We grow them because we love them. Are they easy? Not always, but their delicious ripe rewards confirm why tomatoes continue to be the most popular crop grown among home gardeners.
In this, Part II of tomato care through the summer (read Part I here), let’s explore what can go wrong despite our good garden practices as we cruise into the harvest period.
The number one uncontrollable possibility in mid-summer is continuous high outdoor temperatures, which can affect flowering and fruiting. When days are consistently in the 90s, the yellow-colored flowers can dry up and fall off, which means no flower pollination and no tomatoes from the spent blossoms. One way to help reduce intense sun and high temperatures is to shade the plants.
Depending on the shade cloth material and weave, sunlight penetration under shaded plants can be reduced as much as 20% or more. Less intense direct sun can help cool plants and prevent flower drop, sunburnt fruit and foliage.
Check out available shade cloth options at your local independent garden retailer and online. Other materials, such as floating row cover, lightweight bed sheets, towels and burlap, also can work. In my book, shade cloth is worth the small investment. They also work very well for hail protection and can last ten or more years if stored out of the elements in the off-season.
Be sure to place the cloth on a frame of some type or attach it to stakes over the plants. Otherwise, the cover can weigh down the foliage. Although it is time-consuming to cover and uncover plants each day, doing so during the hottest part of the day can relieve stress on the flowers and reduce the possibility of flowers drying. The good news is that any fruit that is already on the vine should continue to grow and ripen, and new flowers will grow again.
Maintain a close eye on tomato plants and all vegetables during high-heat days, as they may need additional watering to keep up with their higher transpiration rates. Consider increasing the water frequency to once or twice a day, without increasing the amount of water which can lead to overwatering.
Other heat-related tomato issues can appear like rolled leaves, blossom-end rot, cat-faced fruit and sun-scalded fruit.
Rolled leaves from heat won’t unroll once temperatures cool a bit and generally don’t cause problems with the plant. Blossom-end rot shows up as brown or black lesions at the ends of the earliest fruit promoted by inconsistent watering and nutrient movement in plants; simply pluck the bad ones. Same for the unattractive cat-faced or contorted-looking fruits, most likely the result of cold weather early in the season that deformed them from that time. Sun-scalded fruit has pale white to yellow spots on areas that face the sun. Just remove the affected fruit since they won’t recover.
Two tomato diseases and a tourist pest insect that arrive from the south in summer are fairly common along the Front Range. The diseases are early blight and tomato spotted wilt virus, while the pests are psyllids. The best defense for gardeners is to be on the lookout for early signs of trouble on the plant leaves and take action if it’s not too late.
Tomato early blight (Alternaria solani) is a fungus that is around on old plant debris, the soil surface or in the soil. It gets started when conditions favor its development–warm temperatures in the 80s, plus moisture, humidity or heavy dew on plants. Discourage possible spread of the fungus by not watering overhead and always rotating crops from season to season, along with using a mulch under plants that helps prevent water splashing on lower leaves since the fungus can remain in the soil and winter over. Removing all vegetable matter that may harbor fungal and other pathogens after the outdoor growing season is always good bed planting hygiene.
Tomato early blight starts showing up after the first fruits get growing and begins on the older, lower leaves first. Look for small, round or angular dark, brownish spots that enlarge to over a half-inch in diameter. The larger spots resemble target-like rings with the tissue around the spot turning yellow. Severe infection causes the leaves to turn brown, wither and die. Stems are also infected, turning dry, brown, and sunken-looking. The fruit is okay to eat.
When caught early, start by cutting off infected lower leaves and branches and discard them, do not compost them. A tomato plant should be fine to continue growing and producing when up to a third of its lower foliage is removed, but no more. Use care when watering not to splash any water up on the plant. If overhead watering is the only option, apply at a time when leaves will dry quickly. Fungicide use may be helpful, discuss options with your master gardener volunteers and reputable independent garden center help desks.
Tomato Spotted Wilt Virus (TSWV) is the result of very small pest insects called thrips that get the virus from infected nearby host weeds and certain ornamental plants, then infect tomato leaves when feeding. Tomato leaves with TSWV initially look bronzed and dark-spotted. Look for purple-colored veins in the leaves as the virus advances. Upper leaves become cupped and twisted and the overall plant may appear stunted. Tomato fruit will have small to large yellow spots and patches. Fruit is edible; however, the plant is not salvageable and needs to be completely removed as soon as possible. Do not compost it. Look for and purchase TSWV-tolerant or -resistant seeds when seeding at home or buying transplants at garden centers. Remove weeds around the landscape and vegetable growing area.
Uninvited pest psyllids (pronounced sill-ids) hitchhike in the wind to the Front Range during the summer. Infestations can be irregular in gardens, some years psyllids may find your plants, other years there’s no occurrence. Psyllids inject toxic saliva into tomato and potato plants causing unmistakable visual damage — color changes and leaf curling.
Early scouting of leaf undersides is advised when looking for them. Small, yellow eggs that grow into green, oval, yet flat nymphs can be seen. As the nymphs feed on leaf undersides, their excretions or droppings (technically named lerps) look like salt or sugar crystals. Adult psyllids, about the size of aphids, are dark in color and can jump when disturbed on plants.
A highly infected tomato looks like a saltshaker was emptied over the plant. The leaves also will look yellow to purple in color and appear to stand on end with a feathered, twirled look. Insecticidal soaps can help when infection is detected early. Be sure to cover both upper and lower parts of the leaves and entire plants. Other control options can be found on the fact sheet under resources.
Later in the summer with Tomato Growing Part III we’ll look at harvest, late-season growing tips, recipes and preservation.
Resources
Recognizing Tomato Problems — extension.colostate.edu/topic-areas/yard-garden/recognizing-tomato-problems-2-949/
Potato or Tomato Psyllids — agsci.colostate.edu/agbio/ipm-pests/potato-psyllid/
Betty Cahill speaks and writes about gardening in the Rocky Mountain Region.
