In order to help make a diagnosis, we could use more information. Can you please share photos of the symptoms and how defoliated the tree(s) look so far? If you need to send more than the system limit if three photo files, you can reply again to attach more, or just paste them into the body of your reply. In order for us to be able to zoom-in to see enough detail, please have the images be at least 1MB in size.

Several diseases can cause leaf browning and premature shedding in ornamental pears. Is their decline sudden, where they looked fairly healthy and normal last year? Or has decline been ongoing for several years? Did anything change in their environment in recent years, like digging or re-grading soil in the root zone? Is there any visible trunk damage? About how long have the trees been in the ground? (Are they fairly young and recently planted, or are they a decade or more old?)

Miri

Is their decline sudden? Yes

,where they looked fairly healthy and normal last year? Yes

Did anything change in their environment in recent years, like digging or re-grading soil in the root zone? No

Is there any visible trunk damage? There is a lot of lichen on the trunks

 About how long have the trees been in the ground? 11 years 

Thank you for the added information and photos. The lichen is harmless, but the foliage symptoms are difficult to diagnose. Our plant pathologist is away from the office for a few days, but we can ask for his assessment as soon as he's available. We can also reach out to neighboring states to see if their plant diagnostic labs have received similar samples in recent weeks. We've had a few submissions from other counties in Maryland thus far with similar-looking symptoms that we have yet to diagnose with certainty.

In the meantime, if you wanted to hire a certified arborist to make an in-person assessment, that might help to reveal potential sources of tree stress, but some arborists are better at diagnostics than others, so you can ask them about their familiarity with pear tree diseases before hiring. Some arborists can collect and send samples to a plant pathology lab for testing if a suspected infection needs confirmation. We will be back in touch as soon as we have more information, though little can be done to cure any disease once symptoms manifest. (Fungicides are preventative measures only, not curative, so at most can only protect healthy growth. Drastic defoliation coupled with sparse canopy growth indicates a tree in decline that probably cannot be salvaged and likely needs to be removed.) Since Callery-type pears (Bradford, Cleveland, and other varieties) are invasive in our region, we encourage gardeners who have to remove one to replace it with a different species.

Miri

Our plant pathologist was able to look over the photos and while it's hard to identify every potential pathogen present, the leaf distortion (cupping, twisting, etc.) and pale blotches appear to be caused by Powdery Mildew, which pear trees can contract. Using a preventative fungicide to discourage future mildew outbreaks is not practical in this case, given the tree's size and status of already being greatly declined. Powdery mildew can infect a variety of plants, but despite looking nearly identical in symptoms, it generally does not cross over from one unrelated plant to another to cause infections on other species. Therefore, a replacement tree, if not a pear, likely will not fall victim to this specific infection. When plants are heavily damaged by powdery mildew, the disease can contribute to premature leaf drop and, eventually, dieback of the canopy due to weakened growth over successive bouts of infection.

Miri

Horticulturists have learned over time about the invasive nature of Callery Pears (and they have spread quite widely in the past decade), if that is the change of advice you are referring to. The Maryland Department of Agriculture only added Callery Pear to the list of invasive species that nurseries and landscapers are required to discourage the public from planting in July of 2018. (Though they are still, for the time being anyway, legal to sell and install. Recent Maryland legislation passed may adjust that degree of invasive species regulation in the coming months/years.) We in Extension now more consistently discourage the planting of known invasive species and encourage their replacement with either non-invasive species or, ideally, native species. Every tree species has multiple potential pest and disease vulnerabilities. This year, we've received more inquiries than usual about problems with pear trees defoliating and declining in home landscapes, so powdery mildew and other diseases seem to have proliferated in this year's weather patterns.

Miri

You have many options, fortunately. We'll assume the site conditions are full sun (or at least mostly-sunny), good soil drainage, and there are no serious problems with deer. (If there are, protection for the young tree will be needed until it's out of browsing height and its trunk is too thick for buck antler rubbing in autumn to risk breaking it or stripping off bark.) If the soil is more poorly-drained (unlikely, as then the pear probably would have died back sooner), a couple of the candidates below may still be suitable. All have white flowers in their default form unless noted, though a few also have certain cultivars with other flower colors (generally pink). Botanical names are given in parentheses, since sometimes common names vary. This is not an exhaustive list, but hopefully gives you some ideas. We're skipping mention of the widely-planted Asian flowering cherries, which contain many white-flowered cultivars, since they sometimes seed around in wooded areas.

In no order of importance, here are some native tree options:

• Serviceberry/Shadbush/Juneberry (Amelanchier canadensis, A. laevis, and several other species and their hybrids)
  Mid-spring bloom; edible blueberry-like summer fruits; showy fall foliage color. Can be multi-trunked or single-trunked. Mature size varies a bit by cultivar, but overall, they are more compact or nor larger than Callery Pear.
• Sweetbay Magnolia (Magnolia virginiana)
  Lemon-scented late spring flowers; red berries in pods that migrating birds enjoy in autumn; semi-evergreen (keeps some leaves in winter, but sheds some as well). Can be single-trunked or multi-trunked. Here too, mature size varies a bit by cultivar, but it won't outgrow a pear.
• Eastern Redbud (Cercis canadensis) - white-flowered forms
  Several cultivars of this normally pinkish-purple-blooming tree are white, either upright or with weeping branches. New varieties enter the market all the time, but white-flowered forms include Cercis canadensis alba, Cercis canadensis texensis alba (may be called Oklahoma Whitebud), 'Royal White', and 'Vanilla Twist'. Yellow fall foliage. Can be multi-trunked, but usually single-trunked; rounded canopy.
• American Fringetree (Chionanthus virginicus)
  Late spring blooms are clusters of thin-petaled flowers that are showy despite their small individual size; slightly fragrant. Flower clusters on male trees are purportedly more showy than female trees, but sexed trees can be hard to find since they're hard to tell apart. Female trees, if pollinated by a male, can produce olive-sized blue-black fruits that birds enjoy. Fall foliage color is yellow. Trees are somewhat slow, so may look like a large shrub when young, with low branches. Their shape is more rounded than the upright egg shape of mature pear.

And some non-native or not-locally-native options that, to our knowledge, are not presently invasive:

• Crabapple (Malus, many species and hybrids)
  While Maryland is home to a couple native species, they can be quite hard to find. Dozens of hybrid cultivars exist these days though, many of which have good resistance to disease. Mature height varies greatly, with some being quite dwarf, but none will get bigger than a mature pear. Pollinators love the flowers, which can be white, though some forms have pink-toned buds before they open. Berries produced can be red, orange-red, or even golden-yellow.
• American Yellowwood (Cladrastis kentuckea/lutea)
  Native to the southeast, this tree can be mid-size when mature (not oak stature, but bigger than a dogwood), which is the height range of a very mature pear. If too large, there is at least one compact, weeping cultivar on the market, though it'll be harder to find. White flowers have a Wisteria-like look and open in late spring. Fall foliage color is yellow.
• Kousa Dogwood (Cornus kousa)
  The East Asian counterpart to our locally native Flowering Dogwood. (You could grow that, but they can be more easily stressed in full sun, whereas Kousa Dogwoods are more adaptable.) Blooms appear in late spring and can last into early June if the weather isn't too hot. Fruits look a little bit like a rounded, pink-red strawberry (not toxic, but not tasty). Bark on mature trees flakes off in patches, giving it a quilted look. Fall foliage is red-orange or burgundy-red.
• various species and hybrids of Magnolia (Magnolia stellata, Magnolia macrophylla or its cousin ashei, and Magnolia loebneri are examples that are usually white among the many other pink- or pale yellow-flowered types)
  Some forms grow slowly and may have either a multi-trunked habit or branches that stay low to the ground, looking shrubby, unless gradually pruned off as the tree ages. Flowers are often fragrant, and when they open depends on the species (early spring vs. late spring).
• Silverbell (Halesia carolina/tetraptera/monticola)
  Native, just not locally. Flowers open in mid-spring just before leaves expand, and are bell-shaped, hanging from the branches. This will approach the max height of a pear, so is on the larger side of the species listed above.
• Japanese Snowbell (Styrax japonicus)
  Fragrant white bells that hang from the branches, but in this case, in late spring, after the leaves emerge; fragrant. There are several cultivars, one of which has darker purplish-black foliage (at least in spring...it probably turns greener with summer heat), and another that is compact and weeping.
• Chinese Fringetree (Chionanthus retusus)
  Similar attributes to the native Fringetree, only it has one or two distinct cultivars with regards to mature size/shape, like 'Tokyo Tower' (a.k.a. 'Ivory Tower') that is more columnar in growth habit.
• Gordlinia (xGordlinia grandiflora)
  Might be hard to find as it's fairly new, a hybrid of two fairly rare Gulf coast species; it was bred with the intent of having the plant be easier to grow than either of its parents. Fragrant blooms appear late summer into early fall, and foliage might be semi-evergreen, but otherwise turns red-orange or red-purple in autumn. Mature stature is on the smaller side (15-20 feet high), and while it can handle full sun, it might do best with a little bit of afternoon shade.
• Stewartia (Korean - Stewartia koreana, Japanese - Stewartia pseudocamellia, Chinese - Stewartia sinensis, or Beaked - Stewartia rostrata)
  Sometimes-fragrant blooms are white (occasionally with hints of pink blush) and appear between late spring and early- to midsummer depending on the species. Bark tends to flake off into multi-colored patches with age. Fall foliage tends to be red to plum-red. Growth is on the slower side, and some of these species may be hard to find. (The Japanese is the largest-growing of the group but also the most commonly-sold.)

Miri