Cultural control
Cultural control involves changing the environment to make it undesirable for pests and diseases.
The main forms of culture control are:
- quarantine to prevent pests and diseases coming into New Zealand
- crop rotation
- using resistant plant varieties
- good management and work practices.
Quarantine in New Zealand
New Zealand’s isolation from other countries is an advantage. This means we are separated from many pests and diseases. New Zealand has very strict border control and quarantine rules preventing any plant material including seeds, fruit, and flowers coming into our country. Any plant material must be declared to Biosecurity New Zealand. Clearance and documentation is required before the material can enter the country.
This precaution helps stop the introduction of pests and diseases that could affect our commercial crops such as berry fruit, citrus, grapes, pipfruit and kiwifruit. It also helps us when we market and sell our produce overseas, because New Zealand has a reputation for being free of pests and diseases.
Growers should not bring infected plants onto their properties. Any plant material that they are unsure about should be quarantined and kept separate from other plants. The plants should be carefully inspected and only introduced when the grower is sure they are pest and disease-free.
Plant material must be declared at New Zealand’s borders.New Zealand has strict border controls. Plant material like fruit, flowers and seeds cannot come into the country without being declared to quarantine officials.
Crop rotation
Some families of plants are infected by the same pests and diseases.
If similar crops are planted in the same soil year after year, it is possible that pests and diseases will increase. Crop rotation is planned planting that makes sure the same crop is not planted in the same place again and again. This reduces pest and disease build-up. Rotating the crop breaks the life cycle of the organisms and prevents their numbers building up.
For example, if cabbage, Brussels sprouts and cauliflower (all members of the brassica family) are grown year after year the disease club root can develop. Club root attacks the roots and plant growth is stunted.
These carrots’ growth was stunted.Carrot rust fly builds up in the soil when carrots are grown in the same piece of land repeatedly.
Crop rotation groups similar crops together:
- leaf crops such as cabbage, cauliflower, broccoli, Brussels sprouts, turnips
- root crops such as carrots, parsnips, beetroot, radish
- legumes and other plants such as beans, peas, green manures (including lupins and oats), potatoes, celery, leeks.
Rotating crops is advantageous to the soil.These plants can then be used in a crop rotation as shown in the graphic.
Crop rotation helps maintain balanced nutrient levels in the soil.
Different crops have different nutrient needs. When crops are changed from year to year, nutrient shortages will be reduced.
Legumes supply nitrogen, which is needed in large amounts by leaf crops. Root crops need more phosphorus and less nitrogen than leaf crops.
Resistant plants
Plants that grow despite the presence of pests and diseases are called resistant plants.
Resistance happens when plants contain chemicals that make them inedible to pests, and stop the spread of disease.
Resistance can occur naturally, however scientists continue to try to identify individual plants that show resistance to certain pests or diseases. These are then used to breed from.
Examples are:
- there is a breeding programme involving crab apples to develop black spot resistance
- tobacco mosaic virus (TMV) causes plants to grow weakly and have pale and mottled leaves. Tobacco mosaic virus (TMV) resistant tomato plants are available
- ‘supertom’ tomato rootstock resists a number of diseases in the soil. The rootstock is known as KVFN because it resists corky root (K), verticillium wilt (V), fusarium wilt (F), and all soil-borne fungi and root knot nematodes (N).
The following diagrams show how a chosen tomato variety is grafted on to the resistant rootstock.
Chosen variety grown on the resistant rootstock.
Good management and work practices
Growers use the following practices to prevent and control pest and diseases.
Remove and dispose of infected areas.- Cut off infected areas of plant material and fruit, and burn them or take them to the rubbish dump.
Spray for pests or diseases.- Spray crops to protect them or to control a pest or disease outbreak.
Keep tools clean.- Keep tools and containers clean so infections are not spread.
Train plants to maximise air circulation.- Train, prune and space plants so air can circulate. Good air circulation lowers the humidity levels. Fungi and bacteria spread faster from plant to plant where humidity levels are high.
- The structure shown is called an espalier.
Keep greenhouse humidity and temperatures at suitable levels.- Keep greenhouse humidity and temperatures at suitable levels so fungal infections don’t develop.
- Good ventilation is important.
Ensure suitable drainage.- Make sure soil is well-drained to help stop the growth of soil-borne plant diseases that attack plant roots.
Prune plants of diseased and damaged material.- Prevent injury to plants by making pruning cuts clean and providing windbreaks to prevent damage to stems or branches.
Remove weeds.- Remove weeds by the crop that pests and diseases can live on.
Cultivation can damage the pests and also brings them to the surface to dry out or be eaten by birds. Cultivating under plants like apples can reduce the incidence of pests such as the larvae of apple leaf midge.
Grass grub can be destroyed when the soil is cultivated in spring.
Key points
- Cultural control involves changing the environment where the pest or disease lives.
- Some common methods of cultural control include crop rotation, cultivation pruning, removing weeds, and changing the climate.
What's next?
Go to: 6 Chemical control.