Rust

[johnw]

With this Spring's long stretch of dampness and dead air I have two bouts of rust to contend with.  A podophyllum is affected with circular clear spots with a dark centre as well as about 6 vars of Anemone ranunculoides with tiny bumps of the leaf uppers.  Now my question is should I immediately cut off the leaves and burn them and hope the plants rejuvenate cleanly or is rust systemic  - i.e. down to the very root?

Toss the works in the fire?

johnw

[Robert]

John,

For whatever it is worth.. From time to time (wet years) I've had trouble with rust. For me it has never been systemic, however it can kill a plant if nothing is done and the weather does not change. The rust does kill the tissue on the affected foliage, and if it really gets out of control the stems too. Fortunately, if the weather improves, I've had excellent success doing nothing more than removing the damaged foliage. Yes, I burn the diseased foliage.

Products designed to control rust seem more preventive than a cure.

Ultimately breeding for resistance, horizontal resistance being the best, is the solution. This is generally a huge challenge, and takes time. In the mean time the plants suffer and if you are like me, the gardener suffers too.

Good luck and I hope that I might have been of some help.

[Chris Johnson]

Hi John

I concur with Robert, rusts are not systemic but you will need to remove the affected parts to stop its immediate spread. Rusts have a complicated reproductive cycle, but when they reach the pustule stage they produce vast numbers of aeciospores which will continue to infect your plants, so a fungicide treatment would be a good idea.

It has been a very ‘good’ year for rusts in wild plants. Several, like the Nettle Rust Puccinia urticata are host specific, but others like the Celandine Clustercup Rust Uromyces dactylidis will affect other members of the large Ranunculaceae family.

[Maggi Young]

Ultimately breeding for resistance, horizontal resistance being the best, is the solution.

 Robert  - can you explain what "horizontal resistance" means, please?

[David Nicholson]

Inability to get up in the morning?

[rob krejzl]

One of the most obvious challenges being the narrow genetic base of many cultivated plants.

[johnw]

Now that I have calmed down and pulled myself together after David's comment............

Thanks for the responses.  Aaron thinks the Podo problem is not rust, I will photograph the symptoms more closely.  The Anemone does have rust but we have no hosts.  Back soon.

I have seen rust on a rhodo once, it was growing in dense woods where it was too dark and dank.  The problem abated when it was moved into full sun. With 112 days of fog a year once these things get started they are very hard to control.

johnw

[Geoforce]

John

Your symptom are definitely not those of the common mayapple rust which is endemic to this area.  I have noticed also though in the last few days some spots on a P. pleianthum leaf which have black mold spores apparently on the reverse of the leaf.  That doesn't sound like your description either though.

Geo

[Robert]

Robert  - can you explain what "horizontal resistance" means, please?

I think that David has the simplest explanation. 

Horizontal resistance refers to a situation where multiple and often ever changing factors create resistance to a disease or insect. Think land race. Another example: On the farm I breed and grow my own Lycopersicon esculentum (Tomato) varieties. Generally folks save varietal tomato seed by bagging (selfing) the flowers heads, sometimes with one or only a few plants. These plants are highly inbred and not very diverse.

When I create a new tomato variety I will only inbred to achieve uniformity for the characteristics I want to maintain. After that, I maintain the variety by outbreeding the best plants with each other. This has a number of advantages including horizontal resistance to many problems.

I do this as much as I can with both ornamentals as well as vegetable crops. I get a high degree of horizontal resistance to many problems, and never need to "spray" (including organic sprays) for insects or diseases. The trade off is that my plants varieties are not as uniform as others might want. Also, one reason why continuing to grow bulbs and other perennial plants from seed, from as diverse population as possible is such a sound idea, is that it can create horizontal resistance to many pathogens specific to your own conditions.

On the other hand there is vertical resistance, generally involving only one or a few genes. I do this all the time, too, using recurrent backcrossing. This can work well but sometimes the pathogens learn to work around the resistance.

Hopefully this is simple and clear.

[Maggi Young]

Thank you ,Robert - let's see if I've got this right - horizontal resistance is when resistance to disease etc is bred in across a wide gene range, giving a more stable and long lasting level of resistance ........ that about  right?

[Margaret]

I find your information very interesting, Robert.  On my allotment all the outdoor tomatoes (including Ferline) get blight by the end of the season and a large number of Zinnias succumb to something similar.  Can you recommend a variety and seed source for the most disease free plants?

[Robert]

Thank you ,Robert - let's see if I've got this right - horizontal resistance is when resistance to disease etc is bred in across a wide gene range, giving a more stable and long lasting level of resistance ........ that about  right?

Yes, You've got it. 

I find your information very interesting, Robert.  On my allotment all the outdoor tomatoes (including Ferline) get blight by the end of the season and a large number of Zinnias succumb to something similar.  Can you recommend a variety and seed source for the most disease free plants?

Margaret,

It sounds like Late Blight. And yes there are varieties that are said to be resistant. Remember, Light Blight is basically impossible to control late in the season - the weather is working against the poor tomato plants. Late Blight is not a problem here in summer sunny, dry California so I will look into this for you. I know a lot of farmers. It might take me a few days - busy farming.

Do your Zinnias have powdery mildew? Some varieties of Zinnia elegans are said to be resistant, but for me I have not found this to be true. I like Zinnia elegans and have been working on breeding dwarf cactus types that are resistant to powdery mildew. I still have a long ways to go on the mildew resistance part. If you find a variety that is resistant let me know. This is a case where recurrent backcrossing might work perfectly.

[Robert]

Margaret,

Johnny's Selected Seeds in the U.S.A. offers 3 late blight resistant tomato varieties. They also do international orders.

They are on the web at: Johnnyseeds.com

You can also try Seed Savers Exchange. This might be more work than you are willing to put into the project but there are 1,000's of tomato varieties available.

[Margaret]

Robert

Thank you very much for the advice. I've checked out johnseeds.com and will be ordering tomato Mountain Magic in the autumn. I didn't realise there are two sorts of blight and have done some reading on google. Plant hygiene (not easy on an allotment) seems to be a crucial factor along with the number of days of high humidity.

I've not noticed the Zinnias getting mildew.  A stem will tend to go biscuit coloured all the way through when the plant is growing vigorously. I remove the effected stem immediately but the plant always dies. Usually about 20% of the plants die prematurely.  I grow Thompson and Morgan Giant Cactus Mix - maybe it's time for a change.

[Robert]

Margaret,

Also consider saving seed from your healthy Zinnia plants (Yes, more than one - the more the better). Simple selection can be a powerful breeding tool! Choose a color you like, if you save seed from all the colors mixed together at some point you will end up with all pinks or something close to that.

For many this is more than they want to do, so maybe doing a trial of several different Cactus varieties might help single out the best variety.

Good luck with everything and I'm glad that I could be a small help.