Advice needed re cercospora

[mich]

Hi everyone - it's been simply ages since I've been on the site, mainly due to the fact that I haven't been diligent in the garden for the past couple of years. To my shame, the beds have become very overgrown with weeds but this growing season is different and I'm going gangbusters weeding and planting seeds as we head into spring.

I have a couple of questions that I hope you can help with.

I was doing an intense micro-weed in one of my raised beds yesterday and took a good look at my mostly self-seeded silverbeet plants. They're not growing well and it looks like I have cercospora leaf spot. I'm resigned to pulling out all the silverbeet and destroying it in an attempt to stop the fungus, but am at a loss to know what to plant in its place that isn't likely to be affected by anything remaining in the soil. I'm planning to top up the beds in the next couple of weeks with about 12-15 inches of compost/soil that has come from an outside source.

My questions are:

What can I plant in place of the silverbeet? I want to put down a good crop of beetroot and also celery and bush beans, but worry that the leaves might suffer from the same problem.

Is the top-up of soil likely to be sufficient to remove any remaining fungal issues? If not, is there anything I can apply to fix things?

I've planted potatoes in a section next to the silverbeet. Will the fungus have any effect on them?

I'm intending to place netting over the bed to try and stop pukekos and other birds picking out the young seedlings, as well as avoiding white caterpillars. It's a standard fabric netting that allows air circulation and rain to come through, but would it also encourage further fungal growth?

Thanks in advance for any advice.

Cheers, Mich.

[mskrieger]

Hi Mich,
I looked up cercospora leaf spot on my local agricultural extension service. Admittedly Northeastern US centric, but it claims the only garden veggies bothered by Cercospora are Chenopodia---beets, Swiss chard (I think what you call silverbeet), spinach, amaranth, etc. So the celery and bush beans should be fine. Potatoes, too. And I doubt netting will encourage fungal growth--how humid is your climate?

[mich]

Thanks so much for the reply, mskrieger - much appreciated. Bush beans, potatoes and celery it'll be for that bed this year.

I did some more research and see it's a soil-borne disease that's made worse by lots of weeds and damp, warm conditions. That was certainly the case with this bed (and another I have), where the weeds were rampant. Totally my own fault and I've learned from it. We've had a couple of mild winters in a row - this last one has been wetter than normal - and didn't get much of a summer last year, so humidity was probably worse than in the past.

So assuming that I keep the beds weed-free and plant with plenty of space between the veges, does anyone know if that will be enough to get rid of it in the soil? If not, will the addition of about a foot of new clean soil/compost on top be affected over time by the old stuff underneath? I'm wondering whether I need to totally remove the old soil (difficult - they're waist high beds) or treat it somehow.

Sorry if this seems basic stuff to all the garden experts here, but I'd be really happy to get your thoughts.

Cheers, Mich.

[steev]

Given that it's a fungus, you might be able to control it by getting it out of its pH comfort zone by amending with sulfur or ash, depending on which way you want to push it; certainly less labor than trying to replace the infested soil.

[mich]

That's a great suggestion, Steev - not one that I would have thought of, so thanks heaps. I guess before making a decision I need to think about what I can grow in a changed pH environment. I can put off topping up the soil level for a while so the existing soil has a chance to recover. Did some research and it seems that potatoes and beans (including bush beans) do fine in a slightly lower pH soil - which is what I wanted to grow in one plot anyhow, and they apparently play nicely together. And I might find some good fillers to put in the gaps.

I can try the opposite in the other beds if I find there's a similar problem.

Thanks again for the advice. It's been really helpful - not to mention encouraging. I pulled out all the silverbeet plants, put them in a big black plastic sack and they'll go in the rubbish next week.

Cheers, Mich.

[mskrieger]

Steev's advice is good. Also, basic plant rotation--don't grow any Chenopods in that bed for the next three or four years, if you can avoid it.
(I know this is hard to do in small gardens.)

[mich]

Thanks mskrieger - I'll keep a good record of where I plant stuff - good time to really get that rotation going. Fortunately I have enough room to manage it without too much trouble.

Cheers, Mich.

[mskrieger]

Hi Mich, I was out harvesting beets today and noticed the spots on their leaves. Probably a minor cercospora infection, but the patch has done well and the beets are tasty, so it seems like mostly a cosmetic problem in my garden. Did the silverbeet plants seem like they were really suffering? If not, it's probably not something you should worry about too much. But in case it's useful, here's the link I used for my initial response: ag.umass.edu/vegetable/fact-sheets/cercospora-leaf-spot-of-swiss-chard-beets-spinach

[mich]

Thanks for the link, mskrieger - it was a good read. Re the (now removed plants) - the new leaves were fine, but as they got larger the spots appeared. I feel better now that they're all out. :-)

Am hoping that by following yours and Steev's advice I'll eventually get rid of the disease, or at least keep it to a very low level. I put it all down to bad management (actually NO management) on my part but it's been a real heads-up on the importance of good practices. I really appreciate both your responses. This is a great site and I wish I hadn't left it so long before coming back, LOL.