Axel, the USDA may be working hard at eradicating viruses from commercial stock but the concern may have little to do with the concerns of non-commercial growers. The viruses are out there and pretty much beyond eradication when apple trees sprout up in so many different places and beyond the sphere of the USDA. The reason you are concerned is because it has been a problem for you- maybe because you have so many varieties in so little space from so many different sources. If and when it becomes a problem for me in even one of the scores of orchards I manage, I too will become concerned, but if the problem was as severe as you portray it I don't see how I've avoided it so far with such a wide range of sites where I'm planting new trees next to 100 year+ apple trees multiple times every season. In addition to this I'm often hired as a consultant on sites where I've been sought because of difficult problems others were unable to diagnose. I admit it could possibly be a problem that I'm overlooking where production is less than I'd like but I am unaware of the cause- not every orchard I manage does as well as I would like. Still, I haven't seen any obvious symptoms. Many of my sites have old trees nearby that aren't going to be removed unless they die so viruses are pretty much a fact of life here. We still get plenty of fine apples. Maybe in the climate here the viruses are less destructive.

Rob, The most prevalent stone fruit virus I hear of is X disease (technically not a virus, but behaves like a virus). Supposedly any trees on mahaleb will die fairly quickly. They say a lot of wild chokecherry carry the disease. I really don't know much about identifying viruses in stone fruit, but I think the bad ones are pretty obvious (ringspot viruses, dwarf virus and plum pox). The only experience of wild cherry I have is the sort of wild cherry in my backyard. About 10 years ago my father-in-law dug up a seedling under some grafted cherry tree and planted the seedling in my backyard. The foliage is healthy other than sometimes it gets cherry leaf spot (Surprisingly the fruit is really pretty decent.) The disadvantage is that it sends up tons of suckers I have to keep mowed off.

windeaux, thank you for providing your experimental details. I do not have any virused roses to experiment with. (I am now shutting down my 1000 rose garden due to age and health.) From the literature I would expect that cuttings taken in your zone in August (highest possble temperature) would have the greatest chance of being virus free. Also it appears that old wood may be preferable to new wood. Also, it probably would be advantageous to take cuttings from branches that did not have virus symptoms in the spring (in fact I would recommend that virused branches be removed from the plant when first observed). The first paper that drew my attention to this behavior is (please, keep in mind the reversal of our seasons with theirs): Authors: Dal Zotto, A.; Nome, S. F.; Di Rienzo, J. A.; Docampo, D. M. Author Address: Instituto de Fitopatologia y Fisiologia Vegetal INTA, 5009, Cordoba, Argentina. Title: Fluctuations of Prunus necrotic ringspot virus (PNRSV) at various phenological stages in peach cultivars. Published in: Plant Disease, volume 83, pages 1055-1057, (1999). Abstract: " Fluctuations in Prunus necrotic ringspot virus (PNRSV) concentration were researched in single plants of six peach (Prunus persicae) cultivars-Kurakata, Red Haven, Nectar Red, Start Delicious, Meadowlark, and Loadel-by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) of dormant buds (May, June), flowers (September), new sprouts (November), and mature leaves (January) (Southern Hemisphere). The optimum extract dilution (sample weight per buffer volume) to detect the virus was also quantified. The average absorbance patterns of the six cultivars show a steady increase in virus concentration, ranging from A405nm 0.61 in May to A405nm 0.86 in July for dormant buds, to A405nm 1.22 in September in flowers, to 1.53 in November in new sprouts, where the highest concentration was found. Virus concentrations in mature leaves drop to values similar to those of noninfected plants in January (A405nm 0.12). The yearly average (six noninfected peach trees) ranged from A405nm 0.04 to A405nm 0.08. This drop coincides with an increase in summer temperature and attenuates foliation symptoms caused by PNRSV. Analysis of dormant buds, flowers, or new sprouts with 5-cm-long leaves was reliable to differentiate infected from noninfected plants. Cluster analysis of absorbance profiles for single plants of cvs. Loadel and Meadowlark, however, showed a comparatively low profile, with a drop at flowering time (A405nm 0.20 in September) close to the average of healthy controls. The difference between infected and healthy plants did not become apparent in all cultivars from the analysis of plants at a given phenological stage, for example by the analysis of flower only, the material most preferred to diagnose the virus. Therefore, plants should be analyzed during flowering and sprouting or flowering and dormancy (dormant buds)." Here is a link that might be useful: peach southern hemisphere study

Science can move rapidly. The abstract below was presented at the 2012 Petria -22nd International Conference on Virus and other transmissible diseases of Fruit Crops. Now that it is recognized that plants have an immune system against viruses (RNA Silencing) a logical next step is to use genetic engineering to add more RNA silencing molecular sequences. In the abstract below please note that they recognize that both low temperature and mixed virus infections can decrease the effectiveness of the plants natural immune system: "Since it’s known that some abiotic - low temperature - and biotic stresses - mixed viral infection - could have a detrimental impact on RNA silencing-mediated viral resistances," ---------------------------------------------------- Title: Robust and Wide Spectrum RNA SIlencIng Mediated Resistance TO PLUM POX VIRUS Authors: E. Di Nicola-negri(1), M. Tavazza(2), V. Ilardi(1) (1)Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Centro di Ricerca per la Patologia Vegetale, Rome, Italy; (2)ENEA CR Casaccia, Via Anguillarese, 301, 00123 Rome, Italy Published in: Petria, Vol. 22 (3), 2012, 123-459, Abstract: "Plum pox virus (PPV) is a quarantine virus that causes sharka, one of the most important diseases of stone fruits worldwide. Seven PPV strains have been characterized, of which PPV-D, -M and Rec are the most important from an agroeconomical point of view. The best agricultural sustainable approach to prevent sharka disease consists in developing PPV-resistant plants. In this context we have shown that Nicotiana benthamiana plants transformed with PPV-M sequences (PPVIsPaVe44), covering the 5’UTR region, P1 and HC-Pro genes and arranged to express self-complementary ‘hairpin’ RNAs, are immune to the homologous PPV-ISPaVe44. However, as the RNA silencing-mediated resistance operates in a sequence-specific fashion, transgenic plants harboring the four hairpin constructs were also challenged with viral isolates belonging to different PPV strains. All the transgenic plant lines were resistant to PPV-D, ��"M and Recc strains. Moreover, the transgenic plant line harboring the 5’ UTR/P1 sequence was also resistant to isolates of PPV-EA and PPV-C strains that are distantly related to ISPaVe44. Since it’s known that some abiotic - low temperature - and biotic stresses - mixed viral infection - could have a detrimental impact on RNA silencing-mediated viral resistances, 5’ UTR/P1 plants were challenged with PPV under different conditions. Transgenic plants were resistant to PPV infection both at high (30°C) and low temperature (15°C). Furthermore, no susceptibility to PPV-Was observed in 5’UTR/P1 plants previously inoculated with Potato virus Y (PVY), Cucumber mosaic virus (CMV) or Artichoke mottled crinkle virus (AMCV) suggesting that prior virus-mediated expression of HCPro (PVY), 2b (CMV) and P19 (AMCV) RNA silencing suppressors was not able to defeat PPV resistance. The overall data suggest that the 5’ UTR/P1 hairpin construct can be profitably used to confer resistance to the sharka disease in Prunus species." The above is taken from a 338 page PDF document that gives the abstracts and/or full papers that were presented at that Conference. Here is a link that might be useful: Link to 338 page PDF document (long download)