Vine Mealybugs (Planococcus ficus) are an important pest on grapes and other crops in some areas. Researchers in South Africa have developed a growing degree day model for Vine Mealybugs to help predict when subsequent generations will occur after a the mealybugs are first observed.

Calculating Growing Degree Day Units

The Vine Mealybug growing degree day model uses a lower threshold of 16.6C and an upper threshold of 35.6 C for calculating growing degree day units. The growing degree day units can be calculated from daily maximum and minimum temperatures using these thresholds, or by using the Pest Prophet app, which features this model and is easy to set up and use.

Setting the Biofix date

In order to begin growing degree day accumulation, first a “biofix” date must be set which is the first date, after which growing degree day units will begin to accumulate. For vine mealybugs, this is the date of the first observance in the vineyard, orchard or field.

Approximately 235 GDD(C) after the biofix date the next generation of mealybugs will be observed.

For best results the biofix should be re-adjusted for each generation, based on scouting observations. This will improve accuracy of later crop stage predictions.

Source:

Walton, Vaughn & Pringle, K.L.. (2005). Developmental biology of vine mealybug, Planococcus ficus (Signoret) (Homoptera: Pseudococcidae), and its parasitoid Coccidoxenoides perminutus (Timberlake) (Hymenoptera: Encyrtidae). African Entomology. 13. 143-147.