The Problem of Plant 'Diseases Which Confronts the Gardener 



By J. J. Taubenhaus, M. S. 



Assistant Plant Pathologist. Delaware Agricultural Experiment Station, 



Read before the convention of the National Association 

 of Gardners, at Newark, N. J., November 19, 1912. 



It is indeed a great privilege for me to speak before you 

 today. I am sure that you will agree with me that the 

 subject on which I am about to speak is in accord with 

 the purpose which has brought us all together now. Men 

 unite and combine in all walks of life, and conventions 

 are merely held for the purpose of discussing the prob- 

 lems of the individuals through the guise of the organiza- 

 tions. Numerous as are the problems of the gardener, I 

 shall only deal with those of plant diseases which are be- 

 coming more and more serious. In order, however, to 

 discuss the subject more intelligently, it would not be out 

 of place briefly to inquire what causes disease in plants. 



The prevalent belief among gardeners is that plant dis- 

 ease can only be induced by overfeeding and unfavor- 

 able weather conditions. We do not deny that these two 

 factors bring about physiological disturbances in the life 

 of the plant. Nevertheless, we must not overlook the 

 fact that plant troubles are induced by specific plant para- 

 sites such as bacteria, fungi and insects. Bacteria are very- 

 minute plants which are invisible to the naked eye, and 

 can only be seen when they are magnified with the micro- 

 scope. The average size of a single bacterium is 1/10000 



lus Erw. Smith) is capable of attacking cucumber 

 and melon plants both under glass and outdoor. 

 It also attacks the pumpkin and the squash. The 

 symptoms are a general wilting and a collapse of 

 the plant. This disease can be readily recognized 

 in the field when cutting across an infected stem by the 

 presence, on the moist cut end, of a sticky, gummy, sub- 

 stance, which is exuded and which can be drawn out to a 

 fine thread by touching with the fingers. The germ is 

 distributed from plant to plant by the striped cucumber 

 beetle. This disease is often mistaken for the wilt pro- 

 duced by a Fusarium fungus. 



The Black Rot of Cabbage. — This is another bac- 

 terial disease which often causes great loss to 

 truckers. The germ (Pseudomonas campestris (Pam.) 

 Erw. Smith) which causes this disease is also known 

 to attack cauliflower and several other cruciferous plants. 

 The symptoms are a yellowing of the leaves, with a brown- 

 ing of the margins and a blackening of the veins. 



Crown Gall. — This disease attacks a great variety of 

 plants, such as the peach, apple, grape, walnut, rose, daisy, 

 and many others. Young nursery stock, as well as older 

 trees in the orchard, are alike subject to it. The symptoms 

 of this disease are swellings, or the production of galls at 



"DAMPING OFF" OF LETTUCE SEEDLING 



•■DAMPING OFF' 



of an inch. Parasitic fungi, too, may be so small as to be 

 invisible to the naked eye, or they may be very large like 

 some of the large mushrooms. Not all the bacteria and 

 fungi are parasitic plants ; but under favorable conditions 

 to the host they can become true parasites. The bread 

 mould, for instance, which is considered as a harmless 

 fungus unable to attack vigorous growing plants, will, 

 under unfavorable storage conditions, induce a soft rot 

 disease of sweet potatoes and other stored crops. As for 

 the insects, everyone knows what they are. 



For the sake of illustration, I will briefly consider a 

 few diseases of each of the above types. 



SOME PLANT DISEASES WHICH ARE INDUCED BY BACTERIA. 



Cucumber Wilt. — The germ (Bacillus tracheiphil- 



ANTHRACUOSE OF SWEET PEAS. 



I.MATU SFEDLING 



the base of the stem, or sometimes on the roots. Dr. Erwin 

 1'. Smith of the U. S. Department of Agriculture, has 

 recently found out the cause of this disease which he at- 

 tributes to a bacterium (Bacterium tumeficians Erw. 

 Smith). 



The above mentioned bacterial diseases are only a few 

 of the many with which the gardener has to contend. 



SOME PLANT DISEASES WHICH ARE INDUCED BY FUNGI. 



Here, as in the case of the bacterial diseases, I will but 

 Iiriefly indicate a few of the types of fungus diseases 

 which are becoming troublesome. 



1. Fungus Diseases Originating with the Seed. — It 

 has been tlefinitely established that some diseases can be 

 carried with the seeds, either as viable spores adhering to 



