Carrot

14. Parsnip

15. Swede/turnip

16. Potato

SALAD CROP

17. Celery

18. Lettuce

19. Tomato

20. Cucumber

21. Radish

22. Salad onions

23. Celeriac

OTHERS

24. Marrow and courgettes

25. Sweetcorn

26. Herbs

THE BRASSICA FAMILY (All members may be attacked by the same pests and diseases)

The family includes:

1. Brussels sprout

2. Cabbages

3. Cauliflower

4. Calabrese

5. Broccoli

The Cruciferae also include swedes, turnips, radish, Chinese cabbage, sea kale, kale and cress.

Soil Requirements for Brassicas

Brassicas benefit from a fertile soil, so they should follow legumes in rotation. They need an alkaline soil, so check the pH in autumn and apply lime if it is below 6.5. Leafy brassicas may need frequent watering in dry spells. Brassicas are greedy feeders, and may benefit from generous fertiliser applications. However, high levels of nitrogen can seriously inhibit germination.

Transplanting Technique for Brassicas

Planting into a ‘drill’ aids establishment – deeper, moister soil, less wind drying -a microclimate.

Plant firmly, firming the soil against the roots (not just firming the roots – which may break them)

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