Pest and Disease Control in Vegetables
The organic gardening philosophy is to let nature take its course, for all organisms to live in balance and therefore accept a level of pest and disease damage. However most gardeners want to harvest good crops relatively free of pests and diseases, grown in a safe environmentally sustainable manner.
This page guides the home gardener to methods of pest and disease control that best suits their needs taking into account:
- Good yields, relatively free of pests and diseases
- Using best garden practices to minimise pests and diseases
- Using only safe environmentally friendly products
- Using products that are commonly available in home garden size packs and are legally registered for the purpose stated.
Minimising Pest and Diseases
Using good basic gardening practices to minimise pests and diseases is common to all gardeners whether conventional or organic. In simple terms - providing the best growing conditions to ensure a strong healthy crop.
The following are the simple basics:
- Raise the vegetable planting area above the surrounding soil to ensure good drainage.
- Add lots of compost and work into the soil.
- Rotate crops - do not grow the same crop species in the same area for more than two years in a row. Grow different crops for two years before returning to the original crop.
- If space allows, rest (fallow) say one third of the vegetable garden each year by planting a ‘green crop’ such as lupins, mustard, oats, barley. This can either be cut and left to breakdown or dug into the soil.
- Provide adequate balanced feeding - sheep manure pellets or a general garden fertiliser.
- Water in dry periods.
- Practice good garden hygiene by removing all diseased leaves and plants.
Using Disease Resistant Varieties
Whilst a few ‘Heritage’ varieties may have disease resistance, modern hybrids are far more likely to be better.
Using disease resistant varieties will ensure better crops, greatly minimising the need to use fungicides. Modern hybrids are also likely to yield more and taste better. This is especially true of tomatoes.
Using Biological Controls
Biological control involves using another living organism to attack the bad one. This is becoming common with commercial growers, but these organisms are not available to home gardeners.
What can be done however is to endeavour to use only pesticides that are soft on desirable insects such as bees, ladybirds and predator mites.
If good gardening practices are followed and disease resistant varieties used, use of pesticides can be minimised. There is a range of very low toxicity, environmentally friendly pesticides available to home gardeners.
Also be aware that some pesticides are toxic - both chemical and natural organic. Being natural organic doesn’t necessarily make it safe. Consult the Vegetable Pest & Disease chart to assist in your choice. It lists options are accurate and comply with legal / registration requirements.
Prevention is better than cure. Once you have gained experience and are aware of what pests / disease attack which crops, you will be able to anticipate, and spray at the first sign, which is more effective and minimises pesticide use.
Download Pesticide Guides and Spray Schedules
What to Use
Birds and Animals
The only effective measure is to cover with netting. Cloches are effective for protecting newly sown seeds from cats digging them up.
Slugs and Snails
Tui ‘Quash’ slug pellets contain sequestered iron which is safe to pets, and breaks down into fertiliser. The most environmentally friendly.
Yates Blitzem pellets and some other brands contain the chemical metaldehdye which is toxic to pets but contains a repellent. It is fast acting low cost, and lasts a few days to a week.
Yates ‘Baysol’ pellets contain the most persistent chemical, are slower acting, but one application lasts four weeks, and is effective even in wet weather.
Yates 'Mavrik' is a very environmentally friendly product being very soft on bees and ladybirds. It controls all insects commonly found on vegetables and is registered for use on all vegetables.
For control of insects close to harvest use Yates Pyrethrum as it only has a 1 day waiting time between spraying and harvest.
Diseases - blight, spots, mildews, rots
Yates Fungus Fighter is an environmentally friendly fungicide made from a mix of a protectant and curative type, to avoid resistance build up.
Fungus Fighter is very effective and registered for control of all diseases commonly found on vegetables.
The NZ Food Safety Authority has set withholding periods for each pesticide, and particular crop. The withholding period is the period that must elapse between spraying and harvesting, and is on the label of each product.
Withholding periods have been set after rigorous testing to ensure pesticide residues have decayed to barely detectable levels well below any risk to people or the environment.
Most home garden pesticides have withholding periods of 3 to 14 days. Always check the label.
If it is necessary to spray close to or during harvest use Pyrethrum for insects and Natures way Fungus spray for diseases.