Recommendation - post-planting spray treatments of individual transplants using a narrow cone nozzle delivering 10 ml of mix containing 0.1% alpha-cypermethrin per plant and aimed to target the zone from the root-collar to roughly 150 mm above the soil. A maximum of two applications can be made in any one year.
Unless transplants are protected from attack by Hylobius abietis, plant losses throughout UK restocking areas will average about 50% over the two years after planting. Treating bare-rooted plants using the Electrodyn Sprayer Conveyor (ESC) or a mechanical spray race for container grown plants is the recommended method of protecting plants during the first growing season. During the second season after planting, the plants remain susceptible to damage, but the insecticide deposit remaining from pre-planting treatments provide no significant protection. At least one application of insecticide after planting is normally necessary to protect the plants in the second season. Although Hylobius may feed whenever temperatures are high enough for activity, two peaks of damage occur. The first is around May, before the insect migrates to new restocking sites and the other starts in August before the insect over winters. Post-planting applications of insecticide protect plants during a single period of damage. For this reason they will normally be applied in April and late July. They are applied using a knapsack or similar sprayer at a concentration that is slightly lower than that used for pre-planting treatments (where longer periods of protection are sought).
Trials carried out in 1999 and 2000 showed that spraying plants with alpha-cypermethrin will provide adequate protection for up to 12 weeks.
The Pesticide Safety Directorate (PSD) has recently approved the use of Alphaguard 100 EC containing alpha-cypermethrin for the treatment of plants after planting. The recommendation for post-planting treatments will be to spray 10ml of mix containing 0.1% alpha-cypermethrin using a narrow cone nozzle. The target zone is the plant stem from the root collar to roughly 150 mm above the soil. Because the stem is often obscured by foliage and site debris, the volume applied is calculated to be sufficient to allow the solution to run from sprayed foliage onto the target stem. Depending on site conditions the application may be applied as two 5 ml sprays to each side of the plant to ensure adequate coverage of the stem. On most sites, it is not possible to respond to insect activity fast enough to protect all the plants. It is therefore necessary for it to be completed before the insects become active, as serious damage may occur soon after the first weevils appear.
Most operators will use a forestry spot gun calibrated to deliver the appropriate dose. The spot guns use pressure from the trigger action to spray the liquid and operators may develop tendonitis during repeated use. For this reason, operators may chose to use a motorised knapsack sprayer that can deliver a measured dose. Unfortunately, the volume of spray delivered by these units cannot be adjusted and the label allows up to 20 ml of insecticide mix at 0.1% concentration to be applied to each plant to enable the legal use of this type of equipment.