12 



The Florists^ Review 



July 18, 1912. 



interests us all alike. I am also glad to 

 take this opportunity and express to 

 you in behalf of the' D'elaware College 

 Agricultural Experiment Station and of 

 the University of Pennsylvania our sin- 

 cerest appreciation of the kindness of 

 all the seedsmen who have so gener- 

 ously sent us sweet pea seeds and thus 

 formed the nucleus for our investiga- 

 tions of the diseases of the sweet 

 pea. 



Your present speaker is a lover of 

 flowers and especially a lover of the 

 sweet pea. The more of this flower I 

 saw, the more convinced did I become 

 that the sweet pea is far from being 

 as free from insect and fungous attacks 

 as the majority of the seedsmen and 

 growers honestly but erroneously be- 

 lieve. In some of our best written 

 manuals on sweet peas the topic of 

 insect and fungous diseases hardly oc- 

 cupies one quarter of a page. 



Too Long in the Same Soil. 



That the sweet pea is becoming more 

 popular with the American people 

 needs no proof. If once we grow 

 sweet peas, we will grow them all the 

 time. However, most amateurs, either 

 for lack of space or unknowingly, 

 grow their sweet peas in the same lot 

 year after year. The result is that 

 diseases set in and make it impossible 

 any longer to grow sweet peas on that 

 same place. Immediately the seeds 

 are blamed and the customer begins 

 changing trade from seedsman to seeds- 

 man, but with no better results. Thus 

 lack of information on the part of the 

 grower or amateur, on the one hand, 

 and the slowness of the seedsmen to 

 admit that the sweet peas can be 

 troubled by diseases, on the other, 

 cause the trade invariably to suffer. 

 Hence, when considered purely on 

 an economic basis, the seedsmen are the 

 losers. Whatever disease the seedsman 

 is willing to admit, he usually throws 

 the blame to high feeding or to the dry 

 weather. From inquiries sent out to 

 most of the seedsmen who grow sweet 

 peas in this country, only two vaguely 

 admitted that their sweet peas are 

 troubled with blight. 



The Need of Investigation. 



We do not for one minute doubt the 

 truth of the statements of all these 

 gentlemen, but we believe that if the 

 seedsmen took this matter more seri- 

 ously, they would soon realize that 

 their interest is at stake. It is some- 

 times good for all of us to be from Mis- 

 souri, in order that we may be shown. 

 We would feel highly gratified and our 

 efforts would be well repaid if we could 

 impress you with the fact that sweet 

 peas suffer from diseases which are 

 caused by either insects or parasitic 

 fungi. It is to the benefit of the seeds- 

 man and the well-being of the trade 

 to admit these facts and recognize the 

 necessity of investigating these dis- 

 eases and finding remedies for them, 

 and of disseminating broadcast the re- 

 sults of these findings to all those in- 

 terested in them. 



Before entering into the discussion 

 proper of the diseases of the sweet pea, 

 we wish to state that the Delaware 

 Agricultural Experiment Station, in co- 

 operation with the University of Penn- 

 sylvania, has made it possible for your 

 present speaker to carry on for the last 

 two years investigations of the diseases 

 of the sweet pea. The information 

 which we are about to give is of ne- 



cessity of a preliminary nature, since 

 we have by no means exhausted the 

 subject. Nevertheless, we believe that 

 we have gathered enough to justify the 

 present address. The information is 

 first-hand, as it is all the result of our 

 personal investigations and studies in 

 both field and laboratory. In Newark, 

 Del., we now have one-half acre of 

 sweet peas devoted exclusively to the 

 study of the diseases. 



Diseases Under CHass. 



In dealing with the diseases of the 

 sweet pea, we have to recognize two 

 classes: First, diseases of the sweet 

 pea grown under glass; second, dis- 

 eases of the sweet pea grown out of 

 doors. 



Under glass, sweet peas are not as 

 extensively grown as out of doors. The 

 time is undoubtedly rapidly approach- 

 ing when the market will call for more 

 sweet peas in the winter. We have 

 no information as to how many are 

 actually engaged in growing winter 

 sweet peas, and the success or failure 

 with which these growers meet. We 

 know of a few growers who have at- 

 tempted to grow sweet peas under 

 glass, but who have failed. For the 

 benefit of the rest of us, we will here 

 consider some specific cases, in order 

 to bring to your attention some of the 

 possible diseases which trouble sweet 

 peas under glass. 



One Qrower's Experience. 



A grower — I cannot give you the 

 name — erected a forcing house for the 

 purpose of growing winter sweet peas. 

 His first attempt was a failure. His 

 plants began to die in spots, and only 

 here and there did a plant remain 

 alive. The grower soon complained to 

 his seedsman and the latter kindly re- 

 ferred him to us. We immediately 

 asked for a complete history of the 

 trouble and for specimens of the dis- 

 eased plants and soil. The following 

 is the story of the trouble as told by 

 the grower himself: "The house the 

 peas are in was built last summer on a 

 piece of ground which had been in 

 grass for over five years. I bought 

 the ground six years ago from a farm- 

 er who had corn in it for several years, 

 but always poor. I gave it a heavy 

 dressing of horse manure and had it 

 plowed and sown with Kentucky blue 

 grass, and red clover seeded on it. The 

 grass was a failure and the clover did 

 not come at all. When I planted the 

 peas, I manured heavily, applying about 

 four inches of cow manure and some 

 little horse manure. Those that did 

 grow did finely; the rest were a failure. 

 It is altogether a puzzle to me, and I 

 hope you will be able to get at the 

 root." 



A Complication of Diseases. 



The diseased specimens which this 

 grower sent us revealed some highly in- 

 teresting things. It was plainly seen 

 that the plants suffered from more than 

 one disease. On the exterior the plants 

 looked healthy, but a closer examina- 

 tion revealed a yellowish, sickly ap- 

 pearance. The seat of the trouble in 

 some cases was confined to the roots 

 only, and in others that part of the 

 stem just above the roots. In the first 

 instance we found a typical case of eel- 

 worms, Heterodera radicicola, better 

 known as root-knot disease. Those of 

 you who grow violets have surely met 

 with this trouble. It is evident that 



roots crippled with eelworm cannot 

 make much headway. Of the other 

 specimens, where the seat of the dis- 

 ease seemed to be located at the junc- 

 tion between the roots and the stem, 

 the latter was found to be covered with 

 a white weft of fine mycelium threads 

 of a fungus. On splitting open tho 

 stem, it was found to be filled with 

 the same white mycelium and inter 

 mixed with small sclerotia. Cultures 

 of this mycelial growth readily gave 

 a pure culture of a sclerotinia, resem- 

 bling in all appearances the Sclerotinia 

 libertinia, a fungus which causes the 

 damping off of lettuce and so many 

 other plants. 



Due to Infected Soil. 



In order to establish definitely the 

 relationship of this sclerotinia fungus 

 to this disease of sweet peas under 

 glass, sterilized seeds were planted in 

 sterilized pots and soil in the labora- 

 tory. All the seeds germinated and 

 the plants were allowed to grow for 

 three weeks, with no disease appearing 

 on them. Then the pots were divided 

 into two lots. One was left as a check 

 and the other was inoculated with the 

 pure culture of the sclerotinia by in- 

 troducing pieces of the fungus in the 

 soil. Both lots, check and infected 

 plants, were covered with bell jars to 

 imitate the moisture condition of the 

 greenhouse. After four to six days, 

 wilting of the inoculated seedlings be- 

 gan, whereas the checks remained 

 healthy. This was repeated several 

 times, with always the same results. 

 This conclusively shows that the fun- 

 gus Sclerotinia libertinia will produce 

 a disease on sweet peas under glass 

 when present in the soil. This fungus 

 is usually brought into the greenhouse 

 with the soil or with the manure. From 

 the account which the grower gave us, 

 it was purely a case of infected soil, 

 and this explains why his sweet peas 

 failed. Cross inoculations with this 

 fungus from the sweet pea and the one 

 from lettuce produced typical cases of 

 wilt in each, thus proving conclusively 

 that this fungus from the sweet pea is 

 the same as the Sclerotinia libertinia of 

 the lettuce, and that the sweet peas are 

 at stake if they are made to follow a 

 crop of lettuce which suffered from this 

 disease. 



Investigating the Soil. 



Several other fungi were isolated 

 from the diseased stems and roots 

 above discussed. Inoculations with 

 pure cultures of these fungi on healthy 

 seedlings proved to be active parasites. 

 We are not here giving our final word 

 on these fungi, as more experiments 

 are still under way. 



While working on the diseases of 

 the roots and stems we have also in- 

 vestigated the soil which was sent to 

 us by the grower. Accordingly, a few 

 sterilized pots were filled with the soil 

 and sterilized seeds planted in it, and a 

 few other sterilized pots were filled 

 with sterile soil and also sown with 

 sterilized seeds. The same amount of 

 seeds were planted in both lots of pots. 

 After ten days the seeds in the sterile 

 soil germinated and grew well, while 

 the seeds in the sick soil germinated 

 only sparingly. Upon closer examina- 

 tion these non-germinated seeds were 

 found to be rotted, and of those few 

 plants which grew one-half had their 

 roots nearly rotted. In culturing 

 these roots the same fungi were ob- 



