mould on citrus
summer you helped my mother with a magnolia disease and now they
are in bloom and looking healthy. But her new problem is with citrus.
The leaves had a lot of black sooty mould, so she sprayed them with
the same copper spray you suggested for the magnolias. However,
they've now lost several leaves and those that are left seem dry
and brittle, although still green. She's worried she might have
mixed the spray too strong. Is there anything that can be done for
sprays can damage soft new leaves and, in strong concentrations,
can also affect mature foliage. Gardeners in cold parts of the country
often apply copper sprays in autumn to harden foliage which can
help many shrubs better survive severe winter frosts. Too much,
however, can cause leaves to drop off.
Fortunately, there should
be no serious damage to the stems and with the warmer weather we've
been experiencing lately I'd expect the trees to break out into
new growth before long. Give them a light feed of citrus fertiliser
and some water if the soil is dry.
The solution to the original
sooty mould problem wasn't to apply a fungicide like copper but
to use an insecticide to get rid of the scale insects that were
almost certainly the source of the honeydew on which the unsightly
black sooty mould was growing. One of the easiest and most environmentally
friendly ways of controlling scale on citrus is to give the tree
a thorough spray with an insecticidal oil, such as Eco Oil, Conqueror
or Clear White Oil. But, like copper sprays, for best effect and
to avoid plant damage you need to mix and apply oils according to
the label recommendations.
Gardener, Issue 181, 2005, Page 36
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.