Bumps on tomato stems start as hundreds of tiny hairs up and down the stalk. Hairs can turn into roots when buried underground. Above ground, they form tiny nubs or nodules, also called root initials, adventitious roots, or tomato stem primordial. They are the earliest stage of development of a tomato’s roots.
Most of the time, bumps are not harmful to tomato plants and are considered normal.
When do bumps on tomato stems develop?
Root initials emerge on a tomato stem as a result of stress – most often when there’s a limit or blockage in the stem’s vascular flow.
Specifically, a hormone named auxin in branch tips sends a signal to the plant’s roots when it’s blocked in the branch.
If there’s a blockage and the hormone can’t flow freely, it accumulates in the stem.
Nodules or bumps emerge. The blockage can occur anywhere on the stem.
Blockages are caused by a number of things:
• internal injury
• irregular cell growth
• high humidity
• overly wet weather
• poor drainage
• in very occasional cases, disease (fusarium wilt or verticillium wilt, for example)
• other root damage
Often the blockage is water-related. A tomato plant’s roots need air as much as they need water. Over-watering or excess rain (including poor drainage) chokes them. The plant compensates by trying to develop more roots out through the stem – hence the root initials.
Root initials can be the same color as the stem. They may also be white or turn to brown.
How do you prevent bumps on tomato stems?
• Plant tomatoes in well-drained soil
• Don’t over-water
• Avoid applying herbicides in areas near the vegetable garden.
Bumps on tomato stems can indicate other problems
Occasionally, root initials can be a sign of other problems, so keep a close check on your plants. Look for signs of:
• wilting (can indicate fusarium wilt or verticillium wilt)
• browning leaves (can indicate root damage)
• stunted growth (can indicate root damage)
For more expert information about this problem of tomato, you can contact us, our expert – advice team in HORTICENTAR – Greenhouse training center.