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Euphorbia Milii Problems

Euphorbia milii hybrids are remarkably problem free plants. Virtually all the problems we see are because we grow them in such large numbers and have been doing so for so long. Young, vigorous plants in good quality growing media, grown a few at a time in relative isolation will get few if any of the following problems.

NUTRITIONAL PROBLEMS:
Given regular feeds along with micronutrients will prevent most problems. An organic slow release material like pelleted chicken manure will also help. The following problems can sometimes be seen:

MACRONUTRIENTS:

NITROGEN:
Lack or low amounts will lead to general lack of thrift and weak, pale growth. Nitrogen is best provided in Nitrate form to prevent soft growth. Excessive amounts lead to rapid, soft growth that is susceptible to disease.

POTASSIUM:
We have never had a problem with this element due to the use of coconut coir media and Potassium nitrate in our feed.

PHOSPHOROUS:
Lack tends to give slow growing, deep green plants. Large amounts cause excessive stem elongation and soft vegetative growth. This is contrary to the general notion that high P will give extra flowering. Plants that are starving will respond to extra P (and almost any fertilizer) but will soon grow too vigorously. We tend to hold P and use it to control growth- if plants are too slow and compact we give P in the form of Phosphoric acid or mono Potassium phosphate to boost growth.

CALCIUM:
We use Calcium nitrate in our feed and as yet haven't had any problems that can be attributed to Calcium deficiency. We have seen some bract edge necrosis which may be due to Calcium shortage but it's very uncommon.

MICRONUTRIENTS:
Euphorbia milii shows distinct micronutrient deficiency symptoms but these are usually seen on old plants growing in the same media for a couple of years or because the media binds a particular nutrient. The main reason is probably rise in media pH though some nutrients get bound to organic materials (e.g. Copper) while others are easily leached away (Boron).

BORON:
Deficiency symptoms include rapid reduction in the size of sequential new leaves with distortion till the newest leaves are tiny, black and abortive. The growing tip dies and surrounding stems show corky tissue. Response to a dilute drench of a Boron containing material such as Borax is rapid. Usually seen in plants in extremely well drained media that has not been replaced for two or more years.


Severe Boron deficiency- note the corky tissue just under the growing region.

Euphorbias are sensitive to excess Boron and will show leaf burn with doses that Adeniums will easily accept. That's why we do not use Boron with Euphorbia on a routine basis but if we see plants with symptoms, all plants are given a very low dose by drenching.

ZINC:
Like Boron, mostly seen in mature plants in old media. Leaves become somewhat smaller and show a yellow chlorosis and typical bending to one side as if one half of the leaf is growing faster than the other.


Zinc deficiency- the side ways, asymmetric growth of the leaf is typical, along with some chlorosis.

A spray with chelated Zinc will correct the problem. We also use Zinc sulphate along with the Copper sulphate drench as a preventive

COPPER:
We see this once in a while, even on young plants. It occurs because our highly organic media binds Copper, making it unavailable to the plants. Symptoms are typical and distinctive: new leaves remain tightly closed, trapping emerging leaves, leading them to bunch up at the top of the plant in a twisted mass. If not treated immediately, the outer leaves will not open and will need to be torn off manually to allow normal new leaves to emerge after treating with Copper.


Typical bunching of new leaves- copper deficiency prevents full opening of new leaves, so emerging leaves get trapped.
Usually these intertwined leaves will have to be opened up manually to allow normal growth, even after treating with Copper sulphate.

Use a drench of 50 grams Copper sulphate per 1000 Liters of water to solve this deficiency; use half that dose every six months to prevent it. Zinc sulphate can also be added to the drench.

IRON:
Deficiency is seen as a chlorosis on younger leaves. Rarely seen, and if so usually on plants that have been pruned and are giving many new shoots.



It may be a result of gradual increase in media pH due to the use of Calcium and Potassium nitrate and alkalinity in the water. We now use acid (Phosphoric and Nitric) to bring the water pH down to 5.4 or so.

PESTS:
Though Euphorbia milii is resistant to most of the common horticultural pests, we have a fair share of specialist pests which seem to target Euphorbiaceae. This may be because another succulent Euphorbia is a common hedge plant around us and some of our common weed species may also support these pests so we do keep our eyes open. That said, these pests are a minor irritant rather than a regular problem and we do not need to spray pesticides more than a few times a year.

LEPIDOPTEROUS LARVAE:
These are several species that will eat Euphorbia milii- though I am not aware of which species is involved, the two most common are the Looper and the Web Forming caterpillars.

The Looper starts small and grows relatively slowly and if spotted at an early stage, the damage is minimal. However, we sometimes miss them and when full grown they can eat through a batch of seedlings from top to bottom. You can spot them by looking for partly eaten leaves and their frass- this may be dark green to black if they are feeding on leaves and colored if they are gorging on flowers. Fresh, moist frass means the caterpillar is near by - follow the spoor and hunt it down!




Above: Loopers start out tiny and difficult to spot. Color is also variable, depending on whether they have been eating flowers or leaves.
Left: A big caterpillar can do a lot of damage - the chewed up leaves and frass on this plant is obvious but we should have got it at an earlier stage

Spraying is rarely needed- just pick them up before they become adults and start an epidemic. Our experience with Lepidopterous pests is that they normally stick to the food that they were reared on. Once in a while they will jump species onto an ornamental and then the adults will continue to lay eggs on this new species. If these early adapters are eliminated the problem is usually sorted out for a while.

The eggs of web forming caterpillars are laid in groups and the presence of these pests can be easily identified by their web. It's a dark mass littered with granular frass that they spin around themselves to form a nest. They will eat the whole top of plants and bore into the soft stems.





Web forming caterpillars can be inconspicuous at the start but will hollow out thick stems in a couple of weeks. Small plants like this seedling on bottom left can be killed by them. Usually they are many caterpillars in each nest and they are rarely seen- the photo on bottom right shows one.

The actual caterpillars are difficult to spot unless the web is torn apart and stems pressed. We just cut off the affected stems- web, caterpillars and all.

MEALY BUGS:
These are real problem pests and are extremely difficult to get rid off. They will affect all soft growth including the shoot tips, flowers and roots.



Mealy bugs in flowers are difficult to see and very persistent, since most sytemics don't get to the flowers. Cut off all flowers when treating with Imidacloprid to get long lasting cures.

Over the years we have tried everything including Imidacloprid (Marathon, Confidor & other brands); nothing is totally successful. This is partly because it's difficult to get the systemic insecticides to enter flower tissue- it's a good idea to cut off all flower stalks before treating with systemic insecticides, especially if the infestation is persistent. We now spray with Neem and use physical means of elimination- use a brush to just rub them off or paint them with alcohol. Control of ants, have a symbiotic relationship with mealy bugs, also helps.

Its best to avoid the problem in the first place- check all new plants for mealy bugs and other pests before bringing them into a collection. Old plants that look weak and have lost their vigor are the most likely to harbor these chronic pests. So are rapidly grown plants with soft growth and low resistance.




Above: Mealy bugs are usually seen on soft young growth, where they look like soft, white or pinkish cottony growth. These insects can move along plants quite well and are often associated with ants..

Left: Under some conditions, they may creep into nooks and crannies such as this graft union- here they are almost immune to insecticides and will form an egg cocoon, which will later hatch to give a new generation of mealy bugs.

Root mealy bugs are difficult to spot- ants going in and out of the media are often the only indication of their presence. Plants that are neglected, allowed to dry out and planted in very open, soilless media are most affected. Knock out and examine the root ball of any plant that looks unthrifty for no special reason but don't mistake perlite or Styrofoam in the media for mealy bugs (I often do)! A hand lens serves well in such situations.

Recent improvements in our growing techniques have resulted in much healthier plants and a noticeable decline in mealy bug populations and vigor; I now think that a substantial and persistent problem with mealy bugs (and maybe Spider mites on other plant species) is an indication of plant stress and growers and hobbyists must look at overall cultivation techniques and standards in such situations rather than just try to eliminate the pests directly (think strategy rather than only tactics!).

BEETLES:
We have problems caused by one small beetle - because of its color we call it the Golden Beetle. It's small, up to 3mm long, and causes limited damage unless in large numbers.



Skeletonized leaf with the culprit on top Flowers are eaten too- the beetle can be seen at the top of the picture.

These beetles feed on the epidermis of young leaves and flowers and the areas where they have fed are skeletonized rather than clean cut like typical caterpillar damage. They tend to jump off when disturbed but with some practice they can be caught and crushed.

If present in large numbers, we spray with a pyrethroid or organophosphate insecticide. It is important to use a fine spray from a distance so that a mist falls gently on the plants- the beetles will other wise jump off and may not be hit by the spray.

SLUGS:
Euphorbia would seem an unlikely food for slugs, with their poisonous sap and sharp thorns. However, we sometimes see some damage to plants kept on the ground; the only evidence that the damage is due to slugs is the silvery slime trails they leave behind.



Compact, heavily branched hybrids are more susceptible as they afford cool moist zones within their clustered stems. Slugs are not a big problem and can usually be found- most often under the pots. Crush or throw into salt water to kill.

OTHER PESTS:
We haven't had problems with any other pests so far. Euphorbia milii plants seem totally immune to spider mites as of now nor do I remember ever seeing scales on these plants. I have seen two problems in other countries that merit attention:

WHITE FLIES:
I saw a lot of these with a grower in Bangkok- he is an excellent grower but the plants were being grown too fast and soft. They did not seem to be causing any damage to either the plants or the flowers and I have not seen them in subsequent visits to the same grower. Nevertheless, it shows that the plants are susceptible, at least under some situations.

THRIPS:
I saw a lot of thrips damage at a specialist commercial grower in Holland. In fact several new varieties being tried by him were rejected because of thrips damage to the flowers. The popular variety Vulcanus was unaffected in the same greenhouse.


A pink variety under trial with a large Dutch grower of Crown of Thorns: severe thrips damage can be seen. I must mention that the grower did not take even basic anti thrips measures, since his main cultivar, Vulcanus, does not show any damage at all.

We have never had thrips damage on our Euphorbias or Adeniums; this may be due to the fact that we grow in the open with plastic only on top and populations of thrips do not build up as they would in a closed greenhouse. I do feel the grower could have done more about the problem, such as not holding over material from year to year and fumigation of empty greenhouses but he chose to simply avoid susceptible varieties and grew Vulcanus almost exclusively. This show's how new varieties can fail commercially, however good they are in limited trials.

DISEASES:
Despite its succulent nature, Euphorbia milii is quite resistant to disease. Partly this is due to its intrinsic toughness but selection of the right clones also plays a part. For example, some Thai hybrids are very susceptible to leaf spot- we have discarded most of these in our own propagation program.

SEEDLING DAMPING OFF:
Very young seedlings are susceptible to various soil borne diseases; using a clean, disease suppressing media probably helps but nevertheless it does strike once in a while. Planting seeds in plug trays or at least separate community pots as opposed to seed pans can limit the damage to a smaller number of seedlings. Disease is spread by water drops so avoid splashing while watering and isolate affected pots.

It is a good idea to use new pots and high quality, well drained media to sow the seeds and to keep the pots evenly moist- cycles of bone dry to sopping wet are supposed to stress and damage tender roots and predispose to damping off.

STEM ROT:
Discoloration and soft rot of stems occurs primarily with cuttings being rooted in poorly aerated or disease infected media. Once plants are established there is little or no problem except under exceptional circumstances like extensive leaf rot during the monsoon progressing into the stem.



Soft rot of cuttings is seen within a few days of sticking. Dry rot of established plants is occasionally seen, especially in old and neglected plants.

Generally, by the time the problem is noticed the cutting is lost. It is best to throw away diseased material from the propagation area along with all fallen leaves.

Dry and wet rots of mature plants can occur are but surprisingly rare for a plant which is definitely succulent. In case the problem occurs on a larger plant, cut off the diseased portion well into healthy tissue.

LEAF & FLOWER DISEASES:
Compared to the stem, the flowers and leaves are more susceptible to disease. Mostly these occur when plants are exposed to long periods of wet weather.

LEAF SPOT:
Brown or black spots, most likely of fungal origin, form on mature leaves. Some cultivars are particularly susceptible. The solution is to keep the plants clean and spray with a systemic fungicide like Tilt whenever needed.


Leaf spot on Poysean leaf- note the halo around each spot.

LEAF ROT:
This is primarily a monsoon disease- when closely packed leaves (particularly in large leaved yet compact cultivars like Sri Amporn) cannot dry for days on end, they begin to rot. Soft, brown rot spreads on the affected leaves and flowers, causing the whole mass to stick together. If allowed to progress, fine, thread like fungal hyphae can be seen. We grow almost all our plants under plastic now so this problem is rare and occurs only on really dense growth because watering is still by hand. Drip irrigation should eliminate this problem altogther.

BOTRYTIS:
Similar to the above and occurs under similar conditions except that flowers are more affected and the fungus forms profuse amounts of spores, which fly off like smoke with the slightest disturbance. Again, the solution is to keep the leaves and flowers dry.



ODD PROBLEMS:
Some odd problems we have seen over the years:


Cascuta or Dodder, a complete parasite, grows vigorously on E. milii and is almost impossible to eliminate if established- the tiniest piece will re-grow and spread. Though rarely seen, this is a potentially deadly problem if neglected as it can spread rampantly in a short time.



Monstrose growth on the otherwise excellent Poysean cultivar Duang Tavang: the stem on left is affected while the one on right is normal. This kind of growth is seen only in this cultivar. A closer view shows small leaflets instead of axillary buds, so these growths never flower or branch. They do grow very aggressively and need to be removed as soon as noticed.


We all know Euphorbia milii is toxic but this one can bite! Many years ago we found this small but deadly saw-scaled viper hidden within the thick growth of an E. milii mother plant. Luckily it was spotted before it bit someone. We now rarely see snakes at the farm- human activity has driven them away.

This picture also illustrates how soft, lush and green our plants were then, due to liquid feed containing NPK agricultural fertilizers.

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