The white peach scale (Pseudaulacaspis pentagona) is an insect belonging to the order Rhyncota, family Diaspididae, which particularly affects peach and mulberry trees. In some texts, it is referred to as a synonym of Diaspis pentagona, while it is commonly known as the white peach scale and mulberry scale. This parasite is native to the Far East, probably from Japan. It was accidentally introduced to Europe at the end of the 19th century, through Northern Italy. Since then, it has spread cosmopolitanly and is currently distributed in most territories of the 5 continents between the 45° north and south latitudes.
Let’s take a look at how to recognize it, the damage it causes to tree crops, agronomic prevention techniques to reduce its presence in orchards, and biological defense on already infested plants.
Description of the White Peach Scale
Pseudaulacaspis pentagona appears in different forms, both female and male. The female follicle is circular or sub-circular, cream-white with reddish exuviae in a shifted or, more rarely, central position. It measures 2-2.8 mm in diameter. The adult female is orange in color, slightly pear-shaped, with the mesothoracic part more developed and well-marked thorax and abdomen lobes. The antennae are close together, with a large conical basal tubercle topped by a seta. This species of white peach scale is characterized by the presence of bifurcated glandular lateral spines. Then we have the male follicle, which is linear and weakly keeled, white with yellowish apical exuviae. It measures 1 mm in length. The adult male is yellow-egg in color, equipped with a single pair of wings and a long caudal stylet. It measures 0.9 mm in length. Finally, the eggs are orange if they originate females, white-yellowish if they give rise to male individuals.
The white peach scale Diaspis pentagona is not only one of the main peach tree pests, but it is also extremely polyphagous, capable of attacking countless tree, forest, and ornamental crops. We have already mentioned the mulberry tree, both white and black varieties, but it also targets the paper mulberry (Broussonetia papyrifera). Other fruit trees that host the white peach scale include kiwi, apricot, plum, almond, cherry, papaya, walnut, currant, and occasionally, apple, pear, and quince. Rarely, the grapevine is affected. Among the forest and ornamental plants, we have: nettle tree, catalpa, euonymus, ash tree, geranium, wisteria, hibiscus, cherry laurel, privet, lilac, oleander, passionflower, paulownia, peony, sophora, etc.
Damage Caused by White Peach Scale
Pseudaulacaspis pentagona primarily infests the branches and stems of various host plants, resulting in thick encrustations. The affected vegetative parts wither, and in severe cases, they dry up. On fruits such as peaches and cherries, reddish spots appear at the points of attack, very similar to those caused by the San Jose scale (Quadraspidiotus perniciosus), only slightly fainter. The affected fruits are of poor quality and certainly not marketable.
The white peach scale Pseudaulacaspis pentagona overwinters as a mature, fertile female, protected by the follicle, cortical films, and the ventral veil that covers it entirely. It resumes its activity at the end of April, laying up to 170 eggs, which accumulate under the shield and hatch staggeredly. Upon hatching, the nymphs remain torpid for an hour, then move to attach themselves to other parts of the vegetation. After attaching, they begin to form a provisional follicle using a substance secreted by abdominal glands. Towards the end of May, when some of the eggs are still hatching, the first nymphs undergo the first molt, followed by a second after about 15 days. Between the first and second molts, they build the definitive follicle. The development of male nymphs is faster. Winged males appear when the females are completing the final molt, and they are therefore fertilized at a young stage of development.
Under normal conditions, the eggs of the second generation are laid from late June to the second decade of July, and from these, the new nymphs emerge by the end of July. Between the last decade of August and the first half of September, the third egg-laying occurs. From early September, the overwintering nymphs of the next generation appear. Thus, Pseudaulacaspis pentagona completes 3 generations in a year, but in climatically unfavorable years with delays in fertilization, there are only 2 generations.
Natural Predators of Mulberry Scale
Fortunately, there are numerous insects that play the role of antagonists against the white peach scale Pseudaulacaspis pentagona, some are predators, while others are parasitoids. Among the predators, we have: Chilocorus bipustulatus, Exochomus quadripustulatus, Lindorus lophantae (ladybird beetles); Cybocephalus rufifrons (cybocephalid beetle); Antrocnodax diaspidis (cecidomyiid fly). Among the parasitoids, we have: Encarsia berlesei (endoparasitic chalcid wasp); Aphytis diaspidis, Aphytis proclia (ectoparasitic chalcid wasps); Pteroptrix orientalis (afelinid wasp, widespread in Campania with high parasitization rates). Of course, to ensure that these beneficial insects establish themselves in the habitat and perform their natural control role against the white peach scale, it is necessary to avoid the use of harmful chemical pesticides in the orchard environment.
Mechanical Defense Against Mulberry Scale
To defend the orchard against the white peach scale, you can start with the mechanical removal of the parasite from the vegetation. Using a natural bristle brush (like this one), vigorously brush the branches and limbs where the white peach scale has settled. It is advisable to follow the brushing with vegetation washing, preferably using potassium soaps. Brushing should be done when the leaves fall, typically in autumn or winter. Another mechanical intervention against white peach scale is carried out during routine winter pruning. In pruning cuts on trees infested by the scale, remove the most affected branches, and then burn the resulting debris. It is obvious that pruning and brushing would be more effective if performed synergistically.
Eliminating White Peach Scale
Among the products allowed in organic farming, the most commonly used to eliminate white peach scale is mineral white oil (available here).
Treatment with white oil is preferably done in winter, targeting the overwintering forms of the insect. The effectiveness is not very high since the scale is well-protected by the follicle, so it’s always a good practice to follow up with brushing after treatment. In spring and summer, a viable alternative to mineral white oil, which can cause phytotoxic reactions in hot weather, is sweet orange essential oil. The correct usage methods are explained in the corresponding article. With the spring treatment to be carried out in May, you will also target the new nymphs of the white peach scale Pseudaulacaspis pentagona.