Pesticides - Do we need them? Are they safe? What does the science say?

Let's start by looking at the recommended science proven practices that prevent or control pests and diseases.

• Add compost and in clay soils raise planting areas to improve drainage and aeration. 

• Rotate crops in the vegetable garden to avoid build-up of soil diseases.

• Feed plants with a balanced NPK fertiliser—ideally with K as high as N

• Ensure spacing or pruning to allow good ventilation. 

• Use soak hoses or drip lines for watering. Avoid using sprinklers if possible. 

• Select disease resistant varieties where possible.  

• Maintain good hygiene, by removing diseased leaves at first sign.

• Remove alternate host plants as much as practicable. The plant world equivalent to ‘social distancing’ or ‘lockdown’.

• Beneficial insects contribute to control, but not to a satisfactory level.  

• If pests or diseases appear, spray at very first sign with a safe pesticide approved for the crop involved. Take time to learn more about each pest and disease—the time and conditions each pest or disease attacks, its life cycle, alternate hosts and pre-empt the attack using the appropriate product for the pest/disease/crop, and spray at this time. 

Pesticides - an overview.

Pesticides of yesteryear were relatively toxic, broad spectrum with some environmental impact. They were so effective gardeners used them as the ‘solution’ to control pests and diseases. Most of today’s garden pesticides are less effective, harmless to people, safe to bees, with very low impact on beneficial insects and the soil. 

This means in order to achieve a satisfactory result we should implement as many of the above practices as possible. Ensure the pesticides selected are effective and use them at the correct time, applied thoroughly.

Sadly, the news media (social media, garden magazines and mainstream media) have demonised pesticides using false information.

Of the approximate 50 garden pesticides available in NZ, 7 are classified ‘harmful substances’ (classification 6.1D, 6.1E) and the remainder are classified as ‘Not Harmful’.

Poisons—classification 6.1C, are banned from sale and use in home gardens and are no longer available. Known carcinogens have always been banned for commercial or home garden use. 

All home garden pesticides are safe to bees once the spray has dried on. Spray early morning or evening when bees are not present.

It should also be remembered that — 

• ‘A substance is not a poison; it is the dose’. 
  Many medicines we take are poisons at higher doses. 

• ‘Synthetic chemical is not always toxic and natural organic is not always safe’  

• A synthetic copy of pyrethrum (Yates Mavrik) is lower toxicity to people, bees and beneficial insects than natural pyrethrum. 

Although more than 80% of garden pesticides are classified ‘Not Harmful’, no gardener wants to use a pesticide more than necessary or if it can be avoided. However, they remain an important tool among several as listed above. Each of these tools on its own is not the answer, but if all are used in unison, the need for pesticide use is significantly reduced. However, the appropriate pesticide used at the correct time remains a very effective tool in controlling garden pests and diseases. 

The law covering pesticides is stricter than that covering foods. For example, if alcohol was  a pesticide it would be banned —it is a known carcinogen and body organ toxicant, killing over 500 New Zealanders every year. Organic vinegar is banned as a weedkiller in concentrate form because it is classified a poison—it can only be sold in diluted ready to use form.

Cost effective, very low toxicity, low environmental impact pesticides that we recommend;

For vegetables  

Grosafe Enspray 99 + Grosafe BioNeem  for aphids, white fly, thrips, mites (also powdery mildew).  Add Yates  Mavrik if chewing insects appear.

Add  Grosafe Free Flo Copper  (copper hydroxide) if diseases appear. These products are all safe to bees once spray has dried. The  Grosafe  products mentioned are all certified organic, approved for use on all edibles and have a nil withholding period. Yates Mavrik is a man-made copy of pyrethrum which is safer and more effective.

For fruits 

Grosafe Enspray 99 + Grosafe BioNeem  for aphids, white fly, thrips, mites (also powdery mildew). Add  Yates Success Ultra  if caterpillars, codling moth, or beetles are a problem.

Alternative products

-Yates Natures Way Natrasoap can be used in place of  Grosafe Enspray 99 but is more expensive.

-Yates Success Ultra can be used on vegetables in place of Yates Mavrik for chewing insects, but we prefer Mavrik because it controls sucking insects at the same time reducing the need for an additional type of product.

Do not use unregistered remedies on edibles —

-Unregistered brands of Neem – Native Neem, Oakdale Neem, Wally’s Super Neem

These brands contain only 25% of the active ingredient compared to others, and they may have unknown levels of a natural toxin.

-Do not use  Diatomaceous Earth, DeBug etc. on edibles. 

We do not recommend  pyrethrum as this is toxic to beneficial insects.

Cost effective, very low toxicity, low environmental impact fungicides that we recommend;

Grosafe Free Flo Copper  as a general fungicide for fruit and vegetable (avoiding copper sensitive plants/periods). It provides superior results compared to copper oxychloride at lower cost, and lower copper footprint. Liquid coppers are effective and low cost, but must be used alone, and have many sensitivities. 

Grosafe Enspray 99 oil is effective in prevention and cure of Powdery Mildew.

For brown rot or botrytis, try Botry-Zen but it is vital it is not used within 2 weeks of a copper spray and fungicides can't be applied after application. It has to be applied at strategic times but it has no withholding period. It is also proving effective against Rust on Garlic when applied from sprout emergence.

Companion planting

Companion planting contributes to making the garden attractive, but based on science, provides little or no benefit to pest and disease control.  

For more information on pests and diseases, pesticides, disease resistant varieties subscribe to Garden Advice Pro (coming soon!) or purchase Garden Pest & Disease Control book click here