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When humanity domesticated edible wild plants and improved their performance through breeding, the plants also became more attractive to pests and diseases.
To deal with these problems, a number of the cultural tools developed from experience in those early days have stood the test of time and been proven by modern science. But there are also old techniques still used, based solely on belief or philosophy that have very little or no effect.
As an advocate of sustainable best practice, I think we should use every science-proven technique that is practical to achieve the best result in our home orchard.
MARTIN DE RUYTER/STUFF
Bill Brett is the author of Garden Pest & Disease Control and The Home Orchard. A lifelong gardener and working in the garden industry, Bill was recently awarded Associate of Honour Royal NZ Institute of Horticulture.
Fruit tree pest and disease prevention
I use the word prevention because preferably the problems should be avoided or minimised. Use the following science-proven prevention practices.
Select a warm, sunny location
An airy and well-ventilated spot allows plants to thrive.
Develop free-draining soil
Add lots of compost and raising the planting area. This reduces risk of soil fungal diseases – phytophthora, alternaria, fusarium, rhizoctonia, sclerotinia and verticillium being the most common ones.
READ MORE:
* Compost and mulch saved my garden from the heat and rain
* Grow great citrus organically with science on your side
* A scientist makes the case for farming and gardening organically
Select disease-resistant varieties
This is especially important for apples and stone fruit.
Ensure trees are well fed
Apply an annual dressing of lime. Apply a compound NPK fertiliser such as Tui Novatec Premium, Nitrophoska, or a citrus and fruit tree NPK mix where the potassium (P) level is as high as nitrogen (N) or close to it.
A fertiliser with high potassium content encourages flowering and fruit development, and in addition ensures hardened leaves which are less likely to suffer disease attack. Apply in September and March.
123RF
Some 15 cultivars of apple have a high level of resistance to black spot and mildew. Most of these are the new varieties which also have good taste and reliable yield. These include ‘Blush Babe’ (early season), ‘Adore’ (mid-season) and ‘Baujade’ (late season).
Avoid overhead watering
Weeper soak hoses or irrigation drippers are best. Regular watering of foliage increases humidity around plants which provides perfect conditions for fungal diseases.
Practice good garden hygiene
Remove and destroy diseased leaves immediately when they appear. Presence of spots, rusts and mildews indicate the presence of spores of disease which are spread rapidly especially by wind, but also by water and physically through handling.
Removal of diseased leaves from plant and soil surface removes the source of infection. In the case of powdery mildew, where this could mean removal of all leaves, an alternative is to use a spray which kills the spores.
The options are Grosafe Enspray 99 oil (which also kills sucking insects present) or OCP Eco Fungicide – potassium bicarbonate. These products simply kill the spores and do not offer ongoing protection, which means repeat treatment is required.
SALLY TAGG/NZ GARDENER/Stuff
These raised vegetables beds in Waiheke gardener Robyn Toomath’s garden were built to a convenient height for harvesting and maintenance.
Prune to ensure good air flow through the trees
Some older gardeners say a bird should be able to fly through the tree. This is largely true and for two different reasons: Sun needs to penetrate the tree to initiate flowering, fruit set and ripening. Sun and air also need to penetrate the tree to ensure conditions where pests and diseases are less likely to develop.
It is worth noting that if the tree is open, it is easier to obtain full spray coverage if a pesticide is to be used. Many backyard citrus trees become too dense because they get trimmed to size like a hedge but in addition, they need to be thinned to allow good ventilation or sucking insects like whitefly, aphids, thrips, mealy bug and scale thrive.
Remove alternate host plants to pests and diseases
These include any plant that is also a favoured host to pests or diseases that also attack your selected fruit trees. They could be vegetable crops, ornamental shrubs or perennials, or even weeds. Some companion planting theories add alternate hosts, resulting in increased insect pressure – not less. Apart from growing host plants to beneficial predators, companion planting offers no benefits in insect control.
Harnessing nature’s beneficial organisms
In practice, in most cases this reduction is not enough because the high numbers of the predator required can’t be achieved (though it is successful in enclosed spaces such as greenhouses). Moderate success is sometimes achieved in a favourable year, in areas of a hectare or more. Fortunately, most home garden insecticides are soft on bees and beneficial insects, which helps foster beneficial organisms.
BotryZen is a non-pathogenic fungal culture sprayed on during and immediately after flowering colonises the area, and prevents the development of the brown rot disease in stone fruit and grapes. It is an organic alternative to Fungus Fighter. Results with BotryZen are more reliable if temperatures are moderate to warm following application during flowering.
When pests or diseases attack
Identify the problem
Then learn more about the life cycle, temperature or humidity level, method of spread, alternate hosts, best prevention and control tools.
Take prompt action
Early intervention provides the best control, especially if a pesticide is required. For most insect pests, there is an optimum time in the life cycle to apply an insecticide. This is usually early in the life cycle – eggs, nymphs or first instar for caterpillars. If the first two generations are controlled, the problem is minimised.
It also means that there is no need to apply insecticides in the last six to 10 weeks before harvest, resulting in no pesticide residues.
With several fungal diseases, especially the notorious brown rot of stone fruit, the infection occurs during flowering or immediately after, which is three to five months before the brown rot becomes visible. Hence control treatments must be applied during flowering, whether it be a fungicide such as Yates Fungus Fighter, or an organic treatment using BotryZen.
NZ GARDENER/Stuff
Good garden hygiene can help mitigate the worst effects of pests, such as guava moth larvae damage in a feijoa.
Use the correct pesticide
For food crops, it is important to select a pesticide that is registered under the Agricultural Compounds and Veterinary Medicine (ACVM) Act and approved for use on the crop and purpose.
There are, in fact, a number of BioGro-certified organic products that are not registered and not approved for use on food crops.
It is important to remember that organic does not automatically mean safe or free of natural toxins.
BioGro-certified organic simply means free of synthetic chemicals. Again, organic is not always safe and synthetic is not always toxic.
The most cost-effective, eco-friendly, sustainable, low toxicity pesticides recommended are:
- Enspray 99 or similar spraying oil – for control of sucking insects such as aphids, thrips, white fly, mealy bug and scale.
- BioNeem, *Eco-Neem or Naturally Neem – most effective when used in mixture with an oil as above for sucking insects. (Other brands of neem are not registered or approved for edibles.)
- Yates Success Ultra – for control of chewing insects such as codling moth and leaf roller as well as adult beetles and weevils.
- Copper spray for autumn, winter, early spring protection from fungal diseases on deciduous trees and year-round for citrus. *Free Flo Copper (copper hydroxide) is the preferred form of copper, but liquid coppers are also satisfactory in many cases.
- Yates Fungus Fighter – A systemic fungicide for black spot, powdery mildew, rust and brown rot on pip and stone fruit.
- BotryZen – An organic alternative to Fungus Fighter above for brown rot.
Products with an asterisk are BioGro-certified organic. Success Ultra is an extract from a natural soil bacteria but not certified organic. Fungus Fighter is the only synthetic chemical product, very effective and of low toxicity. No home garden pesticides are poisons or carcinogens.
BRADEN FASTIER / STUFF/Nelson Mail
No home garden pesticides are poisons or carcinogens, says Bill Brett.
Integrated pest management (IPM)
To achieve the most effective control, in the most sustainable eco-friendly manner at the lowest cost, use as many of the methods described above as are applicable to the crops and cultivars you are growing in your own garden or orchard.
Each of the prevention methods above, used alone, will only make a small difference, but used collectively, they have a big impact.
Timely, judicious use of recommended pesticides should be included in the programme – not used as a last resort to recover from an onslaught.
Pip and stone fruit require a programme of methods and pesticides to prevent diseases and insect damage. Citrus that are uncared for often have a build-up of multiple sucking insects causing severe damage, reduced yields or dry fruit, which will take several pesticide treatments to bring under control. A mineral oil mixed with an approved neem, applied three or four times a year will prevent build-up of aphids, thrips, whitefly, mealy bug and scale, keeping trees healthy.
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