Crop Diseases Ned Tisserat Bioagricultural Sciences and Pest Management Colorado State University Ned.Tisserat@colostate.edu Plant Disease Identification Ned.Tisserat@colostate.edu 970 491 6527 Diagnostic labs CSU, Ft. Collins Jefferson County Extension Tri River Area, Grand Junction Please submit a representative sample and complete description of problem Web Links Tri River Area http://www.coopext.colostate.edu/tra/index.html#m ain.html High Plains IPM Guide http://wiki.bugwood.org/hpipm:main_page org/hpipm Main Page Greenbook (labels and MSDS) http://www.greenbook.net/ Crop Data Management Systems (CDMS) http://www.cdms.net/ CSU Web Links Bioagricultural Sciences and Pest Management Department http://www.colostate.edu/depts/bspm/ Tri River Area http://www.coopext.colostate.edu/tra/index.ht ml#main.html Plant Disease is a dynamic process and involves interactions among the host, pathogen and environment over time Host Sterol Inhibitors Group 13 Tilt propiconazole Nova myclobutanil Bayleton triadimefon Folicur, Elite, Bite tebuconazole Procure triflumizole Quintec quinoxyfen (fruits) Environment Causal Agent 1
Triazole fungicides have low toxicity However, may be endocrine disruptors Endocrine disruptors are exogenous substances that act like hormones in the endocrine system and disrupt the physiologic function of endogenous hormones. Troubles in Europe? These are becoming increasingly scrutinized by EPA Endocrine Disruptors Endocrine disrupting activities in vivo of the fungicides tebuconazole and epoxiconazole. Taxvig et al. Toxicol Sci. 2007 Theseeffects effects strongly indicatethatthat one major underlying mechanism for the endocrinedisrupting effects of azole fungicides is disturbance of key enzymes like CYP17 involved in the synthesis of steroid hormones QoI inhibitors (Strobilurons) Group 11 Quadris, Heritage (azoxystrobin) Flint, Gem trifloxystrobin Headline pyraclostrobin Sovran kresoxim methyl Reason fenamidone (onions, potato, tomato) Shift in pathogen populations (to a population less sensitive) is a problem Daylily Rust Preventing Fungicide Resistance Recommendations of Fungicide Resistance Action Committee (FRAC) Mix with other fungicide groups Strobilurons group 11 Sterol Inhibitors group 13 Alternate with other fungicide classes Avoid multiple serial applications in a season Still debate as to whether these practices work Fungicide Combinations Oils & Extracts Quilt = Banner MAXX +Quadris Stratego= Bayleton + Flint Tanos = famoxadone + cymoxanil Switch = cyprodinil + fludioxinil Pristine = Boscolid + Headline Horticultural Oils Highly refined oils that are applied to surface. Controls powdery mildews, and may inhibit rusts Plant Oils & Extracts Neem, clove, rosemary and many other plant oils Used as foliar sprays and seed treatments Cinnamaldehyde 2
Plant Defense Activators Compounds or microbes that induce a defense response in the plant and that inhibit or reduce infection by a plant pathogen. salicylic acid like compounds acibenzolar S methyl (Actigard) bacterial proteins Harpin (Messenger) Biological Control Control of plant diseases through the use of a biological control agent (usually bacteria and fungi) Bacteria Pseudomonas, Agrobacterium, Streptomyces and others Fungi Trichoderma, Giocladium and others Biological Control Natural systems (biological balance) rarely see epidemics compared to monoculture organisms in state of dynamic equilibrium Optimally biocontrol tries to mimic natural ecosystems Historically biocontrol has not resulted in complete suppression of the pathogen How do Biocontrols Work? Competition for food or space Predation or parasitism Production of toxic compound (antibiotic) Induces plant resistance Problem: Application and establishment of bioagent Biocontrol Products Bacillus licheniformis EcoGuard Bacillus subtilis Rhapsody Trichoderma harzianum Biotrek, Turfshield, Turfmate Biostimulants Organic materials that enhance plant growth and development Active ingredient varies (humic and fulvic acids, sea kelp extract, hormones, micronutrients, microbes, etc. Marketed to reduce turfgrass stresses Efficacy in reducing disease severity inconsistent Not a fungicide but may be combined with fungicide to reduce amount of product applied 3
The Powdery Mildews May be most conspicuous plant pathogen May reduce yields by 40% or more Found on both grasses and dicots (broadleaf plants) Powdery mildews tend to be host specific with specialization at plant genus or family level although some mildews have only one known host Many foliage diseases suppressed by arid conditions, but not necessarily powdery mildews One of few species of fungi that can infect in the absence of moisture on the plant surface Water may actually inhibit disease development Powdery Mildews Powdery Mildew Symptoms and Signs One of the easiest diseases to identify Formation of white dusty mat on the upper or lower surface of leaves Actually seeing the fungus (mycelium and spores) Powdery mildew fungi have different reproductive structures Cleistothecium (chasmothecium) Spherical structure that contains spores inside Durable structure t Splits open in spring during rains Release of Ascospores from Cleistothecium Appendages swell and lift cleistothecium off leaf surface One side of appendage thicker than other and with high relative humidity the appendage will move and prop up cleistothecium Aircurrentsmay thenpickup cleistothecia and move to new location or ascocarp may dropto another surface Mucilage formed on top of cleistothecium Sticks to surface Cleistothecium opens and releases ascospores Ascospores airborne Powdery mildew fungi have different reproductive structures Conidia (spores) develop on the leaf surface and reinfect during the growing season 4
Infection Cycle After penetration the fungus forms haustoria Morphology of haustoria may differ with species Purpose of haustoria is nutrient acquisition from host (without killing host cell) Generalized Disease Cycle of Powdery Mildews Three general types of life cycles Powdery mildew may be active year round, producing mycelium and conidia on new leaves Mildew overseasons as cleistothecia and starts new infections by producing spores Fungus may colonize leaf buds, small twigs and overseason in that tissue Could be important in perennial crops like apple, peach, grape, etc. Powdery Mildew of Pumpkin, Squash Two species of mildew Sphaerotheca most common Symptoms include white dusty fungal growth on upper and lower surface Symptoms generally appear in mid late August Powdery Mildew on Muskmelon Symptoms include white dusty fungal growth on upper and lower surface Control of Powdery Mildew Resistance Level of resistance in some muskmelons varieties can be high Resistance may break down to new races Resistance in squash and pumpkin more variable ibl ranging from resistant it tto tolerant t (develops mildew but still yields relatively well). Check resistance or tolerance for variety you choose 5
Fungicide Control of Powdery Mildew Make fungicide applications before appearance of disease It is critical to scout fields Look on undersides of leaves for initial colonies Make additional applications at approximate 2 week intervals to keep foliage mildew free through fruit development Rotate fungicides (fungicide classes), especially for the new labeled products Fungicides May be used for susceptible varieties or to augment control on tolerant varieties Strobiluron products Flint (trioxystrobin) Quadris (azoxystrobin) Pristine (boscalid and pyraclostrobin) Sterol inhibiting products Nova (myclobutanil) Be careful with the number of sequential applications per year Fungicides Sulfur products may provide some level of control; may cause toxicity Microthiol Copper products Kocide 2000, Microcop Biorationals and others Natural oils Neem oil (Trilogy, Trilogy90EC, etc) Cinnamon oil (Cinnamite, Valero, etc) Rfi Refined oils JMS Stylet Oil Potassium bicarbonate Armicab100, Kaligreen, FirstStep, Remedy, Milstop, etc Powdery Mildew of Grape Erysiphe (Uncinula) necator Impacts Premature leaf drop Reduced yield Poor quality Overwinters as mycelium in buds or as cleistothecia on bark Method of overwintering depends on geographic location Overwinters in buds in California Doesn t survive in buds in Colorado! Makes a difference in terms of management Requires high humidity but not a film of water on leaf surface for infection Free water may wash off spores or burst them One of the only fungal pathogens that doesn t need free water Photo courtesy Oregon State Photo courtesy Ohio State Univ. 6
Powdery Mildew Symptoms Leaves Powdery Mildew Symptoms Fruit Powdery Mildew Symptoms Canes Powdery Mildew Control Prevent excess vigor Shading favors infection Remove suckers Results in shading Also more succulent growth more susceptible. Summer pruning/leaf removal Varieties vary in resistance Not necessarily major criterion when selecting a variety Management of Powdery Mildew Cultural practices Canopy management Fungicide applications Organic vs. synthetic products Resistance management Timing of applications Regular schedule vs. forecasting method Powdery Mildew Control Sulfur products DMI Fungicides (resistance problems) Strobilurons (QoI fungicides) Impact fungicides Refined oils (JMS stylet oil and others) Fatty acids (M Pede) Bicarbonates Biologicals 7
Fungicide Spray Programs Based on host phenology For example, sprays would be put on at 10 inch growth, flowering, etc.; maybe 5 6 applications per year This is a very common way fungicides are applied to fruits and vegetables Fruit spray guides developed to tell growers time of season when disease may be active and when and what applications to make See following website for example of spray schedule for grapes http://www.extension.iastate.edu/publications/pm1375.pdf This methods assumes conditions are always favorable for infection Schedule provides optimal coverage and protection from infection Best in regions where mildew severity very high Problem Usually results in over application of fungicides because weather conditions rarely remain optimal for fungal infection More expensive and less environmentally sound Fungicide Spray Program Disease Forecasting Based on pathogen development We know optimal environmental conditions necessary for infection and colonization Monitor those conditions using weather data loggers temperature, leaf wetness most critical, assume presence of inoculum Use computer models to predict disease onset. Better timing of sprays so less wasteful, more environmentally sound More complicated More risk since if you predict wrong disease may develop Powdery Mildew Forecasting in California In California infection may occur early in year because of bud infection Requires and early spray just at leaf emergence in Colorado mycelium doesn t overwinter in buds; early sprays are not required. May not need applications until late in season until after rain to release ascopores. Follow forecasting system later in the growing season Critical period for powdery mildew control in apple is early in season Powdery Mildew of Peach survives as mycelium in bud scales and as cleistothecia Protect fruit from infections Many products including sulfur, myclobutanil, propiconazole, pyraclostrobin Powdery Mildew of Cereals Blumeria (Erysiphe) graminis Host specialized forma specialis that infect different cereal crops for example, B. graminis f. sp. tritici infects wheat but not barley, oats, etc. Wheat powdery mildew More injuryineastern UnitedStates and in irrigated wheat Inoculum comes from conidia on volunteer wheat or from ascospores See video for neat images of powdery mildew 8
Management of Wheat Powdery Mildew Avoid excessive nitrogen Higher stand numbers (i.e. crowding) will contribute Resistant varieties However there are races of the pathogen Some races will overcome resistance genes that have been deployed Fungicide applications Fungicides rarely used to control powdery mildew on dryland wheat in Colorado but occasionally for irrigated wheat See handouts for fungicides Resistance to Wheat Powdery Mildew Race specific resistance Over 30 genes have been identified effectiveness of race specific genes is temporal, generally less than 5 years, in commercial cultivars before development of new races Adult Plant Resistance (horizontal resistance) resistance is controlled by several genes each having additive effects More durable but harder to develop Marker Assisted Selection identify DNA markers that are adjacent to resistance genes and to use these markers to select elite wheat lines and cultivars possessing multiple genes 9