I appear to have plum rust on one of my plum trees (yellow mottling on upper sides of leaves, brown powder on the undersides) with about 90% of the leaves on the tree being affected. What, if anything, should I do about this? Collins Guide to the Pests, Diseases and Disorders of Garden Plants suggests spraying with zineb. Is this a good thing to do? Can it be treated organically? Is it likely to spread to damsons, cherry plums, sloes and another plum tree growing nearby? Will it reappear next year? Any comments will be gratefully received.
Heather Hooper
Sorry to say that there is no approved cure for plum rust these days, Zineb
went some time ago and its near substitute, Mancozeb, is not approved for
use on plums. Nowadays it is illegal to use or recommend a chemical for any
other purpose than what it states on the label.
However, all references that I have agree that it is not a severely
disabling disease unless it occurs every year on young trees. This year was
very wet and fungus conditions flourish in such circumstances.
However, if you are an anemone lover, the fungus causes a severe weakening
of both wild and cultivated species, easily recognised by a lack of leaflets
on affected leaves and the whitish ‘cluster cups’ on the reverse side. As it
is incurable in anemones, any affected one should be burnt and healthy
specimens moved away from the plums.
There are approved fungicides for plum rust used by commercial growers. At least one of these myclobutanil (Systhane) is available to amateur gardeners in various formulations such as Bio Systhane Fungus Fighter. The other main chemical fungicide used fenbuconazole (Indar) is as far as I know is not available to the general public. Both are very effective. One spray in mid July is sufficient.
I fully agree with Howard that plum rust is usually not a severely disabling disease. It looks a lot worse than it is. The trouble is that some popular varieties such as Victoria are very susceptible. Severe attacks can weaken trees but because the infection occurs quite late in the season when most of the summer’s growth is already finished the damage to leaves and their premature shedding does not have very serious consequences. Up until three years ago we did not spray our plum trees at Keepers Nursery for rust without much adverse effect.
So if I leave my plum alone is there any hope the fruit will be edible next year. I think it is rust and it seems to be spreading to my hollyhocks. Any help will be gratefully received. I have moved the plum tree twice in the last three years due to moving house, the plum tree is approx five years old.
I am not sure that you should be blaming your plums for the rust in your hollyhocks.
There are a lot of ‘rust’ fungi – some of which are very specific to certain hosts. As a gardener I have been led to believe that plums and anemones share the same rust fungus (‘Tranzschelia discolor’), whereas hollyhocks and other members of the mallow family are affected by ‘Puccinia malvacearum’
However, I am not a mycologist and am more than willing to be corrected on this subject if I have not got this right.
Plum rust does not have any direct adverse effect on the fruit. So I am not sure what you mean by ‘if I leave my plum alone is there any hope the fruit will be edible next year.’ If there was a problem with the fruit it would have been caused by something other than plum rust.
If the rust is bad it prevents the fruit from ripening because the foliage has been compromised too much. I have had problems for the last few years, some years the the plums were inedible, other years they were not their usual intense sweetness. I’m trying Yates lime/sulphur this year and hope it will make a difference.
I am a new plum tree grower and am wondering if I should remove rusted leaves before mother nature does so?
Removing leaves is not really a viable option. First as it affects a very high proportion of leaves it is quite impractical. Second by removing the leaves (I presume you do mean manually defoliating the tree) you will be doing the damage that rust does to the tree even worse. However it is not a bad idea to sweep up fallen leaves and to burn or otherwise dispose of them. This removes a high concentration of a potential source of next year’s infection from the immediate vicinity of the tree – the fungus overwinters in dead leaves. This will not stop infection altogether next year. Rust is spread by airborne spores which get blown about by wind over long distances. The chances are that there are many sources around you from which new infections next year will come even if you were to manage to remove and dispose of every single infected leaf from your tree.
I have a number of fuchsias planted alongside my Victoria plum and some of these have also been badly affected. I am wondering if it is the same fungus. The plum is losing its foliage prematurely but cropped well.
Same as you Jeremy. Our plum tree is badly affected this year and all our fuchsias now have rust too (as did the antirrihnum but I believe that is definitely different).
We have some definitive answers to the rust queries from the fruit disease expert Dr. Angela Berry at East Malling Research, Kent, UK.
Rust fungi are quite complex fungi having several different spore stages, which can require two completely unrelated hosts to complete the life cycle. So for example the rust on black currant has the Five needle pine as its alternate host. Some spore stages can continue to infect black currant and hence cause an epidemic whereas later spore stages can only infect pine. Later spore stages on the pine will only be able to infect black currant.
Plum rust is caused by fungus Tranzschelia pruni-spinosae. This fungus infects plums and the rust also infects Anemone coronaria as its alternate host. So in the case of plum rust the fungus alternates between plum and anemone but does not infect fuchsia or hollyhock.
Fuchsia rust is caused by the fungus Pucciniastrum epilobii and also infects willow herb (Epilobium spp). The alternate host for this fungus is Abies spp. So this fungus will alternate with fuchsia/willow herb and Abies with different spore stages appearing on both.
Hollyhock rust is caused by the fungus Puccinia malvacearum. This has a wide host range also attacking Abutilon, Hibiscus, Lavatera, Malvastrum and Sidalcea. This rust however, does not appear to have an alternate host or at least one has not been identified.
Thanks a lot for all the useful information.
I was wondering if there is some kind of biologic fungicide to fight plum rust.
I am not sure what you mean by ‘biologic’ fungicide. Perhaps organic? If that is the case I do not know of an organic fungicide to control plum rust. The fungicide most commonly used is Systhane. This is not an organic fungicide. This is available to the general public as Bayer Systhane Fungus Fighter. You need to spray in July. The timing is important. So I would advise you spray once in mid July and repeat at the end of July to make sure the infection period is covered. Systhane does give very effective control but spraying is probably only worthwhile if you are getting severe rust infection. Minor rust infections do not do much harm.
Could an alternative host for the plum rust be tomato plants by any chance? My tomatoes and green beans developed bad rust, followed by the plum tree close to them.