Propagation Problems
Posted by Phytopath on Apr 1, 2011
Do your seedlings fall over and die? Or your newly taken cuttings turn brown and rot?
Losses can occur when propagating plants: many of these can be avoided if you are aware of the conditions that trigger or encourage disease.
The problems that can occur during plant propagation can be divided into two broad categories; soil-borne diseases and air-borne diseases and pests.
Therefore good hygiene should always be practiced in the area where you are propagating your plants.
Today I will cover the soil-borne diseases of fungi and nematodes.
Microscopic fungi can infect seed within 24 hours of sowing. The seed simply rots in the soil; this is known as pre-emergent damping off.
Rotting of the stem at ground level, commonly called damping off in seedlings or collar rot in established plants, is usually caused by a soil-borne fungus called Rhizoctonia. The plant sometimes falls over and at other times remains standing.
Root rot is another fungal disease where the roots start to rot from the tips and then travel upward toward the stem. One of the fungi responsible for root rot is called Pythium which can occur in both young and mature plants, the other is called Phytophthora.
Rhizoctonia
Rhizoctonia is most active in warm humid conditions, so ventilation is important.
The young roots of plants are particularly prone to attack and visual cues to look for include; a mass of mycelium threads that look like fine spider webs, on the surface of the pot and infected tissue often has a reddish-brown colour.
The fungus can survive on plant debris, weeds and in the soil, so keeping the area free of old plant material and weeds is important. 
Pythium
Pythium is a water mould and occurs when the rooting medium is over-wet. There are a number of different Pythium species which attack soft, young tissue. Softwood cuttings and newly germinated seedlings are particularly susceptible.
The fungus can penetrate the stem and enter the cells causing rotting of the tissues. It also has the ability to survive in soil without a host plant therefore is able to infect subsequent plants if the potting medium is re-used.
Phytophthora
Phytophthora prefers warm, wet conditions. These fungi grow rapidly when the temperature is between 20°C and 30°C.
Other favourable conditions include: poor aeration and drainage of the potting medium, excessive irrigation over a long period of time and cool, wet weather.
The spores are spread via irrigation water, tools and equipment and can overwinter for up to nine or ten years in the soil.
The root system and stem base of cuttings are prone to attack. Lesions can be seen at the base of the stem when the bark is removed.
Visible symptoms include foliar wilt, yellowing or dying back of foliage and eventually death.
Nematodes
Nematodes look like teeny weeny worms, not that you can see them with the naked eye.
They are spread by transferring soil already infested with adult nematodes and/or eggs, or in water or infected plant material.
They feed on plants causing swelling on roots (galls) and stems. Leaves can die and plants can show signs of stunting or poor development.
Different species of nematode can attack different parts of the plant.
As you can see from this short list, hygiene becomes extremely important when working with not only propagation material but general gardening practices.
Taking plant cuttings
Posted by Phytopath on Feb 13, 2011
It is almost my favourite time of the year.
I just love autumn. The deciduous trees colour up before losing their leaves.
The days are still warm but the nights start to get colder, but best of all, it’s the best time to take cuttings.
From late February until early May, semi-hardwood cuttings (Northern Hemisphere) strike the best.
The best material for taking cuttings, has high carbohydrate levels and low nitrogen levels.
To test this, use the ‘snap test’. If the piece of stem cutting snaps when you bend it rather than just bend, then it has low nitrogen levels and would have made a good piece of cutting wood until you just broke it. (she laughs)
The next selection criterion is the age of the stock plant.
Cuttings form roots much quicker when the material is taken from a young plant. Cuttings taken from older plants do not form roots as readily.
The area on the stock plant where the cutting is taken from is also important.
As a general rule, lateral growth (side shoots) is better than terminal growth (shoot tips). The lateral growth can often be removed with a heel. This provides a larger surface area for roots to develop from.
The size of the cutting will depend on the individual plant and how far apart the nodes are along the stem.
For small plants whose nodes are close together, a typical cutting would be 35mm to 60mm. Larger plants may need the cutting length to be 60mm to 80mm. But if you are taking cuttings from a plant like the Tree Dahlia – well, the nodes can be as much as 40mm or 50mm apart, so the cuttings will be quite long.
Non flowering material is best. If the plant has not quite finished flowering – wait for it to finish. If it is just starting to flower, forget about taking cuttings until flowering has stopped.
The time of year that you would take a cutting, is specific to each species of plant. Try a few cuttings throughout the seasons and see which works the best.
Time of day can also be important. Cuttings should be taken in the shade or on a cool day, not in the heat of a warm afternoon.
Make sure your secateurs or cutting implement is sharp and clean. Hygiene is important in the propagation area.
If you cannot deal with the cuttings immediately and need to store them for a while; wrap the cuttings in damp newspaper rather than leaving them in a plastic bag.
Root promoting hormones can be applied to the end of the cutting if you are not certified organic. The most common are IBA (indolbutyric acid), IAA (indoleacetic acid) and NAA (napthaleneacetic acid).
These root promoting hormones can be purchased as a liquid, gel or powder. If you are a bit clumsy, use the gel.
Local rose growers tell me they have great success with rose cuttings after soaking them in a bucket containing a solution of water and Willow twigs and leaves.
The environmental conditions where the cuttings are housed, is also important.
Moisture levels and humidity levels need to be correct for the species being propagated.
Temperature is also important and for most plants grown in warm temperate regions, the day temperature should be around 21°C to 27°C and the night temperature between 15°C and 18°C for best results.
If you can provide bottom heat near the base of your cuttings and ensure that the difference in temperature between the root zone and the air near the top of the cutting is around 10°C, then you will surely have success.
One last thing – make sure you put the cutting in the pot, the right way up.
Seed storage
Posted by Phytopath on Feb 25, 2010
Here in the Southern Hemisphere autumn is just around the corner. It’s time to start collecting and storing seed of your favourite vegetables, herbs and flowers.
When on a quest to collect seed, make sure you have all of the equipment ready and at hand.
You will need paper bags or envelopes, pen or pencil, glass jars, sieve, paper towel and silica gel crystals.
Most flower and vegetable seed have a viability of about three to five years under good storage conditions but there are always exceptions to the rule so this blog post is a general guide.
Generally, the larger the seed or the thicker the seed coat, the longer the seed will store for. Why don’t seed store indefinitely? Because they are a living organism and while in storage they are still respiring even if it is very slowly – a bit like being in a coma. So if you can provide optimum conditions while they are hibernating – they will last that little bit longer.
The aim is to keep the temperature almost constant and the humidity level low, 5% to 10% if possible. This should keep the life process of the seed at the lowest rate. For most vegetable seed the ideal temperature is around five degrees centigrade, so for long term storage a refrigerator would be ideal.
It is also extremely important that the seed are dry before storing. If the seed are damp they can soon generate their own heat and if they have been placed in a plastic bag or sealed container they will go mouldy. If they are not in a sealed container but in open-air conditions, the seed will absorb moisture from the atmosphere and if the temperature is to their liking, they may sprout.
The thickness of the seed coat will dictate the rate at which the seed absorbs moisture.
At low moisture levels the seed are also able to handle temperature fluctuations better.
To save storage space it may be beneficial to extract the seed from the fruiting body. A good example would be parsley seed. If you harvest the whole seed head, they are bulky and get tangled and just take up too much room, but if you rub the umbels between the palm of your hands or run them over a sieve, the seed easily falls out of the umbel and is much easier to store.
Label the paper bags with the name of the seed, the date, the place of collection and the collectors name (this could be a friend or relative from out of town). I also like to jot down any peculiarities the seed may have. For example “refrigerate for two months then warm, moist stratify for two months” or “extra long germination, up to 18 months”.
Place the seed in the paper bag or zip-lock plastic bag if you are absolutely sure it is dry, then put the paper bag into a glass jar (several small paper bags can go into one large glass jar). At this point, I drop in a silica gel sachet that I acquired when I bought my last pair of shoes, or that leather handbag [grin]. I am always telling friends to save those little sachets for me. Close the lid on the glass jar and place in the refrigerator, or at least in a dark cupboard where the temperature is pretty even.
A note about tropical and sub-tropical tree seed. They cannot be completely dried. Drying destroys the embryo inside the seed. Most sub-tropical seed have a very short viability and need to be sown soon after harvest.
Once they have germinated, the young seedlings can be held in their containers in a dormant state, if placed in a moist shady position. When they are given more light the growing process will continue.
Rain-forest seed are cool-stored in moist peat in a plastic bag until planted out. Palm tree seed can be stored and germinated in this way.
As mentioned earlier, there are always exceptions to the rule (there’s one in every crowd). Citrus seed cannot be dried out nor should they be stored under low relative humidity. They are best sown in moist sand and kept in high humidity under refrigeration.
If all goes well and you have managed to store the seed without any weevils or other insect pests, then you can hope for a good germination rate when the time comes to sow the seed.
