One of my apple trees has this yellow mottling on the leaves. The tree is Granny Smith on M111. It also has a grafted Gordon limb that shows identical symptoms. The Fuji tree six feet away has normal leaves. Is this cedar apple rust or something else? I have looked at pictures on the net but don’t see any that seem to exactly match.
Looks like apple mosaic virus to me
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That does look more like a virus than a fungus.
I found a picture of apple mosaic virus that is identical to those pics above. The research also says that Granny Smith is highly susceptible. The tree has many grafts from the CRFG exchange and also from a commercial vendor so I surmise that one of the added scions was infected and spread the virus throughout the tree.
I suppose this infection is one of the risks of multigrafting a tree with uncertified material.
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I’ve seen a similar look some years on my Granny Smith. Some years nearly defoliates.(Granny Smith is NOT an apple to plant if you are an organic grower.)
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I wonder if viruses aren’t more a problem in CA and warmer growing areas. I’ve been a promiscuous grafter for a long time now in SE NY and undoubtedly move a lot of dirty wood around when I take it from and graft it to 100 year old trees and saplings and have not suffered the consequences of seeing any leaves that look like that or any symptoms I can attach to viruses. There is a very experienced Santa Cruz apple grower (whose name escapes me) on this forum who has sounded the alarm about the danger of spreading viruses while grafting- I assume from direct experience.
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Good question. The literature seems to indicate that temperature does play a role in the apple mosaic virus’s metabolism.
I am also theorizing that some cultivars are somewhat asymptomatic resulting in the supplier unwittingly sharing infected material when exchanging scions. The viral infection only later becomes apparent when grafted to a susceptible cultivar.
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Alan may be thinking of Axel, I think was his name, from the cloudforest cafe.
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Mine came from Miller Nurseries in Canandaigua NY in 1991.
That sounds right, he hasn’t contributed for a while. This is a subject his participation would be particularly helpful with from direct experience. .
Someone once posted here that many heirloom varieties haven’t been indexed for virus contamination, even coming from nurseries that guarantee virus free nursery stock of modern varieties. I never tried to verify this information. I should send ACN a question about it once they’ve gotten through spring shipments.
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I’ve never seen any viruses like that here in So Calif. Most of my scions have come from experienced growers that would know a virus if they saw it.
Axel moved from Santa Cruz… he now has a place in Hawaii and a place in Southern California, if I remember correctly, near San Diego.
I hope whoever bought his property saved his massive apple colection. Though I think maybe it was seperate from his house location.
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@danchappell ,
If it is Apple Mosaic do not remove the tree. This is a good article describing the disease which is not transferred by insects or any method other than people https://utahpests.usu.edu/ipm/agricultural/fruit/apple-mosaic-virus.
Also from Wikipedia:
"Samples of various plant tissue from young leaves, flower petal, dormant buds, and phloem were taken at different time of the vegetation period. In this study, ELISA was used to detect ApMV in the different samples from the five apple trees. The relative concentrations of the virus in the leaves and flower were highest in the earlier spring months such as March and April.[9] This suggests that the virus propagates better when it is under colder weather conditions .[9] Furthermore, during cooler months, the virus’s relative concentration is highest in the leaf and flower, rather than the phloem and dormant bud. Once May and June occur, the relative concentrations of the disease severely decreases. This was evident by Svoboda and Polák’s study because as the temperature rose from spring to summer, the ELISA test detected lower relative concentrations of ApMV.[9] "
This description is consistent with my observations. Only the early spring foliage, which formed under cool weather conditions, is discolored and necrotic. All of the later growth is normal. At this stage I can not discern any negative effects on fruiting characteristics. The tree is still quite vigorous in spite of the infection, so I will keep it in my collection unless it begins to decline.
The more serious problem that I have observed on this tree is a few cankers that nearly girdle some of the branches. I am assuming that those are a completely unrelated issue.
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