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Vegetable Diseases

(June 2012)

QuestionPlease tell me why one of my tomato plants has a black spot on the bottom of each tomato.  I have 6 tomato plants in large pots on my patio.  All plants are doing great and look beautiful except this one tomato.


AnswerIt sounds like the one plant is suffering from blossom end rot.  This problem occurs more commonly on some varieties than others. It is a calcium deficiency that is made worse when we have major fluctuations of water—and if a plant is vigorously growing.  The calcium gets pulled from the bottom end of the tomato and you are left with a water-soaked area, which then rots or turns black.  Mulching (even in pots) can help to moderate moisture.  Adding a little lime into the soil can also help at planting, or you can lightly work it into the soil in the pot.

(November 2010)

QuestionWhen I plant my tomatoes in the ground they start out pretty good for the first two weeks. Then when they start coming up, during the next two weeks they just start drying out.  After blooming and producing the tomato the same problem is occurring. As the blooms come out they will dry and fall off.  Needless to say the tomatoes plants have a short life span. They will totally stop producing around the middle of the summer.  I was told by the agriculture dept. that I was probably splashing water up on the plants too much when watering. This last year I only had a soaker hose on them.  The agent said to put straw down around the bottom of the plants, but to no avail.  Maybe there is a better method that you can help me with.  Are there other solutions that you might know?


AnswerFirst, get your soil tested.  Take a pint of soil to your local county extension office and see what the pH is and the levels of N, P and K.  I always want to start with the foundation of the plants, which is the soil.  If your soil is pitiful and rocky, you can enrich it with compost.  How is the drainage?  If they are sitting in waterlogged soil, they will die quickly.   We recommend that you rotate where you plant your tomatoes every year because many tomato diseases are soil borne, and attack the plants earlier each season, but problems beginning within two weeks of planting is pretty amazing.  I think we might have something else going on.  Mulching the plants to keep soil from splashing on the stems can slow down the disease spread, but again, it doesn't usually occur within two weeks of planting, nor does it cause the flowers to dry.  Most tomato diseases either start with the leaves dying from the bottom and it progresses up the stem, or we have a dramatic wilting and dying from one of the vascular wilts.  It sounds like your problem is more about fruit set than plants dying.  How much sunlight do the plants get? They need at least 6 hours a day.  Some varieties quit setting fruit when the temperatures get above 90 degrees during the day or stay above 75 degrees at night, but if the plants look good, they can kick back in and produce well into fall.  I think we need to investigate further.

QuestionWe have been having problems with our "Sweet Ones" tomatoes since early summer.  The leaves are covered in tiny spots. We sprayed with Sevin several times to no avail.  We are hoping that you have an answer for us as to what it is and how we can stop it.  This is the first time in all the years that we have planted tomatoes that this has happened.  It seems to start at the bottom of the plant and work its way up to the top of the plant and go from plant to plant.  Thankfully our plants have continued to flower and yield tomatoes up until this week when either the disease and/or the weather got them.


AnswerWhat you have is a disease, not an insect problem, so the Sevin was totally ineffective, since it is an insecticide.  There are several leaf spotting diseases.  The most common is septoria leaf spot, but there are others as well including early and late blight.  Many tomato diseases are soil-borne, so rotating where you plant your tomatoes is important.  There are preventative fungicide sprays for tomato diseases, including Daconil and Bravo.  Make sure you read and follow the label directions for the waiting period between applications and harvest. Many of these diseases hit annually, so I think you are lucky you haven't seen them before.  Often you can harvest enough fruit not to worry about spraying.  Treating once you have the problem is often ineffective, it can slow the disease down, but it doesn’t get rid of it.

(June 2010)

QuestionIs there any way to treat soil that would help fight tomato wilt?  The only information I can find in garden books is to "buy disease resistant plants" and throw away the ones affected.  I bought disease resistant plants and for the second year in a row, my tomato plants are healthy and have tomatoes on them one day and are wilted and dead the next.  It is very discouraging.  Can I plant anything in the fall (like clover) that might aid in cleansing the soil?


AnswerMany tomato diseases are soil-borne.  That means they persist in the soil for years and can attack your tomatoes quicker each season.  Planting disease resistant varieties helps, but only to a point.  For one thing, disease resistance doesn’t cover every disease out there.  Secondly, a new strain of the disease can build up especially if you plant over and over again in the same area.  Rotating tomatoes in the garden is ideal, but again, that alone may not do the trick.  The best idea is to sterilize your soil using soil solarization.  Till the soil as deep as you can, then saturate the soil, getting it really wet.  Once you have wet the soil, cover it with clear plastic, making firm contact between soil and plastic.  Leave it covered for six to eight weeks between July and September and you should start off with clean soil next year.  Cover crops such as clover and vetch can help to build up your soil, but do little to control diseases.  You can also take a plant sample in to your local extension agent when you have the disease, they can pinpoint exactly which disease issue you have.


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