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Plant Diseases/Bottom leaves on heirloom tomato plants curling and discoloring

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Question
Hello:

I am a very experienced (30+ years) organic gardener.  I live in CT in zone 5B.  I have a large yard-based veggie garden and 7 raised bed gardens for various herbs and spring/summer/fall crops.  I also have a huge variety of heirloom roses as well as several perennial flower beds.

The only fertilizer used in my garden is rabbit manure, comfrey leaves and if needed - crushed oyster shells for extra calcium.
I use a variety of hanging pest strips and visual deterrents to manage pests - I don't use chemicals of any type.  I add ladybugs and lacewing eggs every 3 weeks to control the soft-bodied insect pests.

My soil is outstanding. Each year I amend it with lots of leaves, manure, comfrey, yard clippings, a small amount of rock dust, and lots of worm castings which are created from my vermicompost windrow.  The soil has excellent drainage, is loaded with earthworms and thriving with beneficial insects and good bacteria.

Everything I plant thrives - they grow big and produce well.

On to my problem:  This year I expanded on the varieties of tomatoes I grow.  I don't buy any plants; I grow everything myself from home-saved seed.  Of course - if its a new variety, I have to buy the seed the first year.  I buy only organic, NON GMO seeds.

I have 35 varieties of tomato plants growing - all unique heirloom varieties; some are very unusual.

The bottom leaves on several of them are curling and discoloring - they either turn brown or yellow.  Some are worse than others.  The mineral balance of the soil is perfect, as is the PH level.  The plants are on drip-irrigation and neither under or over watered.  I inspected the leaves carefully with a magnifying glass and there are no pests, no fungus, or anything visible to reveal the cause.

I read online that heirloom tomatoes are subject to something called "splash-back" where the bottom leaves that get "splashed" from watering will curl and turn yellow.  Splashing is not a problem since I use drip irrigation, however, we have had several very hard thunderstorms with torrential rain falls/flash flooding.  Thing is - the storms have been mostly over the past 10 days and this issue started about 2 weeks ago.

The top growth is still strong and the plants are blossoming.  
I researched the issue on the web and several sources said to cut the wilted leaves off and several sources said do not cut them off - so I'm not sure which to follow.

Even though we have had some hard rains, the ground around each tomato plant is mulched with torn comfrey leaves so there shouldn't have been enough "splash" to cause this issue.

I'm stumped.....  I *think* the plants are going to be ok even with the lower leaf issue, but I really want to know what it is so I can correct it and prevent it from happening in the future.

What is going on?

Thanks for your help.

Lisa L.

Answer
Hi Lisa,

It sounds like you have a wonderful garden!  I'm a gardener and a home canner, so I also have a big garden to tend to.  It's no fun when things don't go as planned.

Based on the information, it sounds like you have good fertility in the garden.  It may be helpful to confirm this with a soil test since sometimes lower leaf yellowing is due to a nutritional problem.  However, if you feel confident that the fertility is fine, we can move onto other causes.

The splash problem you mentioned is possible, but since it developed before the rainfall, it doesn't sound like the cause.  Continue to monitor this as a cause, but I think more may be going on.

The two most common problems that I find with yellowing on tomatoes are bacterial leaf spots and Septoria leaf spots.  Sometimes, you don't see the obvious leaf spots and the leaves just turn yellow.  The problems tend to be more severe on the lower leaves because humidity is highest at the bottom of the plants.  

For both of these diseases, one of the recommendations is to pick off and remove the affected leaves.  Often, these leaves are going to fall anyway, so the purpose is to remove them before the debris contaminates the soil.  Both diseases can survive on debris in the soil for a few years and they may not be broke down by composting.  So, I would advise you throw these leaves in the trash.  

So where do these diseases come from.  Septoria can blow in on wind currents and bacteria leaf spots often start with contaminated seed.  There are hot water treatments that can be done on seed to reduce the bacteria on the surface.  You can search for these treatments on the internet.  Usually, it involves keeping the seed at a certain temperature for a certain amount of time.

Other than the cultural suggestions listed above, rotation out of Solanaceous plants is advised for at least 2-3 years.  Most problems that affect tomatoes will also affect peppers, eggplant, etc to some degree.  So, it would be best to avoid planting in these areas.  You can also monitor your plants and select less susceptible varieties.  If some of your varieties are especially susceptible, perhaps avoid them in the future or plant them in areas with excellent air circulation.  The less humidity will reduce the level of disease.  There is not much we can do about rainfall, but you can time your irrigation to early or mid-day rather than late in the day.  If plants are watered late in the day, they stay humid all night and are more likely to develop disease.

It does not sound like you would be interested in chemical options, but I will briefly mention it in case you get desperate later.  You could use copper or sulfur based sprays.  Both of these are labeled for organic use and would be effective for both diseases.  

For some pictures, you can check out these links.  As your tomatoes develop fruit, be sure to look for spots since it can help distinguish the exact cause for the symptoms.  
http://vegetablemdonline.ppath.cornell.edu/DiagnosticKeys/TomLeaf/BacSpot_Tom.ht
http://erec.ifas.ufl.edu/tomato-scouting-guide/diseases/bacterial-spot.shtml

http://vegetablemdonline.ppath.cornell.edu/DiagnosticKeys/TomLeaf/Septoria_Tom.h
http://www.ipm.iastate.edu/ipm/info/plant-diseases/septoria-leaf-spot

Good luck with your garden!

Plant Diseases

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Jennifer Olson

Expertise

Plant diseases affecting vegetables, fruits, nuts, lawns, trees, shrubs and ornamental plants. I have just volunteered as an expert on this site as of 01/2011.

Experience

Identification and management of plant diseases. Have been employed as a Plant Disease Diagnostician since 2002 and currently work in the Plant Disease and Insect Diagnostic Laboratory at the Oklahoma State University.

Organizations
National Plant Diagnostic Network, Great Plains Diagnostic Network

Education/Credentials
B.S. Biology - Lebanon Valley College; M.S. Plant and Soil Sciences,concentration Plant Pathology - University of Delaware; Ph.D. in progress - Oklahoma State University.

Past/Present Clients
Home gardeners, Hobbiests, Plant Breeders, Extension Educators, Nurseries, Greenhouses, Golf Courses, Departments of Agriculture, Industry professionals

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