Saturday, 26 April 2014

Horse chestnut scale and azalea gall

Slightly Unusual Problems
Horse chestnut scale
      I was looking at my picture library and a couple of things stood out which may be worth a few words: the first one is horse chestnut scale (Pulvinaria regalis). The poor old conker tree, which is currently suffering attacks by a number of enemies, has lent its name to this one although lime, sycamore, cornus, elm, magnolia, acer and bay laurel are also prime targets. It is an unwelcome immigrant from Asia, probably introduced on plants, and is most common in urban areas. Apparently the reason for its prominence in these parts is down to the fact that gardeners and park-keepers sweep up leaves and, lodging on them, the pupae of a tiny parasitic wasp which influences the spread of scale - a case of babies and bathwater in the cause of tidiness. On occasion a whole trunk can be covered with the females shown, giving it a mottled appearance.

      The females shown in the picture breed by a process of parthenogenesis - don't mate with males- so that a close look shows them looking pretty bored. The white 'skirt' is where the eggs are, about 2,000 per scale, and mother dies when she's finished laying. The corpse remains attached to the egg sac, giving some protection to the contents but presumably not much satisfaction to mum.

      All scale are sap-suckers but usually the host plant is so large that there is little real damage apart from aesthetically. This is good because controlling the problem on a large tree, short of burning it to the ground, is next to impossible. This brings to mind the old Benny Hill sketch where he pulverises a tomato plant with a large lump hammer:

      "Don't do the tomato much good", he says with a cheeky smile and what I take to be a west country accent, "but it gets rid of the greenfly". For more about horse chestnut problems go to this.
Azalea gall
      The second thing worth a word or two is the Azalea gall (Exobasidium vaccinii). I first saw this many years ago on an evergreen azalea at Bodnant Gardens and, in my ignorance, thought it was a fruit. However it turns out to be a fungal problem and it fairly quickly becomes white with spores which are thought to be passed to other plants via rain splashes. From what I can make out, the one in the picture is fairly unusual in the regularity of its shape - usually it is far more lumpy and can look a bit like peach leaf curl.  Flowering can be reduced, so the galls are best removed before reaching the white, spore spreading stage. I have seen a recommendation that the infected plant should be sprayed with Bordeaux mixture early in the year, but have no experience of the efficacy of such treatment, so retain an open mind.

     The main thing my researches have come up with is the fact that no one seems to know a lot about the problem so, if you're really worried about it, try growing spuds.

Saturday, 12 April 2014

Marigold and Rue

Marigold (Calendula officinalis)
From our supermarket - stocked citadels we tend to see marigolds as simply a pretty flower providing a splash of annual colour in the garden. However, there's a bit more to them than that:

The common name comes from 'Mary's Gold', as it was so called in honour of the Virgin Mary. Why this should be is open to conjecture, but the scientific name, Calendula officinalis is a bit easier to explain: 'Calendula' comes from the Latin 'Calendae', meaning the first day of the month and possibly refers to the fact that, in its native Southern European and North African habitat, it can often be seen flowering throughout the year; 'officinalis' applies to plants with perceived medicinal properties. Dipping a leaf in boiling water for a second, then bruising and applying it to a wound controls bleeding and speeds the healing process. When you hear a fact like this, there's a tendency to think this would be really useful if you were to injure yourself in the countryside. However, if you think about it, the presence of boiling water on the spot is about as unlikely as a comfrey plant growing next to the nettle that stung you. (I think it probable that no one is absolutely sure whether comfrey eases nettle stings, because by the time you find some the pain has naturally dissipated or you've died of old age).

Herbalists also use marigold internally for a bewildering list of ailments ranging from colitis to athlete's foot and as if its medicinal properties aren't enough, the plant has numerous uses in the kitchen: a complete flower dropped into a stew will add a pleasing flavour, while the petals have a similar effect in salads and soups. It also provides a pretty good substitute for saffron because, when soaked in milk or water, it can be used as a colouring for rice, cakes and puddings.
Rue (Ruta graveolens)
Not all plants are as benevolent as the marigold: rue (Ruta graveolens), derives its name from 'graveolens', meaning 'heavily scented' and 'rue' refers to 'bitterness' or 'unpleasentness'. The latter feature manifests itself through its powerful oils. In contact with the skin, these render it sensitive to sunlight, resulting in eruptions similar to those caused by giant hogweed. In nurseries the gardeners wear protective gloves which cover to the elbows when they are dealing with the plant. Although seen as a tonic and stimulant to digestion in small doses and chewing a leaf may relieve tension headaches, it is toxic in stronger solutions, so should be used advisedly. Sprinkled dried and powdered over seeds as sown, the herb protects against seed - eating birds and insects who presumably don't like the potential skin eruptions or death which it promises, and, rubbed through the coats of dogs or cats, it repels fleas.

The variety 'Jackman's Blue' is readily available in garden centres and the 'blue' the name offers gives a nice evergreen contrast to a bed, or, at a height of about two foot, provides an attractive low hedge round a border. Apparently neither rue or basil will thrive if planted close together, although this is a problem I've not personally encountered.