The symptoms pictured include rust, a very common fungal disease that cannot be cured or treated (once symptoms manifest) with a fungicide, even if root-applied and absorbed into the canopy. Rust is a disease that moves back and forth between its rose family host (this tree) and our native wild redcedar (juniper) trees. It requires both types of plant to complete its life cycle, though spores can travel a mile or more on the wind, so it's not really practical to try breaking the cycle of reinfection by removing the other host tree. Since rust infections are cyclical and annual, preventative treatments using fungicide to protect still-healthy foliage each spring would require multiple treatments every year (at least with a topical fungicide), which would be fairly expensive for a disease that can be unsightly but is not usually a threat to long-term tree health. (Especially considering the dosage required to drench the root zone of this size of tree, or the expense of hiring a certified pesticide applicator who has the right equipment to spray the canopy or inject the trunk.)

The foliage, bark, and growth habit of this tree appears to belong to a Callery Pear (Pyrus calleryana), not a Crabapple (Malus), though blooms and/or fruit would be a confirming ID feature. Callery / Bradford Pears are invasive trees and we encourage gardeners to replace them if an existing tree is in decline; they're regulated by the MD Dept. of Agriculture as well (as of 2018 anyway) as one of a group of invasive species that nurseries and landscapers should caution consumers about before selling/installing them. Both Callery Pear and Crabapple can contract rust.

The leaf darkening and shedding is unrelated to the rust, and may be due to any number of other infections that Pear (and Crabapple) can contract. We've received several inquiries recently from other gardeners about Callery Pear trees shedding leaves and developing canopy dieback, and in at least some of the cases, the responsible pathogen was powdery mildew. We can't see clear indications of mildew on your tree, but it might not be showing up well in the photos. If you wanted to have the tree examined in person, you could have a certified arborist look it over for this and other causes of tree stress.

Since a soil-drench fungicide would have limited ability to suppress an existing disease if applied after symptoms appeared, it's more likely that the product you applied happened to be used after the disease ran its course and the seasonal change in weather trends (drier and hotter conditions, probably) reduced re-infection potential (if any was still happening by that point, since most infections begin in early or mid-spring, long before symptoms manifest). While a couple types of mite can infest pear foliage, they cause very different symptoms (many small pale-colored bumps) and that component of the pesticide combo was probably not needed. The insecticide component was also probably unnecessary, and some systemic ingredients run the risk of contaminating the nectar and pollen of the next set of flowers, which is the primary reason they were regulated in Maryland for legal use only by certified pesticide applicators. Given several state-level regulations, some pesticide manufacturers have replaced those ingredients in their combo mixes with other insecticides that are not as restricted, but some have not, and even the same brand or product line might have two different formulations. Due to that, the active ingredients list on the label should be examined prior to purchase to determine which components are being used in that specific formulation.

Even setting aside whether this tree is a Pear or Crabapple, and which exact pathogen caused the second set of symptoms (the other is definitely rust), there is no treatment you can apply yourself that will have any significant impact on its state of infection, because fungicides cannot cure existing disease. Fallen leaves, should they become more abundant than just a handful any given day, can be raked-up and disposed of, but that's not a foolproof measure, since spores tend to travel easily from far afield, and years with wet spring weather generally promote more infections than drier years. We have seen Callery Pears and Crabapples persist and keep flowering and growing for years with recurring infections, so neither dooms the tree at this point, but if the tree reaches a tipping-point of stress tolerance due to some other factor at some point, decline could be more rapid.

Miri

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