Insect activity in lavender has increased, with four-lined plant bug and spittlebugs being the biggest issues. Four-lined plant bugs are in the late nymph (Figure 1) or adult (Figure 2) stages. Look for pale red nymphs with black wing pads or black and yellowish green striped adults causing brown spotting and deformities at the tip of the developing flower shoots (inflorescences). Although the damage they cause does not seem to greatly reduce flower yield, the damage is unsightly and degrades the marketable quality of dried bundles.
Figure 1. Four-lined plant bug nymph
Figure 2. Four-lined plant bug adults
Spittlebugs (Figures 3 and 4) suck plant juices from the stem and create a ball of foam around them as protection while they feed. Like four-lined plant bug, the damage they cause does not seem to affect yield much. They also do not cause substantial damage to the plant. They generally degrade the appearance of the plants but can cause minor shoot distortion at high levels.
Figure 3. Foam of a spittlebug on a lavender shoot
For both pests there are not many control options. Physical removal/squishing of the insects is possible for a small number of plants. Knocking the spittlebugs off the plants with a quick burst of water from a hose or sprayer during the middle of a dry day may kill them, since they cannot live long without their foam covering because they dry out under these conditions. For four-lined plant bugs, insecticidal soaps registered for aphid control in lavender may kill some nymphs. If they are at the adult stage, there are no effective controls. They will feed for a few weeks and then lay eggs and die off. Note where they are a problem in the field so next year you can try insecticidal soaps early on when they may be more effective.
Lavender Harvest Timing
The earliest cultivar in my cultivar verification trial (Super Blue) will likely be starting to bloom next week. Now is a good time to ensure everything is ready for harvest. The timing of harvest for lavender depends on what your end purposes of the flowers are.
Dried Bundles and Buds
For dried bundles and buds the flower petals (corollas) themselves are irrelevant because they die after harvest anyway. Ideally, you want all the buds (calyxes) fully formed but as few open as possible. Corollas stick to the calyxes and turn brown after they die. Depending on the cultivar, you may have to wait up to a week after the first corollas open to harvest, if many of the inflorescences are still developing when the first corollas open. Harvesting too early will result in poor bud colour, weaker stems and lower yields in these underdeveloped inflorescences. The best cultivars for dried bundles and buds have flowers that all mature at the same time, so you can harvest with as few flowers open as possible.
For fresh bundles you want as many open flowers as possible because they remain in bloom until sale. However, you also want as few dead corollas as possible because the brown, dried petals detract from the overall appearance of the bundle. For this it best to wait until about a third of the flowers are either open or past bloom to ensure most of the inflorescences on the plants have reached the bloom stage.
Within a single flower bud, the amount of essential oil increases up to the point the corolla opens and then remains steady or gradually declines thereafter. Looking at the whole flowering inflorescence, some buds continue to develop after the first buds open. On some cultivars, some whole inflorescences continue to develop after the first inflorescences are fully developed. As a result, the amount of essential oil on a plant usually peaks after 50% bloom. There is only a slow decline in oil content and quality after that point unless there is very wet weather conditions that promote mold growth. Also, in some cultivars (e.g. ‘Folgate’), buds can fall off the inflorescence after bloom is finished, further decreasing oil yields. Some growers intentionally wait until after bloom to harvest for oil to ensure the maximum amount of time for agritourism activities.