SYMPTOMS OF DISEASE IN PLANTS. 231 



SYMPTOMS OF DISEASE IN PLANTS. 



BY F. D. HEALD, PH. D. 



Professor of Agricultural Botany and Botanist of the Experiment Station, 



University of Nebraska. 



It is highly important that all persons engaged in general farming, 

 truck gardening, fruit raising or floriculture should be able to recognize 

 the presence of disease. In their mute way plants tell us when they 

 are suffering from constitutional or contagious diseases if we are only 

 able to interpret their language. It is evident that many people do not 

 recognize the presence of disease for it is not an uncommon thing to 

 receive replies like the following to the letters of inquiry that are sent 

 out over the state: "There are no plant diseases present in our locality." 

 "All the crops in our region are free from diseases." "No diseases in 

 our county." 



The diseases that affect plants may be divided into three different 

 groups: First, those disturbances of nutrition which are due to unfavor- 

 able conditions in the environment of the plant, or to the conditions 

 inherent in the plant itself; second, troubles due to the presence of 

 parasitic plants, generally either bacteria or fuhgi, which deform, stunt 

 or kill the affected plant by their presence; third, those caused by insect 

 pests, which are in many cases very evident, and in other cases not 

 easily detected. Many of these insect troubles are hardly to be classed 

 as plant diseases, while many are as truly diseases as those produced 

 by parasitic fungi. In the nature of the resulting symptoms there are 

 no sharp and fast lines that can be drawn between many insect and 

 fungus troubles and often a careful microscopic examination is necessary 

 in order to diagnose the disease. The first thing of importance for the 

 farmer is to detect the presence of the disease and then to endeavor to 

 find out its cause, nature, and probable outcome and the treatment which 

 should be employed, by consulting those who have made the subject a 

 special study. 



The following outline will give a survey of the principal symptoms 

 of disease in plants, placing most emphasis on those diseases included 

 in the second group. 



1. Discoloration or change of color from the normal. 



(a) Pallor. Yellowish or white instead of the normal green. 



(b) Colored spots or areas on leaves or stems. 

 AVhitish or grey: mildews; white rusts, etc. 

 Yellow; many leaf spots. 



Red or orange: rusts, leaf spots, etc. 

 Brown: many leaf spots. 

 Black: black rust, tar spots, etc. 

 Variegated: leaf spots, etc. 



