Symptoms and Signs
Phytophthora spear rot is characterized by soft, water-soaked lesions on shoots at, slightly above, or below the soil level. The lesions elongate rapidly and become light brown. As the lesion collapses and shrivels, the affected side of the spear becomes flattened, and the shoot becomes extremely curved and may even collapse. This symptom is not diagnostic, however, as insect and mechanical injury can result in crooked spears. Infected young storage roots appear water-soaked but firm.
Crowns infected with Phytophthora spp. have yellow-orange colored tissue. In severe infections the tissue appears waterlogged and fibrous.
Comments on the Disease
Phytophthora is a soilborne fungus; it infects the shoot near or just below the soil line during very wet periods. Heavy spring rains can induce severe disease losses. Although crown and spear rot is erratic in California, the fungus is present in all production areas of the state. Desert areas, however, usually escape the disease unless conditions are unusually wet. Infected spears, if hydrocooled during packing for market, may contaminate the water and spread the pathogen to other spears, causing extensive rot during transit.
Whenever possible, plant in Phytophthora-free soil and use disease-free transplants. Provide good drainage and do not overwater. If symptoms occur, treatment may be necessary.
Organically Acceptable Methods
Avoid Phytophthora-infested soils and use disease-free transplants when growing an organically certified crop.
|Common name||Amount per acre||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following materials are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.|
|(Ridomil Gold SL)||1 pt||48||1|
|MODE-OF-ACTION GROUP NAME (NUMBER1): Phenylamide (4)|
|COMMENTS: Cutting beds: Apply 30 to 60 days before the first cutting. For additional control, make another application just before the beginning of harvest. New plantings: Apply after planting seedlings or after covering 1-year-old crowns.|
|(Aliette WDG)||5 lb||12||110|
|MODE-OF-ACTION GROUP NAME (NUMBER1): Phosphonate (33)|
|COMMENTS: Apply once over the top to fully expanded asparagus ferns. Control with fosetyl-al is erratic.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.|
|1||Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode-of-action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action group number.|