Citrus (forum)

Henry starts with ...
Whilst pruning my citrus (orange, lime and mandarin) trees last week, I noticed the presence of some white powdery substance on the trunks as well as on the leaves. Would anyone know what this is and how I should treat the problem, please.

Time: 7th August 2009 8:03pm

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About the Author Henry
Blacktown
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Reg Wong says...
Henry

Based strictly on your description, ie "white powdery substance...on the leaves", then the problem is powdery mildew. Control by spraying with dinocap or benomyl or wettable sulphur.

With citrus, powdery mildew is most unusual unless you are in a very damp and humid area.


But the presence of the same symptoms on the trucks poses a puzzle. How far up the truck is this "powdery substance"?

Remember that citrus plants are shallow rooters. If planted too deeply in poor draining soil, they suffer from collar rot. Use a sharp small-blade knife to cut into the affected area of the truck to ascertain if it is collar rot. If it is not too advanced, treat accordingly. If it is too far gone, learn from the lesson and buy a new plant.

Are you sure you haven't got borers in the truck? If they are there, you'll be able to dig them out with a large needle. If not, spray methylated spirits into their burrows to bid them a blissful death. After that you'll need to seal the "wounds" with hot wax or, preferably, molten tar.

I grow the following citrus varieties : orange (2), Tahitian lime, Kaffir lime, lemonade, mandarin and tangelo (see picture)- all growing profusely.

Reg Wong of Sydney Northern Beaches
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Picture: 1
Picture: 2

Time: 8th August 2009 11:21pm

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Mark says...
Yep, Powdery Mildew. Reg Wong said it all better than I could've done. Just go wit His advice!

Time: 9th August 2009 12:56am

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About the Author Mark12
Frankston,Vic.
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Henry says...
Thanks for the advice, Reg, much appreciated. The white powder is just like caked powder, and they come off quite easily with a paint brush. Those on the trunks were found from ground level to max 30cm up. I have just sprayed the trees including the trunks with lime sulphur as advised. No collar rot and no borers, thank heavens.

Time: 11th August 2009 4:41pm

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About the Author Henry
Blacktown
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amanda says...
Hi Henry - I just thought I might add to this... the powdery mildew on the trunk is a bit odd - has there been rank weeds growing around the trunk? are u using drippers/sprayers that wet the trunk? Is the lower leaf canopy close to the ground?

It might b worth making sure the trunk is clear of weeds etc and lifting the canopy, increasing airflow thru pruning etc. I am sorry I am so ignorant - but don't know where Blacktown is and how "soggy" it may get there over winter!?

Time: 11th August 2009 10:49pm

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About the Author amanda19
Geraldton. WA
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Henry says...
Hi Amanda, I water my trees twice a week, and no weeds. Admittedly, I have erected a concrete wall (blocks) around the tree for beautification reasons, and can now see that there is insufficient air flow at the base of the tree, and this may have resulted in the powdery mildew on the trunk. Perhaps I should only water once a week. Blacktown is one of Sydney's outer western suburbs west of Parramatta. Thanks for your input which has shed some light on what I should do next.
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Time: 13th August 2009 10:38am

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About the Author Henry
Blacktown
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Michael says...
Hi Henry,
From your edibles page I see that you are growing ambarella,longan and lychee? Have any of your trees fruitied ? I also grow these trees but have yet to see any fruits .Blacktown is not too far from Wakeley so our climate is very similar.

Time: 13th August 2009 1:13pm

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About the Author Michael
Wakeley
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Henry says...
Hi Michael, Yes, I do have the ambarella and longan (no lychee) but they are both only knee height and have not flowered yet. I bought them from Daleys in Jan 2008 and I hope to see more growth this summer. I will shortly (couple of weeks perhaps) be posting pics of all my fruit trees in the edibles page. Besides the two above, I also have a Duffy Feijoa, a Starkrimson Cherry, a Stella Cherry, a Nectarine, a Eureka Lemon, a Kensington Pride Mango, a Michelia Alba (flowering tree), a multigraft Plum, a multigraft Apple, a Nagami Kumquat, an Arnold Blood Orange, a Hawaiian Guava, a Cherry Guava, a Red Shahtoot Mulberry, two Satsuma Mandarins, a Valencia Orange, a Tahitian Lime, an Okitsu-wase Mandarin and a Red Panama Passionfruit. I am hoping to buy an All-in-one Almond tree next week (hopefully).

Time: 14th August 2009 8:58pm

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About the Author Henry
Blacktown
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