New Zealand's major lawn and pasture pests, native grassgrubs (Costelytra zealandica), decided on a change of diet and moved from chewing grass roots in our lawn to chomping shallow grooves in oka tubers that grew fairly close to the soil surface.
The offspring of a velvety-brown flying insect, grassgrubs are pale grey or cream and are recognisable by their tendency to curl in a C shape.
The adults emerge in spring and a female can lay 40 eggs.
In lawns, toxic chemicals are commonly used to treat grassgrub - and porina caterpillars, which do similar damage - but are not recommended for areas where food crops are to be grown.
Neem tree granules can be used safely but because grassgrubs live in the top 15cm of soil, deeper planting of oka may be all that is needed, with a bit of pest-control help from starlings and blackbirds.
When a member of the Dunedin Vegetable Growers Club recently said he thought damage to his Jerusalem artichokes was caused by wireworm, I was sceptical, as I had never heard of wireworm in artichoke tubers.
Wireworms are the larvae of an Australian click beetle (Conoderus exsul), named because when the beetle lands on its back, it can use a click mechanism between the two parts of the shell to jump up and right itself with a click sound.
Wireworms are well known for the damage they cause burrowing into potatoes. Because they tunnel through the soil, they are less likely to be found in fine, well-cultivated ground, where tunnels will collapse.
They can also be deterred by mulching potatoes with loose material such as spent oats or hops, or by sowing mustard as a green-manure crop and digging it in before planting the potatoes.
Mustard can have a drawback. It is a member of the brassica family, which includes turnips, swedes, cabbages, cauliflowers and broccoli.
All these food crops can be affected by clubroot, caused by a minute parasite that creates deformed roots unable to supply nourishment, resulting in stunted plants.
As the roots break down, they leave clubroot spores in the soil and these are almost impossible to eradicate.
Other suggested control methods are liming soil to bring the pH above 7, or applying boron and calcium cyanamide, the latter breaking down in soil to calcium oxide (lime) and urea.
To eliminate the risk of introducing clubroot on plants brought into a "clean" vegetable garden, growing brassicas from seed is recommended.
Imported pests such as wireworm and clubroot have been found in New Zealand gardens for more than 150 years but some are more recent migrants, such as the American gooseberry mildew disease. It arrived here in 1984, probably on rhododendrons.
Except in a few places, such as parts of Central Otago where rhododendrons will not grow, gooseberry mildew attacks older varieties, and the only solution seems to be replacing them with mildew-resistant Pax and Invicta.
Also new on the scene is another import we would rather not have, the lettuce aphid (Nasonovia ribisnigri), first found in a market garden near Christchurch in 2002. Its hosts also include currant and gooseberry bushes.
Because the green or orange aphids usually feed at the centre of the lettuce, it is difficult to control except with heavy applications of chemicals.
However, a range of lettuces have been bred using a wild European variety naturally resistant to the pest.
Bug Off is one widely used by commercial growers, while others are Green Frill, Red Frill, Green Butterhead, Green Oakleaf, Red Oakleaf and Cos.
Pests and diseases have probably been in the garden since Eve had that ill-fated conversation with the snake, but keeping ground well worked and well fed, and not growing members of the same vege family in the same spot two years running, can help reduce the bugs.
