Brown spot around cut leaflet scar near soil on stem

by Melissa
(Vancouver, WA)

Q. I thought I was preventing disease by cutting the low leaflets when the plant was small, but now that it is large (5 feet tall) I just noticed a dark brown spot around the scar. The scar is grey (not unlike the other scars from other cuttings on the plant) and the area does not seem soft or moldy. I am assuming something from the soil crept into the weak spot from the cutting; I added a compost mix which unfortunately seemed to have some relatively raw grass manure in it.

At this point I hope there was something to do to keep it from spreading through the whole stem as it is at the main stalk and there are countless green tomatoes on the plant. It still looks very healthy with lots of vibrant blossoms, and leaves are not curled although near the spot I did find yellow spots on this one leaf. Another tomato is planted a few feet away so the worst thing would be if this infection spread to it. Please help me harvest at least some tomatoes off this plant!

A. Excellent observations! And also congratulations on what appears to be a truly healthy plant thus far.

Because the scar is close to the soil, there are many opportunities for water to splash up onto the stem and its surrounding leaves. As you are well aware, splashing water spreads fungi and bacteria in the soil. But you can take precautions to prevent further spread of potential disease.

• Prevent splashing. Lay down newspapers around this tomato plant as well as others nearby. Alternatively, you can lay down a biodegradable weed mat or recycled plastic weedblock. A barrier between the soil and the plant will help prevent unnecessary water on stems and leaves.
  
• Treat proactively. The yellowed leaves may be an indicator that early blight, late blight or Septoria leaf spot are on the prowl. Take a proactive stance to prevent any further spread by spraying with a biofungicide like Serenade or a fungicide such as copper spray. Follow manufacturer's instructions. Make sure to spray the nearby tomato plant, too, as a precaution to prevent the potential spread of any disease.
  
  
  Good luck and happy gardening!
  Your friends at Tomato Dirt