Plants are living material. They'll stay healthy if we make sure
all the climatological conditions are right. We've already stated
earlier that this involves light, air, water, clean surroundings,
and green fingers. Controlling the climate, in all its aspects,
is the best way to prevent diseases and insects. That doesn't
mean that the careful weed grower, who has everything well in
order, will never be bothered by plant diseases and pests. We do
want to say that good climate control considerably reduces the
risks of disease.
8.2. Diseases
An easily preventable form of disease is deficiency- or
deprivation illness. The plants lack some necessary ingredient in
their feeding. A shortage of iron produces yellowed (and falling)
leaves. The pH value plays an important role in the prevention of
deficiency disease. Keep the pH value around 5.8. If this value
is too low, the plants can't absorb calcium as well. Consequence:
the osmotic processes are impeded. Too low a pH number causes
less iron in-take, with the well- known results. A second form of
deficiency disease is caused by a shortage of the primary
nutrients (NPK). It often involves a lack of nitrogen (N). A
nitrogen shortage delays growth, and makes the lower-most leaves
turn yellow and drop off. Less often, we see a shortage of
phosphate (P). With a phosphate shortage, the leaves turn deep
green, and they remain small. Yellowing and dying lower leaves
happen here, also. Potassium shortage (potassium is 'K') is
another seldom-occuring problem. The noticeable feature is first
the yellowing of the point of the leaf, after which the whole
leaf turns yellow and brown, and dies off. A lack of potassium is
more often caused by an acidic soil than by an actual potassium
shortage. So, make sure to maintain an optimal pH! The remedy
advised for these kinds of deprivation sicknesses: use NPK
fertilizer. We don't encounter deficiency disease as a
consequence of a shortage of the secondary nutrients very often.
This usually involves a lack of magnesium and/or calcium. It can
usually be remedied by using an NPK mixture containing trace
elements. The same counts for the micro-elements. We must make an
exception for iron, since there is rarely too little iron. In
that case, the pH value is usually too high. Moulds can
completely destroy a garden in a short time. If the climate in
the grow room is well-controlled, moulds, in general, have little
chance. Moulds and fungi thrive very well under hummid
conditions, preferably without much air circulation. Under these
circumstances, mould spores, which are always present in the air,
search for a spot to grow into mould cultures. If you don't
succeed in preventing mould growth, then you must do something
about it as quickly as possible. With light mould growth,
immediately remove the affected plant parts, and then create a
climate in which cannabis does well, and moulds don't (good
ventilation, control of humidity and temperature, and putting
your plants on a medium which is not too wet). If there's already
too much mould present, you don't have much choice but to spray
with poison (fungicide). Repeat the treatment after a few days,
even if you think the first application has definitely helped.
Still,; improve climate control and groth conditions. Fungicide
treatment should always be a last resort. It's not healthy for
young plants or people, so here, it's also: 'prevention is better
than cure' An often-occuring mould affecting cannabis is pythium.
This mould causes root-rot, and rot in the lowest part of the
stem. It appears most in young plants, and in cuttings. Larger,
healthy plants are less sensitive to pythium. Plants get
'falling-over disease' with a serious pythium attack. We don't
have to explain what that means Pythium is recognizable by the
bark at the base of the stem turning brown. In the beginning, the
'brown attack' is easily removable. Later, the rotting process
eats deeper into the base of the plant. Pythium is a fungus which
flourishes best in wet and humid environments. Pythium spores
spread only through water. Two kinds of spores are formed;
Swarming ones and stable ones. The swarming spores germinate best
at a temperature of approximately 15 degrees Celsius, while the
stable spores germinate if it's relatively warm; around 28
degrees C. To prevent a pythium attack, a constant temperature of
the soil or rockwool is needed. Large fluctuations in temperature
should be avoided. Pythium can only be fought in a limited manner
with chemicals. A proper relative humidity must also be
maintained (not too high). Leaf moulds, such as mildew, and
thread moulds occur less frequently than pythium. Mildew can
cause tops to rot, among other things. Also here counts: ensure
optimal climate control. Contrary to other moulds, mildew
flourishes well at a low relative humidity. Mildew can be more
easily fought with chemicals, and fortunately, is not often found
with cannabis. Rotting tops occurs the mainly at the end of the
flowering phase. The more compact the plant, the bigger the
chance for tops to rot. You can identify toprot by the sudden
yellowing of the top-most leaves. These yellow leaves are fairly
loose on the plant, and can be easily removed. To prevent the
whole plant from being affected, you must, unfortunately, remove
the whole top. The appearance of toprot can be prevented in some
cases, by lowering the relative humidity during the dark period.
8.3. Plagues and Pests
The most frequently occuring plague in cannabis cultivation is
spider mite. A spider mite isn't an insect, as many people think,
but actually a tiny spider. A spider mite is small, and difficult
to discover for the inexperienced eye. But the damage caused is
certainly visible. The mite feeds on the sap of the plant, mostly
underneath leaves. White specks appear on the upper side of the
leaf. After that, you can find spider mites on the undersides of
the leaves, and on the stem of the plant. Spider mites make small
webs, which you can detect by spraying with water. If there
aren't to many spider mites, you can try to get rid of them by
removing them by hand. A tedious job spidermites predator mite
Treating with insecticide generally gives a better result. In any
case, repeat the application after a few days, otherwise, you
risk the chance that the whole garden will be eaten. Spider mites
can also be controlled with their natural enemy Phytoseiulus
persimilis; a predator mite which feeds on spider mites. White
flies are also a formidible opponent of the weed grower. It can't
be repeated enough: control the climate, and take care of healthy
plants. Then, insects will have the least chance to
propagate.
white flyassassinator wasp
White flies behave just like spider mites. The insect hides
underneath the leaf, and sucks it's dinner from it. Result: white
spots on the top side of the leaf. White flies are easily spotted
with the naked eye. If you shake the plant a little, they'll fly
around. They look like little white moths, around 2 millimeters
in size. A sizeable infestation can be combatted with
insecticide. If you're not so anxious to use such strong methods,
you can purchase a certain type of 'assassinator' wasp: the
ichneumon fly (the Latin name is Encarsia formosa). This natural
enemy doesn't sting people, but works well at eliminating white
flies. Since it's only a small wasp (smaller than the white fly
itself), it takes a while before all the white flies have dis
appeared. Additionally, you have to put new assassinator wasps
out approximately every two weeks.
lice thrips
Another common herbivore is thrips. They are small, fast-moving
insects with wings. They rasp, or grate the leaves open, and then
suck the sap out. Thrips prefer bloom tops, and fresh, young
leaves. Affected leaves have shiny, silvery spots. This is caused
by the thrips, which suck the chlorophyll out of the leaves. In
spite of the fact that they're small, you can see thrips marching
in columns on an infested plant. Thrips can be fought with
insecticide. It's more environmentally friendly however to
unleash the thrips' natural enemy: the predator Amblyseius
cucumeris. Lice are found inside as well as outside. During the
summer, when lice do the best outside, they also do as well
inside. Lice are the most interested in plants with questionable
health. There are two methods to kill lice: spraying with
insecticide, and setting out assassinator wasps. The problem with
most flying pest- destroyers is that they're attracted by the
high-pressure gas lamps, which draw them to a fiercy death.
8.4. Summary
The starting point for cultivating cannabis is successful climate
control. This goes two ways: the plants do well and produce the
greatest possible yield, and diseases and pests get the least
possible chance. So, create a good climate, and don't forget
hygiene If you're bothered by diseases and/or insects, preferably
use natural methods of control rather than chemical remedies. You
can fight your pests by releasing their natural enemies, or by
spraying with organic solutions for diseases and/or pests. Use
chemical pesticides only if nothing else works. Always stop using
pesticides a few weeks before harvest, otherwise, you'll be
smoking some of the poison later. Ultimately, fighting diseases
and pests works best only if you know how to optimally control
the climate at the same time. Along with climate control, the
prevention (and if necessary, curing) of deficiency disease
demands an optimal mixture of fertilizers, and the control of the
pH.
INDEX
Absorption power, - of leaves
Air, - intake of water
Air exchange ventilator
Air humidification Air pump Algae growth, - prevention of
Amblyseius cucumeris America Bird feed Boccaccio Boron Box
ventilator Buyer Calcium Capillaries Carbon dioxide Carbon filter
ventilator Cellulose China Chlorophyll Clean-up Climate control,
- after harvesting - with regards to diseases and insects CO2, -
controller - enrichment and growing tempe rature - necessary for
cannabis - raising the content of Combination lamps Communicating
vessels Cuttings, - and climate control - and hygiene -
illumination period - necessities for - transplanting - waiting
time for Cutting tray Dark period, - and relative humidity Dark
response Decontamination Deficiency disease, - and the pH value -
due to improper feeding - prevention of Diseases Dodoens Drain
sets Drain water Drying Dumas Electrical ballast equipment
Electrical conductivity (EC), - calibration of EC meter - EC
meter - EC value - optimal EC value - optimal EC value for
cuttings Encarsia formosa Fertilization, - influence on THC
production Floor Fluorescent lamps Flowering period Flowering
phase Fungicides Generative phase Glucose Golden Age growing
space, - contents of - layout Growth, - principals of Growth
phase Growth point of cuttings Halogen lamps Harvesting, - female
plants - male plants - methods of Heating element Herodote
High-pressure gas lamps, - and safety - cleaning - life of - use
of Hugo Illumination period, - in the flowering phase - in the
growth phase Immersible pump Insecticides Insect pests Internode
Iron Irrigation system, - construction of - testing of - with
timer clock Lace -wing flies Ladybugs Lamps, - 1000 Watt - choice
of - distance from the plants - light yield - power Law of
minimums Law on narcotics Leaf green Libra trays Lice Light, -
blue - red - wavelength of Light bulbs Light intensity Light
response Magnesium Manganese Matt white paint Medicine, - hemp as
Mercury -iodide lamps Moulds, - sprays against Mother plant, -
for cuttings Necessities for home growing Netherlands, The NPK, -
remedy for deficiency disease Nitrogen Nutrients, - micro -
primary - secondary Osmosis Osmotic filter Outside air, - CO2
content in Over-fertilization Paris Polyethylene filter
Polyethylene hose pH meter, - calibration of pH value, - for the
roots of cuttings - ideal Phosphate Photolysis Photosynthesis
Phototropism Phytoseiulus persimilis Plant physiology Potassium
Predator Pruning Pythium Rabelais Reflective value Relative
humidity, - for cuttings - for the roots of cuttings Remedies, -
for diseases and pests Rockwool blocks Root hairs Safety, - and
high-pressure gas lamps - and use of electrical power - and water
- 'invisible' cultivation Saltpetre/phosphoric acid Salts, - and
osmosis Sap flow Semi-professional, - growing Shopping list
Sifting Skytes Skuff Sodium lamps Soil -the conditioning of
Sowing Spider mite Sprinklers Stomata, - function of -
vulnerability of Storing, - of the harvest Sulphur Super-wide
-angle reflectors Table fan Temperature, - and air exchange
ventilator - for rooting clones - ideal - in the dark period - in
the growing space - in the plant - of the ground - of the
nutrient water - when calibrating EC and pH meters Thermometer
Thrips Timer switch Topping Toprot Trace elements Vegetative
phase Ventilation, - and CO2 needs - and relative humidity -
capacity - drawing off heat - for rooting clones Ventilation
system, - construction of Vinkenoog Water, - functions of -
quality of Water purification White flies Wide-angle reflectors
Zinc.
spidermites 
predator mite
white fly
assassinator wasp
lice 
thrips