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Pear tree problems

Several things can blemish Pears

By: Sandy Feather ©2009
Penn State Extension


Q. The last couple summers, the pears growing in my yard had a mottled/speckled surface with slight darkening of the flesh just inside some portions of the skin. This did not seem to affect the taste. I sprayed every couple weeks this summer with an insecticide and a fungicide, and also killed about a dozen stink bugs on the leaves every other day by hand. Did they cause this damage?  Also, my peaches had a grey/brown dust covering most of the surface of the fruits. After I noticed the problem, I bought a fungicide and sprayed every couple of weeks, but it did not seem to help. Do you have any suggestions?
  
  A. While brown marmorated stink bugs (Halyomorpha halys) do cause damage to pears and many other fruits, the symptoms you would see on the outside of the fruit would look more like a dimple or a sunken, slightly discolored spot. The flesh just under the dimple would be brown. They feed with piercing-sucking mouthparts, and inject a bit of toxin as they feed that breaks the cellular contents down into a slurry they can slurp back through those straw-like mouthparts.
  

Other Possibilities

Two other possibilities come to mind to explain the mottled/speckled appearance of the pears: pear scab or sooty mold.

Brown marmorated stink bug
Brown marmorated stink bug

Pear scab is closely related to apple scab, a very common disease on apples, crabapples, hawthorns and other members of the Rosaceae family, and the causal fungi are closely related as well. Both diseases result in black speckles and spots on the fruit that impact the underlying flesh. Scab diseases are more severe during wet spring weather than dry weather, although pear scab is less common and less virulent than apple scab. We did have very wet weather last spring as fruit was forming on your pear tree, so it pear scab is not out of the question. You did spray every couple of weeks, but if you missed the initial infection, it is possible that subsequent applications were not able to get the disease under control. Most fungicides should be applied preventatively rather than curatively. Once those spots are present, no amount of spraying can make them go away - it just keeps uninfected tissue from being affected. The fungicides in home orchard spray products easily control pear scab as long as you adhere to the spray schedule strictly.

Sooty mold is another issue altogether. It is a secondary fungus that invades honeydew produced by a number of insects. Honeydew is a polite term for insect excrement, specifically from those insects that feed in the tree’s vascular system with piercing-sucking mouthparts. Insects such as aphids, psylla and whiteflies insert their mouthparts into the part of a tree’s vascular system that transports the carbohydrates produced by photosynthesis. Their carbohydrate-rich excrement is an ideal substrate to support the growth of sooty mold. As the name suggests, sooty mold appears a black film over the fruit, leaves and twigs – any place where the honeydew drips from higher in the tree. A real clue is the fact that the honeydew is very sticky and usually attracts bees, wasps, ants and other nuisance insects that feed on it. Although it is unsightly, sooty mold does not really harm the tree or the fruit. Controlling the insects is the only way to get rid of sooty mold. Again, the insecticide in home orchard sprays should provide control of these pests as long as you adhere to the spray schedule.


Sooty mold on Magnolia leaves

Brown rot is one of the most common and troublesome peach diseases growers have to contend with that fits your description. It affects other stone fruits such as cherries, plums and nectarines and can cause blight on the flowers and twigs, cankers, leaf spots and fruit rot. Again, the wetter the weather in spring, the more severe brown rot is likely to be.

Disease Cycle

The fungus overwinters on mummified fruits that fall to the ground or remain attached to the tree, on infected twigs, and in cankers in the bark of twigs and small branches. Brown rot reproduces by spores that form as the flowers begin to open in spring. The spores are released into the air where they land on blossoms – those blossoms may become brown and blighted, and infected blossoms result in infected fruit. Fruit decay begins as the fruit begins to ripen, usually starting as small brown spots. When environmental conditions are favorable – warm, humid and wet – the entire fruit can rot in a few hours. Infected fruits may be covered with gray to brown fungal tufts that resemble dust.

Fungicides

Again, fungicides must be applied according to a strict spray schedule and they must be used to protect blossoms and fruit from infection. Once infection starts, it is very difficult to control, especially with the limited fungicides available to home gardeners. You may follow the spray schedule on the home orchard spray you are using, or check out Penn State’s recommended spray schedules in the publication Fruit Production for the Home Gardener. It is available on line at http://agsci.psu.edu/fphg

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