spots on citrus
HAVE citrus fruit in pots at our back door. Every year the lime
tree seems to get a black spot on it which, when I pick it off,
seems to be an insect. They appear in clusters and can completely
cover some branches and the undersides of the leaves. Sometimes
the leaves have a black, sooty look. What is this bug and how can
I get rid of it? Also the mandarin has lost all its leaves and just
has spiky looking branches left. Is this caused by lack of water?
problem is scale, which suck the sap and excrete honeydew, which
drops on to the leaves below causing the growth of sooty mould.
Picking them off won't control them as the young scales, which you
can hardly see, usually greatly outnumber the hard-shelled adults.
Spraying is the only efficient way to get rid of a serious scale
For a non-toxic option,
use spraying oil such as Clear White Oil, Conqueror or Super Spraying
Oil. You need to make sure you spray it on to the scale underneath
the leaves and on the stems. It's best to spray oils on a cloudy
day to avoid the risk of leaf burn. Spray the tree before it breaks
into new spring growth. The oil is harmless to people, so you can
eat fruit even after it's been sprayed.
During summer, if there
are still signs of scale, apply another couple of sprays, this time
using a product like Confidor or Rogor 100. Once you control the
scale, the sooty mould problem will disappear.
It does sound as if
the mandarin problem is lack of water, though severe cold damage
could also cause it to lose its leaves.
Gardener, Issue 156, 2004, Page 28
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.