Can you see the mountain?

As a boy when I lived at home in Norway there was a joke that if you could see the mountain it was about to rain, otherwise it was raining! OK, not very original, but at least we did not have to suffer Arthur Askey! (US readers will probably not understand that reference to a busy bee). Well, this weather here in the mid-west of England is getting beyond a joke. I’m beginning to reconsider that it must be the global warming thing. The weather is so unpredictable.

If you think about it, extra heat causes extra evaporation from the sea causes extra rain. Now I’m sure some scientists are jumping up and down shouting ‘Idiot!’ but you can’t get away from the fact that we’ve had years of summers more like monsoons.

It seems that we do get some dry-ish weather and the moment I think I can head for the main Canna collection beds, down comes some more rain. Anyway, we managed to grab a few hours down there today, but we have already has 3 weeks of high winds that are violently draining all moisture from the ground and foliage, so much that my bean crops have stopped growing 3 weeks earlier than normal. Digging shows no water for 6" down into the soil, in spite of the rain showers.

Really, it was quite depressing in Cannadom. Nothing has grown to its full height, there is very little seed to collect and everywhere there is poor foliage. We have had a couple of weeks of half-decent sunshine and the later leaves that have unfurled are showing good healthy photosynethis and show no signs of stress markings, unlike those for the previous 6 weeks which sometimes did not have the energy to unfurl themselves and displayed signs of chlorosis. We had to manually unfurl the leaves to enable the growing point to continue upwards and not just rot inside the unfurled leaf. The resultant leaf is a mixture of green and yellow and often looks like it has virus. Maybe it has, and the lack of vitality that stops the unfurling of the leaves is due to that cause, or just as likely its the lack of light causing stress in the affected plant, which can't then unfold it's leaves. Sending to the labs will establish the cause, visual inspection is not enough.

With every other genus people accept that lack of light causes foliage damage, but in Canna there is a vocal minority who cannot acknowledge that poor light causes foliage stress, even though all learned treatises for 150 years state that Cannas must have their 8 hours of light every day. It beggars belief! If they don't get their 8 hours of light, what do they do? Start dealing cards and join a poker school? Of course not, they display stress through the only mechanism they have, i.e. their leaves. Now they have a limited vocabulary and such stress can easily be mistaken for one of the few virus types that affect Canna foliage. 

The defintion of chlorosis is "The loss of chlorophyll from the tissues of a plant, resulting from microbial infection, viral infection, the action of certain phytotoxins, the lack of light, to magnesium or iron deficiency, etc. Chlorotic tissues commonly appear yellowish. "

Lack of light, infection, and mineral deficiencies causes chlorosis. Can you see the mountain?

Mineral deficiences in plants

In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green colour of leaves, chlorotic leaves are pale, yellow, or yellow-white.

The affected plant has little or no ability to manufacture carbohydrates through photosynthesis and in extreme cases may die unless the cause of its chlorophyll insufficiency is treated. Specific nutrient deficiencies (often aggravated by high soil pH) produce chlorosis, which may be corrected by supplemental feedings of missing compounds in various combinations. Different mineral deficiencies act in subtly different ways.

Deficiency of Nitrogen (N)
The characteristic deficiency symptom of nitrogen is the appearance of uniform yellowing of leaves including the veins, this being more pronounced on older leaves. The leaves become stiff and erect. If the condition of nitrogen stress persists, then the result is decreased foliage and shoot growth.

Conditions inducing Nitrogen deficiency include heavy rain causing leeching, low organic matter content of soils, denitrifcation (losses of N2 and N2O to the atmosphere).

Deficiency of Magnesium (Mg)
Magnesium deficiency causes yellowing, but differs from that of nitrogen. The yellowing takes place in between veins of older leaves and veins remain green, this is followed by necrosis (unnatural death) of tissues. Interestingly, Mg deficiency may be induced in tomatoes by high levels of ammonium in the nutrient solution (Kafkafi et al., 1971).

Deficiency of Iron (Fe)
The principal veins remain conspicuously green and the surrounding portion of the younger leaves turn yellow. Conditions inducing Iron deficiency include calcarous soils, soils high in P, Mn, Cu, or Zn, high rate of liming.

Deficiency of Potassium (K)
Under potassium stress condition, the yellowing of leaves starts from the tips or margins of leaves extending towards the center of leaf base. The yellowing is interveinal and these yellow parts become necrotic (dead spots) with leaf curling.

These are some of the more common causes of mineral deficiency, and as there are many more minerals making a contribution to the Cannas growth, then we can see that these are the first causes that should be investigated when chlorosis is spotted on foliage.

What is the best way to overcome these Environmental deficiences? Well, that is obviously to deliver the missing minerals to the chlorotic plant. The best immediate source of trace minerals is a liquid feed with seaweed fertilizer. However, that is only a temporary fix, as the basic soil deficiency has to be corrected by introducing the missing element(s).

And what happens if there is no improvement from the upgraded feeding regime? Then it is now time to think the worst and start considering the possibility of chlorosis induced by Canna virus, more of which later.