Highbush Cranberry

Once the leaves drop, go over the youngest twigs and look for straight rows of small raised bumps on the undersides, each a capped pit holding five to eight eggs. Prune those twigs out and destroy them any time between October and bud break. Every female lays up to 500 eggs sealed into last season's twigs, so the whole of next spring's larval population is sitting on wood you can see and cut while the plant is leafless.

In late dormancy, before the buds break, spray horticultural oil at the dormant rate of 4 percent and cover the young twigs thoroughly, where the egg pits are. The eggs are glued into pits on the stems and the oil smothers them before hatch, which is far easier than chasing larvae once they are spread through the canopy.

As the new leaves unfold, turn them over and look for clusters of small greenish larvae skeletonizing the undersides. Spray insecticidal soap at 2 percent or spinosad while the larvae are still small, and repeat once if they persist. American cranberrybush is one of the most susceptible viburnums and a heavy larval year can strip the shrub bare, and both soap and spinosad only work well on the youngest instars, which hatch just as the leaves are expanding.

Once the white lacecap flowers finish, take out crossing, dead and crowded stems and shorten the shrub to the size you want. It is an 8 to 15 foot shrub left alone. Highbush cranberry sets next year's flower buds on wood it grows this summer, so pruning right after bloom leaves a full season for the replacement wood to form buds, while a late-summer or spring cut removes the flowers before they open.

From July into September, check the foliage for golden-brown adult beetles chewing ragged holes, and for fresh egg pits appearing on this year's twigs. Note which twigs they are using so you can prune them out after leaf drop, which is the control that costs you nothing and does not touch the fruit. There is one generation a year, but the adults that emerge in July feed a second time and then lay eggs into the twigs right up until frost, which is what sets the size of next spring's larval attack.

Cut whole clusters once the fruit has coloured scarlet and turned translucent. The flavour is better if you pick slightly under-ripe and after a frost has hit the bush. Expect nothing for roughly the first five years after planting. The americanum form is tart rather than bitter, and cold sharpens it into jelly fruit - fully ripe, unfrosted berries are musky and the seed and skin dominate.