ON-AIR QUESTIONS EXPLAINED
GARDENING VIA AM RADIO IS CHALLENGING!
MANY readers of this weekly article may be aware that I’ve recently taken on the Saturday morning Gardening Talkback segment on ABC Southern Queensland (AM 747), usually working on a fortnightly roster with the knowledgeable and effervescent Penny McKinlay.
Answering questions from concerned and enquiring gardeners on-air really tests your mettle and level of recall, but so far I can really say I’ve had an absolute ball being put on the spot with the full gamut of horticultural conundrums that most gardeners encounter in their patch.
I’m happy to be able to provide some solutions for those with reasonably straightforward challenges, but am also comfortable to say that for some I don’t know the answer, and always try to get back to the gardener with an eventual solution.
Because many of the questions relate to common challenges we encounter in most gardens, I thought it might be helpful to revisit some and provide a few solutions as well.
1. Ian rang in and asked about the white flower buds on his rose bush, which were forming, but not opening.
A number of issues may cause this to occur. One common cause is an inconsistent supply of moisture to the plant.
If the unopened buds also turn brown around the edges, this could be as a result of plague thrips, small (about 1mm long) sap-sucking insects that lay their eggs inside the unopened buds.
Being small and hard to see on the bush, shake a flower bud onto white paper – they’ll be easily spotted then.
And Lisa asked about small wasps buzzing around the damaged new shoots of her roses – they were probably Ceranisus wasps, predators of thrips, looking for a meal!
2. Therese called to ask about the unsightly swellings on her citrus tree branches, and how to control them.
They are the result of a small black insect, the citrus gall wasp, laying it’s eggs under the bark, where the larvae feed and pupate, emerging as adult wasps in spring.
Lemons, grapefruit and finger limes are the main targets of these pests. The best thing to do is to prune the affected wood from the plant by the end of August, and mulch the prunings (or place them in a black plastic bag, and leave in direct sun for a couple of weeks).
There are some commercial insecticides that may help control gall wasps, but seem to be only available in larger, quite expensive quantities. There is also a predatory wasp (Megastigmus) that will help control the gall wasp numbers.
3. Leith asked about the “curly” leaves appearing on her newly emerged beans.
It’d be a fair chance that the new growth was being affected by some type of sap-sucking insect or arthropod, such as thrips or mites.
Another possibility is that the new seedlings have been infected by aphids carrying the bean common mosaic virus.
It’s difficult to determine the actual cause without seeing the plants, but the disease is hard to control, apart from checking if the variety you are growing is resistant to the virus.
As for mites, wetting the underside of the leaves with water for about a week can disrupt their breeding cycle.
Soap sprays, oil sprays and wettable sulphur are all effective against both mites and thrips.
If all else fails, natural predators such as tiny black ladybeetles (Stehorus) and predatory mites may arrive to control large numbers. (Watch for an upcoming article on commercial production of predatory insects and mites!)
4. Controlling running bamboo was the subject of Barry’s call in late October.
I think Barry’s conundrum was that it wasn’t his bamboo, but next door’s clump deciding that his yard looked pretty good to attempt to colonise as well.
Firstly, I’d say that there should be a law against selling running bamboo to anyone who lives in suburbia. However, if you do need to control this beast of a plant then there are two options.
First option is to dig a 30-40cm deep trench about 50cm out from the outermost culm. Rhizomes of running bamboo are usually quite shallow, so you should see any heading your way when they emerge from the sides of the trench.
You can simply cut them off as they appear, and apply a cut-stump glyphosate mix.
Second option is to lay root barrier, usually made from high density polyethylene (HDPE), and available from bamboo suppliers (ironic!). It should be at least 45cm deep, but best results will be with 90cm deep barrier.
Once again, a trench must be dug, to the depth of the barrier, and the plastic laid sloping slightly away from the approaching bamboo, with the top of the barrier just above soil or mulch level (to see any sneaky rhizomes that may creep over the barrier).
The join must overlap a good distance to prevent incursion as well.
5. Black spot on pawpaw was Ken’s challenge. This disease is common where winters can be longer and cooler than in the tropics, and can be exacerbated by poor nutrition.
It’s vital that pawpaws are fertilised with adequate potassium, magnesium and phosphorus for optimum health.
A complete fertiliser in late spring, and another application in autumn will help keep these nutrients in good supply.
Also, if you’re trying to grow pawpaws in areas that get cooler winters, like Toowoomba, it raises the chances of fungal attack significantly, as the fruit remains on the plant longer than the normal times for tropical areas.
To reduce disease, plant resistant varieties in warm, sheltered areas of your yard.