Improved knowledge of factors contributing to carrot rot (VG15066)

What was it all about?

This two‐year study was tasked with investigating the complex causes of carrot crown rot disorders, and the field and soil factors that are conducive to its development in Tasmanian production regions.

Its work revealed five different types of carrot crown problems that can affect carrot marketability and reduce returns to growers:

• Ring crown rot
• Smooth crown rot
• Corky crown rot
• Soft watery crown rot
• Black ring.

All except black ring are classified as major defects, meaning that affected produce ends up in waste bins. Carrots that have black rings in the crowns downgraded to lower grade carrots and sold at less than half the premium-grade carrot values.

In looking at the contributing factors to these crown rot conditions, the researchers found that soil environment has a major influence in crown rot disease development. Ground prepared and crops sown under wet weather conditions had increased incidence of crown rots, as well as other major defects such as forked and misshapen carrots.

High levels of stones, cloddy soil, poor drainage and soil crusting also contributed to increased levels of ring crown rot and smooth crown rot. Meanwhile, corky crown rot appeared to be related to carrot crown exposure to fluctuating surface soil moisture and temperature.

In a study on irrigation, low soil moisture (12mm at weekly intervals) at the 6 to 9 leaf stages, followed by 30mm of irrigation at weekly intervals from 9 leaf to harvest, increased crown rot incidence.