E. Lireni Kikon
SMS, Plant Protection, KVK, Longleng, Nagaland
Geraniums are becoming very popular ornamental plants in Nagaland. While there is still a demand for the traditional florist or zonal geraniums from cuttings (Pelargonium X hortorum) there is also a demand for seed grown hybrids, Ivy geraniums (P. peltatum), Martha Washington or Regal geraniums (P. X domesticum), and scented and perennial geraniums (Geranium spp.). Geraniums are susceptible to different diseases with 45 diseases being reported but fortunately most of them don’t occur with any frequency. Geranium diseases are described by the type of the causal agent or pathogen.
DISEASES ON STOCK PLANTS AND CUTTINGS
- FUNGAL
- Leaf Spot
Causal organism: Alternaria tenuis, Ascochyta sp., Cercospora brunkii., Pleosphaerulina sp.
Symptoms: Different types of leaf spots occur and cause considerable damage. Small water soaked spots of variable sizes develop on the lower surface of the leaves. Larger spots are brown with concentric rings.
- Grey Mould Botrytis Leaf Spot or Blossom Blight
Causal organism: Botrytis cinerea
Symptoms: Fungus attacks leaves, stems and flowers under humid conditions and they rot in case of severe infection under favourable environmental conditions.
LEAVES: Symptoms vary from discrete spots or lesions to large, dead areas often with concentric rings. V-shaped lesions can also develop. Lesion usually occurs when spent flowers petals fall onto the leaves.
CUTTINGS AND STEM: Symptoms appear at the base of cuttings as light to dark brown lesion which can result in complete basal rot. Stubs on stock plants can develop brown lesions after cuttings are taken. Petals are discoloured and the flowers wilt and fall. The pathogen produces a brown decay on the cuttings
FLOWERS: The first evident symptoms usually premature fading and drying of flowers. Flowers turn brown and drop prematurely. During periods of high moisture and relative humidity, senescing flowers are covered with a gray, fuzzy mass.
- Rust
Causal organism: Puccinia pelargonii-zonalis
Symptoms: Characteristics symptoms develops on the under sides of the leaves in the form of reddish brown spores in the concentric rings. Corresponding yellow areas appear on the upper surface of the leaves. Pustules break open and release the rusty colored spores for which this disease gets its name. Leaves eventually turn yellow, dry and drop prematurely. This disease is prematurely a problem for zonal geraniums.
- Black stem rot
Cause organism: Pythium splendens
Symptoms: Fungus infects the full grown plants and causes dropping of leaves, stunting and eventually death of plants. Cuttings are also infected and the rotting starts at the base and progresses upward until the leaves wilt and die. Blackening of the stem of older plant progresses towards the tip, the lower parts become sunken and defoliated.
- Black Leg
Cause organism: Fusarium sp.
Symptoms: Stems are affected by the fungus and produce coal black lesions.
Management:
- Practice good sanitation by using a clean house and equipment and a sterile, well-drained medium
- Use disease free cuttings
- Select the soil or rooting medium which are relatively sterilized by chemical means
- Avoid overhead irrigation and water early in the day
- Use biocontrol agent Trichoderma harzianum for cutting treatment and foliar spray
- Spray Dithane Z-78 @ 2 g/litre water or Thiram 2.5 g/litre water for leaf spots and rust
- Benlate 1g/litre or Bavistin 1g/litre for grey mould
- Drench the soil with Benlate @ 1g/litre for Black leg and Captan 2g/litre or copper oxychloride 3g/litre solution
- BACTERIAL
- Bacterial blight (Bacterial leaf spot, stem rot or wilt)
Causal organism: Xanthomonas campestris pv. Pelargonii
Symptoms:
LEAVES: Infected leaves typically develop two types of symptom: small, discrete, water-soaked or brown spots and V- shaped angular lesions. Some leaves develop distinctly darkened veins and wilt at leaf margins.
STEM: When infection is systemic, the entire plant develops typical wilt symptoms, often first appearing in the lower leaves. Leaves become flaccid and branches wilt and dieback. Stems can blacken and shrivel into a dry rot. Infected cuttings fail to root and slowly rot from the base upward. Stems become dull black-brown and are drier than Pythium root rot. Plants with systemic infection collapse and die. Systemically infected ivy geraniums don’t wilt but develop systems that can be confused with nutritional or inset problems.
Management-
Ø Start with a clean house and equipment
Ø Isolate stock plants from propagation area
Ø Use disease-free cuttings
Ø Keep geraniums from different suppliers separate
Ø Separate seedlings geranium from cuttings
Ø Avoid growing perennial geraniums (Geranium spp.) near Pelargonium spp.
Ø Avoid placing ivys in hanging baskets above seedling or cutting geraniums
Ø Use drip irrigation if possible (esp. on stock plants)
Ø Rouge and remove diseased/symptomatic plants as soon as possible
Ø Wash hand frequently while handling the plants
Ø Avoid unnecessary handling of plant material
Ø Minimize traffic flow in house
Ø Use copper sulfate pentahydrate
- Southern Bacterial Wilt
Causal organism: Ralstonia solanacearum (formerly called Pseudomonas solanacearum)
Symptoms: Initial symptoms appear as a general wilting of lower leaves followed by yellowing and necrosis. V-shaped chlorotic or dead areas similar to those associated with Bacterial Blight can develop on flaccid leaves. Brown discoloration of the vascular system is sometimes visible. Roots of infected plants often turn brown or black and eventually collapse and die. No discrete leaf spots are associated with this disease.
Management: same as Bacterial blight except-------
-----------Chemical control is not effective in preventing infection since this pathogen generally infects through openings or wounds in the roots.
III. VIRAL
- Cucumber Mosaic Virus:
Causal Agent: Cucumber Mosaic Virus (CMV)
Symptoms: Foliage appears mottled with light-green interveinal and dark-green veinal areas. Infected plants become dwarfed with small leaves and shortened internodes. Purple pigments are affected or rearrange on flowers. Symptoms are most severe in winter and are often completely masked during long summer days.
- Pelargonium Flower Break Virus:
Causal Agent: Pelargonium Flower Break Virus (PFBV)
Symptoms: Most diagnostic symptom is a white-streaking on the backs of the petals (= color - breaking). A subtle chlorotic mottle or ringspot pattern can also develop on leaves and plant growth can be retarded.
- Tomato Spotted Wilt and Impatient Necrotic Spot Viruses:
Causal Agent: Tomato Spotted Wilt Virus (TSWV) and Impatient Necrotic Spot Virus (INSV)
Symptoms: Symptom is highly variable that ranges from stunting, ring spots, sunken purple-brown lesions on leaves, stems, and petioles. Symptoms vary with plant age and physiological condition, level of infestation, and timing.
Management for viral diseases –
- Use disease-free, virus-indexed cuttings
- Rogue and destroy symptomatic plants
- Avoid unnecessary handling of plant material
- Attention to insect control, when necessary; thrips monitoring and management are very important
- ABIOTIC
Oedema:
Causal factor: It is considered to be caused by water imbalance which develops during periods of cool, cloudy weather or when the soil is moist and warm and the air is moist and cool.
Symptoms: First appear as chlorotic spots on the upper leaf surface which develop into water-soaked blisters on the undersides of leave that later become corky and rusty brown in color. Entire leaves may become yellow, die, and drop off and can sometimes mimic Bacterial Blight. It is most serious on ivy geraniums.
Management –
- Use a well-drained potting medium and maintain pH levels approx. 0.5 pH unit lower than zonals
- Maintain proper nutrient levels (increased N and Fe have been reported to reduce incidence)
- Avoid overwatering during cool, humid weather
- Reduce humidity and space plants to promote good air circulation
