Story at a Glance
- If an insect is attacking a plant, there is some indication the plant is not healthy.
- The fastest way to determine plant health is to test the plant leaf sap with an optical refractometer to measure plant sugars or Brix levels.
- Plants with Brix leaf sap in the 12-20% range are healthy, under 12% are often unhealthy.
- Over 8% Brix, water use reduces up to 50% and insect resistance begins.
- Half of plant sap sugars made in the leaves are sent to the roots and exuded into the soil to feed the microbes in the soil.
You may already know this, however by the amount of insecticides and fungicides purchased in Australia and from our customer on-farm research, we believe many don’t.
Foliar Fertilising – Really Effective and Saves You Money
We’re all suffering from the escalation of fertiliser costs, especially dry powder and granular products. Using foliar fertiliser sprays will reduce the total amount of fertiliser needed on your crop be it fruit, vegetables, trees or vines.
This is our thinking on crop health
According to Entomologist Dr Thomas Dykstra, insects do not attack healthy plants. Insects only feed on plants that are unfit, nutritionally poor, dead or dying.
What constitutes a healthy plant? According to Dr Dykstra, if an insect is attacking a plant, there is some indication the plant is not healthy. With modern farming methods using insecticides and fungicides, it is difficult to tell if the plant is healthy or unhealthy.
Measuring plant health
Is there an objective, scientific way to measure plant health?
You can send leaves off to a laboratory to have the leaf tissue analysed but that can take a week or two and your crop can suffer in that time.
Don’t rely on these indicators
Height: how tall or stunted a plant is does not indicate health across all plants.
Grow rate: bamboo grows fast, but is not the healthiest plant out there.
Greenness: iron will green up a plant temporarily.
Flowering: Only angiosperms are flowering plants.
Roots: Not all plants have the same root system. Think thick, long tap roots and fibrous shallow roots.
Even growth? Not necessarily the best measure.
I grow it myself. Can’t replicate elsewhere.
The fastest way we know to determine plant health is to test the plant leaf sap with a refractometer or a chlorophyl meter. The optical refractometer, in the photo above, provides a good reliable start and you get a result in a few minutes. It primarily measures brix levels (total dissolved solids) which gives an indication of plant sugars, minerals and vitamin content.
The chlorophyl meter is also handy to measure leaf health by measuring the chlorophyl content or “greenness” of your plants. The measurement quantifies subtle changes in plant health long before being visible to the human eye. Measuring chlorophyl levels will reduce the risk of yield-limiting deficiencies or costly over-fertilising.
You may already use a Brix refractometer to measure sugars in your fruit as a percentage of the total juice in the fruit. The refractometer can also measure sugar in the leaf sap. This is the important bit. Leaf sap sugars are primarily in the range of 1% to 20%. Plants (trees, vegetables or vines) with leaf sap in the 12-20% range are healthy, under 12% are unhealthy.
Photosynthesis is vital as it produces the sugars. Brix is the measure of photosynthesis (health) via the amount of sugar in the leaf sap.
Fifty per cent of plant sap sugars made in the leaves are sent to the roots and exuded into the soil to feed the microbes in the soil. A healthy plant takes care of itself above and below the soil as well as the microbes, that in turn help the plant.
Leaf Brix Chart
There are four levels in the leaf Brix chart measuring 1 to 20+Brix.
1-2 Brix – plants will die quickly. You can force feed them but they are not healthy at all.
3-7 Brix – plants have a fighting chance. You will need to feed them 1-2 times a week to keep healthy as they are not good at taking care of themself. MOST of our crops are in this range. Plants will stand up, not fall over, will grow, put out leaves, fruits or flowers but are not doing great.
At 6 Brix – plant secondary metabolites increase. Molecules that give it colour, flavour and smell kick in at 6 Brix. Eg vine ripened tomatoes you buy at the shop may only be 5.2 Brix and are tasteless. At 6 Brix, starting to smell like a tomato.
8-12 Brix – sword and shield. Plants can start to defend themselves. Water retention is better and water use reduces up to 50%. Insect resistance begins.
12-20 Brix – plant is objectively healthy with healthy components all over it. No insects or disease are on the plant. The food is fit for long term health and longevity. This is very rare on farms using current farming practice.
How to create high Brix
To be high in Brix, plants require 4 components.
Sunshine – UV light is required on each leaf. High density planting lowers sunshine coverage and lowers Brix levels.
Water – if you don’t have enough water, the microbes can’t swim and this won’t help the root system. If it’s too wet the microbes will drown.
Air – healthy aerated soil will help the microbes breathe. Compacted soil and high magnesium levels will lower the Brix level and will proliferate anaerobic microbes.
Nutrients – key nutrients are required to reach a high Brix to reduce or remove insect or fungal pressure.
In our next newsletter we’ll tell you
- what lowers Brix
- how to quickly increase Brix
- how to increase crop nutrient density and reduce costs
We’ll have to be quick with it because the growing season is under way. If you are impatient, you can always phone Kendon for the latest guidance about our theory on crop health.