JULY 18, 1912. 



The Florists' Review 



13 



View in the Lecture Hall at the National Sweet Pea Show, Boston. 



tained. Cultures made from this sick 

 soil produced the same fungi as those 

 found on the diseased roots and stems. 

 Our experiments are as yet incomplete, 

 but the results obtained so far point 

 to the fact that these fungi in the 

 soil are the cause of this soil sickness. 

 The debris found in this sick soil also 

 readily yielded a pure culture of the 

 Sclerotinia libertinia, of which I have 

 just spoken. All these fungous diseases 

 just described can also, at any time 

 and under certain climatic conditions, 

 attack the sweet peas grown outdoors. 



Another Grower's Troubles. 



Complaints of another grower of 

 sweet peas under glass reached us. The 

 following are his own words, which 

 speak for themselves: "I grow sweet 

 peas under glass for cut flowers and 

 have been seriously troubled with a 

 disease that spots or mottles the foliage 

 with a yellow color, disfiguring the 

 foliage and flowers, and when it be- 

 comes pronounced a diseased plant 

 never recovers. Both the weak winter- 

 blooming and the stronger grandiflora 

 or Spencer type are subject alike to 

 it outdoors, as well as under glass. We 

 know nothing of this trouble, every 

 grower we have spoken to having a 

 different theory. Some believe that 

 the puncture of green fly or aphis is 

 the cause. Our observations led us to 

 believe that the use of green manure 

 IS responsible. Any light you can turn 

 on this trouble will be greatly wel- 

 comed. Early in the spring of 1911 it 

 started in the greenhouses and spread 

 rapidly, destroying fully one-third of 

 our crop. Last fall it showed up again. 

 )Vo carefully pulled out all plants show- 

 ing it and gradually it disappeared. As 

 the weather became hot this spring, 

 much of it was noticed, but it was too 

 late to do much harm." This closes 

 the quotation. 



As this same spotting or mottled dis- 

 •ase is also a serious trouble of outdoor 

 «weet peas, we shall discuss it later 

 under the heading of diseases of the 

 sweet pea out of doors. 



Parasitic Insects. 



Before taking up these diseases, it 

 would not be out of place to mention 

 the insects which are parasitic on the 

 sweet pea, though this could constitute 

 an address by itself. 



Among the biting insects we have 

 the corn root worm beetle, Diabrotica 

 longicornis, so called because the larva 

 often injures the corn crop in the 

 south. The ©eetle is greenish yellow, 

 with six blaek spots on its back. It 

 resembles the cucumber striped beetle. 

 Another biting insect is the striped 

 potato beetle, Epicauta vittata. The 

 cutworm, when present, often causes 

 great annoyance, sometimes destroying 

 the entire crop. The wireworm also is 

 to be dreaded, especially when sweet 

 peas are planted in a soil which was 

 previously in sod. 



Among the sucking insects we have 

 the red spider, Tetranychus telaruis, 

 which is especially troublesome to peas 

 under glass. Finally, the green aphis, 

 which is also quite troublesome, is more 

 to be feared in dry weather. So much 

 for the insects. I have mentioned them 

 not only for the harm^ they inflict by 

 themselves, but, as you will soon see, 

 for the important role they play in 

 spreading about the fungous diseases 

 of the sweet pea. 



Diseases Outdoors. 



As to the fungous diseases, it seems 

 that some erroneous belief has crept 

 into the minds of some growers and 

 even into those of some of our sweet 

 pea specialists; namely, that the sweet 

 pea is a plant unusually free from dis- 

 eases, that the diseases, if ever present, 

 are induced by dry weather or excessive 

 feeding, and that when the plants are 

 growing naturally they are practically 

 immune from the attacks of any dis- 

 eases. We do not mean to deny that 

 high feeding may predispose the plants 

 to diseases, though this has to be ex- 

 perimentally proved before we can ac- 

 cept the statement as valid. We be- 

 lieve that growing sweet peas under 



natural conditions will not render them 

 immune from diseases of any sort. In 

 fact, our own experimental plantation 

 of sweet peas, which we have at the 

 Delaware Agricultural Experiment Sta- 

 tion, is as free from excessive feeding 

 as one could ask for. The soil is ordi- 

 nary clay loam. It bore two years ago 

 a crop of hay and last year a crop of 

 potatoes. The potatoes last year re- 

 ceived a regular potato fertilizer and 

 this year no manure of any kind was 

 appliad. The sweet peas are, of course, 

 given the necessary cultivation and no 

 more. Yet, in spite of this, they are 

 suffering from two of the worst dis- 

 eases, of which I am about to speak 

 presently. 



The Mottled or Mosaic Disease. 



I have a,lready mentioned to you the 

 spotted or mottled disease of sweet 

 jjeas under glass. This is a new disease 

 to thi? country and it is an exceedingly 

 dangerous one. This disease in its at- 

 tacks is not restricted to greenhouse 

 conditions alone, but it is also a serious 

 disease of sweet peas outdoors. For 

 the sake of convenience we will call 

 this the mosaic disease. It is readily 

 distinguished by a yellow dotting or 

 mottling of the leaf, presenting in some 

 instances a beautiful mosaic structure; 

 hence its name. Affected leaves seem 

 to linger for a time, but they eventually 

 lose all the chlorophyl and soon drop 

 oflF. 



A better symptom of this disease is 

 a curling of the leaves at the tips, 

 much resembling the curling of leaves 

 induced by the green aphis, but with 

 this case the aphis has no association. 

 The disease makes its appearance after 

 the seedlings are from three to four 

 weeks old. Often the disease is so bad 

 and the curling so pronounced that the 

 plants thus affected cannot make any 

 headway and remain dwarfed. An at- 

 tempt is made among these curled parts 

 to produce a few flowers, but the latter 

 are borne on extremely short peduncles 

 as compared with the long peduncles of 

 healthy plants of the same variety. 



