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Copyright 2005, Board of Trustees, University
of Florida

INFLUENCE OF FERTILIZATION ON SEVERITY OF ERWINIA
BLIGHT AND GROWTH OF DIFFENBACHIA HI ji L A

A. R. Chase and R. T. Poole
IFAS, University of Florida '
Agricultural Research Center -Apopka
ARC-A Research Report RH-82-6 .F S. o

One of the most serious diseases of dieffenbachias in Florida is Erwinia

blight caused by the bacteria Erwinia chrysanthemi and E. carotovora. Erwinia

blight was first described in 1960 in California (6) and in 1961 in Florida (5),

and is characterized by dark, water soaked leaf spots and mushy, slimy stem

lesions at the soil line. Lower leaves also wilt and turn chlorotic under severe

infections. The bacteria inhabit the interior of the stem and since none of the

chemicals presently available for bacterial disease control are highly systemic,

the disease is very difficult to control. Alternative means of decreasing

disease losses are therefore important. The ability of a host plant to resist

disease can be influenced by the nutritional status of that host. The following

study was conducted to determine the relationship of Erwinia blight and nutrition

of dieffenbachia.

The first experiment was conducted between October 1980 and April 1981 on

D. maculata 'Perfection' and 'Rudolph Roehrs' obtained from pathogen-free tissue

cultured plants. Ten cuttings of each cultivar were rooted and grown in steam

sterilized potting medium without fertilizer for 4 weeks. N, P, and K was

obtained from NH4NO3, KNO3, and H3PO4 with a N:P:K ratio of 2:1:2. Dolomite and

Micro Max were incorporated at 7 and 1l pounds per yard prior to potting into

6 inch pots. The recommended rate is 1,200 pounds/acre/year of nitrogen (1).

Fertilizer treatments initiated on November 24, 1980 consisted of the following

rates applied as a liquid on a weekly basis: 1000, 2000, 3000, 4000, 5000, and

6000 Ibs N/acre/year. On April 2, 1981 plant height was recorded and leaves

were inoculated with Erwinia chrysanthemi by injecting a suspension of the

bacterium into them in 15 locations/plant. After 2 weeks the number of

lesions (leaf spots) and their sizes per plant were recorded (Tables 1 and 2).

The middle fertilizer rates produced the tallest plants and lowest disease

ratings.

The second experiment was performed between May 1981 and September 1981,

using D. maculata 'Perfection' plants. Fifteen plants established as described

earlier were used for each of the following treatments: 1) 1000, 2) 2000,

3) 3000, 4) 4000, 5) 5000, 6) 6000, 7) 7000, and 8) 8000 Ibs N/acre/year applied

as 14:14:14 Osmocote, 4 grams per 6 inch pot is equivalent to 1000 bs N/acre/year

when applied 4 times annually. The remainder of this experiment was performed

as described earlier. Plant height and disease severity were both affected by

fertilizer treatments (Table 3). The same trend in optimum plant growth and

minimum disease for the intermediate treatments was seen in this experiment.

Treatments 3 and 4 gave best plant growth combined with lowest disease severity.

Little research has been conducted to investigate the role of host plant

nutrition on disease severity in foliage plants. High levels of nitrogen

resulted in low levels of Phytophthora leafspot of philodendron while lower

levels supported the best plant growth (3). Similar results were found for

Xanthomonas disease of the same plant with high nitrogen decreasing disease

severity (2). Results from Erwinia studies with Philodendron selloum indicated

that high levels of nitrogen again decreased the disease severity (4), while also

reducing plant growth. Our studies indicate that excessive fertilizer can have

a different effect on disease severity. Plants produced under middle nutrition

levels (3000-4000 Ibs N/acre/yr, 1200 Ibs recommended rate) (1) would be more

resistant to Erwinia leafspot than those produced under stress conditions

resulting from either insufficient or excessive fertilizer regimes. Since our

conclusions differ from those of research from the past on other plants, it

seems likely that the influence of nutrition on disease resistance cannot be

stated as a single rule for all diseases and plants. The influence of nutrition

on disease should be investigated in each situation to determine optimum levels

for plant growth and disease reduction,especially in situations where disease is

poorly controlled with chemicals.

Table 1. Effect of fertilization on height and Erwinia
leaf spot severity of Dieffenbachia maculata 'Perfection'
(Expt. 1).

Treatment Plant ht Mean No.
Ibs NPK/acre/yr (cm) leaf spots/plant

1000 56.3 5.0
2000 56.7 2.4
3000 56.7 1.6
4000 54.3 1.6
5000 51.6 1.0
6000 49.1 3.6

Table 2. Effect of fertilization on height and Erwinia
leaf spot severity of Dieffenbachia maculata 'Rudolph
Roehrs' (Expt. 1).

Treatment Plant ht Mean No.
Ibs NPK/acre/yr (cm) leaf.spots/plant

1000 57.3 2.0
2000 65.2 3.0
3000 68.4 1.6
4000 63.6 1.6
5000 63.7 2.0
6000 58.7 3.4

Table 3. Effect of Osmocote fertilization on height and
Erwinia leaf spot severity of Dieffenbachia maculata
'Perfection' (Expt. 2).

Treatment Plant ht Mean leaf spot
Ibs NPK/acre/yr (cm) size (mm)
1000 40.9 9.25
2000 44.6 8.10
3000 44.3 6.45
4000 45.2 6.20
5000 44.6 6.88
6000 41.2 7.52
7000 42.3 7.32
8000 41.1 7.85

Literature Cited

1. Conover, C. A. and R. T. Poole. 1981. Guide for fertilizing tropical
foliage plant crops. ARC-A Research Report RH-81-1.

2. Harkness,R. W. and R. B. Marlatt. 1970. Effect of nitrogen, phosphorus
and potassium on growth and Xanthomonas disease of Philodendron oxycardium.
J. Amer. Soc. Hort. Sci. 95(1):37-41.

3. Harkness, R. W. and J. E. Reynolds. 1964. Effect of nitrogen and
potassium nutrition on the phytophthora leaf spot of Philodendron
oxycardium. Proc. Fla. State Hort. Soc. 77:475-480.

4. Haygood, R. A. and D. L. Strider. 1982. Influence of nitrogen and
potassium on growth'and bacterial leaf blight of Philodendron selloum.
Plant Disease 66: (In press).

5. McFadden, L. A. 1961. Bacterial stem and leaf rot of dieffenbachia in
Florida. Phytopathology 51:663-668.

6. Munnecke, D. E. 1960. Bacterial stem rot of dieffenbachia. Phytopathology
50:696-700.