Top-notch tomatoes

Tomatoes are the star of summer. But unlike the stars in the sky, they often inspire us to zoom in and think more physiologically than philosophically. Weather, animals, insects and disease all pose challenges when growing tomato plants. Understanding how to manage common problems can help set growers up for success. The following are three tomato problems we saw at the PanAmerican Seed research station in Illinois during the 2024 growing season, as well as suggestions to control those problems.

Septoria Leaf Spot

This fungal pathogen shows up on the lower leaves of plants, covering them in small spots. The spots eventually converge and cause defoliation. Extreme infection and defoliation can lead to plant death. The best way to manage septoria leaf spot is to choose resistant tomato varieties, such as WonderStar Red and new WonderStar Pink Beefsteak Tomatoes from PanAmerican Seed.

Other management options include increasing airflow, cleaning up infected fallen leaves and crop rotation.

Yellow Shoulder

This occurs when the shoulder of fruit does not ripen fully. The exact cause of yellow shoulder on ripening fruit is not certain, but there seem to be several contributing factors. Some varieties may be more susceptible than others. Availability of potassium to developing fruit is thought to be a major contributor. Temperature extremes (very high >90 °F, very low <60 °F) or major differences between daytime and nighttime temperatures seem to exacerbate the symptoms.

Understanding soil fertility though soil testing is a great first step to managing this problem. However, this should be done before symptoms appear, as the yellow shoulder is not reversible.

Blossom End Rot

This physiological disorder causes the bottom of the fruit to break down. The movement of calcium — or lack thereof — causes the blossom end of the fruit to rot. Conditions that impact plant transpiration and root uptake can influence the movement of calcium — relative humidity, soil moisture, etc. When there are high fluctuations in these environmental conditions, calcium accumulates easier in the leaves, which transpire more than fruit. The best way to prevent this disorder is to have consistent water availability with good drainage (no super soaking or letting get bone dry), make sure plant roots are healthy and make sure soil fertility is good via a soil test.