Thanks for digging that up Rob. Its good to get a confirmation on its resistance to brown rot, I only had my own experience.
Did I ever post the Plums of NY writeup on Middleburg? It is glowing, here it is.
MIDDLEBURG
It is somewhat remarkable that so good a plum as Middleburg should have so long escaped the attention of fruit-growers and even of pomologists. Not even Downing has recorded it, though he lived not more than a hundred miles from the place of its origin, which must have taken place in his time. The fruits may be surpassed somewhat by other purple plums in appearance but few of them are better in quality, either for dessert or for cooking. It is especially valuable too, because it ripens late, hangs well to the tree and ships and keeps well, in the latter respect equalling the best of the prunes. Out of a collection of about three hundred sorts on the Station grounds, this would undoubtedly be chosen as the favorite purple plum of its season. The trees, while of only medium size, are robust, healthy, hardy and usually productive. In Schoharie County, eastern New York, where this variety originated and has long been grown, black-knot is usually epidemic and Middleburg and Palatine are said to be the sorts most free from the disease so free that neither is much troubled by it. From its behavior here it is certain that, belying the looks of either fruit or tree, Middleburg will improve upon acquaintance and that when well known it will be wanted in home collections at least and more than likely some commercial fruit-growers will find it profitable.
Middleburg came from Middleburg, Schoharie County, New York, where it was found as a chance seedling. Mr. S. D. Willard, of Geneva, first called attention to the variety in 1886 at a meeting of the Western New York Hortcultural Society. Its origin is much older than the date given, as it has been extensively grown in Schoharie County for a half-century or more.
Tree above medium in size, vigorous, round and open-topped hardy, productive; branches ash-gray, smooth, with small lenticels; branchlets of medium thickness and length, with long internodes, greenish-red, changing to brownish-red, overspread with light bloom, dull, somewhat pubescent, with few, inconspicuous, small lenticels; leaf-buds of medium size and length, pointed, appressed.
Leaves folded upward, oval, one and one-half inches wide, three and one-half inches long, rather thick, stiff; upper surface dark green, sparingly pubescent on the grooved midrib and larger veins; lower surface silvery-green, pubescent; apex and base acute, margin doubly serrate, with a few, small, dark glands; petiole eleven-sixteenths inch long, pubescent, tinged red, glandless or with from one to three small, globose, greenish-brown glands on the stalk or base of the leaf.
Blooming season early to medium, short; flowers appearing after the leaves, one inch across, white, borne in scattering clusters on lateral spurs, singly or in pairs; pedicels three-quarters inch long, overspread with fine, short pubescence, greenish; calyx-tube green, campanulate, pubescent at the base; calyx-lobes obtuse, thinly pubescent on both surfaces, glandular-serrate, somewhat reflexed; petals roundish or obovate, entire, with short, abrupt claws; anthers yellowish; filaments five-sixteenths inch long; pistil glabrous, equal to the stamens in length, with a large, pubescent ovary.
Fruit very late, season long; one and five-eighths inches by one and one-half inches in size, distinctly oval, compressed, halves equal; cavity very shallow, narrow, flattened; suture usually lacking; apex roundish; color varies from light to deep purplish-red, overspread with thick bloom; dots numerous, small, russet, inconspicuous; stem one inch long, thinly pubescent, adhering well to the fruit; skin thin, slightly sour, separating readily; flesh light yellow, rather juicy, somewhat coarse, firm, sprightly when first mature, becoming sweetish, strongly aromatic, pleasant flavored; very good; stone semi-free or free, one inch by five-eighths inch in size, irregular-oval, with pitted surfaces, slightly acute at the base and apex; ventral suture narrow, winged, faintly ridged; dorsal suture acute or with a shallow, narrow groove.
