Miconia calvescens is a tree that grows 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 percent shade, killing 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 to 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 people, through the mud on boots and other equipment including bulldozers. Seed is also dispersed by birds. In Hawaii, dispersal is presumably by the Japanese white-eye, the common mynah, and perhaps the northern cardinal. In trials in Tahiti, 1 square yard of the top 2 centimeters of soil from a dense Miconia stand produced more than 17,000 miconia seedlings in six months.
Miconia was introduced to Tahiti in 1937 and has since destroyed nearly 70 percent of the native forests and is directly responsible for threatening 25 percent of its native forest species with extinction. Miconia also causes serious landslides due to its shallow root system.
For many years, the Big Island Invasive Species Committee (BIISC) has worked to maintain a miconia-free buffer zone and stop miconia from spreading to upper-elevation, pristine watershed forests. Funding is now inadequate to continue this focus. For more information, contact BIISC at (808) 430-3090, or email at firstname.lastname@example.org.
Today, the strategy for control is to implement a series 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 that attacks the leaves, causing premature leaf drop. There is a BIISC hotline to report new infestations, 961-3299.
See the invasive species website at http://www.hawaiiinvasivespecies.org/pests/miconia.html for more information.
Cucumbers attacked by melon flies
I picked some cucumbers the other day and noticed some of them had a slight depression with a minute hole in the center. Inside was a small worm. What insects are causing this? There is a slight brown discoloration inside the fruit, too.
The cucumbers are being attacked by the melon fly. It has been a major pest of cucumbers in Hawaii for a long time. Adult female flies lay their eggs into the fruit; this may cause the fruit to curve. The eggs hatch into maggots which feed inside the fruit. As a secondary problem, fruit will often rot from fungal and bacterial infestations. All infected fruit must be removed from the area, but the uninfected portion can be eaten if it has not rotted. Placing some type of paper or netted bags around young fruit soon after pollination may help control damage. Protein bait sprays will also help. For complete control measures, see my website at www.gardenguyhawaii.com, search “fruit fly”; or pick up a brochure on fruitflies at the Komohana Street Extension Office of UHCTAHR, or your local state Department of Agriculture.
Note: Pickleworms can also infest cucumbers. See www.gardenguyhawaii.com; search “pickleworm.”
Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at email@example.com.