14 BULLETIN 1038, U. S. DEPARTMENT OF AGRICULTURE. 



TRANSMISSION. 



In the investigation by Orton and Rand (56) negative results 

 were obtained with inoculations using bits of diseased buds or tissue 

 taken from beneath the bark of rosetted shoots, inserted into slits 

 in the terminal branches of healthy nursery trees. Cultural methods 

 and microscopical examination likewise gave negative results, show- 

 ing the apparent absence of fungi or bacteria in still living rosetted 

 twigs and branches. 



Normal buds or scions worked on rosetted stocks all developed 

 rosetted shoots except in one case where the stock itself recovered. 

 On the other hand, rosetted buds and scions worked on apparently 

 healthy stocks usually developed into normal shoots; in the cases 

 where rosette did develop in such buds or grafts the percentage was 

 no greater than in adjacent stocks worked with supposedly normal 

 buds or grafts in the commercial propagation. 



ENVIRONMENTAL RELATIONS. 



The observations and orchard records by Orton and Rand (56) 

 showed that pecan rosette is not absolutely limited to any soil type, 

 topography, or season. The disease was found at least to some ex- 

 tent in practically all kinds of soils where pecans were observed, 

 with the single exception of parts of some orchards where the land 

 tended to be swampy. In the latter case very little growth was 

 made, and the trees finally developed a diffuse general chlorosis, 

 but no signs of any phase of rosette. The disease, however, was 

 observed to be particularly prevalent under poor soil or cultural 

 conditions for the species, such for example as in the dry uplands 

 of Texas, or the washed-out hillsides of the Southern States. The 

 disease was found to be comparatively rare in the alluvial river bot- 

 toms of Texas, Louisiana, and Mississippi, where the tree is under 

 native environmental conditions. 



In most cases where rosetted trees were transplanted into appar- 

 ently better local soil conditions, the larger percentage of such trees 

 and often all of them resumed normal development ; and all rosetted 

 nursery trees recovered when shipped from the South and trans- 

 planted in the open or in potted garden soil at Washington. 



Nearly all healthy trees' used to replace rosetted orchard trees 

 subsequently developed the disease ; whereas only about half of those 

 replacing healthy trees later contracted the disease. 



In a three-year fertilizer test on level uniform soil cases of rosette 

 developed in 9 out of 11 plats where lime was used ; and the largest 

 number of cases and severest attacks occurred on two plats each 

 receiving lime* and acid phosphate, in one case combined with 



* Fertilizers were applied at the following rates: Lime (CaO acted on jointly by air 

 and water), 1 bushel per tree; nitrate of soda, 8 pounds; cottonseed meal, 32 pounds; 

 muriate and sulphate of potash, 8 pounds ; acid phosphate, Thomas phosphate, and 

 ground bone, 24 pounds ; stable manure, a liberal application. 



