by Ryan Pankau, University of Illinois Extension
Nothing beats a homegrown tomato! Even when in season, the store-bought varieties just cannot compare to a fully ripe tomato harvested at its peak from your own garden. So many gardeners across American choose tomato plants for their vegetable patch each year for this reason, making it the most planted garden crop in the US.
I receive a lot of questions about tomato care each growing season, with many focused on disease control later in the season as pathogens prevail on infected tomato plants. This year, get a step ahead of tomato problems with a plan to combat the most common issues central Illinois gardeners encounter each summer.
Perhaps the premier pest on tomato plants, the tomato hornworm, has just debuted for the 2020 growing season in my garden. These defoliating larvae emerge from pupa in July after overwintering in the soil. They are native to North America with a large home range spanning sea to sea.
It is often very easy to identify the damage that ensues after they hatch. The little critters are big consumers of leaves, fruits, and smaller stems on tomato plants leaving very noticeable damage in as little as a day. I have always had excellent control from timely hand removal of these caterpillars. It does take a watchful eye to notice damage promptly and remove the culprit. During the daytime, these guys hang out in the shady lower portion of the plant, waiting for their favorite time to feed which is after dark. At night, they are easily found feeding in the tip-tops of plants. I make the rounds each evening to easily pluck them off the branch tips as opposed to a more difficult daytime search.
Early blight is a foliar disease caused by the fungal pathogen, Alternaria solani. It appears as yellow spots on lower leaves which enlarge into dark brown spots, eventually withering and killing infected leaves. The disease always originates on lower, older leaves and moves upward, creating a noticeable pattern. As the infection worsens, it is known to attack petioles, stems, and fruits also. Alternaria solani overwinters in infected plant debris at or near the soil surface. During favorable spring conditions, the fungi produce spores that are spread by splashing raindrops or wind to infect leaves.
Since this pathogen moves from soil to leaves, a mulch barrier is one of the most effective control measures. In fact, I’ve had excellent control of this condition simply by mulching immediately after planting my tomatoes, offering no opportunity for raindrops to splash the fungi up onto leaves. Watering plants with drip irrigation can also help immensely.
Providing good air circulation from staking and some light pruning can limit its spread by reducing favorable conditions, such as wet leaves. Preventative fungicides may also be used to limit infection and spread, although it pays to remember that fungicides do not “cure” infected leaves, but simply limit spread to new leaves. Infected leaves need to be removed and destroyed. Fortunately, I have never had to use any fungicides, accomplishing adequate control from cultural measures such as mulching, staking, pruning, and prompt removal of infected leaves.
Septoria leafspot is another fungal pathogen that infects leaf tissues. It is characterized by small black spots on leaves, with centers that later turn white and develop tiny black dots. This disease also begins on lower leaves, thriving in wet weather, and spreading up the plant. It is transmitted from the soil, much like early blight, with control recommendations identical for each pathogen.
Both of these fungal diseases can also be addressed by keeping plants healthy to limit susceptibility. Good fertilization and adequate watering can really help build resiliency in tomato plants. Consider soil testing to better understand the needs of your garden soil. While nutrient levels are important for vegetable production, I tend to focus on boosting the organic matter content of my soil to fuel natural nutrient cycling processes, retain more moisture, and build nutrient holding capacity.
Blossom end rot is another very common problem on tomatoes that is not caused by a pathogen but rather is a physiologic condition of tomato plants related to the soil environment, which limits calcium uptake. It is characterized by large dead spots on developing tomatoes, often becoming brown and leathery before secondary fungi move in to rot the fruit.
Developing tomatoes need a lot of calcium to support rapid growth. Although calcium is plentiful in the soil, it must be dissolved in water for plant uptake. Greatly fluctuating soil moisture, with extreme swings from wet to dry, can disrupt calcium uptake which often leads to blossom end rot as fruits develop. A simple solution to this issue is also mulching, which will regulate extremes. Appropriate watering as needed from fruit formation to maturity will also limit extremes and maintain more uniform soil moisture.
Some simple steps now, such as mulching, staking, and appropriate watering intervals combined with scouting for hornworms in the coming weeks, can really set up your tomato patch for success this season.
If you have any questions about the tomatoes in your garden, feel free to reach out to me at firstname.lastname@example.org.