The content of this article was prepared by Carlos Quiroz E. / INIA Intihuasi, by www.inia.cl, and has been revised and republished by FreshFruitPortal.com.
There are several species of mealybugs that can affect table grapes in Chile, the most significant being Pseudococcus viburni (Signoret), considered a quarantine pest for fruit exported to the U.S. and other markets.
It is a pest that is difficult to control as it hides in the rhytidome or the plant tissue, the trunk, crown and arms or among the berries, rachis or axis and pedicels or stem that attaches the flowers in the cluster.
During almost the entire year, mealybugs can be found on the vines and on the weeds that grow in the vineyard or its surrounding areas.
The adult female is oval in shape, flattened dorsoventrally, approximately four millimeters (mm) long and covered by a powdery whitish wax. It has lateral white wax filaments, which reach greater length in the tail end, the males are winged and do not exceed two millimeters in length and have thin wax filaments.
The eggs are protected in cottony masses containing between 200 and 300 eggs, 0.4 mm long, pink to slightly orange in color. The "crawlers" or migratory nymphs that emerge, disperse through the different structures of the plant protected from direct sunlight.
In the Norte Chico area all stages of development have been observed throughout the year, while in the Central Zone, depending on local conditions, a resurgence of females laying eggs can be seen in spring, causing nymphs that move down the trunk in various directions.
Some are established under the rhytidome of the same trunk, others migrate and are located in the lower part of the main arms, at the base of the shoots of the season and less frequently on the underside of the leaves. The clusters are infested mainly from pressing or filling and the fruit that touches the trunk or the main branches is attacked more frequently (Photo 2).
Pseudococcus viburni feeds on the sap that it extracts from the plant tissues and because of this it does not normally produce a decrease in yields or quality. Its economic significance is due to “cosmetic damage", that is to say, the presence of egg sacks in the bunch deteriorates the commercial value of the production and is the main cause of export rejection.
Adequate monitoring is essential to making pest control decisions. Observation under the rhytidome, trunks, arms, shoots and clusters, also the inspection of the roots of weeds is recommended, which can indicate the level of infestation. The presence of ants is also a good indicator of the mealybug infestation (Photo 3).
Reliable monitoring must be carried out biweekly in each area of the vineyard for at least ten plants, recording the results on spreadsheets specifically designed for this action. Monitoring should begin in winter and continue until harvest, examining at least 50 bunches per quarter beginning from berry formation.
Mealybugs disperse by involuntary action of humans (clothes, tools, machinery), birds and the wind is capable of transporting the migratory nymphs through the air. Special attention should be paid to adjoining vines attacked by the pest and from which the prevailing winds can disperse the infestation.
Shady or heavily vegetated areas present ideal protection and development conditions for mealybugs. Therefore, excessive foliage and overfertilization should be avoided, which also provides nutrients that stimulate pest development.
Avoid leaving clusters very close to or stuck to the tissue of the arms or in contact with leaves or wood of any kind. Similarly, unharvested fruit or branches must be taken down after harvest.
Given that it is a quarantine pest for many countries where Chilean fruit is sent; the presence of mealybugs can mean the rejection of an entire batch. Therefore, if they are detected during monitoring, applying an insecticide should be taken into consideration.
If it is deemed necessary to use pesticides, the less toxic and more selective ones should be chosen. It is essential to only use the products registered in the buyer markets and to comply with their waiting periods.