Growing tomatoes in Colorado is rewarding, challenging


Nothing can beat the taste and juiciness of a home-grown tomato. And in spite of our short season, backyard growers can be successful. If you have a greenhouse of some sort, you have probably been enjoying this tasty summer treat for some time. Some gardeners, however, are beginning to see some problems on their tomato plants and fruit. Good cultural practices can help reduce or eliminate many of these problems.

Blossom end rot

This is the most common problem that tomato growers have experienced this season. Blossom end rot begins as light tan, water-soaked lesions on the blossom end of the fruit. These lesions enlarge and turn black and leathery. The cause is thought to be a combination of cold temperatures or excessive heat during blossom set, and fluctuations in water supply. When these two factors occur simultaneously, calcium often becomes unavailable to the plant. Hence, a calcium deficiency occurs during fruit formation. To manage the problem, fertilize and water properly. Avoid setting out transplants too early in the season and use mulch to help reduce fluctuations in moisture levels.


Sunscald is common on fruit exposed to too much sun. This problem often occurs when infestations of hornworms are high and defoliation or pruning of leaves is heavy. To help control sunscald, shade the plant and reduce the fruit’s exposure to the sun.

Curly top virus

Curly top virus is transmitted by the beet leafhopper. Infected plants turn yellow and stop growing. Upper leaflets roll and develop a purplish color, especially along the veins. Leaves and stems become stiff and fruit ripens prematurely. Hot, dry springs with predominantly southwest winds usually indicate increased problems with this disease since leafhoppers migrate from southern areas. No chemical controls are effective, but you can use row covers to protect tomato plants from leafhopper infestations.


Catfacing is a term that describes tomato fruit that is misshapen, with scars and holes in the blossom end. The cause is thought to be cold weather during blossoming and, perhaps, high levels of nitrogen. To manage it, avoid setting out transplants too early in the season.

Tomato or tobacco hornworms

These insects are large, green or gray-green caterpillars with white to tan V-shaped or dashed markings on their sides. A green to reddish horn protrudes from the hind end. They are voracious feeders, stripping leaves from stems and even eating unripe fruit. Pick them off by hand. The caterpillars are susceptible to Bacillus thuringiensis (Bt), as well as to many common vegetable insecticides.

Fusarium wilt and fusarium crown rot

Symptoms of these diseases begin as yellowing of older leaves. With fusarium crown rot, the leaves often turn brown or black and eventually wilt. With fusarium wilt, the yellow leaves turn downward and droop. The cause of both diseases is a common tomato fungus that lives in the plant’s vascular system which carries water from the roots to the leaves. To see if either of these diseases is present:

  • Check watering practices. Both over and under watering can mimic disease symptoms.
  • Check the roots. Discolored roots indicate root rot.
  • Cut the lower or main stem and look inside at the vascular tissue. Look for a dark brown discoloration within the vascular tissue. The crown rot disease causes a rot or canker at the base of the stem and possibly a root rot.

To avoid these problems, purchase tomato seeds or transplants that are labeled with a code such as “VFN,” “VFNA,” and “VFNT,” etc. Do not plant tomatoes, potatoes or eggplant in the affected area for two or three years. No fungicides are labeled for control.

Many of these problems can be avoided and/or minimized by using proper cultural practices:

  • Improve garden soil by adding organic material such as compost.
  • Use disease-resistant varieties.
  • Eliminate competition from weeds.
  • Keep the plant growing vigorously with proper water and nutrients.
  • Keep the garden clean of plant debris.
  • Rotate crops.
  • Space plants for maximum air circulation.
  • Monitor for pests.

To manage pests, identify the source of the problem by assessing the symptoms. To help you identify the symptom and problem, and to read more about potential tomato problems, refer to Table 1 in the Colorado State University Extension Fact Sheet No. 2.949, “Recognizing Tomato Problems,” written by S. Newman and L. Pottorff which can be downloaded at

Free wood chips available for pick-up

We are cleaning up the fairgrounds and all of the wood chips that helped keep things dry during the fair are available to anyone for pick up. If you are interested, just bring your pickup truck and haul it away. No need to call the Extension office for permission.

Greenhouse classes

Colorado State University Extension and the Geothermal Greenhouse Partnership are co-sponsoring a series of classes to help backyard gardeners and small growers be successful. Classes will be taught by both state and regional Extension specialists and local gardening enthusiasts. Don’t miss this opportunity to learn from the experts.

Greenhouse tour

On Wednesday, Sept. 3, meet at the CSU Extension building to tour local greenhouses and grow domes and learn from other local growers from 4-6 p.m.

The cost is $5 and pre-registration is required. To register, call 264-5931. Call the Extension building to get details and addresses for the tour.

CSU Extension programs are available to all without discrimination. If you have a disability for which you seek an accommodation, please notify the office at 264-5931 at least one week before the class.

CPR and first aid

CPR and first aid certification classes are offered monthly by the CSU Extension office on the second Monday and Wednesday of each month from 6-10 p.m. Anyone needing to receive or renew certification can register by calling the Extension office at 264-5931.

We will also schedule classes on additional dates with five or more registrations. Cost for the classes are $80 for combined CPR/first aid and $55 for individual CPR or first aid. The type of first aid information provided will vary by the needs of the audience. Group rates are available. Call the Extension office at 264-5931 for information.