Nov 19, 2024

Plum factors:  Successful varieties offer growers opportunities

In North America, there are two groups of plum species which enter into commerce. The most well-known are the Japanese types — the ones most shoppers know as fresh plums because they are in most chain stores for many months of the year.

These diploid plums are typically dark-skinned, spherical, with firm flesh and cling pits. They usually possess a good balance of acid and sugar, with modest sugar levels rarely exceeding 15 brix. The other plum species, Europeans, are hexaploid. They have been domesticated more than 2,000 years, so their average fruit quality usually surpasses the diploids. Some of them can attain sugar levels of 25-30 brix. What I find incongruous is that essentially none of them enter into our fresh markets in any widespread fashion.

The only European plums sold widely are mostly the California dried ones. There may be several reasons for this odd pattern. Some of the European plums may be more perishable and struggle on distribution durability.

Another problem may be the need to educate the public about their varietal names so the plums can enjoy repeat business. The Europeans are often more unique in fruit character than many of the diploids found in the chain stores. In my experience, very few of the Japanese types are ever presented in the chain stores under their varietal names. The following are varietal descriptions of some of the plums that typically grow well in Western New York, presented in Geneva ripening time sequence.

Diploids

Early Golden is a medium-size plum with yellow skin, red blush and good fruit quality. It ripens in mid- to late July. Kuban Delight fruit is almost spherical, 1.6-inch high by 1.75-inch in diameter. It possesses a darker maroon skin, and flesh is medium yellow with a reddish tinge by the skin, which is firm and tart. The variety ripens in mid-July in Geneva. It is probably a cross of a salicina and a cerasifera plum species. It was bred in Russia at the Kuban Station on the east side of the Black Sea. Obilinaya is a larger plum with purple-red skin and good fruit quality ripening in late July.

Shiro is a medium-size plum with yellow skin and good fruit quality if not overset. It ripens in late July. Vanier is a medium-size plum with red skin and good fruit quality that ripens in mid-August. Hexaploids or Europeans Castleton is a medium-size fruit with good quality and blue-black skin that ripens in mid-August in Geneva. Longjohn is a large, elongated plum with good quality.

The skin is purple-blue. It ripens in the second half of August. Reine Claude Conducta is a large Gage-type plum with high sugar and fine fruit quality. Reine Claude is the French name for the Gages. It ripens in Geneva in the second half of August. In France, a gourmet industry is based on presenting Reine Claude plums as fresh fruit on a widespread basis with legal rules on how to grow and market the fruit.

Like some sweet cherries, most Gage types are subject to rain cracking. When they crack, they typically suffer from brown rot. Cacak’s Best is a medium-large, blue plum with good fruit quality. It has some pleasant astringency, which is comparable to Italian (which grows poorly in Western New York) and ripens in late August.

Bluebyrd is a medium-size plum with good quality with dark purple skin ripening in late August. Valor is a medium-size fruit with good quality, dark purple skin and ripens in the last half of September.

Autumn Sweet is a dark blue skinned medium-size fruit with very high sugar. It ripens near the end of September. Future diploid plums North America is the world center of wild diploid plum species. We have at least a dozen native plum species.

This is a genetic wealth which is uncommon for North America. This is a substantial opportunity for future plum breeders to develop new, useful varieties.

Processing plums

Stanley

The most common varietal plum name in the Northeast is Stanley or, perhaps, Italian. Many people mistakenly believe Stanley is a fresh variety. It was named about 100 years ago by Cornell’s Geneva Station as a processing type for canners. Up until a few decades ago, Stanley was grown by many New York farms for Beechnut for baby food. When Beechnut moved production to Michigan, many New York growers simply dumped Stanley varieties into the fresh market despite a mediocre quality for this use. This action tended to degrade the whole category of fresh plums for many New York consumers.

Damson

Damson is the most well-known European plum used for jam in North America. It comes off the trees in mid- to late September in Geneva. Because of its high sugar and tannin, it lately has been increasingly used in alcohol. The Damson name relates to Damascus, Syria, brought to Western Europe by returning Crusaders.

European Brandy plums

Lately there has been increased interest in using the high-sugar brandy plums for various processing purposes. The three best known for this use are Pozegaca, Lohr and Wangenheim.

Disease susceptibility, cold hardiness

The fungal disease called black knot is native to North America. Most diploids with American ancestry are unaffected by it, while the Europeans are typically susceptible. If black knot is not controlled, it can quickly kill trees.

Because the diploid plums typically bloom a week to 10 days earlier than the Europeans, affected trees are more at risk of losing part of a crop to late spring frosts, particularly on sites with poor air drainage. In a similar fashion to peaches, some tender diploid plums may lose flower buds in the winter if the air temperature drops to -15° F.

Many plums are not self-fertile and a diploid will not set fruit on a European, nor will the reverse pattern set fruit. Diligent nurserymen should offer pollination charts for both the Europeans and the diploids.

Written by Jay Freer

Jay Freer is a stone fruit and pear technician at the Cornell University Agricultural Experiment Station in Geneva, New York.