With two-million or more cordylines and phormiums grown each year, downgrading and annual losses from these disorders are estimated at more than £1m.
Building on findings of a previous project - in which viral infection, nutrient imbalance, high fluoride and environmental stress were investigated as possible causes - this project aimed to identify practical measures to minimise the incidence of both conditions.
Leaf tissue analysis indicated less potassium and calcium were present in plants with symptoms. Calcium nitrate as a foliar feed and potassium nitrate as a liquid feed were shown to reduce the incidence of both tipburn and yellow leaf spot in cordyline when used at the correct dose.
The best commercial option was suggested to be an application of calcium nitrate (liquid feed, 75mg/litre calcium) plus potassium nitrate (liquid feed, 75mg/litre potassium). This resulted in the best-quality plants, even though leaf spot reduction was not statistically significant.
As a result of the project, a number of growers have started to use calcium as a foliar feed for cordylines and are seeing less severe tipburn and yellow leaf spot syndrome, although symptoms have not been completely eliminated.
The full grower summary for HNS 171a can be accessed online at www.horticulture.ahdb.org.uk.
For details on all AHDB Horticulture activity, see horticulture.ahdb.org.uk.