Friday, June 10, 2022

Miconia "Sound the Alarm!"

                                                  Clearing Miconia stand in Tahiti

Miconia calvescens, is a tree from 35 to 50 feet tall with large leaves up to 3 feet in length. Although attractive with its beautiful leaves, green on top and purple on the bottom foliage, it is perhaps the most invasive and damaging, alien plant species to the wet forest lands of the Pacific Islands. These trees will form a large, thick canopy which can produce 100% shade, killing out or inhibiting the growth of all native species below. Miconia plants are a threat to completely take over moist and wet forests.

Miconia was introduced to Hawaii as an ornamental in the 1960s and now poses a threat to completely take over forests receiving 75-80 inches or more of annual rainfall. If left uncontrolled, it is estimated that miconia could invade up to 121,000 acres on Oahu. On Maui 37,000 acres could potentially contain miconia.  Presently, the Big Island has large infestations on the windward side, particularly on the Hamakua Coast and smaller populations on the leeward side.

A single mature tree has the potential of producing 3 million seeds, two or three times a year. These seeds can remain viable in the soil for 10 years or more. The seeds are spread by man, through the mud on his boots and other equipment including bulldozers. Seed is also dispersal by birds; in Hawaii, dispersal is presumably by the Japanese white-eye, the common mynah and perhaps the northern cardinal. In trials in Tahiti, a square yard of the top 2 cm. of soil from a dense Miconia stand, produced over 17,000 miconia seedlings in six months.

Miconia was introduced to Tahiti in 1937 and has since destroyed nearly 70% of the native forests and is directly responsible for threatening 25% of their native forest species with extinction. Miconia also causes serious landslides due to its shallow root system.

Hawaii residents: For many years the Big Island Invasive Species Committee (BIISC) has worked to maintain a miconia-free buffer zone and to stop miconia from spreading to upper-elevation, pristine watershed forests. Funding is now inadequate to continue this focus. For more information, you may contact them at (808) 430-3090 or email at

Today, the strategy for control is to implement a serious of biological control measures: to introduce natural enemies from Miconia’s origin in Brazil. The approach is to use a variety of agents including weevils which bore out the stems, caterpillars which feed on the leaves, and other larvae which feed on flowers and seeds. The list of biological control agents also includes a fungus which attacks the leaves and causing premature leaf drop.  

Tuesday, April 5, 2022

Diatomaceous Earth, An Organic Insecticide

Diatomaceous earth (DE) is an inert dust mined from the remains of fossilized silica shells of certain algae known as diatoms. It is composed of approximately 3% magnesium, 33% silicon, 19% calcium, 5% sodium, 2% iron as well as other trace minerals such as titanium, boron, manganese, copper and zirconium.

DE works in two ways to kill an insect. 1) It absorbs water-protecting fats and oils from the outer, waxy layer on the surface of the insect and causes desiccation, or dehydration.  2) Being highly abrasive, DE scrapes and cuts the insect’s cuticle layer, contributing to more desiccation. However, it is virtually nontoxic to mammals.

Around the home, dusting the powder on the floor, carpets and crevices will kill cockroaches, silverfish, ants, and fleas.  Since the powder must stay dry in order to be effective, repeat applications may be necessary in humid areas; DE will be more effective in drier climates. It is also used to control beetles where grains are stored.

The same basic principles used to kill indoor insects can be applied to insects which attack plants outdoors. Some gardeners will dust plants with diatomaceous earth in order to kill insects such as aphids and beetles which feed on the plants. DE is moderately effective against slugs and snails as long as the material remains dry. The problem with outdoor use is high humidity and rainfall. When DE becomes wet, its effectiveness is diminished. DE, however, can be mixed with water as its carrier and applied to such targets as ant nests. When DE dries out naturally, it will begin to take effect. Nonetheless dusting plants with DE is the most effective application method. The dust can cause eye irritation so wearing goggles and a dust mask is recommended. 

Insecticidal DE is not the same as the DE used in swimming pool filters. Other chemicals are added to pool grade DE, and the product is heat treated. This causes it to assume a crystalline form and is a respiratory hazard. Pool grade DE should never be used for pest control.

Wednesday, January 5, 2022

Edible Landscape

Since the early 1900’s Americans began the great migration to the cities, and in doing so gave up their foraging practices. In earlier times people often searched their property and nearby fields and hills for edible food. In some parts of the world this is still a common practice. 

The time has come to begin foraging within our ornamental gardens and see what nutritional edibles can be gleamed. Caution: Proper investigation is necessary to verify that the chosen plants are safe to eat.  Consuming the wrong plant can be disastrous.

Here is a short list of some well-known edibles in the United States. Check the internet, especially university websites for a more comprehensive list.

A. Weeds - If you can’t beat them, eat them!
1. Dandelions, Taraxacum officinale -Fresh dandelion leaves can be eaten raw, in salads, added to a stir fry, or boiled and steamed like spinach. They have a bitter taste, but boiling will help take that out. Dandelions also make a great addition to soups and stew. They are high in carotenes, iron, calcium and vitamins A and C. As a detoxifying agent, dandelions aid with liver, urinary and gall bladder disorders, diabetes and high blood pressure. Dandelion root tea is sold in local health food stores. 
2. Lamb’s quarters (Chenopodium album) is also called wild spinach with similar nutritional value to spinach. 
3. Burdock (Arctium Lappa) is a weed rich in potassium, iron and calcium. 
4. Common mallow (malva neglecta) the leaves, stems, and immature seeds are eaten raw or cooked. Mallow is reported to be rich in calcium, magnesium, potassium, iron, selenium, and vitamins A and C.
5. Purslane (Portulaca oleracea) is a succulent; the leaves, stems and flowers can be eaten either fresh or cooked. The leaves contain more omega-3 fatty acids than any other leafy vegetable plant.
Other edible weeds include chickweed, white and red clovers and plantain.

B. Edible Flowers
1. Marigolds are one of the most commonly grown ornamental annuals. When dried and crumbled, the petals of marigolds can substitute for the most expensive spice in the world: saffron. 
2. Roses, both the petals and the rosehips (fruit), are edible. Rose water is often used in scones, cakes, sherbets, salads and icings.  
3. Sunflowers – in addition to the commonly eaten seeds, the petals can be added to soups and stir-fry dishes. The sunflower buds can be steamed and eaten like an artichoke.
4. Daylilies (Hemerocallis sp.) - Some species (especially H. fulva) are cultivated in Asia for their edible flowers. The petals can be eaten raw or more commonly dried and used as a flavoring in soups. The young shoots should be cooked and have a pleasant sweet flavor. Even the roots are edible.
5. Nasturtium, violas, borage and calendula flowers are also edible and frequently used in salads.  

Here is a final thought: some vegetables can be planted as ornamentals in landscape gardening. As shown above, swiss chard with the bright red stems and large leaves of cabbage add a delicious touch to the surroundings.

Photo: University of California Master Gardeners of Sacramento County