Prep Course

Front 1

Plant Disease Basics

Back 1

• Caused by living (biotic-look similar to symptoms) or non-living (abiotic-drought, lack of nutrients, wind damage)
• often hard to identify - laboratory testing
• fungi (most common in CA
• bacteria
• viruses

Front 2

Causes of Diseases

Back 2

• close relationship between plant & disease organism.
• severity of disease depends on: plant sensitivity/susceptibility to disease, environmental factors (weather, humidity)

Front 3

Fungal Diseases

Back 3

• composed of fine, threadlike structures that from on, or in susceptible host plants
• found on foliage or soil
• spread by spores/similar structures - spread by wind, rain or on equipment/animals
• most require warm, moist conditions
• symptoms: leaf/flower spots, twig/stem dieback, wilting/curled leaves, root rot

Front 4

Control Strategies for Fungus

Back 4

• proper planting techniques - fungus grows in areas with insufficient drainage
• poor irrigation - some types grow rapidly under moist conditions
• pruning & disposing of infected plant parts
• fungicides can only be used to prevent establishment in early stages. Most have poor control after disease is established

Front 5

Important Fungal Diseases

Back 5

• Dutch Elm Disease
• Fusarium Blight
• Fusarium Patch
• Leaf Spots
• Powdery Mildew
• Pythium Blight
• Rhizonctonia Brown Patch
• Rust
• Scab
• Vascular Wilts

Front 6

Dutch Elm Disease

Back 6

• killed thousands of trees in 1930s
• spread primarily by bark beetles carrying spores
• hosts: American, English & Scottish Elms
• symptoms: yellow &/wilting leaves, dead leaves remain on trees but are curled & dark streaks on wood
• control: plant resistant varieties, remove infected trees (sometimes remove just limbs), fungicides typically not effective in CA

Front 7

Fusarium Blight

Back 7

• affects turfgrass (Kentucky Bluegrass/cool season grown in warm areas)
• symptoms: small/circular/green-gray areas, center of infected spots survives ("frog eyed" appearance), dead foliage appear bleached, crown of infected stems have reddish rot
• control: proper irrigation, proper fertilization, resistant varieties, remove thatch, use higher mower setting, fungicide preventative only

Front 8

Fusarium Patch

("pink snow mold")

Back 8

• affect turfgrasses that get snowfall, occurs below snowline, cool-season grown in warm climate most susceptible
• hosts: annual bluegrass/cool season in warm climate
• symptoms: small/circular/pink-colored areas, whitish/pink fungal threads (mycelia) & small/whitish spore masses
• control: good drainage/don't over irrigate, proper fertilization (avoid excess nitrogen) & apply fungicides in fall before weather is cold/wet

Front 9

Leaf Spots

Back 9

• caused by multiple fungal organisms that thrive in moist/warm conditions
• hosts: affect a wide variety of species
• symptoms: discolored spots/blotches on leaves, begin as dark & pinhead-sized discolorations, as they spots grow they develop a yellow halo & premature leaf drop
• control: avoid overhead irrigation, prune & dispose of infected leaves/stems, foliar fungicides for prevention only

Front 10

Powdery Mildew

Back 10

• caused by several fungal organisms (symptoms similar), which tolerate drier conditions & spores cannot germinate when plants are wet
• hosts: apple, crabapple, euonymus, rose & sycamore
• symptoms: grayish/white powdery growth on leaves, yellow leaf spots, leaf distortion, death & premature leaf drop
• control: plant resistance varieties, plant in sunny areas w/good air circulation, prune & dispose of infected leaves, foliar fungicides can be used as preventative, overhead irrigation can keep mildew from spreading

Front 11

Pythium Blight

Back 11

• turfgrass disease, does best in warm conditions
• hosts: wide variety of species
• symptoms: small/circular spots that run together, leafblades turn dark (black) & then reddish brown, turf has greasy appearance, cottony mycelial grown see in morning when dew is present
• control: don't over irrigate, avoid excess nitrogen (especially during warm/humid weather), apply fungicide as preventative

Front 12

Rhizoctonia Brown Patch

Back 12

• turfgrass disease, affects cool-season grasses
• hosts: wide variety of turfgrasses
• symptoms: during 1st stage turf is purplish followed by browning, infected areas may have smoke ring appearance & tan lesions on leaves (reddish brown)
• control: provide good drainage & don't over-irrigate, proper fertilization (avoid excess nitrogen) & apply fungicides in fall before diseases appear

Front 13

Rust

Back 13

• infects plants & turf, favored by mild/moist weather, infects plant foliage primarily (stems can sometimes be affected)
• hosts: Birch, Cottonwood, Juiper, Pine, Poplar, Rhododendron, Rose & turf
• symptoms: dry/rust-colored spore masses on underside of leaves, leaf discoloration & premature leaf drop
• control: avoid overhead watering, destroy infected plant parts, fungicide can prevent establishment of disease if used in early spring

Front 14

Scab

Back 14

• affect a variety of landscape plant species, gets name from scabby spots that appear on fruit
• hosts: Apple, Manzanita, Olive, Pear, Photinia, Pyracantha, Toyon & Willow
• symptoms: olive green spots on leaves, premature leaf drop, scabby/velvety spots on leaves & fruit
• control: remove/destroy infected leaves, avoid overhead irrigation, prune trees to increase air circulation, foliar fungicides used for prevention only

Front 15

Vascular Wilts

(Fusarium/Phytophthora/Pythium/ Verticillium)

Back 15

• caused by soil-borne fungal organisms & affet mostly water conducting (vascular) systems of plants
• block vascular system & prevent movement of water up from roots
• hosts: Ash, Camphor, Chinese Pistache, Fuchsia, Maple, Olive, Rose, Pepper Tree & Willow
• symptoms: leaf discoloration (yellow/brown), wilting of individual branches/portions of canopy, dark streaks in wood & disease progresses slowly (may take years for large tree to die)
• control: proper irrigation, planting in well-drained areas, use resistant varieties

Front 16

Bacterial Disease Basics

Back 16

• one-celled, microscopic organisms
• generally require warmth & moisture
• cannot survive away from host plants (unlike fungus)
• cannot enter plants directly (must enter through wounds)
• commonly spread by splashing water, can be spread by people/animals or infected equipment

Front 17

Symptoms of Bacterial Diseases

Back 17

• leaf spots
• stem dieback
• cankers
• scabs
• wilting
• galls

Front 18

Control of Bacterial Diseases

Back 18

• avoid overhead irrigation/sprinkler which cause splashing
• prune & dispose of infected plant parts
• disinfect pruning equipment
• avoid unnecessary wounds when bacterial present
• very few bactericides can be used to control, most fungicides are preventative only

Front 19

Fireblight

Back 19

• common & destructive to several landscape species & commercial apples/pears
• hosts: Apple, Cotoneaster, Crabapple, Hawthorn, Pear & Pyracantha
• symptoms: bacterial ooze from cankers on branches/twigs, ooze leaves dark streaks on trunk/branches, flowers/shoots/young fruit shrivel & die, dead plant tissue blackened (looks burnt), dead/blackened leaves & fruit cling to tree, terminal shoots die & bend
• control: avoid excess nitrogen fertilizer when weather is warm/humid, avoid excess pruning that stimulates new susceptible growth, avoid overhead watering which spreads disease, prune out and properly dispose of infected plant parts, disinfect pruning tools (10% clorox solution), bactericides have limited practicality in most landscape settings

Front 20

Bacterial Blight & Canker

Back 20

• affects fruit trees (stone fruits & many ornamental)
• hosts: variety of herbaceous landscape species & stone fruits
• symptoms: bacterial ooze from cankers on branches/twigs, ooze leaves dark streaks on trunk/branches, flowers/shoots/young fruit shrivel & die, some species (olive & oleander) may develop galls
• control: avoid excess nitrogen fertilization when weather is warm/humid, avoid overhead watering which spreads disease, avoid excess pruning which stimulates susceptible growth, prune out & dispose of infected plant parts, bactericides have limited practicality in landscaped settings

Front 21

Viral Disease Basics

Back 21

• non-cellular & sub-microscopic
• cannot be seen with ordinary microscope
• cannot survive/reproduce without host
• many spread by insects
• often don't kill host
• plants remain infected for life
• no chemical control

Front 22

Symptoms & Controls of Viral Diseases

Back 22

• symptoms: plant stunting, discoloration & deformation
• control: plant resistance varieties, control insect vectors (generally impractical & ineffective in most landscape settings)