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Disease on avocado-?anthracnose

    14 responses

Rhys starts with ...
I've recently noticed some new branches on my avocado going black...i pruned them off, but have now noticed a section of the trunk going black as well. Some of the leaves are also a bit funny. It's been in a relatively sheltered position for most of summer, so i'm pretty confident it's not sunburn, and i suspect it's anthracnose, but before i start spraying with anything, i thought i'd ask around to see what other people thought.
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Picture: 5
 
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Getafix
Newcastle
12th March 2011 11:53pm
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Wayne says...
I don't think it is anthracnose Rhys, pic 1 suggests mites to me but pics 4 & 5 do look like a fungus disease. Others might have a better idea
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Wayne
Mackay QLD
13th March 2011 7:27am
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Brendan says...
Hi Rhys,
It wouldn't hurt to spray with copper oxychloride & mancozeb plus, 30g of each, in 4 litres water, plus a 'good' wetting agent, at least 30ml.
Spray once a week for 4 weeks, then once a month untill it's gone.

Photo 3 looks like it's lacking phosphorus (P) fertilizer.

Could be the start of either Anthracnose or Phytophthora (dying branches), the above spray should fix it.
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Brendan
Mackay, Q
13th March 2011 9:08am
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Original Post was last edited: 13th March 2011 9:14am
Rhys says...
Thanks guys.

Brendan, how crucial is the mancozeb component. I already have some copper oxychloride, but wondering whether i should go and get the mancozeb as well. Would it be ok to spray with the copper initially and then add in the mancozeb when i get a chance to buy some.

As for the wetting agent, i have some Amgrow Wettasoil liquid which i'm assuming should be OK for the job.

I've been giving it some seasol, but it probably is due for a feed as well...see how we go!
Thanks again
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Getafix
Newcastle
13th March 2011 12:43pm
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Wayne says...
The mancozeb is not crucial Rhys but the wetting agent is. Try with what you have making sure the wound stays wet, not the spray just running off
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Wayne
Mackay QLD
13th March 2011 1:18pm
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Brendan says...
Hi Rhys,
Please DON"T use Wettersoil as a wetting agent, it's not made for that.
Bunnings here sell 'Spredmax' in a 200ml bottle. Or use Spreadwell, Agral etc. (I use Activator).

Yeah, as Wayne says, the wetter is the key, BUT, I would get the mancozeb plus asap. Try the Copper Oxychloride first if you have to, but add some Spredmax, say 30ml to the 4 L of water.
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Brendan
Mackay, Q
14th March 2011 8:46am
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Original Post was last edited: 14th March 2011 8:47am
Peter says...
I would exclude Phytophthora (P. cinnamomi). It's soilborne and black stem discoloration would happen base towards top. So maybe Anthracnose.
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Peter36
Perth
15th March 2011 11:32am
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Rhys says...
Thanks again,

Peter, yes i was a bit worried about Phytophthora but when i read the NSW DPI document about avocado diseases, anthracnose did seem to be a better fit, so we'll see.

Brendan...ummm...how bad would it be...er, hypothetically...if, say, i had already used the wettasoil...hypothetically!?!? I will go and buy some proper stuff tomorrow!

The other thing i was wondering, it's a pretty small tree, and takes less than 500ml to wet the whole thing, but only making up 500ml involves some pretty small volumes/weights, so i was wondering how long the mix would last if i made up a bigger batch, or is it best to make it fresh each time?
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Getafix
Newcastle
15th March 2011 9:06pm
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Brendan says...
Hi Rhys,
I'm fairly sure it says on the wettersoil bottle, if it's sprayed on leaves etc, to wash it off? It's actually used to drench the ground and make the soil around the roots 'wetter'.

Would have to disagree with Peter about phytophthora, it has killed at least 3 avocado trees of mine, luckily they were 'only' seed grown, what happens is the leaves all start to droop, then they fall off, then the branches start going black from the top down (not the other way 'round).

I would only mix the amount of spray needed for say one week :-)

Just remembered, you can use 1/3 cup of Lux flakes, dissolved in some hot water, for your 'wetter'. Just add that to 4 litres of water, copper oxy etc., but that brew doesn't keep very long :-(
Just mix up a smaller amount.
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Brendan
Mackay, Q
16th March 2011 9:44am
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Original Post was last edited: 16th March 2011 9:50am
Peter says...
To make a simple test for Phytophthora:
1) Dig up some soil with some of the avocado roots and put it in a take away container about one third full
2) Fill up the container with rainwater
3) Create a clean water surface by pushing aside floating particles and keep them in place with some plastic stuff (not metal)such as a cut piece of shadecloth etc.
4) Put some soft leaves (not hardened old ones) on the watersurface (some leaves work better than others).

The container should be at room temperature. Within 1 to 7 days, mostly after 2 to 3 days the leaves turn rapidly brown to black all over.
This is only an indicator, but a quite good one as only a few other root pathogens make swimming spores which then swim towards the watersurface to infect the leaves. Therefore point 3) is important to have no soil particles to touch the leaves - otherwise all sorts of other organisms in the particles invade the leaves. If it takes many days for a discolured leave area to expand then it is most likely not Phytophthora.
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Peter36
Perth
16th March 2011 10:38am
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Rhys says...
Thanks guys.

Brendan...with the wettasoil, it actually says on it something like that it wouldn't harm plants, grass, animals etc which was why i initially thought it would be OK...anyway, i have now bought some spredmax.

The lesion on the main trunk eventually "ringbarked" the tree and the top section died off, but there has been quite a few new shoots sprout below this spot so i am hopeful the plant will survive.

One other question i had was, given that in its current location it is quite sheltered and gets no direct rain on to it, would i still need to spray as often. I'm assuming that in the absence of rain that the residue would hang around on the leaves longer. Is my assumption correct?
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Getafix
Newcastle
21st April 2011 9:51pm
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Brendan says...
Hi Rhys,
I'd cut the dead bit off and spray again weekly for 3 or 4 weeks. Then, once a month.
Actually, the rain encourages the anthracnose to spread, especially if the lower branches are close to the ground, the rain can splash the spores onto the low branches.
Another good idea is to spray the trunk and the ground under the canopy spread, to kill the anthracnose spores.
I'd add mancozeb to the copper oxychloride and wetter. Try adding 30ml of wetter (or more) to the 4 litres of spray.
Fertilize it with sulphate of potash, that will harden-up the plant tissue, and I'd give it some gypsum as well.

Btw, what type of avo is it?
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Brendan
Mackay, Q
22nd April 2011 7:39am
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Original Post was last edited: 22nd April 2011 7:55am
Rhys says...
Thanks Brendan...yes, i've already cut the top section off, and so far so good. I've been giving it the occasional drink with seasol and powerfeed, so hopefully those two should give enough potassium.
Does it need gypsum given it's in a pot?

It is a Secondo avocado bought from Daleys last year.
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Getafix
Newcastle
23rd April 2011 10:07pm
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Brendan says...
G'day Rhys,
Does it have to live in a pot? If so, try some 'liquid gypsum', sometimes known as Groundbreaker.

The seasol & powerfeed is very good! Good luck.
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Brendan
Mackay, Q
24th April 2011 7:01am
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Avacodo leaf dis says...
Can anyone tell me what this is and how to treat it? Make it go away for ever
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Avacodo leaf dis
dorothy1924
2nd June 2016 5:42pm
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