FIELD TRIP 
This first exercise consists of a field trip taken to points close to the 
laboratory. The purpose is to introduce the student to a variety of plant 
diseases as they appear in the field. Attention will be directed to such 
diseases of all sorts of plants as are found. . 
The student himself should seek to discover diseased plants. He will 
be expected to collect at least ten specimens of diseased plants for study 
and report. Healthy specimens for comparison should also be taken. 
(See REPORT at end of exercise.) 
For field identification of diseases one must depend largely upon 
symptoms and signs. By symptoms is meant those changes- induced 
in the diseased plant which distinguish it from the healthy. Signs of 
disease are incidental or experimental evidences of disease and not the 
direct results or expressions of the diseased conditions. 
SYMPTOMS 
Symptoms are usually the expression of structural changes of one kind 
or another (histological or morphological). Diseases in plants are of three 
general types within each of which are exhibited a considerable variety 
of symptoms. These three types of disease with some of their more 
characteristic symptoms are:— 
NECROTIC DISEASES—those in which the most striking effect on 
the host is the death of the affected tissues resulting in such symptoms as:— 
Rot—the term applied when the killed tissues become discolored 
and decayed. If the tissue in such lesions are dry and firm it is called dry 
rot; if soft and mushy, soft rot; if firm or tough but very watery or soggy, 
wet rot; if white in color, white rot; if black, black rot. The term rot, coupled 
with the name of the part or organ affected serves to designate a variety of 
symptoms such as, stem-rot, bud-rot, crown-rot, collar-rot, root-rot, heart-rot, 
Soot-rot. 
Blight—the term applied when there is rapid killing of the affected 
parts often accompanied by wilting and withering of the foliage. This 
term coupled with the name of the host organs gives, twig-blight, blossom- 
blight, body-blight, leaf-blight, and the like. : 
Wilt—the term applied where all or a portion of a plant becomes 
limp due to loss of turgor. Wilt differs from blight in that the causal 
factor does not directly affect the wilting or dying organs. The injury 
results from the activities of the causal factor usually in the vascular 
system somewhere below the wilting organs. 
Spot—the term used to designate necrotic areas, usually those in 
Jeaves, fruits and herbaceous stems. This term is used in numerous 
combinations to designate a variety of spot-symptoms as, Leaf-spot, 
Srutt-spot, pod-spot, and the like. : 
x Shot-hole—the term applied to limited necrotic spots on foliage 
where the dead tissue drops out leaving a hole. Peculiar largely to the 
foliage of peaches, plums and cherries. 
Damping-off—used to designate the symptom resulting from the 
rotting of the stems of seedlings at the base and the consequent falling-over 
of the tops. A form of stem-rot. 
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