Vegetables: Pest & Disease Control

A guide to controlling pests and disease in Vegetable Gardens

Pest & 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 article 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 & 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. 

Using Pesticides 

If good gardening practices are followed and disease resistant varieties used, use of pesticides can be minimised. There are 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. 

Prevention is better than cure. Once you have gained experience and are aware of what pests/diseases attack which crops, you will be able to anticipate and spray at the first sign, which is more effective and minimises the overall use of pesticides. 

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. This is the only environmentally friendly slug and snail killer on the market. 

• Insects - 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 – Blights, spots, mildews, rots. Yates Liquid Copper is an environmentally friendly fungicide. Yates Fungus Fighter is very effective and registered for control of all diseases commonly found on vegetables 

Withholding Periods 

The NZ Food Safety Authority have 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. Most home garden pesticides have withholding periods of 3 to 14 days. Always check the label.