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All of my pear trees are starting to develop a black tinge on the outer edge of the leaves. I do not know what course this will take, but it looks like the black will slowly consume the entire leaf. Attached is a picture of a couple of leaves that are showing this problem. Any help would be appreciated.
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You don't mention your location (pop it in your profile
) nor the variety of pear, but I would guess that it is scab, which is a fungal disease that is made much worse by prolonged rainfall.
Another possibility is a mild case of fireblight, but that would also cause the young stems to bend over into a "shepherd's crook" shape and look like they're scorched by fire (hence the name).
If it is scab and the fruits remain of edible quality, I would not worry.
If the black-brown spots appear on fruits, followed by fruit splitting as the spots merge, then you may need to consider a fungicide spray. If you are in a high-rainfall location, you may struggle to grow pears, which prefer moist soil but dislike wet weather. Also watch out for cankers, which will be prevalent in the same high-rainfall regions as scab.
If it is fireblight (unlikely) the treatments is removal (pruning) of affected twigs. If the young shoots are not turning black and bending, it is unlikely to be fireblight.. -
Thanks for the info. I am located in Washington State, USA, on the eastern side where it is normally dry. We have had a really wet spring, wetter than is normal, which helps support your diagnosis.
The pears are Bartlets, D'Anjou, and three varieties of Asian Pears.
Is there any harm in using the fungicide spray now? My concern is that these are young trees that didn't grow much last year. I am hoping to have a strong growing season this year.Comment
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I don't think that the scab on your trees is doing much damage, but if it bothers you, there is no reason why you can't spray. Commercial orchards spray several times or more per season.
Spraying of fungicide won't reverse the damage that has already been done, but may reduce further damage.
However, scab has a lag period of a week or two between infection occurring and the symptons being seen, so the scab may worsen before any spray is able to hold it at bay.
If the scab is only mild, I recommend not spraying because you will encourage development of fungicide-resistant strains of scab, which will be very difficult to get rid of. The damage to your trees is mild and is nothing that the trees can't outgrow after a good feed of 7:7:7 N:P:K general-purpose fertiliser and adequate mulching of the soil to retain moisture.
Leaf area damage of up to 10% has negligible impact on the tree. Only once you get to 25% of most leaves being damaged will the tree noticeably reduce in vigour.
I don't use fungicide on my fruit trees and they sometimes suffer as much as 50% leaf damage to scab in really wet seasons. In fact, you may find that the more the trees are sprayed with fungicide, the more they need further spraying due to fungicides causing an imbalance in the environment of other fungi that would otherwise compete with the disease-causing fungi.
A previously sprayed orchard that stops fungicide will be ravaged by disease for a couple of years, but after those couple of years, the trees often start to become more resistant again, due to a better environmental balance of microorganisms..Comment
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Hadn't thought of it that way. Thanks very much for the info. I'll hold off on the spray and keep up with the fertilizer.Comment
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