Ask our ex­perts


NZ Gardener - - Contents -

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?


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, 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?


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?


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

Newspapers in English

Newspapers from New Zealand

© PressReader. All rights reserved.