Fusarium Wilt
It has been estimated in studies in the United States that 24010 of the forage and 90/o of the seed yield of lucerne are lost annually through disease. Although no data have been gathered, losses of these magnitudes could also be occurring in southern Queensland.
Diseases reduce yield, forage quality and persistence, cause defoliation, increase damage from environmental stresses, and reduce the efficient use of water and nutrients. The importance of each disease may vary among districts as well as seasons because of the varying conditions under which the crop is grown.
This section including the articles titled: Diseases of Lucerne: Problems and Identification, Seedling Diseases of Lucerne, Leaf and Stem Diseases of Lucerne - Viruses and Bacteria, Leaf and Stem Diseases of Lucerne - Fungi, Root and Crown Diseases of Lucerne Part 1 and Part 2 describes only those diseases caused by biotic agents. More than thirty lucerne diseases have been recorded in Queensland — some rare, some common and some causing significant losses. They can be divided into three main categories — seedling diseases, leaf and stem diseases, and root and crown diseases.
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Seedling blight
Cause
Seedling Blight or Damping off
• The fungi Pythium spp., Rhizoctonia solani, Phytophthora medicaginis, Aphanomyces euteiches.
Occurrence
• These are common, occasionally severe diseases, occurring in all seasons.
Symptoms
• They all cause seed rotting before, and after, the seedling has emerged. The plant below the main leaf becomes water-soaked and flaccid, finally collapsing.
Infection and spread
• Pythium, Phytophthora and Aphanomyces survive as thickwalled, resistant spores (oospores) in the soil or infected plant tissue. Rhizoctonia survives as resting bodies (sclerotia) in the soil or by living off decayed matter in the soil.
Control
• Early seedbed preparation, allowing for the breakdown of organic residues, minimises the occurrence and severity of seedling blight.
• Avoidance of heavy irrigation in the early stages of growth.
• The fungicide product Apron 350SD® at 200 g/100 kg of seed (as a seed dressing) is registered to control phytophthora seedling blight.
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