Now that lavender plants have “greened” up, it is obvious that this was a very damaging winter for lavender. Generally young plants, plants in sheltered areas, plants under row cover and hardier cultivars (i.e. ‘Folgate’) have performed better, but damage is present on most plants.
Angustifolia cultivars with top damage generally have new shoots growing from the base. Removing the dead growth above these new shoots can get more light to them and result in faster recovery of the plants. Mowing is an option, but rotary mowers should be avoided because they cause too much damage to the remaining branches, which could then be an entry way for diseases to get into the plant. These plants will have a small bloom this year, but could be back to a productive plant next year if given proper irrigation and fertility this year. If the root system is still intact, the plant can grow much faster than a newly planted plant, so there is no need to replant. If there is no green visible anywhere on the plant now, then the plant is dead and will need to be replaced.
Lavandin cultivars with top damage do not tend to send new shoots out from the base of the plant unless the whole branch is alive. If most of last year’s growth is dead now, then the plant will not likely recover and will need to be replaced. If some branches are alive scattered around the plant, then there may be recovery if the dead branches are removed and light can get at the base of the live branches. These may send up new shoots near the base of the plant, and the plant can be pruned later in the season to get back to a more rounded shape. If half or more of the plant is alive (Figure 1), then removing the dead branches will help, but is not necessary. Eventually the dead leaves will fall off and new growth will fill the holes in the plant canopy.
Figure 1. ‘Grosso’ plant with damage to the centre of the plant. This plant can likely be recovered to a rounded shape later in the season as new growth from the base of the live branches gradually replacing the dead tissue.
Four-lined plant bugs have begun to emerge. Look for speckling damage to the top of developing shoots and red-coloured, small, fast-moving nymphs trying to hide under the leaves as you approach the plant. In my small four-lined plant bug host preference trial at the Simcoe Research Station, four hosts were planted – lavender (‘Grosso’), black-eyed susan, bergamot (bee balm) and spearmint in 2016. This year, all of the nymphs that developed were on spearmint (Figure 2), with no damage to any of the other hosts. It may be possible to lure four-lined plant bugs off of lavender to spearmint at the adult stage so they lay their eggs on it instead. This will need to be tested in a grower field.
Figure 2. Four-lined plant bug damage to spearmint in the host preference trial at the Simcoe Research Station.