Archive for the ‘Pest and disease control’ Category

It has been a long held belief that Rosa x fortuniana Lindley is the only rootstock suitable for local conditions in Western Australia. Rosa x fortuniana Lindley has produced outstanding yields under conditions in Florida (McFadden 1962). The reasons for its superior performance include better adaptation to warm weather and sandy soils. Resistance to soil borne pathogens such as Pythium, Phytophthora,  Rhizoctonia and crown gall has been found in Florida trials. Hybrid vigour is also a possibility – Rosa x fortuniana Lindley is believed to be a hybrid of R. banksiae x R. laevigata. Superior uptake of iron during hot weather could also be a factor.

Rootstocks found in Western Australia include R. multiflora, R. x fortuniana, R. indica major, R. ‘Dr Huey’, R. manetti and R. canina inermis. Some of these are being used for inground cutflower production whereas others are used in the home garden as well.

Characteristics of a rootstock which are important include:
1) Ease of propagation
2) Lack of suckering
3) Disease resistance and/or tolerance to nematodes
4) Vigour
5) Tolerance of local conditions eg salinity, heat and drought.

Multiflora is noted as being more salt sensitive and more cold tolerant. It is less tolerant of alkaline conditions. It also picks up virus infections from the scion material very easily (however in Australia there is no virus free material, I can write separately on this topic). There are numerous lines of multiflora used internationally and at least two lines have been found Western Australia. One line is greatly lacking in vigor and displays a multitude of trace element deficiencies. Even the other line of multiflora seems susceptible to trace element deficiencies, especially copper and iron. Studies, both at the Department of Agriculture and overseas have shown it to be an ideal host to both root knot nematode and to lesion nematode, but particularly, root knot.

‘Dr Huey’ appears to perform quite well especially on heavier soils. In both McFadden’s study and in that of the Department of Agriculture, it came second to fortuniana. I have not seen any obvious problems with ‘Dr Huey’. It is reported to be susceptible to black spot which may be a problem in more humid climates.

R. manetti, used commercially, appears to have some degree of resistance to nematodes and has solved grower issues with trace element deficiencies. The growth is far superior to R. multiflora and on a par with ‘Dr Huey’.

R. canina, also used commercially, also appears to have some degree of resistance to nematodes. Studies overseas have supported this. R. canina is extremely tolerant of root knot nematode and reasonably tolerant of root lesion nematode (Coolen and Hendrickx, 1972). Growth is superior to multiflora and trace element deficiency symptoms not evident.

R. x fortuniana is planted extensively in home gardens and to a lesser degree in commercial inground production. It is definitely superior to multiflora. It does seem to have some issues with trace element deficiencies. One disadvantage is that it is more difficult to propagate. It also suckers more freely.

Trials in Florida (Gammon and McFadden, 1979) compared flower production between bushes on fortuneana, odorata, multiflora and manetti. Odorata produced the highest yields, followed by fortuneana, manetti and multiflora. They also found large differences in the accumulation of trace elements. Fortuniana accumulated five times more manganese than odorata but this was not related to flower yield. Odorata was a superior accumulator of potassium and under low nutrient conditions both fortuniana and odorata were good accumulators of nitrogen and potassium and this was related to flower yield.

The results of the trial at Medina Research Station (1980 to 1982) did seem to support the superiority of fortuniana, especially for bloom counts. However the following factors should be borne in mind:

• High pH water and soil (both around pH 8),
• Medina soil is a Spearwood sand unlike most of the soil in the metropolitan area with is much poorer in nutrient status, and
• Climate – Medina is recognised as being a particularly cold spot in winter.

All these factors could have a significant bearing on the performance of any rootstock. Finally the experiment at Medina lasted for only three years when the normal lifespan of a bush in the average home garden is many times that.

In Western Australia which has a hot climate and nutrient poor sandy soils prone to nematodes and with poor water holding ability, R. x fortuniana is the logical choice. However home gardeners often modify their soils to varying degrees which may decrease this advantage. In areas with colder night temperatures multiflora may perform better than on the Swan Coastal Plain. In the clayier soils of the scarp, ‘Dr Huey’ also does well.

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OK, I know I have done much for a while but this came up on a forum today so it seemed like a good opportunity.

Nematodes are tiny worm like creatures. They are a particular problem around Perth because we have sandy soils. If you live in one of the older suburbs you probably have them for sure!

How can you tell if you have them?

Plants will be unthrifty, they may simply appear unwell, nutrient deficient or they may be getting a lot of other problems. For example roses or eucalypts with nematodes often have stem cankers as a secondary problem. If you dig the plant up and examine the roots they may have knots on them – or they may not. Most people aautomatically think of root knot nematode when they think of nematodes however many other species of nematodes don’t produce galls or knots. You may just see roots that seem more branched and profuse then normal (not to be confused with proteoid roots on banksias, hakeas etc. Or on leaves, you may see angular blackened sections.

Types of nematodes

Most nematodes can’t really be seen by the naked eye – the commonest species may be up to 1mm long. Some nematodes feed from the outside of the root (dagger, needle or stubby-root nematodes), or they may go inside the plant and either stay in one place (eg root knot nematode) or move around inside the plant and feed along the way (lesion or burrowing nematodes. Some other types of nematodes move around inside the plant but feed on above ground parts such as leaves or stems (such as Aphelenchoides that infect leaves of eg Chrysanthemum or some ferns)

How do you get nematodes?

They can come in on plant material which is already infected or in soil/soils mixes.

What conditions do they like?

Ideal soil conditions vary with species. Moist soil is required by all to reproduce and move. The optimum temperature varies with species. The pore size of the soil affects nematode movement. The small pores of clay soils make movement difficult so the nematodes have to move in the spaces between aggregates. The larger pores in coarse sands may be too big to allow nematodes to gain leverage between particles.


The home gardener has a different range of options to a commercial grower. Nematicides used to be available to the home gardener (Nemacur® granules) but aren’t any more. They are all S7 pesticides so pretty nasty! Over time the microbes in the soil that break the chemical down build up numbers so over a period of a few years the pesticides become less and less effective. There are natural predators of nematodes – such as fungi or other nematodes but these aren’t really commercially available. Method more suited to the home gardener include:

Rotation – the use of a rotation crop that is resistant to the particular nematode. So for root knot, that may be something from the grass family eg a grass or sweetcorn or sorghum. This will not eliminate them entirely but reduces numbers to levels that don’t cause problems.

Fallow – leaving an area fallow has a similar effect to rotating with a resistant crop – numbers fall because they can’t reproduce.

Solarisation is another option. The use of clear plastic laid over tilled moist soil for several weeks during the hottest part of the year.

Bio-fumigation – there are some crops that can be grown and hoed back in that contain chemicals that will help control pests and diseases including nematodes – such as some of the mustards. These crop residues are planted densely and hoed in while in full flower. Castor oil plants and marigolds have root exudates that may kill nematodes – they can be grown as rotation crops and hoed in. The type of marigold matters, not all are useful. Tagetes patula has traditionally been the one to use but some other species also work.

Sugar and molasses – In some Brazilian work, 300g granulated sugar per litre of soil at 7 days intervals controlled root knot.

Work in Australia on field grown tomatoes found 150 m³/ha of sawdust plus urea (600 kg/ha) to be quite effective. Molasses at 375 litres/ha per week for 14 weeks helped reduce numbers but was inferior to the sawdust.

In some other trials, urea concentrations of 4% totally eliminated nematodes but adversely affected plants. A combination of urea and molasses reduced the phytotoxic effects. Some papers mention molasses in water with a final sugar concentration of about 2% reduces nematodes numbers by about half in just over a week.

Other plant extracts – many have been trialled. Things like calendula, rosemary, lantana, onion, fennel, datura and liquorice which are ground up and put in water. What works probably depends on the type of nematode and the crop. Many of these trials have been in vitro and not in field situations.

The APPS website has some good info if you’d like to do any further reading.

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This post is a bit longer and more technical than usual.  I originally wrote it for a different audience and this is my attempt at making it user friendly for most people.  Like many things in nature it’s complex.

Healthy soils teem with microbes. Inoculating soil with with microbes to boost crop production is all the rage at the moment with companies sprouting – well, like microbes! Usually they are being sold to the commercial grower but more and more they are also being marketed into the home garden market where cost is less of an issue (ie home gardeners don’t have to make a profit).

Whether you can parachute in foreign organisms and expect them to live and prosper is really open to debate.  In most studies it doesn’t happen.  And in sandy soils with virtually no organic matter there is nothing there for them to feed on so it is even less likely.  Sure you can add composts and manures but these don’t tend to hang around much in sands, they burn off very quickly unless some clay is also added.  And large amounts of compost and manure provide phosphorus far in excess of plant needs which means it leaches down into the groundwater, potentially getting into waterways and causing algal blooms.

I have seen some papers showing how mycorrhizae have increased plant growth, even without fertiliser being added.  Those papers carefully omitted to cite a soil analysis!  One thing to bear in mind – I certainly don’t dispute that some substances can increase plant growth but they can’t do it forever without, at some stage, the food supply having to be replenished.  What you are doing is mining the soil.  It might work once or twice but then you run out of food.  Plants can’t feed on fresh air!  OK I can hear you saying they can fix nitrogen from the air – yes – but not phosphorus or potassium!

Mycorrhizae may alter root architecture – ie the way roots branch and proliferate.  That can make plants take up nutrients more efficiently by exploring more of the soil.  So you might see a growth spurt – but again, that nutrient will have to be replenished if that response is to be repeated and maintained.

So lets look at microbes.

A changing population

Populations of fungi are not constant. They change frequently in response to a whole range of factors. Even those associated with a single plant, change with the growth stage of that plant. Figure 1 shows the relative amounts of different fungal species over time for a pea plant. In the vegetative stage, Fusarium is most common but diminishes over time in contrast to Heliotales which increases as the plant matures.

The relative amounts of each fungus also change with fertility (Figure 2) and crop health (Figure 3).

                     Vegetative                                                    Flowering





Figure 1.  Change in microbial populations with growth stage in the rhizosphere of pea. (Note the rhizosphere is that thin coating of soil left on the roots after the rest of the soil is shaken off).

OM rates

Figure 2  Relative amounts of fungal species in pea roots grown with either nil or three levels of organic fertiliser (OF)


Figure 3.  Relative abundance of fungal species associated with the rhizosphere of healthy and diseased pea plants.

You will note that in all the examples above there is a mixture of ‘good’ (e.g. Glomus sp.) and ‘bad’ species of fungi (e.g. Olpidium sp.).  This is normal and disease only occurs when this balance is disrupted in favour of the pathogen and other conditions in the environment and host are right for infection and disease development.

Mycorrhizae are one group of fungi known to have beneficial effects on plant growth in some circumstances, but this is highly variable. The term mycorrhiza covers a large number of genera. Glomus species are some of the most prevalent. Examples of their effects on plant growth are provided below.

Highly specific effects

Example – Three mycorrhizal species were studied on basil.  None affected plant phosphorus level.  Only one significantly affected plant growth and increased the amount of one essential oil produced while the other two increased the amount of a second oil and decreased that of a third.

Microbes can also have adverse effects such as growth suppression

Example ‑ A trial on onion and plantago showed varying effects of mycorrhizae on plant nutrient levels.  The authors expected the mycorrhizae to increase host nutrient levels, however in some cases they reduced them.

Example – Twenty-three different mycorrhizal strains were evaluated for their symbiotic response with Piper longum (long pepper).  Almost all resulted in increased plant growth, biomass and nutrient content (nitrogen and potassium) over the control, however six species depressed growth.

It’s Complicated!

Example – A comparison of mycorrhizal versus non-mycorrhizal roots showed phosphorus uptake doubled and was independent how much was in the soil. There was no additional benefit of the mycorrhizae on plant growth other than that due to increased P uptake.

Example – The effects of a mycorrhiza on growth and photosynthesis of cucumber were studied using different rates of nutrient supply, phosphorus ratio and different forms of nitrogen.


Plants inoculated and given full-strength nutrient solution showed a 19 per cent reduction in total biomass compared with mycorrhizal (AM) plants (Figure 5).

The highest percentage of mycorrhizal infection in cucumber was found at the low P treatment, however a 90 per cent reduction in total nutrient supply almost totally counteracted the potential positive impact of a low concentration of P on mycorrhizal infection.

The extent of mycorrhizal infection in cucumber was correlated with a low root P concentration, which agrees with other studies that plant P status influences mycorrhizal infection.

Not all plants are mycorrhizal

Some plants do not form relationships with mycorrhizae even when inoculated. Brassicas, beetroot and spinach are among those.

Local species usually prevail

This is probably the most important consideration of all.  Any microbe placed in a field situation will face competition from local species and may eventually be displaced.

Example.  A Turkish study took 70 soil samples from 25 different plant varieties grown in local fields.  Arbuscular mycorrhizal fungi (AMF) were found in 59 soil samples; 58 of these were identified as Glomus and one as Gigaspora.

The effect of the local Glomus sp. was compared to a commercial preparation on tomato and cucumber plants.

The local Glomus species increased cucumber and tomato plant growth, but the commercial mix did nothing.  The local Glomus species colonised plant roots at almost twice the rate of the commercial one.

The relationships are very specific

Each plant species, and even variety, tends to have a preference for certain mycorrhizal species. It is difficult to manipulate relationships and so the effect of inoculating a soil with mycorrhizae depends on many factors.  If there are already successful mycorrhizal associations present, those existing association may be stronger and the introduced species may fail to displace those already present, or it may displace a proportion of the existing associations.  Inoculation with mycorrhizae does not necessarily mean more root colonisation in terms of either numbers or species.

And lastly – Beware trial results!

Many research results, when you read the fine print, are from work that has trialled mycorrhizae under unnatural situations, whether using sterile media or in a laboratory. Those results are not often reproducible in field situations.  They work because the introduced (foreign) microbes have no competition.  A better approach and one more likely to succeed, would be to use local species, bulk them up and inoculate back.

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The longer you have a garden, whether it be vegetable or ornamental, the more likely you are to be slowly building up a reservoir of problems. There are several viruses that can take hold and be real problems in the home garden. Tomato spotted wilt and tobacco mosaic virus, for example. There are some other very serious viruses (tomato yellow leaf curl virus) that are not yet in WA. Then there are other problems such as phytoplasma that cause witches brooming (not to be confused with witches brooming from boron deficiency). And then there are root rots and other soil borne diseases such as Sclerotinia and nematodes.

All of these diseases, once contracted by a plant, usually kill it. In low numbers, nematodes may simply stunt plants and largely go unnoticed. Often plants succumb to other problems which are often secondary to the real issue of nematodes. Stem cankers in roses are often the result of undiagnosed nematode problems.

Chemical control of these problems is often only achieved with highly toxic chemicals. Sclerotinia forms highly resistant resting stages that last for years in the soil. Viruses and phytoplasmas cannot be cured, one can only stop them spreading and that is why it is really important to pull out and get rid of infected plants.

Non-chemical measures such as hygiene and rotation become critical in the control of all these diseases. For viruses and phytoplasmas, control of the vectors of the diseases is the only way out. Depending on the individual disease, that is often a leaf hopper or thrips (though Tobacco Mosaic Virus is spread mechanically, not by insects). And the problem with these pests is that they can fly around and hop on and off plants very easily. This is where weed control and control of alternate hosts becomes important. Even capeweed is suspected as an alternate host of some viruses. Alternate hosts are not necessarily from the same family. They may even be other ornamental plants in your garden such as petunias.

So where you are sowing successive crops of tomatoes, eggplant or potatoes, for example, you can expect to have increasing levels of virus building up over the years – assuming your level of insect control is not perfect. Sometimes the only way around it is to have a fallow period where no hosts are present for a period of time – say three months. And of course one problem here is that because these little critters can fly, the alternate host may not be in your backyard! It could be on the front verge or in the neighbours garden.

For nematodes you may need to have a fallow period to get numbers down to low levels. If that is not possible try sowing a non-host for a while such as any grass or sweetcorn. Incidentally, the reason we grow roses on fortuniana ropotstock in Western Australia is because it is relatively resistant to nematodes, unlike many of the rootstocks used in the Eastern states. Further information on some tomato spotted wilt can be found here. This farmnote gives information on Tomato Yellow Leaf Curl Virus and this, on Tobacco Mosaic Virus.

Here is a really good chart, albeit for Victoria, on what to use in various rotations and why.

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This may be short but it is topical for me at the moment. And not without relevance for the home garden.

I am lucky I guess because I know my block was bush before I bought it. And still is in part. So I can grow veges and have chooks and eat their eggs without worrying what they might contain. But many people on newer blocks, or even not so new, may not know their history. Land around me that was orchard for years is being turned into housing. There is certainly land in the metro area that was a dumping ground for rubbish in the past. If you’re intending to grow veges and eat them, or run animals on your land and eat them or their products whether they be eggs or meat, it may just be worthwhile getting a soil test done first to ensure the land you’re on doesn’t have any nasties in it. Old farming land may have organochlorines. Rubbish dumps – who knows what!

Then there’s the question of water. If you’re drawing water from a dam or bore also consider having it tested. Especially if there’s any sort of commercial activity nearby.

Also consider what you bring on your property. Those manures/composts you bring in may also be contaminated via the land they are from. Particularly if the composts are not made to the Australian Standard which does test for all those sorts of things. Even just simple soil may contain almost anything and its hard to go back once you’ve got any sort of contamination, especially disease. Look at the sting nematode debacle around the metro area at the moment! And of course dieback.

Finally consider the things you grow. Some crops accumulate nasties. Brassicas are known to be good at accumulating heavy metals, spinach also accumulates cadmium, tea- aluminium and so on. Plants that take up lots of heavy metals can be used for bioremediation and that is a good thing but you wouldn’t want to eat them!

So surely if you’re buying a new place its worth doing a bit of checking and testing to see if there are any potential issues lurking in your land.

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This was inspired by a talk I gave last Sunday.  By chemicals I mean the things you use for pest and disease control.

Firstly I’d like to point out that at least one of the chemicals registered for use in organic gardening is actually quite toxic to humans.  Rotenone or derris dust has been implicated in both Alzheimers and parkinsons disease recently so maybe best avoided.

If you are looking to use chemicals that don’t harm beneficial insects and other non-target organisms then you need to stay away from any organophosphates eg malathion or Rogor.  In fact, Rogor has just been withdrawn so you won’t be able to buy it in the future.  All carbamates such as carbaryl are also dynamite on beneficials including bees.  Confidor, used as a foliar spray and Lebaycid, used for fruit fly are also bad.  All synthetic pyrethroids and even natural pyrethrum are bad news for beneficials.  While sulphur is used widely, it can be hard on non target organisms eg predatory mites.  Copper kills earthworms it if gets into the soil in sufficient amounts

Chemicals that are generally OK to use include:

  • Neem – NOT registered for use on food crops in Australia. Insecticidal and antibacterial, antiviral and antifungal. Prevents insect feeding and oviposition, and act as a growth regulator. Active against whitefly, thrips and mealybug. Relatively harmless both bees and earthworms.
  • Dipel (Bacillus thuringiensis) – low toxicity.  Used for caterpillar control.  Needs to be kept in fridge and has a short life.
  • Insecticidal soaps – Contain fatty acids derived from plants or animals. To be effective must contact pests directly.  Can burn in hot weather. May also kill beneficials but are not residual.
  • Spray Oils. Kill insects and mites and eggs of both on contact. Act by suffocation and can therefore also kill beneficials but not residual.  Many plants are burnt by oils.
  • Eco carb/Eco fungicide (potassium bicarbonate).  Used for powdery mildew control.  Relatively non-toxic.  Not residual so needs to be applied frequently.
  • Milk.  Good for powdery mildew. 1:5 to 1:10 dilution.  Too strong and you get sooty mould. Low fat milk is less effective than full cream milk. Use at 7-10 day intervals.  Good coverage is essential.
  • Natural Pyrethrum. Often mixed with piperonyl butoxide to make it more effective. Contact only, paralyses pests. High toxicity for some beneficials, eg Encarsia formosa, predatory mites. Three to 10 day residual effect.
  • Garlic and chilli – relatively non toxic.  Good for aphids.
  • Derris dust (rotenone). Human LD 50 of 300 to 500 mg/kg , implicated in Parkinsons, highly toxic to fish and marine animals.  Degraded by UV so lasts less than a week.
  • Diatomaceous earth –milled from the shells of fossilized diatoms. Abrades soft-bodied insects, so they lose fluids and dry up, therefore works best in dry weather.  Contact only, insects take up to 12 hours to die. Irritating to lungs. Kills bees.
  • Ryania. Derived from the roots and stems of Ryania speciosa, More persistent selective than rotenone and pyrethrum. Generally not harmful to parasites and predators, some  toxicity to predatory mites.
  • Sabadilla Dust. From the crushed seeds of a tropical lily. Can be mixed with water and sprayed, but clogs nozzles.  Not very residual, little effect on most predators and parasitoids. Highly toxic to Typhlodromus pyri, a predatory mite active in some apple orchards. Kills bees.
  • Success.  A new class of chemical called strobilurins made from actinomycetes.  Generally safe for use with beneficials but hard on wasps and bugs.

Just to finish a couple of recipes for home made sprays.  The Solanum recipe comes from an African paper (The effectiveness of home made organic pesticides derived from wild plants (Solanum pindiriforme and Lippia javanica), Garlic (Allium sativum) and Tobacco (Nicotiana tobacum) on Aphid (Brevicoryne brassica) Mortality on Rape (Brassica napus) Plants.  Mhazo ML, Mhazo N and Michael T. Masarirambi.  2011.  Research Journal of Environmental and Earth Sciences 3(5): 457-462. They used Solanum panduriforme but I’m sure other species would work just as well.  Just watch where you leave any fruit or spare spray, we don’t want any pets or children getting poisoned.  I haven’t listed the tobacco recipe as it didn’t work on aphids.

Garlic and chilli spray: 1 garlic bulb, 1 L water, 1 medium onion, 1 tablespoon cayenne pepper, 1 tablespoon dishwashing soap.  Crush garlic finely. Add finely chopped onion to the mixture and rest of ingredients except soap. Wait for 1 hour before adding the soap to the mixture. The spicy ingredients must sort of stew or steep almost like tea. Add the soap, the non-toxic spray is ready to use. Spray can be stored in the fridge for a week.

Garlic Buttermilk spray (called so because it has paraffin oil in it as a wetter.  It is more effective but more apt to burn in warm weather).  1 pint (568 mL) water, ¼ cup dishwashing soap, 2 teaspoons paraffin, 6 tablespoons chopped garlic. Soak whole garlic in liquid paraffin for at least 24 h. After a day finely chop the garlic, add dish liquid and water. Shake very well and strain the mixture. Store in a glass jar lasts around a week.

Solanum spray: 10 Solanum fruits, 1 L water, 1 tablespoon dishwashing soap.  Chop Solanum fruits and put in container. Add waterand allow mixture to set for 24 h. After a day strain, add liquid soap. Spray can be stored in a glass jar in the fridgefor about a week.

Solanum buttermilk spray: 1 pint (568 mL) water, ¼ cup dishwashing soap, 2 teaspoons paraffin, 6 tablespoons chopped Solanum fruits.  Soak whole Solanum fruits in liquid paraffin for at least 24 h. After a day finely chop the Solanum, add dish liquid and water. Shake very well and strain the mixture. Store in a glass jar lasts around a week.

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