Karragullen's tree doctor

Karragullen horticulturalist Chris Oliver is an expert when it comes to reviving old, diseased or damaged fruit trees.

"My philosophy is if you can keep a tree healthy, then you are strengthening it to be able to resist a pest and disease attack," he said.

"The healthier the tree, the more environmental resistance it has. It's virtually like our bodies, if we become weak and tired we are prone to all sorts of problems."

Plying his trade in the Perth Hills under the banner Wilburnia Fruit and Flowers, Chris said every case of fruit tree regeneration was unique.

"You have to size up the ecosystem first, and every tree presents a new challenge. You need to know the history of the tree before you can develop a plan," he said.

"Each stage that you go through, from pruning deadwood to fertilising and watering, needs to be monitored carefully so that you can see the response."

When developing a rejuvenation plan, Chris draws on knowledge gained personally as a grower and from his long career at TAFE as a horticultural lecturer.

He keeps abreast of new technologies and believes in a combined organic and inorganic approach when it comes to growing fruit trees.

"It's a thrill to see how trees respond and having the knowledge that you can do the job," he said.

"I miss communicating that to students."

Each regeneration project starts with a site analysis.

The horticulturalist takes into account a tree's health and surrounds, soil health, environmental conditions and water supply.

Work then begins on bringing the tree back to good health using a step-by-step approach.

"When trees are under stress, things go wrong and they get pests and diseases far easier," he said.

Speaking from experience, Chris has been regenerating two Bedford cherry trees in his orchard, which is home to a range of stone fruit varieties, pomme fruit, citrus and four varieties of nuts.

Chris said canker (Pseudomonas syringae), a bacterial airborne disease that causes limb dieback, had set into the cherry trees several years ago after a severe water shortage.

"They are an old variety of cherry. They used to produce about 22kg of fruit a year, which was quite a big yield," he said.

While several of the cherry trees have already died, Chris still has hope for the remaining two trees.

Site analysis

When he established his orchard almost 30 years ago, Chris faced the challenges of laterite outcrops, nutritionally deficient soil and a diminishing water supply.

"When I set my orchard up, I meant it to be a demonstration of what can grow in this area. We had to windrow the soil, because the laterite outcrops were close to the surface and they minimise soil depth for growing fruit trees," he said.

"The gravelly soil is also poor on organic matter.

"For years I have been building up the soil mainly using composted brewery sludge, together with animal manures.

"It's fantastic as a mulch and it's marvellous at holding nutrients."

Remnants of the natural fertiliser are scattered around the bases of the fruit trees, but it has been difficult to source of late.

"I used to get it from the old Swan Brewery," he said.

"When it came off the truck it was a solid mass of half-set jelly, and you had to spread it out to dry until it was granular in form.

"My water use reduced from every day to twice a week after using the sludge."

Water is a major problem in the area. Chris uses bore water but said supply was intermittent and he bought in water over summer.

"It's just one of the things with change of climate that you have to deal with," he said.

Back to life

With canker spreading rapidly from branch to branch in his Bedford cherries, Chris said it was important to remove signs of the disease by pruning away the deadwood.

"It's the initial stage of getting them back to new life," he said.

"If they are weak, the main thing is to not depend on cutting it back to a growing bud, which you normally do in pruning, but to cut it back to a living shoot.

"I generally do that prior to winter so I can see where the deadwood is."

Now that winter has arrived, Chris said his next task would be to selectively and lightly prune the trees. The amount of material to remove depends on the type of fruit and the condition of the tree.

"You have to be very careful as to how much you prune back," he said.

"The main reason is you want as much leaf area as possible for photosynthesis, which will help to build up the root system."

Chris said he would apply a rapid release, NPK, plus trace elements fertiliser in spring, just before bud burst to give the trees a boost.

"The main thing is you have to be astute in where you apply the fertiliser. It has to be around the drip line, which should be 300mm to 400mm from the base of the trunk," he said.

"I aim to get the nutrients taken up as quickly as possible in that burst of new growth, and then as the rains diminish I put on a light mulch."

Chris uses leafy tree clippings for mulch, applied about 300mm from the base of the trunk to about 300mm outside the drip-line.

He builds the mulch up to a thickness of about 80mm. He spreads cow manure under the mulch, which helps to hold in the nutrients.

At the end of summer, Chris applies a balanced fertiliser such as NPK Red.

He uses a testing kit to take random soil samples from around the tree to work out average pH.

"I monitor the soil once a month," Chris said.

"Too alkaline and I will need to balance the soil with an acidifier like ammonium sulphate.

"If it's too acidic, I add limestone calcium carbonate."

While there is no quick fix for diseases such as canker, he believes he has found the formula for regeneration success.

With perseverance and careful monitoring, Chris hopes to change the fate of not only his Bedford cherries but countless other fruit trees in the Perth Hills.

For more information on reviving old fruit trees, email wilburn1@bigpond.net.au.