Enhance your gardening skills with these expert tips for planting, support, fertilization, and harvesting from Guest Contributor and CSU Horticulture Agent Cassey Anderson!
Troubleshooting Tomatoes
Summer means fresh garden tomatoes, right? Well, mostly. However, I often make the joke that tomatoes are the princesses of the vegetable garden, they can be impacted by many diseases, environmental issues, and issues with cultural care. I can’t go into detail on every one but let’s take a look at some of the heavy hitters that we see in the office frequently.
What do tomatoes need to grow well?
First off, they need well-drained soil that gets regular water, whether from the sky for those of you lucky enough to get enough natural precipitation, or from irrigation. For successful fruit production tomatoes need to be fertilized regularly, but not too much, and we’ll get into why on that in a bit. Finally, tomatoes need temperatures that are warm, preferably above 60 F, but not too hot, as they get finicky with daytime temperatures above around 90 degrees and nighttime temperatures above 80 degrees F.
Common issues caused by environmental or cultural practices
Blossom End Rot – BER is often blamed on insufficient calcium in the soil. And while the damage is caused by poor movement of calcium, it is rarely the case that lack of calcium in the soil was to blame. Rather, BER occurs often when soils are irregularly watered, or are too cold. Once soils warm up, and a regular water practice is put in place. How do you know you’re watering right, well try to water so the soil dries out a little, but does not get bone dry, and avoid watering so much that the soil is completely saturated. BER can show up on other fruit as well, including pepper, melon, cucumber, squash etc.
No fruit – lack of fruit is an unfortunate and common experience for gardeners. Generally, there are two causes: high temperatures, and over fertilization.
I mentioned above that tomatoes get finicky when temperatures raise to higher levels, something that is increasingly common in summertime. That, however, does not mean that all hope is lost. You can invest in shade cloth for your vegetable garden. Shade cloth can be purchased in varying levels of shade reduction. Reducing the intensity of the sun by 30-40% can reduce the ambient temperatures and help ensure that tomatoes continue to set fruit rather than dropping it.
It can also be tempting to follow the practice of “if a little is good, more is better” when gardening. In the case of fertilizer, this is not good practice. Not only could you be adding to the salt load of your soil which will cause plant growth issues down the line, but too much nitrogen on a tomato plant can lead to excessive leafy growth and a dearth of flower production. Essentially, you are creating an environment that is so ideal for the plant that it sees no NEED to set flowers and produce fruit, it’s living in the lap of fertilizer luxury. If you see this issue, reduce how much you are fertilizing (or potentially stop for the season). You can also do a soil test to see where your soil is at.
Zippering - the male flower parts remain attached to the fruit as it developed, if tomatoes remain small it won’t cause much beyond a small “scar” on the surface of the tomato fruit. If the tomato gets large it can cause distortions in growth.
Catfacing – distortion of the flower end of the fruit that can be caused by low temperatures during flowering (60-65 degrees F), potential herbicide drift, or by varietal type as heirloom varieties are more susceptible to developing catfacing. These tomatoes are still perfectly usable even if they have developed scar tissue, you can cut out the affected area or use it in processed recipes.
Cracking – cracking is most often caused by overwatering or erratic watering. If temperatures become high during periods of rapid water uptake, the fruit to grow faster than the skin can expand. To prevent splitting, harvest at or just before maturity, water uniformly, use shade cloth, and select varieties less prone to splitting. Cherry tomatoes, for example, are very prone to splitting, whereas larger beefsteak types may only split if conditions are right.
Biotic issues, those that are caused by a virus, fungus, careless human etc.
Early Blight – characterized by small, dark spots on the leaves, typically the oldest foliage near the ground shows symptoms first. Tissue surrounding the spots may yellow and the leaves may eve
On fruit the spots can develop that are leathery and black and often develop near the stem. If the infection persists it may lead to fruit drop. To manage, watch for leaf spots and remove quickly, water at the base rather than overhead watering. When removing infested leaves or fruit do not put them in your home compost as the pathogen (a fungus) can persist and reinfest new crops. Staking plants and pruning to increase airflow has also been shown to be an effective management option.
Tomato spotted wilt virus – Spread by small insects called thrips, this virus develops systemically throughout the plant, so symptoms can show up on leaves and fruit. Leaves may start with a bronze coloration, and then develop a cup shape and have spots, fruit has concentric rings and blotches. Management of TSWV is typically removal of the plant once symptoms have been identified. There are not effective treatment options. Additionally, control weeds in your surrounding area to reduce additional transmission. Be sure to check new plants for signs of disease, or buy from reputable sellers.
Tobacco mosaic virus – symptoms on leaves include stunted growth, thickening or strange coloring. This virus can remain persistent in seed, so be sure to check your sources when acquiring materials. As with TSWV, there is no treatment, so removal of infected material is necessary, and not in a compost system. If you or anyone in your household is a cigarette smoker, be sure to wash your hands thoroughly before handling your tomatoes as it is possible to pass the virus from cigarette to plant. Diagnosis of TSWV and TMV often will require lab testing to positively confirm, but if you see symptoms consistent with these viruses, as there is no treatment the best approach is to remove the plant and sterilize any support structures. If the issue persists through years seek out resistant varieties.
Herbicide damage – finally I want to address that there are several ways tomatoes can be subjected to herbicides. The first one is through the mulch or compost you use. There is an herbicide called aminopyralid that remains persistent in the plant and/or through digestion in an animal’s digestive system. This means that if you use straw, hay, or compost that had treated grass in it, you may expose your vegetable plants to it. Buy certified organic straw, or double check your sources for your compost to avoid this issue.
The second source of herbicide exposure is through drift. Herbicides like 2,4-D can become volatile or turn into a gas form when temperatures are high enough (usually about 85 F), if the day is windy this could lead to the herbicide getting on vegetable plants. If you see characteristic cupping, thick leaves, or other symptoms you may have been exposed to an herbicide or have a virus. Either way, the best management plan is likely to remove the plant.
As always, if you have any questions reach out to your local Extension office. Tomatoes are totally worth the effort as there is not much better than a garden fresh tomato.
Gardening in Colorado? Check out Grow & Give www.growandgivecolorado.org and in particular our Colorado Vegetable Guide https://growgive.extension.colostate.edu/colorado-vegetable-guide/ for more crop information on all of the above plants.
What if every gardener planted just one extra plant to share?
One small donation can have a tremendous impact. Just imagine, if every gardener planted one extra plant to share, collectively, we would have an abundant source of fresh, healthy produce available to be distributed to families experiencing food insecurity in our own communities! The free Fresh Food Connect mobile app connects you to a local hunger relief program, then manages and tracks your donations of homegrown produce throughout the season. Download the app today!