Southern diseases of tomatoes

[mensplace]

From a recent contact from Auburn

"
Last year we saw an increase in fungal and bacteral diseases due to the extended periods of cool, wet weather that favor these forms of pathogens. We will have to see how the weather plays out this year to see how much disease pressure we come under in 2010. One of the best ways to reduce damage from plant diseases is to start off with a healthy plant. In general, a plant growing under stress is more susceptible to disease.
With tomatoes, we really have resistance to only four diseases:
1) Fusarium wilt and (2) Verticillium wilt which both survive in the soil for many years in the absence of disease
3) Root-knot nematodes, which can also survive many years in the soil
4) Tomato spotted wilt virus (TSWV), which is carried from plant-to-plant by thrips (and insect) that transmit the virus while feeding
　
*Verticillium wilt is uncommon in Alabama.
Fusarium wilt is common throughout the state. There are many varieties that have resistance to this pathogen. I would choose a variety that is resistant to Fusarium based on its yield potential in your area and/or fruit quality as it is not possible to differentiate levels of resistance within the various Fusarium wilt-resistant varieties on the market. You may need to do your own experiment to determine which variety you like best in your garden/field.
Root-knot nematode is an organism you can check for through a soil test designed to detect nematodes. These are best done in the Fall at the end of the season when populations are at their highest. A soil test now (January) might not give an accurate reading on this pest because populations plunge with winter temperatures. If you already know you have root-knot in your planting area then you should plant a nematode resistant variety. As with Fusarium it is not possible to choose one root-knot nematode resistant variety over another based on its level of resistance.
Tomato spotted wilt virus has become a more common problem in Alabama in the last 10 years. If you live in south Alabama or have had a history of this disease in your area, then I would suggest planting a TSWV-resistant varieity. However, there are only a handlful of these available with "Amelia" being the best from what I have heard from other growers.
As far as the buffer zone around the garden, it has been determined that about 85% of the viruses that attack tomatoes come from virus-infected weeds that survive the winter within 30 ft of a field. So, if possible, providing a weed-free buffer around the garden prior to planting can reduce virus pressure on tomatoes. Of course, insects can still bring in viruses from other sources outside this buffer zone as many of that plant viruses that infect tomatoes are spread by insects such as aphids and thrips. About 90% of all viruses are spread by insects..
As far as other cultural control methods for a tomato patch. I would strongly recommend avoiding overhead irrigation. Water once or twice a week using drip irrigation or soaker hoses, if possible, in an attempt to keep the foliage dry. Wet foliage provides conditions that favor development of both fungal and bacterial foliar diseases."

[b54red]

I believe the main culprit is the high humidity which makes it difficult for foliage to stay dry or dry off after rain or morning dew. I remember a few summers when we had unusually low humidity and foliage diseases were nearly nonexistent.
Because of the humidity in the Gulf Coast region I live in I have changed the way I support my tomatoes and the way I manage their growth and the types I try to grow. I used to grow mostly determinate types that I would stake or cage. The problem with this is the heavy bushy growth allows little air flow and the leaves remain wet too long. This leads to devastating foliar disease starting in the densest area and quickly spreading. I now only plant determinates very early for a quick crop and even prune them to keep them more open so they will remain healthy long enough to make.
I now plant mostly indeterminate types and grow them on a trellis so they can spread out more. I also prune to keep the foliage under control so air and sun can reach most of the leaves. Despite unbelievable rainy wet conditions last year I had the best tomato season in over 30 years of gardening. I just wish I had started doing this many years ago.
As for tilling in the winter cold to help control nematodes; if you do it during a long cold spell you don't have to worry about killing too many beneficial worms because they have already moved deep to avoid the cold.

[mtbigfish]

mensplace
years ago nematodes were removed via vapam (spelling) but taken off the market - I always just went to containers -

I have moved to a new city and also have two garden plots where I moved from. I am curious how I am going to get around nematodes in the plots sandy soil (I have amended, added serenade, actinovate, plant success and Bacillus MB1600 via PROMix with biofungacide for general plant health but nothing for nematodes). some people have had nematodes in their plots while others haven't so I was thinking about seeding parasitic nematodes and also using some containers

does anyone have experience with the parasitic nematodes that kill off the bad ones?

Thanks for any info
Dennis

[b54red]

I had a terrible nematode problem years ago. I mucked out some horse stalls and put the fresh manure and tilled it in immediately without composting. Then started adding aged horse manure for the next few years and the nematodes have been well under control since then. I read somewhere many years ago that horse manure contains a type of mold that traps nematodes. I don't know if that's true but it had an amazing affect on my garden. I still get a few nematodes in cucumbers, squash and the occasional heirloom tomato; but not enough to stop them from having a very productive season.
My next door neighbor whose garden was literally a couple of feet from mine used that poison that has since been banned for two years and then had no nematodes for about a year. After that the nematodes totally took over his garden and after a few years the only thing that would live long enough to produce was hot peppers. He finally gave up gardening because of the nematodes. That was over 15 years ago.
From my own experience nematodes don't like onions, garlic, hot peppers, most bell peppers nor any herbs that I have grown. I try to rotate as much as possible; but with 80% of my garden in tomatoes I can't do too much. Even so I only had 3 or 4 tomatoes showing nematode damage last year out of around 65 plants. I always check the roots when pulling up my dead or dying plants.
This winter I added some fresh cow manure to some of my beds that had a little nematode activity to see if it also has the therapeutic properties of horse manure.
The easiest way to tell if you might have nematode activity that is damaging your plants is if they seem to be lacking water even after a good rainfall or watering. I have also noticed that plants plagued by nematodes usually have spider mite infestations.

[mtbigfish]

b54
Thanks will plant companion plants -
Dennis