University:
Washington State University
Course:
BIOLOGY 401 | Plants and People
Academic year:

2021
Views:

228

Pages:

40
Author:

Athena Harrison

Phytophthora root and crown rot of lavender Planned research projects • Phytophthora species on lavender in WA • Screen lavender cultivars for susceptibility/resistance to PRCR • Best Management Practices for lavender growers Lavender root rot • Fusarium • Phytophthora • Pythium • Rhizoctonia Occurs in wet soils. Overwatering aggravates the problem. - The disease triangle Phytophthora • What is it • Where does it come from • How do I know I have it • How do I get rid of it Phytophthora – the plant destroyer More than 100 species identified P. infestans – responsible for the Irish potato famine in 1845 P. sojae - soybean stem and root rot Several Phytophthora spp. cause disease on cacao P. cinnamomi – causes damage to forest ecosystems worldwide “Perhaps no other single plant disease has resulted in such widespread human suffering and sociological impact.” P. ramorum – causes Sudden Oak Death (SOD) Phytophthora Chlamydospores (P. ramorum) Sporangia containing swimming zoospores (P. ramorum) Oospores of P. megasperma Phytophthora is microscopic and species can be identified by spore stages and/or DNA sequencing P. alni oospore Phytophthora Seasonal Activity What time of year is Phytophthora active? Not all species are active at the same time • Germination and infection – wet season • Symptom expression – in dry season Seasonal activity for Phytophthora species Phytophthoras on lavender Germination, infection Symptoms of Phytophthora root disease will become obvious in the dry season when plants are under water stress. Cool Season – cool, wet soil Warm Season – greenhouse, warm soil • P. megasperma • P. cactorum • P. capsici/palmivora • P. cinnamomi • P. citrophthora • P. drechlseri • P. nicotianae/parasitica • P. tentaculata “Root nibblers” • Attack fine roots • Opportunistic in flooded habitats • Very common in water and soil P. gonapodyides P. chlamydospora P. lacustris Photo: Natural Resources Wales Damage caused by Phytophthora spp. P. ramorum foliar and shoot blight on Vaccinium at a nursery P. cinnamomi root disease on Eucalyptus Root disease Bleeding cankers Shoot blight Foliar lesions Bleeding cankers caused by P. citricola on Alder Where PRCR comes from • New plants • Existing infestation in field soil Phytophthora Major Host Families P. nicotianae Solanaceae P. cactorum Rosaceae, Liliaceae P. megasperma Rosaceae, Fabaceae P. capsici Solanaceae P. drechsleri Rosaceae, Myrtaceae, Pinaceae Phytophthoras that attack lavender tend to have many hosts Symptoms of PRCR Dead patches – sudden wilting or dieback during summer Brown staining under bark at root crown Black, necrotic roots Above ground symptoms often do not appear until most of the root system is destroyed. Cinnamon colored stain under the bark Look for dead patches at base of plants Extensive symptom development on in-ground plant Winter damage or Phytophthora? Winter damage – top of plant New shoots grow at base = healthy root system Phytophthora infestation in field – Dead plants have been removed Area of poor drainage, heavy soil Phytophthora spores were probably already in soil You might have contaminated soil if • In-ground plants are symptomatic in an area • Batches of potted plants from a media pile are symptomatic • There is standing water indicating a drainage problem • The soil tests positive for Phytophthora Photo: Jay W. Pscheidt. Testing plants for Phytophthora using Agdia test strips • Direct testing of roots and stem tissue does not work for lavender • Use baiting method Testing for PRCR on lavender roots or soil Collect water from root zone of symptomatic plants 1 Positive result 3 2 Test symptomatic leaf bait with Agdia kit Bait with rhododendron leaves Does not identify Phytophthora to species, only +/- Pythium symptoms: water soaked lesions Phytophthora symptoms: dry, brown lesions Critical Control Points Concept originally developed for food safety to prevent hazards rather than destroy contaminated foods at the end of the production cycle. It has been adapted for ornamental nurseries in response to P. ramorum but will prevent outbreaks of any pathogen or pest. Maintaining a clean operation prevents unwanted pests and diseases from entering the nursery or farm. It is much easier to prevent than to eradicate. Recommended cultural control for PRCR • Prevention – keep it out • Sanitation • Plant in well drained soil and avoid areas prone to standing water • Do not incorporate large amounts of compost or mulch that will retain water around plants • Excess N fertilizer will produce succulent growth that is susceptible to Phytophthora and other diseases Sources of inoculum • People and their vehicles • Plants • Dirty pots, tools, and equipment • Soil • Water • Plant debris and cull piles • Weeds, algae, and associated insects (shoreflies and fungus gnats) People and their footwear The Sequim Lavender Festival attracts many visitors that move from farm to farm. Preventing soil movement • Control access • Create a barrier between feet and soil: boardwalk, bark chips, etc. • Avoid standing water and muddy areas • Manage equipment - tires, hoses, tools Potted plants in nursery or retail area Use pallets or benches underneath pots Pots should not be in contact with soil Gravel layer of 4-6” will provide drainage and separate plants from soil surface Potting mix Re-using media is risky Composting may not kill everything Loads of media can be treated with aerated steam at the rate of ~1 cu yd/hr using a cart or conveyor belt system. Plants Incoming plants should be examined on arrival Plants can be quarantined for at least 30 days and monitored for symptoms, insect pests Reject plants that are symptomatic or test positive for Phytophthora Pots • Soil and plant material clinging to used pots and trays are a source of pests, diseases, and weeds • Pots can be treated with disinfectant, steaming, or hot water dip This steam cabinet was built on a relatively low budget by a nursery in OR Hot water dip tank for 4” pots Managing Phytophthora in a field Dig up and remove infested plants and also at least 1 adjacent plant on each side Remove soil around root zone of infested plants Prevent spread of disease – • Restrict water movement through the area • Cover soil in mulch, gravel, or cover crop • Prevent movement on machinery, footwear, equipment Improve drainage Do not plant new lavender into infested soil – Make it a feature or plant a non-host species Treatments for contaminated soil Soil amendments/ Biocontrol Solarization Steam Fumigation Some soil organisms are beneficial Normal Pr chlamydospore Cellulase producing fungi Bacteria and actinomycetes produce antibiotics Photo: CDC/Dr. David Berd (PHIL #2983), 1972. Streptomyces spp. are common in soil and produce antibiotics Several species of Trichoderma are antagonistic to Phytophthora spp. Pr chlamydospore parasitized by Trichoderma Chemical fumigation • For large areas of soil • Kills beneficial organisms • Dazomet – granular formulation • Chloropicrin • Metam sodium – can be worked into soil or applied through irrigation Check label for approved crops and application methods before use Heat treatment Temperatures necessary to kill various groups of soil organisms Solarization Heats top layer of soil to kill pests and pathogens. Need 4-6 weeks of clear skies, long days, high temperatures. Pots and media can also be solarized Soil steaming Contaminated hoophouse at a nursery Sheet steaming and steam boiler.

Phytophthora Root and Crown Rot of Lavender

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