676 



HOETICULTUEE 



November 16, 1912 



PRESENT KNOWLEDGE OF SWEET 



PEA DISEASES AND THEIR 



CONTROL. 



A paper bv J. J, Taubenhaus, Delaware 

 College Agricultural Experiment Sta- 

 tion, Newark. Del., read before the 

 American Sweet Pea Society, 

 Boston, July 13, 1912. 



(CoHlinuni from fage bsb) 



It has been also definitely proved 

 that the mosaic disease is a contagious 

 one, since it can be produced at will 

 by artificial inoculations. I believe 

 with Professor T. F. Manns, chief path- 

 ologist and bacteriologist of our Dela- 

 ware Experiment Station, that the mo- 

 saic disease is caused by a protozoic 

 organism which neither our micro- 

 scopes nor our present cultural and 

 staining methods are sufficient to de- 

 tect. The symptoms produced in arti- 

 ficial inoculations of this disease are 

 similar to those in the field, namely, 

 a yellowish spotting or mottling of the 

 leaves and a tendency of the leaves of 

 the tips of the plant to curl. Judging 

 from all our observations, it does not 

 seem probable that this mosaic disease 

 of the sweet pea is either introduced 

 or carried with the seeds. The mosaic 

 disease has not once made its appear- 

 ance in the laboratory during two 

 years work on the sweet pea diseases, 

 and in sowing both sterilized and un- 

 sterilized seeds were used all the time. 

 However, it must be added in this con- 

 nection that we have always used ster- 

 ilized pots and soil. This at once sug- 

 gests the possibility of the soils being 

 the source, where the organism is 

 harbored. On this point we are now 

 working. Should we find the soil to 

 harbor the organism then we shall be 

 on the road to discovering some means 

 of treatment. 



In England the sweet peas suffer 

 from a disease known as "streak." 

 This disease is very much dreaded by 

 the English gardeners, as it causes 

 great losses. From the descriptions 

 given of that disease it seems to be 

 similar to the new mosaic disease of 

 this country. However, we refrain 

 from passing final judgment until we 

 have the opportunity of seeing the 

 English specimens and of making com- 

 parisons. In England the streak dis- 

 ease is attributed to a fungus, Thilavia 

 bassicola, which attacks the roots. In 

 our investigations we have not found 

 the Thilavia fungus or any other or- 

 ganism associated on the roots of mo- 

 saic affected plants. In fact, such af- 

 fected plants were found to have as 

 normal a root, with as much in the 

 way of legume nodules as the healthy 

 ones. If our mosaic disease proves to 

 be the same a,-5 the streak disease of 

 England, it will be safe to assume that 

 the Thilavia in England is secondary 

 and merely follows the already weak- 

 ened mosaic affected plant. 



The Anthracnose of the Sweet Pea. 

 This is another new and American 

 disease of the sweet pea. It was first 

 described by Prof. Sheldon of the West 

 Virginia Agricultural Experiment Sta- 

 tion. The disease, although recently 

 worked out, is apparently an old dis- 

 ease known under the name of "wilt" 

 or "drop." In some works on sweet 

 peas it is spoken of as "bud drop," and 

 is attributed to heavily manuring and 

 also to wet seasons. A rich soil and 

 wet climates cannot produce the drop. 

 These are only factors which help the 

 disease In its destructive work. The 

 cause of the anthracnose disease is a 



fungus (Glomerella rufomaculans), 

 which also is the cause of the bitter 

 rot of the apple. Cross inoculations 

 have been carried on with these two 

 organisms, and their identity definitely 

 established. This means that if your 

 sweet peas grow near some apple 

 orchard, and if the latter suffers from 

 the bitter rot, it will be carried readily 

 by the wind or some insect to the 

 sweet peas and produce the anthrac- 

 nose disease. We have also proved 

 that the organism which cause the an- 

 thracnose of the pepper, the persim- 

 mon fruit, and the May apple fruit 

 will also produce the anthracnose dis- 

 ease of the sweet pea and the bitter 

 rot of the apple. It is thus seen how 

 serious a proposition this becomes 

 when we consider the many hosts 

 which can communicate this disease to 

 the sweet pea. 



The symptoms of the anthracnose 

 of the sv/eet pea are diverse. Some- 

 times the disease is manifested in a 

 wilting and dying of the tips. These 

 diseased parts become whitish and 

 brittle and soon break off. Sometimes 

 the dying works downward, and this 

 involves the entire branch. Often- 

 times the leaves are attacked and they 

 soon die. On the leaves the disease 

 soon starts as a white spot, which en- 

 larges and involves the entire area. On 

 the blossoms the fungus either attacks 

 the junction between the flower buds 

 and the peduncle— in this case the bud 

 drops off leaving the peduncle intact— 

 or it attacks both flower bud and 

 peduncle, and this time both dry up 

 but do not tall off. The seed pods are 

 also attacked in all their stages of 

 development; in this case the fungus 

 works inwards until it reaches the 

 seeds. The fungus is capable of living 

 over winter on diseased parts of the 

 plants, in the soil or on the seeds, as 

 was definitely proved. 

 Mildew. 

 There is another disease knov.-n as 

 mildew. This disease is caused by a 

 fungus which lives on the surface of 

 the leaves and sends suckers into the 

 interior tissue of the host. The fun- 

 gus attacks both indoor and outdoor 

 sweet peas. However, it need not be 

 feared as it is easily controlled by 

 sulphur dusting. 



Methods of Control. 

 Little is done or known in the way 

 of controlling the diseases of the sweet 

 pea. There are, however, certaia 

 measures of control which we cai 

 adapt from methods applied to ctber 

 plants which suffer diseases in nature 

 similar to those of the sweet pea. For 

 the nematodes and all the other loot 

 and soil diseases of the sweet pea un- 

 der glass we would recommend the 

 same treatment as that recommended 

 in Ohio by Prof. Selby for Lettuce 

 disease under greenhouse conditions. 

 The treatments recommended are of 

 two kinds, namely, steaming the soil, 

 and formalin treatment of the soil. 

 The formalin treatment of the soil 

 consists first in spading the soil and 

 bringing it to a good tilth condition a? 

 to moisture content. Then the soil is 

 treated with a solution of formalin 

 made of two pints of a 40 per cent. 

 formalin in 50 gallons of water, at the 

 rate of one gallon of the preparation 

 to each square foot of the surface. 

 The application may be given with an 

 ordinary watering can. After the 

 "heavy wetting down" the soil should 

 be left tree for about two weeks, until 



all the formalin evaporates. This 

 treatment will rid the soil from all 

 fungus pests. But it will not be ef- 

 fective in controlling the nematodes, 

 hence the heating method is the best. 

 It is as follows: It is essential that 

 the soil should be sufficiently moiit 

 and at the same time fairly loose. The 

 steaming consists in burying a series 

 of pipes in the soil and letting live 

 steam pass through them. The pipes 

 are perforated, and have cross head 

 and boiler connections. The surface 

 soil is then covered with canvas and 

 the steam passed into the pipes. The 

 temperature for best results is ISl to 

 212F., maintained for a period of one 

 hour. For cutworms the following 

 treatment is recommended: Bran, 15 

 to 20 lbs.; middlings, 10 lbs.; whi.e 

 arsenic, 3 lbs.; molasses, or any chea;) 

 sirup, one gal.; freshly chopped green 

 clover, alfalfa, etc., enough to make 

 the mixture of a greenish tint. Mix 

 thoroughly, add just enough water to 

 allow of molding into small balls. Put 

 a pinch at intervals of the row. 



The biting insects could be con- 

 trolled by the same methods used to 

 control the Cucumber striped beetle, 

 a sprinkling of Paris green and flour. 

 Considering the Important role aphis 

 play in carrying the mosaic disease, it 

 is very important that the sweet pea 

 aphis should be kept in check. There 

 are two ways of accomplishing this: 

 the first is spraying with any com- 

 pound of nicotine, the other is to have 

 Nature do it for us. In Nature the 

 green aphis is parasitised by several 

 species of ladybird beetles. The latter 

 can be seen to feed voraciously on the 

 aphis, hence ladybird beetles should 

 not be molested. Green aphis are also 

 parasitised by a small hymenopterous 

 minute wasp-like insect. 



We now have a series of experi- 

 ments under way on different spray 

 mixtures to control the anthracnose. 

 Although it is early yet to reach any 

 conclusions, it seems that potassium 

 permanganate is the most promising 

 fungicide. A one-half per cent, solu- 

 tion will control the anthracnose. The 

 solution has a wine color but it is 

 more or less colorless when applied to 

 the plant. It spots the flower, there- 

 fore it should be applied after pick- 

 ing. Spraying at intervals of two 

 weeks will be sufficient. 



This concludes my remarks on the 

 sweet pea disease. It does not, how- 

 ever, exhaust the subject. There are 

 many more things that we would wish 

 to know about sweet pea diseases and 

 their control that we do not know. 

 We would like to know more about the 

 relation of lime, manure and fertilizers 

 to the diseases of the sweet pea; the 

 effect' of excessive feeding; the effect 

 of drought and of watering, in their 

 relation to the diseases of the sweet 

 pea; the effect of deep and shallow 

 planting; of thin or thick planting and 

 their relations to the disease. More 

 studies are necessary to be made of 

 this mosaic disease before we can con- 

 jecture any plans for control; and 

 more studies and trials of insecticides 

 and fungicides are necessary in order 

 to get the best results. We believe 

 that one more year of research will 

 yield us the desired information. For 

 some reason or other the experiment 

 stations have not as yet cared for the 

 interests of seedsmen and florists as 

 they have for the interests of the 

 farmers. Plant pathologists have not 



