On ground that has carried brassicas within the rotation interval, a measured soil pH below about 7.2 leaves clubroot's door open; raising it is the lever extension names, and the direction is all we give.

NC State Extension, 'Clubroot of Brassicas', content.ces.ncsu.edu/clubroot-of-brassicas (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'The pathogen germinates in wet soils when the soil temperature is between 18 and 25 ºC (64 to 77 F), and the soil pH is acidic (pH less than 7.0)'; 'Alkaline soils and soils with high calcium content suppress the potential of the pathogen to initiate infection'; 'Liming to raise soil pH to 7.1-7.5 can slowly reduce disease severity, although this strategy is not completely reliable when there is a well-established infestation'; 'Calcitic lime is recommended over dolomitic lime unless the field has low levels of magnesium'; host list 'broccoli, Brussels sprouts, cabbage, Chinese cabbage, cauliflower, collard, kale, kohlrabi, mustard, oilseed rape (canola), radish, rutabaga, and turnip.'

UMass Extension, 'Brassicas, Clubroot', umass.edu/agriculture-food-environment/vegetable/fact-sheets/brassicas-clubroot (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'The disease is favored by soils with a pH less than 7.0'; 'Maintain a high pH by regular applications of lime'; 'Calcitic lime is preferred over dolomitic, except where magnesium levels are low'; 'High pH can lead to boron deficiency in coarse soils'; 'occurs on broccoli, Brussels sprouts, cabbage, cauliflower, turnip, rutabaga, and radish.'

UConn IPM, 'Clubroot of Crucifers', ipm.cahnr.uconn.edu/clubroot-of-crucifers (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Maintain soil pH at 7.0-7.2 where clubroot is a concern. Lime well ahead of planting and incorporate thoroughly'; 'Monitor boron where pH is raised, especially on coarse soils'; 'It affects crops such as cabbage, broccoli, cauliflower, Brussels sprouts, kale, collards, turnips, rutabagas, radishes, mustard greens, and other brassicas.'

Cornell Vegetables, 'Clubroot of Crucifers', vegetables.cornell.edu/pest-management/disease-factsheets/clubroot-of-crucifers (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): host range - most susceptible 'cabbage, Chinese cabbage, Brussels sprouts, some turnips, wormseed mustard, and some species of candytuft'; medium 'kohlrabi, kale, cauliflower, collards, broccoli, rutabaga, seakale, some turnips and radishes'; mildly 'rape (canola), black mustard, some turnip and radish varieties, and tumble mustard'; very resistant or occasionally immune 'wintercress; or yellow rocket, horseradish, shepherd's purse, wallflower, dames violet, peppergrass, garden cress, stock, and some radishes'. On pH: 'soil pH should be adjusted to pH 6.8 with ground limestone'; 'It is essential that hydrated lime be added each year unless the soil pH exceeds 7.5'; 'the use of nitrogen fertilizers will reduce soil pH (nullifying the beneficial effects of liming).'