grainy nodules in bartlett pears

Question: We have two dwarf Bartlett pear trees which are producing well, but almost all fruits contain grainy black nodules.  This has been going on for a few years and is getting worse. Notice the photos.  I've also included a photo of the leaves, which have some black spots and (new this year) rust colored spots which looks like a fungus.  Any idea what's going on?

responder: Rhonda Frick-Wright  Replied September 04, 2024, 5:42 PM EDT
response: Hi Dave and thanks for your very clear pictures of the problems with your pear tree. Let's start with the cut pear on the first picture. This shows clear signs of codling moth. The brown residue is the frass of the larva and you may actually find the "worm" larvae in some of the pears. Here is the treatment for this problem: https://pnwhandbooks.org/insect/tree-fruit/pear/pear-codling-moth  The second issue, the hard stony spots, are what the pear does to protect itself after it has been injected by the Brown Marmorated Stink Bug. This is a 2004 invasive species that has really expanded in the last couple of years and damages multiple crops including grapes, hazelnuts and ... pears! OSU offers the following: Management-biological control   The samurai wasp, Trissolcus japonicus, an adventive parasitoid wasp from Asia was detected in Vancouver, Washington in 2015 and in Portland, Oregon in 2016. This parasitoid is becoming widely established in the Willamette Valley and researchers are actively redistributing the wasp. This wasp attacks the stink bug egg masses, turning them from bright green or blue to black as the wasps develop in the egg mass and eventually chew their way out of the eggs. The wasp is known to be a highly effective parasitoid against brown marmorated stink bug in Asia. Native parasitoids and predators can also  help limit stink bug populations. There are numerous predators (spiders, katydids, lacewing larvae) that attack the eggs and early nymphs. The mature nymphs and adults have fewer natural enemies, but sometimes birds and spiders will target them. Crabronid wasps (Astata bicolor) are specialized predators that sting the nymphs to paralyze them, then carry the paralyzed stink bugs to their nests in the ground where the stink bugs are used to provision the nest for their young. Note that most chemical treatments for BMSB are broad-spectrum, so treatments may negatively impact biological control and cause flare-ups of secondary pests such as scale and aphids. They also recommend neem oil and kaolin clay sprays as chemical controls available to home users.   And thirdly, the issue of the rust spots. These are signs of Pear Trellis Rust which is widespread this year. Usually there is a juniper tree as a secondary host nearby, but many people have the problem this season which indicates the fungus was wide-spread by wind or rain this spring. There are no home remedies yet, although I'm sure they are working on it since pears are such an important Oregon Crop.   The recommended control is to pick off the leaves by mid August before the fungus sporulates. This can be a daunting task if your tree is as infected as mine was, but keep at it as it looks like your leaves have not reached that point yet. Destroy the leaves, don't compost them and hope someone comes up with a remedy soon!  Yes, pears have gone from being an easy sure-fire crop to more complicated spray and hand pick management these days. Hopefully your crop was good, you can cut out the damage and still enjoy the wonderful fruit. It just takes a bit more work to get it!

responder: The Question Asker Replied September 04, 2024, 7:52 PM EDT
response: Hi Rhonda,Thank you so much!  Not great news I’m afraid, but at least now I know what’s going on.  I hadn’t suspected the marmorated stinkbug as part of the problem but that makes sense — we get them in the house during the winter occasionally.  Not nearly as badas 2016 or so, when we must have killed ten or so daily during the cold months.  Thanks again!DaveOn Sep 4, 2024, at 2:42 PM, Ask Extension wrote: