UNIVERSITY OF THE PHILIPPINES – LOS BAÑOS
COLLEGE OF FORESTRY AND NATURAL RESOURCES
In partial fulfilment of the requirements of
EXERCISE 5: DIAGNOSIS OF SEEDLING DISEASES IN THE SILVICULTURAL
FOREST INFLUENCES NURSERY OF THE COLLEGE OF FORESTRY AND
Mary Angela H. Magno
Y – 2L
Mutya Ma. Q. Manalo
Diagnosis of forest plant diseases requires a thorough understanding of the nature of
disease, whether it is infectious or non-infectious. Systematic and careful observations of the
plant, its environment, and other plants in the area are a vital step in determining what factors
have damaged the plant ...view middle of the document...
50 seedlings of Hopea plagata (saplungan) were observed empirically and were measured
according to amount of infection occurring in each of the seedlings with rating and numerical
rating classified in table 1.
Table 1. Amount of infection and its corresponding rating and numerical rating.
Amount of Infection
0% infection (healthy)
1% to 25% infection
26% to 50% infection
51% to 75% infection
76% to 100% infection
Data were summarized using Microsoft Excel and percent disease incidence, average
rating of disease severity, and index of infection were computed.
According to the information gathered by the researcher, it has now been 7 years since
the saplungan seedlings were planted in the nursery by BS Forestry students. Garden soil was
used in planting the seeds and watering is done 3 times a week depending on the weather. No
fertilizer and other chemicals were applied to the plants.
Thirty four percent of the seedlings occur within 26% to 50% (Rating = 3; Numerical
Rating = 1) amount of infection. On the other hand, seedlings with 51% to 75% (Rating = 4;
Numerical Rating = 2) amount of infection comprise only 8% of the total population.
Additionally, 20% of the seedlings were remarked as dead plants.
Figure 1. Percent distribution of the amount of infection of Saplungan seedlings in the nursery.
Percent disease incidence, average rating of disease severity, and index of infection were
computed using the following formula:
% Disease Incidence =
Average Rating =
Number of diseased seedlings
Total number of seedlings
Sum of all ratings
Total number of seedlings
Index of infection =
Sum of all numerical ratings x 100
Total number of seedlings x 3
From the data, it can be inferred that 86% of all saplungan seedlings are diseased, while
disease severity following the ratings and numerical ratings are 2.96 and 1.28 respectively.
Common symptoms found in the seedlings were leaf spots, shot holes, leaf blight, and yellowing
of leaves. Others were eaten by leaf insects and catterpillars.
Diagnosis is a process of gathering information about the disease of a host plant and its
causal agent. Determining the causes of the plant problem is a vital step in recommending a
possible solution or remedy to the problem (Mohan, 1996). These causes may either be due to a
pathogen (fungi, bacteria, viruses, nematodes, and pests) or a physiopath (environmental
conditions and chemicals).
Eighty six percent of the total population of saplungan seedlings are infected with disease
with an average rating of disease severity of 2.96 and index of infection of 1.28. These values
mean that the plants have an average amount of infection ranging from 51% to 75%. Most of the