A Plant Disorder...the fun of diagnosing plant health problems

Over these past few weeks I've learnt so much about pests and diseases at the organic horticulture course I am completing with Agriculture NZ.  For this module we've benefitted from the superb knowledge base on this subject with our guest tutor Vivienne Cruickshank.  Vivienne works with Bio Grow assisting growers to gain organic certification as well as having hands on experience of previously owning and operating a commercial orchard. She has continued study in the large and quite often unknown world of bugs and diseases so we were really fortunate to learn pest and diseases 101 with her.  It impressed me that even with all this experience and knowledge Vivienne is still experimenting and wanting to try new methods of growing on her home property to help mitigate crop loss through disease and pests.

As one of my classmates Lezandra said, "I almost wish I could go back to being blissfully ignorant of what is happening to my plants and sleep easy at night".  Like Lezandra this new knowledge made me feel fearful because a disease or insect can completely devastate a crop.

But looking at the big picture and to what we have been told from the start on this course...get your soil right and the plants can take care of themselves... was also stressed by Vivienne as one of the best defences you can give plants.  The main thing I have learnt from these weeks is that in the world of pests and diseases it's not black and white - there is no one solution but a set of practices called Integrated Pest Management (IPM) that can be used to fight any invasion whether it is pest or disease. You may not always win but the knowledge will make you wiser for next time.

Very proud of my photo taken yesterday of two Monarch butterflies mating - dahlias in the background
at Sanctuary Community Gardens

It has opened my eyes to a whole new world and with eyeglass and camera in hand I am trying to observe and understand this massive world of bugs that previously I never really thought about.

One of our assignments was to observe examples of plant disorders - ill health not caused by insects or disease but by nutrient deficiencies or over supply of nutrients and weather conditions like frost and lack of water.

At our community garden's culinary herb plot the Angelica Angelica archangelica had most of it's older leaves dying off and the newer leaves looking rather striking but I knew something was really amiss.  It has been a very dry and hot summer and this northern European herb likes a cooler damper soil - so first question was - is this the right place for this plant?

No in this case.  But there are no real damp places at our gardens as the beauty of volcanic soil is that it has good drainage.  I then found out from another gardener that there is said to be a rock shelf in that particular corner of the garden making it impossible for the roots of the angelica to dive down for moisture.  But this coloration what did that indicate?

Almost looks like a variegated plant. photo taken 20 February 2015

I looked up my reference materials but it is so difficult to pin point a specific deficiency but on reading about volcanic soils my suspicions were confirmed. In dry conditions volcanic soils often won't allow plants to access Iron.

Iron deficiency typically has paler margins with the leaf veins remaining green.  I cut off the dying older leaves, watered and mulched around the angelica in the hope that we could keep it alive over the summer.

The even younger leaves were unfolding to be a better colour although there was still some yellowing around the margins.

Photo taken 20 February 2015

Nearly one month later and the mulching and watering seems to be working.

Photo taken 17th of March - showing up green for St Paddy's Day

This photo shows the margins could be yellowing but this is mainly due to the photograph on a sunny day.  It's not perfect but the improvement is quite marked.


I have decided we need to move it this winter where the parsley is growing well just a few feet away.  As the parsley grows it will help shade and keep cool the angelica while young.

Full grown angelica in my Otago Peninsula garden 2012

Angelica should grow up to 1.5 metres if its in the right place. It likes the climate and the clay soils at our garden in Dunedin and is a prolific self seeder.  By the way, flies are the pollinators for this herb not bees.