Identifying Proablems in Flowers
Agricultural Extension Service, The University of Tennesee
Symptoms Possible Causes
Controls/Comments
Plants fail to flower; foliage looks healthyRunner BeanBeetrootBroccoliSavoy CabbageCarrotCourgette Wrong season
Some plants have specific day-length requirements for flowering
Low temperatures, freeze injury
Low temperature injury may damage flower buds
Insufficient light
Do not plant sun-loving plants in shade
Too much nitrogen
Do not over fertilise as too much nitrogen stimulates foliage, not flower, production; follow soil test recommendations
Overcrowded plants
Divide perennials at recommended time of year
Immature plants
Biennials and perennials often do not flower the first year; peony may not flower for several years
Undersize bulbs
Too many small flowers Plants not debudded
Some flowers, e.g. chrysanthemum, need to have some buds removed to produce large flowers
Flowers wilt or fail to open; grayish mould appears on flowers and leaves in moist weather conditions Botrytis gray mould (fungal disease) Pick off and destroy affected flowers to remove a source of disease; keep water off foliage or water early in evening so foliage will dry before nightfall; use a registered fungicide
Flowers distorted and abnormally coloured Thrips; small tannish yellow or brown wedge shaped insects mainly found inside flower petals Use registered insecticide
Rosetting of florets; ring pattern on leaves; yellow and light green mosaic or mottle Virus disease (any of several)
Destroy affected plants; insect control may reduce virus spread to non-infected plants
Light green, yellow or white flecks on leaves Spider mites; Tiny 8-legged ‘spiders’ with webbing on underside of leaves
Hard blast of water on underside of leaves; insecticidal soap or horticultural oil or use a registered miticide (insecticide for spider mites) on underside of leaves
Corky, raised spots on lower leaf surfaces Oedema, a physiological problem usually associated with excess humidity Do not over water; space plants to increase air movement around plants, esp. geranium; thinning foliate may help reduce humidity
Brown, dead areas on outside margins of leaves and/or between leaf veins

Scorch, due to hot, dry weather conditions or newly transplanted plants
Supply water by soaker hose; mulch plants; can also occur on plants divided and moved at wrong time of year
Severe nutrient deficiency
Soil test and follow fertilisation recommendations
Chemical injury Severe nutrient deficiency
Salt injury Severe nutrient deficiency
Fungal disease Severe nutrient deficiency
Sun scald and winter sunburn as foliage dries when roots cannot take up enough water to keep foliage alive Severe nutrient deficiency
Bleached leaves Sunburn Move plant under shade; use only sun loving plants in areas with full sun; Moving plants from shade (or from inside house) immediately to intense sunlight will cause sunburn; move plants gradually from one light intensity level to another to acclimate them slowly.
Brown, purple or black dead circular or irregular spots on leaves Fungal, bacterial or leaf nematode disease (any of several) Submit leaf sample for laboratory diagnosis
Grayish-white powdery growth on leaves, stems and flowers Powdery mildew (fungal disease) Use registered insecticide; buy resistant varieties of plants
Pustules containing orange, yellow or brown powdery substance on leaves Rust (fungal disease) Use registered insecticide; destroy infected plants
Leaves wilt, turn yellow and/or drop; roots decayed Root rot (any of several) Many perennials will not tolerate poorly drained soils; check cultural conditions; submit sample with roots and soil for for laboratory diagnosis
Yellow and green mottle or mosaic pattern on leaves  Virus disease (any of several) Remove affected plants; do not touch healthy plants after diseased ones; avoid use of tobacco products (which can harbour plant viruses) before handling plants; wash hands in milk to neutralise virus particles before handling plants; control insects that can spread virus to other plants
Nutrient deficiency  Soil test and follow fertilisation recommendations
Twisted, stunted or puckered leaves, often mottled or abnormally coloured Herbicide injury Check for use of phenoxy type herbicides, e.g. dicamba and/or 2,4-D used in area. May be taken up by root zone (granular herbicide) or drifted on wind up to 1/2 mile.
Tiny white flecks or white interveinal areas on leaves

Ozone injury Some plant varieties are more susceptible to ozone injury (air pollution damage) than others
Spider mites; Tiny 8-legged ‘spiders’ with webbing on underside of leaves Hard blast of water on underside of leaves; insecticidal soap or horticultural oil or use a registered miticide (insecticide for spider mites) on underside of leaves
Thrips; small tannish yellow or brown wedge shaped insects mainly found inside flower petals Use registered insecticide
Light coloured tunnels or blotches in leaves Leaf miners Use registered insecticide; remove affected leaves if only a few are affected
Leaves chewed with ragged holes or may be completely eaten Various insects - usually caterpillars or beetles Submit insect for identification
Leaves chewed with ragged holes; slime trails Slugs Use beer bait or commervial slug bait; check plants at night for actively feeding slugs
Only leaf veins or clear areas left on leaf; no green in these sections Sawfly caterpillars or leaf skeletoniser beetles Submit insect for identification
Leaves with smooth holes or only slightly ragged areas with yellow halo Bacterial shot hole Cut and remove diseased foliage in late autumn or early spring to remove source of disease. Avoid overhead watering or water so that leaves dry before nightfall. 
Black soot or surface of leaf or stem; scrapes off surface easily; may peel off in sheets Sooty mould Secondary fungus growing on surface of honeydew sap left by insects (aphids, scale or whiteflies) as they feed on plant; control insects with registered insecticide
Clusters of insects on stems or underside of leaves; leaves may be curled or distorted; may have sooty mold Aphids; soft bodied round insect with two small ‘stalks’ on rear end, may be green, red or tan depending on plant sap Use registered insecticide or insecticidal soap
Leaves and stems covered with small, soft-bodied or crusty insects that can easily be removed Scale (various) Use registered insecticide
Tiny white winged insects on undersides of leaves Whiteflies Use registered insecticide
White, cottony masses on leaves or stems Mealy bugs Use registered insecticide
Irregular bronze or brown spotting on leaves; adults are yellowish-green with four black stripes down wing covers; immature insects are orange to red with black spots and yellow stripes Four-lined plant bug Use registered insecticide
Grayish mould appears on flowers, stems and leaves in moist conditions Botrytis gray mould (fungal disease) Pick off and destroy affected flowers to remove a source of disease; keep water off foliage or water early in evening so foliage will dry before nightfall; use a registered fungicide
Plants wilt; flowers may drop and leaves may turn yellow; check roots and stems for possible rot diseaseSevere nutrient deficiencySevere nutrient deficiencySevere nutrient deficiency Dry soil Supply water 
Waterlogged soil may drown plants due to lack of oxygen in soil Improve drainage; do not allow plant roots to sit in water or in waterlogged soil; some perennials will not tolerate poorly drained soils
Transplant shock Do not transplant in heat of day; water regularly after transplanting; divide and transplant perennials in autumn or spring
Root or stem or corm rot; may be fungal or bacterial disease Plant in well-drained soil; destroy affected plants; do not purchase plants with brown or black rotted roots
Seedlings wilt; stems turn brown and soft and may be constricted at the soil line Damping-off (fungal disease) Plant in well-drained, disease-free soil; plants should be planted in sterile potting soil
Tall, “leggy” plant; stem and foliage is pale and yellow Insufficient light Pay attention to light requirements of plants (planting a sun loving plant in shade will result in weak leggy plants)
General yellowing of leaves; yellowing may be interveinal; plant may be stunted; but no wilting Nutrient deficiency  Soil test and follow fertilisation recommendations
Severe nutrient deficiency Virus disease    Submit sample for laboratory diagnosis; destroy affected plants as virus may be spread further by insects or through handling plants
Plants stunted and yellow; small galls or swellings on roots Root knot nematodes (Note: galls are normal on leguminous plants) Use resistant species of plants in these locations; replant susceptible varieties in another area
General browning of foliage; on tender, new foliage can look bronze or red; occurs after a cold spell Frost injury New growth should occur below damaged area; do not plant annuals until danger of frost is past
Small, gnat-like flies around potted plants; small 1/4” white maggots (larvae) with black heads in soil around plant roots Fungus gnats Use registered insecticide; avoid overwatering plants; clean up and remove all plant debris in area; if planting in pots or planteds, use sterile potting soil
Plants cut off at ground level Cutworms Worms hide during day in soil or in debris close to base of plants. Spray soil and base of plant with labeled insecticide or uncover and kill cut worms around base of plants.