A Guide to Solving Plant Problems

By Rondalyn Reeser, Howard County Master Gardener

Steps to Follow in Diagnosing Plant Problems

1. Know what the plant normally looks like
2. Notice that there is a problem
3. Note specific symptoms
4. Look for a possible cause of those symptoms
5. Observe the overall pattern of injury
6. Decide on an appropriate control

Causes of Plant Injury

1. Pests: Pests appear slowly and are not uniformly distributed on the plant or on the site.
   • Insects
   • Animals
2. Diseases: Diseases appear slowly and are not uniformly distributed on the plant or on the site. Most plant diseases are very host-specific (only one species of plant will be affected).
3. Fungal
4. Bacterial
5. Viral
6. Environmental/Cultural Problems: Most problems caused by non-living agents will appear suddenly and affect a wide variety of plants on the site. These disorders can weaken a plant and lead to diseases.
   • Above the soil surface
     • Weather conditions
     • Poor site location
     • Air pollution
     • Herbicide damage
   • Below the soil surface
     • Poor soil (compacted, poorly drained)
     • Over or under watering
     • Over or under fertilizing
     • Poor planting techniques (trees and shrubs)
     • Physical damage to bark or root

Damage Symptoms

A. Insect pests:

• Chewed leaves
• Defoliation
• Discolored leaves or blossoms
• Dieback of shoots, twigs, or branches
• Wilting
• Discolored speckles on the leaves
• Curled leaves
• Stunted new growth
  • Products of insects:
    • Honeydew
    • Fecal spots
    • Silk
    • Wax
    • Spittle
    • Pitch tubes
    • Frass

B. Diseases:

• Chlorosis
• Dead or brownish areas on leaves
• Water-soaked or greasy appearance
• Premature defoliation
• Wilting
• Abnormal plant growth
• Rotten spots on leaves or fruit

C. Environmental/cultural problems:

• Dieback; leaf scorch, sunscald
• Thickened, distorted growth
• Plant dies suddenly

D. Nutrient deficiency symptoms:

• Symptoms appear first on older or lower leaves
• Nitrogen deficiency - lower leaves yellow, overall plant light green, growth stunted, small leaves
• Potassium - tips and edges of leaves yellow, then brown, stems weak
• Magnesium - interveinal chlorosis, growth stunted

• Micro-nutrient deficiency symptoms appear first on younger or upper leaves:
  • Calcium - buds and young leaves die back at tip
  • Iron and manganese - interveinal chlorosis, growth stunted - occurs in ‘acid-loving’ plants on high pH soils.