How to Improve Native Plum Fruit Quality Control

Common Plum Defects

• Black knot
  Black knot eventually looks like large thick masses on the branches of the plum tree, although it will start out as green or light brown. The branch will soon die, which means lower plum fruit production and structural damage.
• Bacterial Leaf Spot
  Bacterial spot is caused by Xanthomonas arboricola pv. pruni (XAP) and represents symptoms including fruit spots, leaf spots and twig cankers.
• Brown Rot
  Brown rot is a fungal disease that affects trees and shrubs in the genus Prunus, including plums, peaches, cherries, apricots and nectarines. Initial symptoms occur in the spring as brown spots on blossoms. In addition, fruits that develop from healthy flowers can also become infected when they mature, which leads to a brown fruit rot that encompasses the entire fruit. Eventually, these affected fruits dry and shrivel to form “mummies”.
• Fireblight
  Fireblight is a destructive and highly-infectious disease caused by the bacterium Erwinia amylovora. It attacks plum tree blossoms, leaves, shoots, branches, fruits, and roots. The bark at the base of affected twigs becomes water soaked and then dark, sunken and dry. Eventually, cracks may develop at the edge of the sunken area. As a result, young twigs and branches die from the terminal end and appear burned or deep rust colored, and dead leaves and fruit remain on the branches.
• Hail Damage
  Hail damage can ruin a crop, but it’s all about how you support the fruit trees in recovering after the damage is done. You should remove the damaged fruit so the rest of the yield isn’t impacted, as well as fruit on the ground to reduce pests and bugs.
• Internal Browning
  Internal browning is usually due to cold damage when plums are stored, in warehouses or before being shipped to their next destination. They may look normal on the outside, which can lead to loss of trust from a buyer if the problem reoccurs.
• Perennial Canker
  Perennial canker is caused by a fungus called Leucostoma cinctum. It causes lesions (cankers) that develop on the twigs, branches, and trunks of trees. They begin as areas that appear darker than the healthy bark and become sunken, and as infection spreads, these cankers elongate and widen on the infected branches or trunks. The cankered tissue under the bark appears reddish brown and a gummy, resinous sap exudes from the cankers (gummosis). As this gummosis becomes more severe, a sour sap and odor may appear.
• Pests
  As well as weevils, other pests that can impact plum trees are leaf-curl plum aphids, apple maggots which also impact plums, mites, scale, plum moths and plum sawflies, and thrips. These insects can damage fruit, and quickly spread progressive defects like mold across a crop if the damage isn’t found early.
• Pistilar Cracks
  Plums with this defect will be split open, with a crack through the skin into the flesh of the fruit. If this is a persistent problem, you might find that the plum tree is being over-watered.
• Plum Pox Virus
  This is a virus that impacts plum trees as well as other fruit trees. It not only reduces the yield, but also deforms the fruit - making it less desirable to the consumer. PPV is also highly contagious so infected trees need to be removed.
• Plum Pocket
  Plum pocket (also known as bladder plum) is caused by the fungus Taphrina communis. It is an unusual disease that causes unripe plums to grow abnormally large within a month or two after bloom. The infection begins with a small blister on the fruit and quickly grows to cover the entire fruit. Infected fruit may grow to ten times their normal size and also have a spongy texture. Eventually, these fruits dry out and turn black and usually fall to the ground. In many trees, only a small number of fruit are infected.
• Ring Spot
  Plums with ring spot will have leaves with yellow rings and spots. The fruit itself may also have bumps and tend to drop early from the tree before they are ripe.
• Scarring
  Small crescent-shaped scars on plum fruit are usually because of Plum curculios, also known as weevils. This can also cause the fruit to drop early.