Over the past few weeks we have been tracking the progress of lavender plants in the Simcoe demonstration plot with winter damage to see their potential to recover. It appears at this point that any plants without any signs of life are dead and will need to be removed or replaced. For other plants with varying degrees of damage here are the observations to date:
1. Lavandula angustifolia cultivars: Most plants have “bald spots” with a ring of healthy growth to the sides of the plant (Figure 1). The empty spots are gradually being filled in by new growth from the base. The new growth is slightly delayed in development compared to the stems off of old growth and will likely have shorter flower stems. This will result in a staggered bloom and affect the overall appearance of the plants. Staggered bloom will complicate harvest, especially for flower bundles and buds. For oil production, it is best to delay harvest until the bulk of the stems are near or past peak bloom to ensure good oil quality. A heavy pruning after bloom will likely return the plants to a good shape for next year.
2. Young lavandins: Most young lavandins that have some new growth are quickly growing over the old growth. These plants will have lower and more variable flower yield than they would have had without the winter damage. However, with a heavy pruning after flowering, they will likely return to healthy looking plants for next year, although they will have lost a year’s worth of growth. There may be a few that die later in the season, depending on the extent of the damage to the crown.
3. Older lavandins: Older lavandins were the most affected by winter kill. Some plants only have a branch or two with signs of life from a plant that would normally have 50 to 100 branches (Figure 2). The branches that are alive are sending out some new shoots a few inches from the crown, but there are no signs of new growth from the crown itself. At this point it seems unlikely that these plants will recover fully to have a rounded shape. There is insufficient growth to maintain a healthy root system and it is possible that the remaining branches will die later in the summer. We will continue to track these plants to see if there is any potential for recovery. However, if the overall appearance of a row of lavandins is important for agri-tourism activities, then it is probably best to replace the plants rather than wasting a couple of years trying to recover the existing plants. If this level of damage is present in the field, then then it is likely that there are also many plants that are dead in the same rows, and these will need to be replaced anyway. There are lavandins that have some new growth on branches on all sides of the plant. There is still hope that these plants will recover. Removal of all of the dead growth is necessary for these plants to get light to the new growth and prevent it from stretching towards the light. Selective pruning will be required over time to recover a rounded plant shape.
Growers have also been reporting isolated plants with yellowing and twisting (Figure 3). This may be related to winter damage of the stem, preventing adequate flow of water and nutrients. It could also be caused by root disease. There are lesions that appear to be Septoria leaf spot present on the plant in Figure 3 but Septoria has not been known to cause these yellowing symptoms. Growers should track these plants to determine if the issue continues to develop and spread. If neighbouring plants become affected, then a root disease is likely. If the problem remains localized to individual plants or portions of plants, then it may be stem or root damage.