Question
QUESTION: I have hedge of Leylandii trees planted 1.5m apart. The hedge is no 5 years old and has grown to an average of 5m high.  Since the beginning of this year's summer (I'm in South Africa) I have noticed a browning of the foliage from the bottom up of almost all the trees.  The amount of dead growth now makes up nearly a quarter in some of the trees.
The pipe that takes away my pool's backwash runs along the hedge and has 8mm holes 500mm apart.  So far this has not presented any problems, but I've recently changed pool chemicals.  (still a chlorine formulation)
Can this be the cause?  Why the reaction only now then?
I love these trees and would hate to lose even one of them.  What should I do?


ANSWER: Hi there. You are going to have to do a close up inspection of your plants. You need to see if there are any fungal spores or insects on the plant. One problem I found for cypress in Africa is cypress aphid.

The cypress aphid Cinara cupressi, has been seen in Africa since 1986.  It was first established in Malawi and has rapidly spread to at least eight African countries.  The aphid causes major damage to Mexican cypress which is a very important tree for agroforestry, industry and ornamental plantings.  In urban settings, the tree is of particular importance as it serves as fences.  The cypress aphid is also a threat to pencil cedar.

The aphid is a brownish soft-bodied insect, often with a grey waxy coating.  They are about 2.4 mm long.  Adults are winged or wingless.  They often occur with several young (nymph) which they produce rapidly.  They are commonly seen in colonies along the twigs of infested trees.

They affect the tree by sucking sap from the twigs causing yellowing to browning of the foliage on the affected twig.  The overall effect on the tree ranges from partial damage to eventual death of the entire tree, depending on the severity and duration of the aphid infestation.

The aphid populations and resulting tree damage appear more prominent during dry seasons.
Let me know how you make out. Bill

---------- FOLLOW-UP ----------

QUESTION: Hi Bill,

Thanks for the quick response.

I've just inspected all the trees for any form of insect and found only a few spiders. No colonies or even solitary bugs in sight anywhere.  

Can you think of anything else - it really looks like water stress, but surely not after 5 years of solid growth (under irrigation)

I did notice what appears to be new growth appearing amongst the brown foliage - it is hard to tell whether it is really new growth or just surviving foliage.

Your thoughts please.

Greetings from Cape Town.

Answer
Hi. I forgot to mention that you will need a magnifying glass. Around a 10x. Look for small black dots. They will look like pepper. If so these will be fungal spores. Also check and see if there is any kind of margin between the where the green stops and the brown starts. If not we will try something else. Bill