id,
lant
ANDT
in
ion,
elds.
- 2073 -
potato, young corn, and alfalfa crops. Automatic classi-
fication, however, is probably not apt for practical use,
as corrections have to be made with respect to image position,
vignetting, and film development characteristics. Anyhow, it
does not seem useful because visual interpretation is faster,
and likely to be more accurate.
The same applies to nematode damage interpretation. Densito-
metric measurements of nematode-infested and non-infested areas
in the same fields have shown highly significant (p = .O1)
differences for the transmission of blue, green, and red
light, and differences at p - .001 for white light between
turgid and non-turgid field parts.
The largest doubt as to the reliability of nematode damage
interpretation results is in the possibility of confusing
nematode-caused stress with stresses caused by other influ-
ences. As sugar beet cultivation means a comparatively high
yield in terms of money to the farmer, the fields are very
well cared for. Therefore, soil management techniques, nutri-
ent supplies, and pest and disease control measures are care-
fully conducted, and in general, plant stress due to insuffi-
cient management techniques occurs very seldom only. Irregu-
larities in soil structure, however, may cause the slackening
or wilting of the plants due to local water stress, and there-
fore could result in confusing them with nematode-caused
turgor loss. As stated before, hwever, the animals are spread
passively, which is usually done in the course of field
management procedures like ploughing, sowing, etc. Taking this
fact into consideration, by visual interpretation the spread of
the nematodes can be defined by the slackening plants in the
surroundings of an infestation center, which always extends
in row direction. No such phenomena is to be found with soil-
- caused water deficiency. Several examples underlining this
statement are recorded in our test areas. Moreover, the syn-
optic view that an aerial photograph gives to the interpreter,
showing the soil structure of a larger area as a whole, faci-
litates the decisions. Comparisons between image interpretation
and field status have shown that damage interpretation accuracy
is better than 96 per cent.
