How are your tomatoes growing? It seems there are lots of questions about tomato problems every year.

The most common question is about blossom end rot — the bottom of the tomato turns black and rots as the tomato starts to ripen. Some varieties are more prone to this disease than others. Uneven watering is the cause of this.

It seems like the first tomatoes of the year are more susceptible. When I used to grow Roma tomatoes, I would have problems with them and not the other varieties — even though they were all treated the same.

This year I grew three different varieties in three different large whiskey barrels. Celebrity and Early Girl didn’t have a problem but the third one did — sorry to say I lost the tag for that one. They were all treated the same and watered the same amount.

In August/September there are several diseases that are seen in tomatoes and peppers. They are caused by fungi, bacteria or viruses.

Two of the most common diseases are septoria leaf spot and bacterial leaf spot. After you see the disease, it is most likely too late to treat.

In order to prevent this problem, don’t work with your tomatoes when it’s wet. The disease spores spread easily on your hands and tools.

Trim off the lower branches of your tomatoes but don’t remove more than one-third of the leaves on your plant. Make sure the plants have good air circulation around them. Stake or trellis them, pull weeds and space plants far apart.

When shopping for tomato plants in the spring, pay attention to the initials following the name of the tomato on the plant stake. The more initials the better. Varieties with lots of initials after their name include Better Boy, Beefmaster, Early Girl, Buffalosteak, Lemon Boy, Celebrity, Bella Rosa, Bush Early Girl, and the list goes on.

Clip this list for handy reference next spring.

  • V Verticillium Wilt
  • F Fusarium Wilt
  • FF Fusarium, races 1 and 2
  • FFF Fusarium, races 1, 2, and 3
  • N Nematodes
  • A Alternaria
  • T Tobacco Mosaic Virus
  • St Stemphylium (Gray Leaf Spot)
  • TSWV Tomato Spotted Wilt Virus
  • EB Early blight
  • LB Late blight

There might be more problems this year because disease is more rampant with high temperatures, high humidity and frequent rain — or overhead irrigation.

How to tell if you have septoria leaf spot or bacterial leaf spot? Tomato leaves have small — about an eighth-inch — brown, circular spots surrounded by a yellow halo. The center of the leaf spots often falls out resulting in small holes; tomato fruit often have a waxy white halo surrounding the fruit spot which is a quarter-inch, slightly raised, brown and scabby. The spots occur on green and ripe fruit but do not cause rot.

Bacteria survive on plant debris in the soil for one to two years but will not survive once plant debris is broken down.

It’s best to remove all debris in the fall and get rid of it. Do not compost. Pesticides are available to protect tomatoes and pepper from bacterial spot. Applications should be made when environmental conditions favor disease to be the most effective and repeated, according to label instructions.

Next year, as the ground warms, cover the soil with mulch to prevent that splash-up of the bacteria or fungi. Try landscape fabric, straw, plastic mulch or dried leaves.

Make sure your leaf mulch or grass clippings mulch have not been exposed to herbicides.

Usually if you mow three times after spraying the lawn, the grass clippings are safe to use. And most important, rotate where you plant your tomatoes if at all possible. If you plant them in pots, use new soil each year.

Some of this information was taken from an article by Michelle Grabowski, Extension Educator with the University of Minnesota.

Master Gardener Sue Morris has been writing this column since 1991 for Kandiyohi County newspapers. Morris has been certified through the University of Minnesota as gardening and horticulture expert since 1983. She lives in Kandiyohi County. To consult with a Master Gardener, call your county Extension office.