Black rot of turnips is a serious disease of not only turnips, but most other crucifer crops as well. What exactly is turnip black rot? Turnips with black rot have a bacterial disease caused by the pathogen Xanthomonas campestris pv. campestris. As mentioned, black rot targets members of the Brassica family – from turnips to cabbage, broccoli, cauliflower, kale, mustard and radish. Because the disease afflicts so many crops, it is important to learn about turnip black rot control.
What is Turnip Black Rot?
The bacteria X. campestris enters leaf pores at the margin and moves down into the vascular system of the leaf. Upon inspection, infected leaves are marked by a notched or “V” shaped lesion at the leaf margin and appear to have black to dark grey fibers running through the leaf tissue. Once the leaves are infected, they rapidly degrade. Infected turnip seedlings collapse and rot soon after infection.
Black rot of turnips was first described in 1893 and has been an ongoing problem for farmers since that time. The pathogen spreads rapidly, infecting seed, emergent seedlings, and transplants. The disease is spread by splashing water, windblown water, and by animals and people moving through the crop. Symptoms on a turnip with black rot will first appear on lower foliage.
The disease is most prevalent in warm, wet weather. It survives in cruciferous weeds like shepherd’s purse, yellow rocket and wild mustard, and in crop debris, surviving for a short time in soil. Black rot of turnips spreads rapidly and may be spreading well before any symptoms can be observed.
Turnip Black Rot Control
To control the spread of black rot in turnips, only plant turnips in areas that have been free from cruciferous debris for over a year. Use disease free seed or resistant varieties if possible. Keep the area around the turnips weed free.
Sanitize garden equipment to prevent the spread of the disease. Use a drip irrigation system or water plants at their roots. Remove and destroy any cruciferous crop debris.
Apply bactericides at the first sign of leaf infection. Repeat the application weekly while weather conditions favor the spread of the disease.