Root knot nematode Meloidogyne spp. Galls or knots on roots. Possible wilting of foliage during sunny days. Unthrifty plant appearance. Rotate to non-host crops, move garden site or solarize soil.
Lower leaves drop off, resulting in bare stems and small heads.
Stems have darkened rings inside. Does not cause head rot. Rotate ground for crucifer crops if yellows becomes a problem. Grow yellows-resistant varieties. Consult seed catalogs for current information on resistant varieties.