Tomato Update

I've been fielding lots of tomato questions in the clinic lately. The top four questions and their answers
follow:

My tomato plants were doing great but then the entire plant suddenly wilted. What’s happened?

Southern bacterial wilt and to a lesser extent southern stem rot are the most common culprits. If you cut the bark off of the stem and see brown discoloration in the vascular tissue, southern bacterial wilt is the culprit. If white fungal growth is visible at the base of the plant, it is likely to be southern stem rot. There is no cure for either of these diseases because both are caused by organisms that live in the soil for years. Pull up and destroy any affected plants. Rotate your tomatoes to another spot in the garden or relocate your garden altogether. If this is not possible, consider growing tomatoes in containers starting with clean, bagged soil or potting mix.


My tomatoes seem to have stopped growing and are starting to look stunted. The young leaves are purplish-brown and appear to be dying. What’s going on?

This could be a viral disease called tomato spotted wilt virus (TSWV). The disease is transmitted to the tomato plants by tiny insects called thrips. The symptoms usually appear first at the top of the plant but eventually spread. There is no cure for this disease either. Remove infected plants from the garden. Eliminate weeds in and around the garden that may harbor thrips. We only have one flush of thrips annually here so you can go ahead and replant tomatoes in your fall garden without fear of the disease returning. There are several TSWV resistant varieties of tomatoes available including Amelia, Crista and Talledega.

Why are my tomatoes flowering but not setting fruit?

Tomato pollination and fruit set occurs best when night temperatures are between 60 and 70 F. When night temperatures consistently stay in the mid-seventies or higher, fruit set will diminish dramatically.

What causes rot on the blossom end of my tomatoes?

“Blossom end rot” is a disease that occurs when tomato plants cannot move enough calcium out of the soil. If blossom end rot is a problem in your garden, make sure you sample your soil and lime according to the sample recommendation. Blossom end rot can occur even with adequate soil calcium levels if the plant is not able to take up the calcium efficiently. This can occur during a drought if plants aren’t watered regularly.

I have also seen several tomato plants (and other crops) that have been damaged by herbicides. Tomatoes are very sensitive to certain chemicals including glyphosate. Take special care when using herbicides around the garden and remember that herbicides can drift if the wind is blowing or volatilize if temperatures are high. Herbicide injury frequently results in abnormal “strappy” growth, marginal burn on the leaves or discoloration of the veins of the leaf.

I am seeing a fair number of aphids on tomatoes. This is probably because of the stress the plants are under due to the drought. Aphids can be easily controlled with insecticidal soap, just make sure that you treat the underside of the leaf and the new growth where most of the aphids are found.

Tomato Tips: Things to think about before you buy and plant

Its that time of year and people are rushing out to buy tomatoes.  However, I encourage you to stop and think about what you and your tomatoes need to have a happy, healthy growing season.  This is one time when it doesn't pay to be impatient. 

Tomatoes are a warm weather crop and don't flourish until day time temperatures are well into the 60s and night time temperatures are above 50 F.  If you set your plants out the beginning of April, they will not grow vigorously until the soil and air temperatures warm up towards the end of the month.  Meanwhile, tomatoes are very sensitive to frost.  The last frost date in our area tends to occur around April 15 to 20 although it can occasionally happen as late as the first week in May.  If you buy tomatoes earlier, you will need to protect them from cold nights until the weather warms.  You are better off waiting until after the last frost date to buy and plant your tomato seedlings.  These plants will likely grow more quickly and vigorously than tomatoes planted in cold soils early in the season.

Varietal selection is important when choosing what tomato varieties you want to grow.  At the very least, you need to consider their growing habits (determinant versus indeterminant tomatoes) and disease resistance.

Many of us have heard the terms determinant and indeterminant but what do these terms mean?  Determinate tomatoes bear a single large harvest while indeterminate tomatoes bear fruit over a longer harvesting season. Determinate varieties are often (but not always) more compact while indeterminate varieties tend to grow longer vines and require more support.

So which type should you grow? Determinate varieties are a good choice for people who like to make sauce, can or dry tomatoes. If you use tomatoes mostly for snacking and eating fresh, indeterminate varieties will provide you with tomatoes throughout the season. If you are growing your tomatoes in a container, a determinate variety will tend to be more well-behaved and not require as much support and pruning to maintain as an indeterminate variety. When shopping, look for the abbreviation DET (determinate) or IND (indeterminate) on the label. Most cherry tomato and heirloom varieties are indeterminate.

If you choose to grow determinate tomatoes, you may want to select several different varieties to ensure early, mid and late season crops. Look at the seed package to determine the number of days from seeding until fruit set.  Choose varieties with different maturity dates if you want production throughout the season.  Remember that the seed sowing date and growing conditions will affect the actual fruiting date.

"Suckering", or removing the side shoots that develop between the main stem and a leaf, is a common practice but it is not desirable for determinant varieties because it will decrease yields. You can sucker your indeterminate varieties but it may not be necessary if you have a vigorous, well-caged plant.

Disease resistance is an important characteristic in tomatoes.  Some tomato varieties are naturally more resistant to certain diseases than others.  If you can determine which diseases are issues in your garden, you may be able to choose varieties that are less susceptible.  Two diseases of particular issue in Onslow County are Tomato Spotted Wilt Virus and Southern Bacterial Wilt. 

Tomato Spotted Wilt Virus (TSWV) results in tomato plants that stop growing and look stunted.  The young leaves may look purplish-brown and appear to be dying.  This is a viral disease that is transmitted by tiny insects called thrips.  The thrips transfer the virus from weeds around the garden to the tomato plants.  If you have experienced TSWV in the past, look for a tomato variety that lists TSWV on the package, indicating that the variety carries some natural resistance to this disease.  Also, eliminate the weeds in and around the garden area that harbor this disease.

Southern Bacterial Blight is a common soil-borne disease in our area.  This disease results in plants wilting (despite adequate soil moisture) as the bacteria blocks up the vascular system of the plant.  Initially plants may wilt only on hot afternoons and revive by the next morning.  As the disease progresses, the entire plant will wilt permanently and die.  The bacteria that causes this disease lives in the soil and can persist for years so your best treatment is to relocate your tomatoes (in another part of the garden or another location all together).  You may also consider growing your tomatoes in containers using clean potting mix.  There are very few tomato varieties that are naturally resistant to Southern Bacterial Blight and the few that are do not have high quality fruit.

These are just two of the diseases that can affect tomatoes.   You may see other acronyms on your tomato packet including TMV (Tobacco Mosaic Virus resistance) and N (Nematode resistance). 

So please be patient.  Wait another week or two before buying your tomato plants, choose your varieties carefully, plant them when the soil and nights are warm, and give them the best possible chance to grow and thrive.