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YOUR GARDENING QUESTIONS THIS MONTH

Your questions answered

Q RUSTY CARROTS Our carrots suffer badly from carrot rust fly damage. We have tried diazinon granules to no avail. We now plan to cover them with a clear plastic cloth with holes for the rain. I’ve heard about putting Condy’s crystals in the trench under the seeds. Where can I get them? Is there any other solution?

HELEN BISLEY, MOTUEKA

APulling up a carrot and discovering the nasty excrement-filled tunnels left behind by carrot rust fly larvae can be a nasty surprise as there may be no sign of damage above ground. The black adult flies are about 4-8mm long with iridescent wings. They lay their tiny eggs in the soil next to carrots and other related host plants such as parsnips and celery, which they find by smell. When the eggs hatch a week or so later the larvae burrow into the carrot root. Safe inside the root they munch away for 4-6 weeks before pupating in the soil for a month in summer or over winter. Products containing diazinon granules are no longer sold for home garden use and are banned altogether in some countries. They can still be used in some conditions by licensed operators but are being phased out.

That is because diazinon is an organophosphate that is toxic to people, insects, birds, fish and more.

Condy’s crystals (potassium permanganate) can be found on Trade Me and in garden centres. Dissolved in water as directed it is a mild antiseptic that can be used as you describe.

But I suggest a better solution is horticultural mesh (from garden centres and by mail order from the Biological Husbandry Unit, bhu.org. nz) which prevents flies laying eggs near your carrots. The mesh also protects other crops from psyllids, green shield beetles, cabbage butterflies, birds and wasps. Mesh must be placed over crops before pests arrive and anchored in place carefully as pests will find the tiniest hole.

Other tactics include planting carrots in high raised beds or putting windbreak barriers around the beds as the flies don’t fly higher than 45cm above ground level.

Rotate your crops. Sow seed thinly to cut down on thinning (the smell of leaves crushed during thinning could attract egg laying adults). Onions and garlic planted nearby may disguise the smell of carrots too.

Cover up the carrot “shoulders” with mulch to prevent egg laying. Dispose of infected plant material in the rubbish – not the compost.

Barbara Smith

QON THE MOVE I planted a vireya in the wrong place. It’s now about two feet tall and very healthy with lots of new growth. Will it be safe to move it and if so, how do I go about it?

KAREN EAGLES, TARANAKI

AVireya grower David Brown from Versatile Vireyas in Tauranga suggests removing all the new growth especially if it’s soft. This will save putting too much stress on the damaged root system.

Water the vireya well the day before you move it. Prepare the new site before you dig the plant up.

Dig as large a root ball in diameter as you can practically manage using a sharp spade. The root ball will tend to be shallow and fibrous. Avoid disturbing the roots.

Choose a sunny, frost-free spot with excellent drainage. Vireyas flower better and bushes are more compact where there is plenty of light but they also grow in partial, dappled shade.

Plant the vireya into the new site at the same soil level as last site. Place soil back around the root ball and firm in gently with your hands and not your feet. Mulch with bark.

Water well. If it gets hot and sunny, place a piece of shade cloth over the top of the plant for a couple of weeks and mist occasionally. Remove the cloth if the weather is wet or cloudy.

In a couple of months’ time, apply slow release fertiliser.

The Versatile Vireya website has more growing tips and an extensive mail order catalogue.

Barbara Smith

QPSYLLID DEFENCE My potatoes were ruined last year. How far south will psyllids reach? How early in the season is control necessary? Are sprays effective? Are protective nets a good option?

PAT PALMER, PREBBLETON

AThe tomato/potato psyllid TTP arrived in the country around 2006 and has been moving southwards ever since. It is a strong flier and is spread by the wind and the movement of plant material. TTP needs a minimum temperature of 7°C to develop but prefers 15.5°C to 32.2°C. It flourishes in greenhouses so potentially could reach everywhere in New Zealand.

Peak populations occur in summer. Monitor their arrival by hanging yellow sticky traps among the leaves so you know when to spray.

Spraying is tricky as TTP tend to fly away. Insecticides that control aphids are likely to control psyllids. MPI reports good results with products containing abamectin and spinosad. Avoid products with pyrethroids and organophosphates which also kill TTP’s natural predators.

If you decide to use horticultural mesh, put it in place when the seedlings are planted. If you put up the mesh later, TTP may be inside already and you’ll have made a sheltered spot for it to wreak havoc.

Research is ongoing. It’s likely that biological control (predation by other insects or parasitoids like those used in Canadian greenhouses) will be the best long-term solution.

Barbara Smith