Table 1 Description of treatments.

Control

No treatment applied to the seedlings

Chemical

Vaztak active (50 g/l alpha-cypermethrin)

Suspension with a 1% concentration was applied in an approximately spray volume of 60 l/ha (1.5–2.0 l of suspension per 100 seedlings). Seedlings were sprayed with a knapsack sprayer (referred to as top-up spraying) 3 times per year (April, June, August) and 9 times during the entire study

BASF SE

Ludwigshafen

Germany

Collar

Hylopro anti-weevil protective collar (bioplastic collar)

Biodegradable plastic collar applied in spring 2018. Each collar was opened, placed around the plant base, and then pushed approximately 1 cm into the soil until the lock engaged (Fig. 1a)

Locks were checked once each year, at which time open collars were closed

Grube KG

Bispingen

Germany

Glue

Vermifix (42% polyolefins, 420 g per 1 kg)

One bottle of glue (400 ml) was applied per 70–100 seedlings. Seedlings were treated from the ground to 20 cm height 3 times per year (April, June, August) and 9 times during the entire study (Fig. 1b)

Papírna Moudrý s.r.o

Židlochovice

Czech Republic

C wax

F wax

Eco-wax (Paraffin and additives)

Physical protection by wax coating. Before they were planted at the two sites, seedlings were treated with melted wax (approximately 80 °C; about 5–10 g of wax per seedling that coated the stem from soil level to 20 cm above soil level) by the double fountain machine Heco-V-450NW (ZetaEcotech, Italy)³⁵. After wax was applied, the treated stems were immediately cooled with water (Fig. 1c). C wax is standard; the newly developed F wax is more flexible

Norsk wax AS

Larvik

Norway