Finally it is warming up and lavender should progress very quickly over the next week. The earliest cultivars are starting to show bud colour (Fig. 1), which suggests the beginning of bloom is about 2 weeks away. It is looking like bloom will be slightly later than normal this year, despite the early start to spring.
Insect pest issues have not been very high so far this year in the fields we regularly monitor. The dry conditions last year may have limited their reproduction. However, that doesn’t mean they can’t increase rapidly, especially garden fleahoppers since they have multiple generations per year.
We are seeing some signs of virus infected plants (Fig. 2). Scattered plants in some fields are showing yellow discolouration on parts of the leaves. The leaves remain otherwise healthy and it is unknown if the virus has any impact on yield. Laboratory testing of leaves confirmed the cause this year as alfalfa mosaic virus (AMV). AMV affects many different hosts and is transmitted mainly by certain aphid species. It can also be transmitted by pruning equipment. It is important to sterilize pruning equipment regularly. Click here for more info on viruses on lavender. Never take cuttings from plants exhibiting these symptoms, since the effect on yield and plant growth has not been determined and the daughter plants would definitely carry the virus, even if that particular stem did not show symptoms.
Now that flowers are developing, it is a good time to start your nitrogen fertility program, especially if plants are looking pale green. Fertilizing now is unlikely to affect the rest of bloom and will give plants a head start on vegetative growth after harvest. Our research trials so far suggest a requirement for around 80 kg/ha of nitrogen over the season, which is best split into at least 2 applications between now and the middle of August. The requirements for nitrogen are the same for both conventional and organic production, but the sources of nitrogen would differ. Organic growers can consider an application of manure or compost between the lavender rows. However, this is best done after harvest to avoid any potential contamination of the flowers with human pathogens.
The very wet conditions earlier this year may have caused some root loss in poorly drained fields. Now that it is drying and heating up, plants may have more moisture stress than you would expect given adequate moisture in the soil profile. Watch for wilting flower stems during the heat of the day. Moisture stress at this time of year will likely shorten the flower stems and reduce flower yield.