Answer: Determining the cause for this kind of problem can take some detective work. Sometimes a plant will show stress by reduced foliage, and the stress can be a pest, a disease, the delayed results of drought in earlier years, or a rooting problem and so on. Sometimes a tree will fail to root out beyond the original planting hole and eventually the results of that show as a severely stressed plant. You might find that there is something different about this tree's growing conditions, too. For instance, there might be saltspray from the road, less water runoff so the soil is drier, there could be competing roots or shade from neighboring trees, or the soil could be different in that location. You might trouble shoot a bit and if you think it is a pest or disease problem, work with your county extension to determine the exact nature of the problem and the best way to cope with it. Note too that some varieties of crabapple are far more trouble prone than others, so you might want to look into a different variety if that is the case here.
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