Lavender Crop Update June 24 2015

Angustifolia cultivars of lavender are beginning to bloom in southern Ontario. Normally, peak bloom would be occurring over the next three weeks. However, most plants have had at least some frost damage. New shoots are now emerging from the damaged tissues and many of these have small developing buds (Figure 1). This will result in an extended period of a relatively weak bloom. While an extended bloom may seem like a good thing, it will complicate harvest.

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Figure 1. A lavender plant with flowers at various stages of development. The flowers on the outside of the plant were not affected by frost, the inside of the plant had frost damage and the new shoots have very small buds.

Lavender is normally harvested for buds and bundles at early bloom when only a few flower buds have opened. If growers harvest as normal now, many of the developing buds lower in the canopy will be cut off. If they wait until more flowers are open, some blooms will be past peak. As a result, it will be necessary to selectively harvest some stems and leave others intact. This will greatly increase the labour required.

The decision of when to harvest will be a lot easier if the flowers are intended for distillation. The optimal harvest time for distillation would be the late bloom period in a normal year. However, oil quality only slightly declines beyond that stage. Consequently, it is possible to distill lavender when flowers are finished blooming. This year, growers should consider waiting to harvest until most of the flowers have either opened or finished blooming to get the maximum amount of oil from the plants. This will result in slightly less quality, but that is unavoidable this year.

Four-lined plant bugs have reached the adult stage and will soon die off (Figure 2). This week we were able to locate their eggs on the side of lavender stems. The eggs are laid in clusters of 6 to 10 eggs inserted in several vertical lines up a green stem (Figures 3 and 4). They are very difficult to locate in the plant. These eggs will hatch in the spring next year and there will be no further damage to lavender plants this year once the adults die off over the next week or two. Because the eggs are laid in green tissues, some of the eggs will be cut off during pruning. If populations get very high and plants have considerable damage, it may be a good idea to remove any of the pruned material from the field. This could remove up to half the eggs from the field. While it won’t solve the problem, it could keep populations down somewhat.

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Figure 2. A four-lined plant bug adult on lavender.

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Figure 3. Four-lined plant bugs insert their white eggs in slits in green stems. Note the small white vertical line on the stem near the centre of the photo.

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Figure 4. Cluster of six four-lined plant bug eggs under the microscope. The majority of each banana-shaped egg is inside the lavender stem.

Garden fleahoppers are also causing considerable damage in some areas, with up to several hundred insects per plant. Normally they can be found causing insignificant damage on scattered plants throughout lavender fields, but can reach very high populations in small areas of the field. Look for tiny black adults and green nymphs hopping away from the plant when the plant is vigorously shaken. Placing a white paper next to the plant when the plant is shaken will make it easier to see them. There are multiple generations per year of garden fleahoppers and this can allow populations to increase all season long. If damage is excessive, insecticidal soaps that are applied for suppression of other insects on lavender, may also suppress the nymphs of the garden fleahopper. This may only be necessary in small patches where damage is most severe.

About Sean Westerveld

Ginseng and Medicinal Herbs Specialist, OMAFRA
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