Fusarium Wilt (fungus – Fusarium spp.): When this disease occurs lower leaves turn yellow and wilt, followed by overall plant wilting and death of entire plant. Lower portion of stem near soil line turns dark brown-to-black with brown discoloration in vascular tissues. Planting disease-free cuttings, sterilization of potting soil and benches offer best means of control.
Verticillium Wilt (fungus – Verticillium spp.): This disease is mainly in western areas of Texas. General wilting. Leaves become paler green, turn brown and die. Leaves remain attached to stem. In some case, wilting may not occur. First symptoms are a chlorosis of lower leaves which later turn brown. Infected plants are stunted with flowers reduced in size. Control same as for Fusarium Wilt.
Collar or Stem Rot (fungi – Pythium spp., Rhizoctonia spp., Fusarium spp.): Stem turns dark at soil line, entire stem is girdled and plant turns yellow and dies. Control measures include use of sterilized soil, disease-free cuttings, proper drainage and use of a soil drench.
Powdery Mildew (fungus – Erysiphe cichoracearum): Foliage covered with a whitish, ash-gray powdery growth. With severe infectious leaves may become distorted and stunted. Regular foliar fungicide applications will control this disease.
Leaf Spots (fungi – Septoria spp., Alternaria spp., Cercospora spp., and others): Small yellow spots that gradually enlarge increasing to one inch in diameter. Center of spots turn brown. Infection takes place on lower leaves first. Regular applications of a foliar fungicide for control.
Leaf or Foliar Nematode (nematode – Alphelenchoides ritzemabosi): Yellowish-brown spotting of the leaves. Spots are bounded by larger veins. Spots coalesce until entire leaf is affected. Leaves die and fall. Symptoms start at base and progress up plant. Avoid wet humid conditions, do not water from top. Use a peat mulch. Use disease-free propagating material. Phosphate insecticides will control nematode on plant.