Nessary? No. Reccomended? Highly.
Crop rotation not only helps control desease and pest carry over,it prevents depleting micro-neutrents and trace elements if the crop is a heavy user of one or more. I would reccomend you learn all you can about neutrent requirments,pest control and desease prevention/remediation for your choosen plants. Stated another way,you must be far more deligent growing same crops back to back compared to rotating.

Downy mildew is a killer. You should be able to grow none susceptible crops ther but not cucumbers or relatives. Fusarium (if you have it) is permanent. Fortunately there are varieties with sufficient resistance to give you a crop of tomatoes before they succomb. I am surprised that you would have Fusarium in a raised bed unless you brought in contaminated soil.

As the many previous discussions of this issue will show, those who don't or can't rotate compensate for the issues that creates with great soil amendments as often as possible. Compost, compost, compost several times a year. And then more compost. :)

Dave

Yes, I agree with Dave. If you can't rotate your crops, consider rotating the soil. My garden is on the smaller side, and I can only move things around so much. I amend with lots of compost every year, and have been known to completely dig out and replace the soil in beds where I've had some problems.

For the diseases mentioned, completely diiging out and replacing the growing medium is the best solution. No amount of fertility impresses a soil bourne disease likeFusarium.

I can understand how crop rotation is of major benefit if you have a ton of space, but in my case, I don't see how moving my crops 20' across the garden (to an area they are less suited for) is going to stop most soil borne diseases. I will do the best I can to rotate as much as possible, but for pathogenic diseases that overwinter in the soil, next year I will plant resistant varieties, do all I can to amend the soil to keep healthy plants that resist disease, and apply prophylactic treatments (i.e. sulfur etc)... I feel like all of these things will be of more benefit then shuffling things around my garden plot... I am no expert myself, but I know plenty others that plant the same stuff every year without major issues.

I really hope that It's not Fusarium in my garden.. If yes, then I can plant resistant varieties.. But as for the cucumbers, is downy mildew permanent to? Because I don't have another place to plant cucumbers in the summer :-(

I'd suggest you learn more about the few soil-borne diseases, their symptoms, and how they are diagnosed so that you can accurately determine what the problems you actually have are. There is ample information available on the web about all of them and the link below is a good place to start.

That, rather than focusing on crop rotation and guessing at diseases, will get you much more success in the long run. Plus accepting that neglect or improper care kills more plants than all the diseases put together puts you on the track to understanding what your problems really are.

Not that good soil amending is ever a bad thing, But just assuming you 'might' have one of the rare diseases usually just leads to making bad choices and only compounding the problems.

For example, plants that have survived a month probably do not have Fusarium Wilt. So planting only resistant varieties doesn't guarantee you problem-free gardening. They are merely a little more "resistant", not immune. So if you don't even have the disease why restrict yourself to only resistant varieties when it may well be growing conditions rather than a disease to begin with?

Further given all the info available on Downey Mildew, if that is really the problem, it is easy to learn that while no Downey Mildew is not "permanent", that in no way means you can't get Downey Mildew every year when the growing conditions provided allow it to develop or when there is insufficient plant monitoring and intervention to prevent it.

So shift your focus to learning about the diseases rather than hoping that simple crop rotation will solve your problems. It won't but learning more can..

Dave

Here is a link that might be useful: Vegetable Diseases Caused by Soil Pathogens

Downy mildew is considered a fungus, I have never been able to contol it once established. It is both air and soil bourne. Some fungicides will apparently slow it down, but they are not readily available to home gardeners. The good news is that it does not overwinter in cold climates, so if the ground freezes you should be good to grow. I have tried some of the resistant cucumber varieties with mediocre results.

Here is a link that might be useful: Downy mildew-Cucurbits.

I have been planting tomatoes year after year in the same spot and have never lost a single plant to disease. I mulch with shredded leaves every year and now I am working on a compost pile to add after this growing season for the first time. So based on my experience, crop rotation is def not necessary.

Try growing in the humid south where dew sets on the plants from about 10 pm to 10 or 11 am and the air currents blow the diseases up from overwintering in Florida. Then you would consider crop rotation. It might not help much, but you would still think a little longer about crop rotation.

Farmerdill - It is my understanding that downy mildew adapted back in about 2004 and many of the varieties that claim they are downy mildew resistant are no longer resistant to the new adapted downy mildew. What variety have you found lately that is the most resistant. Every single year my cucumbers die about this time of the summer from Downy mildew and I have been looking for the most resistant variety.

You are correct. Cornell introduced several resistant varieties, but Downy Mildew has mutated to the point that the resistance has been pretty much overcome. Best I have tried has been Marketmore 76 but it succombs rapidly to the current version of DM. I have to find a spot where cucurbits have nopt been grown for 5- 10 years. I realize that that is impossible for most backyard gardeners.

Thanks farrmerdill. I have not planted cucumbers in the same spot since I started this garden at my new house. 3 years and DM every year even though I rotated every time. I found this study that lists their most resistant varieties. It looks like the four most resistant varieties in this test were Ivory Queen (Cornell), Suyo Long (Twin Oaks), Shantung Shuyo F1 352(Fedco), and Green DMR 264 (Cornell). The trial was done in 2013 by Twin Oaks but I have never heard of anyone growing these so I do not know how resistant they are. Marketmore 76 was rated pretty far down on the resistant scale. I also do not know how reliable this study was. Also, cant find a source for either of the Cornell varieties. The file type was not allowed in GW so I just linked it within the body of this post.

http://www.twinoakscommunity.org/docmanhidden/seed-growing/

This post was edited by yolos on Sat, Aug 2, 14 at 13:30

I understand that blight, which is a fungal disease, is well transmitted to succeeding generations of identical plants if planted in the same place. And yes, that stops this soil-borne disease because the disease is splashed up on to leaves by watering. I agree with the idea of soil replacement, including amendment, though another way to do that is to dig the bed deeply. At least blight spores can't survive burial of more than six inches. That is, get your new soil from deep layers, and put the topmost layer deep underneath for a year or so.

Well, Farmerdill, looking at your link, I don't seem to have DM at the end of the season each year on my squash! I just assumed that's what it was! Thanks! (NOT OP!) Nancy

Hey, Nancyjane, I may be mistaken, but I believe that downy mildew can be pretty much avoided in our climate if you use drip irrigation. The summers are too dry for easy propagation of downy mildew. I've seen people who had what I took to be downy mildew it on plants, but they were generally spray irrigated, or ornamental plants in the winter. I am not an expert, though, so take it for what it is worth. ;-)

McKenzie

The same is true in Israel (the OP location). I can not believe that he gets DM. He must be watering with sprinklers. Israel is about as dry as the Central Valley in CA.