Diseases: Symptom to Cause

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Diseases Symptom to Cause

• Joran Viers
• Horticulture Agent
• Bernalillo County Cooperative Extension Service

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Symptoms

• Fine, white powdery growth on leaves, often more
  in shade. Small, black bodies may occur with
  white powdery growth.
• Leaves may shrivel, dry and die. Growth may
  cover significant leaf area.
• Common on rose, cucurbits, apple, grape, zinnia,
  aster, Kentucky bluegrass, bindweed, photinia,
  etc.
• Common in heat of summer.

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Cause

• Powdery Mildew
• Any of a number of fungi cause PM.
• Control
• Prune for open structure and good ventilation.
• Remove fallen leaves to reduce spore count.
• Baking soda spray, oil sprays (Neem), soap
  sprays, and garlic oil sprays.

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• Sodium bicarbonate (baking soda) Hose down all
  the infected leaves prior to treatment. This
  helps dislodge many of the spores. Use as a
  prevention or as treatment at first signs
  disease.
• To make Mix 1 tablespoon baking soda, 2 1/2
  tablespoons vegetable oil with one gallon of
  water. Shake very thoroughly. To this add 1/2
  teaspoon of pure castille soap. Be sure to
  agitate your sprayer while you work to keep the
  ingredients from separating. Cover upper and
  lower leaf surfaces and spray some on the soil.
  Repeat every 5-7 days as needed.

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Symptoms

• Branch die-back (branches, twigs, buds).
• Clear, amber gum exuding from bark, turning dark
  and crusty with time.
• Small, orange, curly fibers coming out of bark.
• Discoloration of cambium at dead areas.
• Appearing on Prunus, aspen and other Populus,
  globe willow, Leyland false cypress, etc.

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Cause

• Cytospora fungal (several species)
• Gets into wounds pruning cuts, insect damage,
  breakage.
• More likely on drought-stressed plants.
• Spores could likely be found on any plant
  surface.
• No treatment.

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Symptoms (in cucurbits)

• Roughly circular lesions near leaf veins.
• Leaf lesions are light brown to reddish in
  color.
• Leaves become distorted.
• Shot hole appearance.
• Lesions on fruit are circular, sunken, water
  soaked areas.
• Early fruit infections may result in abortion
  or mal-
• formation of the affected fruit.

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Symptoms (in sycamore)

• Blight on leaves and shoots.
• Cankers and die-back of twigs.
• Deformation of branches (zigzag).
• In wet spring, defoliation may occur.

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Cause

• Anthracnose one of many fungal agents attacking
  certain host plants.
• In sycamore, not fatal. If severe last year,
  apply appropriate fungicide at bud swell, may
  need to repeat in 7-10 days. Use Bordeaux
  mixture (copper sulfate) or other copper
  fungicide, or chlorothalonil fungicide.
• In curcurbits, cultivar selection, crop rotation
  and good garden cleanup should be sufficient.

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Symptoms

• On apple
• first appears on the leaves as small greenish
  yellow spots which gradually enlarge, changing to
  orange-yellow and becoming surrounded at the
  border by concentric red bands.
• On the upper leaf surface, the spots become
  stippled with black specialized fruiting
  structures (spermogonia).
• On the under side of the leaf, lesions are
  formed at lesion hairlike projections can be
  observed. The leaf thickens around these
  projections, causing the aecium to have a cuplike
  appearance. These cuplike lesions can also appear
  on immature fruit of apples, causing dwarfing and
  malformation.

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Symptoms

• On cedar
• leaves are infected during summer months, and by
  June the following summer, small greenish brown
  swellings appear on the upper or inner foliage
  surface.
• These swellings enlarge and by autumn appear as
  brown, somewhat kidney-shaped galls, each covered
  with small circular depressions. The galls vary
  from 1/16 of an inch to over 2 inches across.
• The next spring, in moist weather, the pocketlike
  depressions in the galls put forth orange telial
  horns. These are a gelatinous material that
  swells immensely. A gall covered with telial
  horns may reach the size of a small orange.

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Cause

• Cedar apple rust Gymnosporagium fungus with two
  hosts.
• Apple and crabapple trees can be protected by
  following a fungicide (e.g. Mancozeb) spray
  schedule starting at blossom time and continuing
  at seven-day intervals until the cedar galls have
  stopped spreading spore.
• Fungicide control on the cedar is not recommended
  since the injury to cedars is not significant.

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Symptoms

• Small, spherical dots (yellow, orange or brown)
  on leaves (for example, vinca or sphaeralcea).
• Occurs in humid, warm (but not hot) weather.
• Leaves discolored, limp.
• Usually restricted to one species per occurrence
  per site.

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Cause

• Rust fungus
• Fairly host specific.
• Avoid overhead irrigation.
• Fall clean up of fallen leaves
• As protection for previously infected plants
• Neem oil
• Mancozeb
• Chlorothalonil

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Symptoms

• Blackish, powdery growth on seed heads of grass
  plants (Poaceae).
• Could be on corn, or bermuda, or Johnson grass
• Follows abnormally wet periods with warm
  temperatures.

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Cause

• Seed smut fungus
• Not common in arid country
• But not uncommon in corn!
• Prized delicacy in Mexico
• By time visible, too late to prevent or treat.
• In most grasses, not too taxing to plant.
• In corn, remove infected ears carefully and
  promptly.

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Symptoms (on blue spruce)

• Needle discoloration yellow to reddish-purple to
  brown
• Premature defoliation
• Premature death
• Black pycnidia (fruiting bodies) may develop on
  infected needles

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Cause

• Needle cast disease of blue spruce
• The fungus Rhizosphaera kalkhoffii 
• Fungicides spray with Bordeaux mixture 8-8-100
  (8 lb hydrated lime, 8 lb copper sulfate, 100 gal
  water) or chlorothalonil fungicide.
• Provides protection against infection, prevents
  spread of the disease within the tree. Apply when
  the new needles are half developed and again when
  they are full length.
• Two years of treatment usually restores
  moderately affected trees to full foliage

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Symptoms

• On catalpa, elm, maple
• leaf curling, drying, or abnormal reddening or
  yellowing defoliation
• wilting dieback and death.
• May be restricted to one branch or may involve
  entire tree. Young trees often killed within one
  year of infection older trees may live several
  years and gradually deteriorate.
• Other symptoms include reduced twig growth,
  branch dieback, and sparse crowns. Vascular
  streaking and discoloration in branch sapwood may
  be evident.
• Slow growth, sparse and stunted leaves, leaf
  scorch, and dieback associated with chronic
  phase.

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Cause

• Verticillium wilt
• Trees suffering chronic infection may benefit
  from simple cultural practices. A balanced
  fertilizer (10-10-10) may help alleviate symptoms
  in infected trees never use high-nitrogen
  fertilizers.
• Infected trees should be watered frequently to
  decrease wilt symptoms, and dead branches should
  be removed and burned.
• Because Verticillium is a vascular wilt pathogen,
  surface-applied fungicides are not effective.
  Even with systemic fungicides, chemical control
  of Verticillium wilt is not practical for
  established trees.
• Resistant trees apples and crabapples, mountain
  ash, boxwood, ceanothus, pyracantha, sweet gum,
  honey locust, oaks, pears, pecans, sycamores,
  poplars, flowering quince, and willows.

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Symptoms

• Chile plants wilting, in spite of receiving
  plenty of water.
• Affected plants sporadic in field, not all in a
  row.
• Roots mushy, soft when pulled up.

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Cause

• Fusarium oxysporum soil-borne fungi, causes root
  rot on many different plants.
• Rotate out of solanaceous plants for a few years.
• Water more deeply, less often allow soil to dry
  out more in between.
• Plant resistant cultivars.

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Symptoms

• Fruit distorted and enlarged
• Up to 10 times normal size!
• Spongy or hollow centers, may be no pits.
• Early symptoms are small whitish spots or
  blisters that enlarge rapidly.
• Later reddish, with velvety gray appearance.
• Fruit dehydrates and leaves only exterior shell.

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Cause

• Fungal infection Taphrina communis
• Overwinters on twigs and bud scales
• Infection occurs during cool, wet weather at bud
  break.
• Use resistant varieties varietal resistance not
  well documented.
• Wild plums serve as source of infection.
• Single fungicide application in late autumn or
  before bud break.
• Bordeaux, liquid lime-sulfur, chlorothalonil.

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Symptoms

• Sour/foul smelling ooze from old wound on tree
  (wound may not be visible).
• Discoloration of bark where ooze has dripped.
• Die-off of plants dripped on by ooze.
• On elm, ash, cottonwood, etc.

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Cause

• Bacterial wetwood, or slime flux a bacterial
  infection common on various hardwoods.
• Generally assumed to be non-fatal, in fact not
  much damage at all.
• No treatment exists. Use plastic tubing to
  direct flux away from problem areas.
• On stressed globe willow, appears to real take
  off! These trees likely to fail anyway.

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Symptoms

• On quince, pear, pyracantha, apple, hawthorn,
• Infected flowers first appear water-soaked, then
  shrivel, turning brown or black.
• As infection progresses, leaves on the same spur
  turn dark brown or black as though scorched by
  fire. The dark, shriveled leaves hang downward
  and usually cling to blighted twigs.
• Infected shoots, twigs, and suckers turn brown to
  black and often bend in a characteristic
  shepherd's-crook.
• Infected immature fruit turns dark, shrivels,
  mummifies, and rots. Mummified fruit may cling to
  the tree for several months.

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Cause

• Fire blight (Erwinia amylovora)
• Bacterial infection.
• Not common in New Mexico, but pears and quince
  particularly vulnerable.
• Proper pruning, fertilizing and watering. Avoid
  stimulating excessive young growth.
• Treat with Agrimycin (agricultural streptomycin).

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Symptoms

• On tomato, possibly peppers and eggplant
• Leaf and fruit deformation.
• Stunting.
• Leaves turn yellow with purple veins.
• Leaves twist and curl upward.
• Leaves become thickened, stiff, and crisp.
• Petioles curl downward.
• Premature fruit ripening.
• Reduced fruit quality and yield.
• Infected young seedlings may die.

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Cause

• Curly top virus
• Over 300 host plants, including solanceous crops,
  beans, beets, spinach, cucurbits, london rocket.
• Only one vector beet leaf hopper.
• Carefully weed out winter hosts.
• Light shading may discourage leaf hopper.
• Resistant varieties? Try Peron Sprayless. Save
  seed of OP resistant plants.

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Symptoms

• On peach
• Color-breaking of flower petals.
• Retarded bud-break.
• Chlorotic spots in leaves (tiny flecks to bold
  blotches).
• Leaves turning darker green by mid-summer small,
  narrow and asymmetric with deformed, crinkled
  margins.
• Fruit often deformed, unmarketable fruit surface
  becomes rough and bumpy.

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Cause

• Peach mosaic virus
• Highly infectious.
• Vector peach bud mite (Eriophyes insidiosus).
• Mite is microscopic, travels on the wind.
• Can infect peach, apricot, almond, plum. Native
  plums carry but dont express. Sweet cherry
  immune.
• Remove infected trees before it spreads.

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Symptoms

• On cherry
• Leaflike projections (enations) along midrib of
  leaf underside.
• Whole leaf may be affected in serious cases.
• Spreads from bottom of plant upwards.
• Affected branches less winter hardy.
• Eventual tree decline.

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Cause

• Cherry rasp leaf virus
• Vectored by a dagger nematode (soil-borne).
• Infectious across wide range of herbaceous and
  woody plants.
• Easily graft transmitted.
• Remove affected tree if concerned about spread to
  other stone fruit (can even get into apples).