on flax and cabbage trees
HAVE sent photos of some of my flax bushes and cordylines which
both have ugly marks on them. The cordylines have yellow splotches
and the flaxes have brown splotches. Is this caused by a bug or
a fungal disease?
LOOKS like you have two separate problems. Some flax varieties,
including variegated ones like yours, can be susceptible to fungal
leaf spot if the conditions they're growing in are rather damp and
humid. Flaxes grow best in relatively open, sunny spots with lots
of fresh air blowing around them. So, to reduce the risk of leaf
spot, prune away nearby growth to expose the leaves to as much light
as possible and allow whatever breeze there is to blow around the
plant and dry out the foliage. It's also a good idea to cut out
badly spotted leaves close to the base, along with any dead leaves,
to reduce the risk of infection. You could spray with a general
fungicide, like Bravo, but if you improve the environmental conditions
sufficiently spraying shouldn't be necessary.
cabbage tree looks like it's been attacked by passionvine hoppers.
The dark brown marks are where the initial puncture wound has become
infected, while the surrounding lighter brown area is where the
insect saliva has digested chlorophyll from the leaves.
Although they can be
a major pest of passion fruit vines, passionvine hoppers attack
a wide range of other plants. They inject saliva into the leaves
as they feed and have been known to spread diseases from one plant
to another. They are suspected of being implicated in the spread
of cabbage tree decline disease which has led to the demise of many
old established native cabbage trees throughout the country.
Adult passionvine hoppers
are about 1cm long and look like small moths but with mottled translucent
wings. You often see several together resting on a twig, and if
disturbed they'll quickly fly off. The young are wingless, have
a fluffy tail, and when disturbed hop high into the air.
Control often isn't
necessary as they seldom do enough damage to trees and shrubs to
warrant any action. But the effect on cabbage trees can be unsightly,
so you may want to try spraying. This can be tricky though, as adults
fly away and nymphs hop off as soon as you try to spray them. It's
best to take action early in summer as soon as you see adults or
nymphs, as by autumn the worst of the damage has been done. You
can use contact insecticides such as Nature's Way Insect Spray or
Garlic & Pyrethrum, but you need to make sure to actually get the
spray on to the hoppers. Late evening or early morning is a good
time to spray as they seem less active then. You could also use
a systemic product like Confidor or Rogor 100 which is absorbed
into the sap and affects hoppers when they feed.
Gardener, Issue 147, 2004, Page 26
Reproduced with permission from Weekend Gardener
The views expressed here are not necessarily those of the RNZIH