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 pageeles@hawaii.edu.

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.  

See the invasive species website at http://www.hawaiiinvasivespecies.org/pests/miconia.html for more information.

Lawn - the Control of Weeds

Broadleaf weeds appear in the grass.

Controlling weeds in the lawn should begin long before chemical herbicide applications are considered. Cultural measures ought to be employed from the beginning. These include: 

• Proper irrigation -  weeds often invade lawns that are either over-watered or under-watered. Perhaps the worst possible irrigation schedule, yet common, is daily watering for 5–10 minutes. Light, frequent irrigation creates a shallow-rooted lawn which is more susceptible to weed invasion, as well as being less tolerant to drought.  In dry areas, where irrigation is employed, water should penetrate to a depth of 6 to 8 inches. The best practice is to allow the soil to partially dry out between irrigation. The top 1 to 2 inches  should be fairly dry before watering again. For more information on irrigating lawns, see UH CTAHR publication, “Watering Lawns”, at http://www.ctahr.hawaii.edu/site/info.aspx

• Proper fertilization – apply suitable amounts of fertilizer on a regular basis; nitrogen is the key nutrient for turf.

• Proper mowing heights – each turfgrass species has an appropriate mowing height. Mowing some grasses too short can weaken the lawn and predispose it to weed invasion.  A typical guide is to remove no more than one-third of the leaf blade at each mowing. If too much is removed, it will take more time for the grass to recover, giving weeds a chance to invade.

• Thatch is a layer of organic matter - stems, stolons, roots - that develops between the turfgrass blades and the soil surface. Regular thatch removal will help keep turfgrass healthy and competitive with weeds.  For Hawaii residents, see the UH CTAHR publication “Removing Thatch from your Lawn” for more information on this procedure.

• Any activities that lead to soil compaction will contribute significantly to turfgrass stress. This in turn, will make it easier for weeds to invade. These activities may include heavy foot traffic as well as vehicles traveling over the area.

 100% weed control in the lawn is impractical. Weeds will occur, but the problems can be minimized with a well-managed, vigorously growing lawn. By combining cultural methods with herbicide applications when needed, weeds will  be minimized.

For chemical control, a grassy weed in a lawn is difficult since most chemicals cannot distinguish between good and bad grass species. Fortunately, certain herbicides can distinguish between grassy plants and broadleaves. It is the chemical composition of the herbicide and the morphology of the plant that will cause certain herbicides to affect broadleaf plants but not affect grasses. Therefore, controlling broadleaf weeds in a grassy environment is relatively easy. Purchase an herbicide with the active ingredient 2,4-D, MCPP (mecoprop), or dicamba (Banvel). These products are often sold in combination, giving better management and a wider spectrum of the broadleaf weeds controlled.

For light weed infestations, spot treating is more appropriate than treating the entire lawn. Apply just enough of the solution to wet the leaf, do not apply to the point that the herbicide is dripping off the leaf. To insure maximum absorption, stop mowing 2 or 3 days before treatment and allow 3 or 4 days before mowing again. This allows sufficient time for the weeds to absorb the herbicide and transport it to their roots.

Caution: these materials are volitle, espectially 2,4-D. The drift can damage other valued broadleaf plants; tomatoes and hibiscus are particularly sensitive.

Weeds in the Lawn

Controlling weeds should begin long before chemical herbicide applications are considered. 
Cultural measures ought to be employed from the beginning. These include 
a. proper irrigation -  weeds often invade lawns that are either overwatered or underwatered. Perhaps the worst possible irrigation schedule, yet common, is daily watering for 5–10 minutes. Light, frequent irrigation creates a shallow-rooted lawn which is more susceptible to weed invasion, as well as being less tolerant to drought.  In dry areas, where irrigation is employed, water should penetrate to a depth of 6 to 8 inches. The best practice is to allow the soil to partially dry out between irrigation. The top 1 to 2 inches  should be fairly dry before watering again. For more information on irrigating lawns, in Hawaii see UH CTAHR publication, “Watering Lawns”, at http://www.ctahr.hawaii.edu/site/info.aspx;  or your local University Extension office or website.

b. Proper fertilization – apply suitable amounts of fertilizer on a regular basis; nitrogen is the key nutrient for turf.

c. Proper mowing heights – each turfgrass species has an appropriate mowing height. Mowing some grasses too short can weaken the lawn and predispose it to weed invasion.  A typical guide is to remove no more than one-third of the leaf blade at each mowing. If too much is removed, it will take more time for the grass to recover, giving weeds a chance to invade.

d. Thatch is a layer of organic matter - stems, stolons, roots - that develops between the turfgrass blades and the soil surface. Regular thatch removal will help keep turfgrass healthy and competitive with weeds.  See the UH CTAHR publication “Removing Thatch from your Lawn” for more information on this procedure.

e. Any activities that lead to soil compaction will contribute significantly to turfgrass stress. This in turn, will make it easier for weeds to invade. These activities may include heavy foot traffic as well as vehicles traveling over the area.

It is impossible to get 100% weed control in your lawn. Weeds will occur, but the problems can be minimized with a well-managed, vigorously growing lawn. By combining cultural methods with herbicide applications when needed, weeds will  be minimized.

When controlling weeds in your lawn it's good to know the name of that weed to see if it is listed on the particular herbicide you have chosen to use. But what's more important, before identifying the species, is to know the type of weed: broadleaf or grassy weed.  Distinguishing between the two will determine the appropriate herbicide to use.  Controlling a grassy weed in a lawn (grass) is difficult since most chemicals cannot distinguish between good and bad grass species.

Fortunately, certain herbicides can distinguish between grassy plants and broadleaves. It is the chemical composition of the herbicide and the morphology of the plant that will cause certain herbicides to affect broadleaf plants but not affect grasses. Therefore, controlling broadleaf weeds in a grassy environment is relatively easy. Purchase an herbicide with the active ingredient 2,4-D, MCPP (mecoprop), or dicamba (Banvel). These products are often sold in combination, giving better management and a wider spectrum of the broadleaf weeds controlled.

For light weed infestations, spot treating is more appropriate than treating the entire lawn. Apply just enough of the solution to wet the leaf, do not apply to the point that the herbicide is dripping off the leaf. To insure maximum absorption, stop mowing 2 or 3 days before treatment and allow 3 or 4 days before mowing again. This allows sufficient time for the weeds to absorb the herbicide and transport it to their roots.

Caution: these materials are volatile, especially 2,4-D. The drift can damage other valued broadleaf plants; tomatoes and hibiscus are particularly sensitive.

Photo by Forest and Kim Starr - Nene, the Hawaiian goose, feeding on weeds and grass in a lawn setting.
 Weeder geese are used with great success to control and eradicate troublesome grass and certain weeds in a variety of crops such as corn, flowers, strawberries and grapes. Note: Geese prefer grass species and will eat other weeds and crops only after the grasses are gone and they become hungry.

ALBIZIA – Beautiful Tree Or A True Menace?

 Hawaii was recently hit by tropical storm Iselle. Many streets in some locales, especially an area called Puna, were strewn with uprooted trees and fallen branches. The following article is about those trees - ALBIZIA. These albizia trees that quickly spring up in vacant lots or recently cleared land have become one of the worst invasive species on the Big Island of Hawaii. It has been called  “the tree that ate Puna”.

This albizia tree, Falcataria moluccana, is also named Albizia falcate, A.moluccana and others), and is a native to such places as Papua New Guinea, the Bismark Archipelago, and the Solomon Islands. The wood is used for light weight construction, cabinets, furniture, toys, and match sticks.

It is a fast growing tree to over 100 ft. tall. The tree can reach heights of more than 20 feet in the first year and to 60 feet by the end of ten years. It is described as a deciduous tree with wide-spreading branches, capable of shading over half an acre.  The tree produces large seed pods 4-5 inches long and about ¾ inch wide. It grows from sea level to about 3,200 feet elevation.  It is a nitrogen fixer, meaning that with the help of some bacteria residing in its roots, it can pull nitrogen out of the air and convert it to a form that roots can absorb. Because of this ability, it is used in many countries to improve soils as well as provide shade in coffee plantations.

This may make it sound like a pretty decent tree. But Dr. J.B. Friday, Extension Forester with the University of Hawaii, states “In Hawaii this tree is invasive in native`ohi`a forests as well as on land disturbed by human activities (especially bulldozing). It causes the`ohi`a  to die off and makes it easier for other invasive species like strawberry guava, clidemia and possibly miconia to grow under it and further degrade the forest. It also improves habitat for the tiny invasive coqui frog. These trees are a distinct threat to our native wet lowland forest ecosystems such as there are in Puna.”

Because of their brittle wood and weak structure, albizias are an even more serious problem to homeowners. Strong winds can cause large limbs to drop onto whatever may be underneath them, damaging homes, other structures and power lines. The fragile branches often cause traffic hazards by dropping branches on the highway.

A major problem, especially in Puna, is that people sometimes hire a bulldozer to clear their land. They clear the native ohia/uluhe forest, which is somewhat resistant to albizia invasion. If they are absentee landowners, they may not return for a few years and when they do return, an albizia forest has sprung up. Albizia is much bigger and faster growing than ohi`a, so the native trees cannot compete. To complicate matters, there is now a source of seedpods for the albizia to invade the neighbors' land. Dr. Friday advises not to clear the native forest on a lot unless you have another use planned for it. Otherwise albizia will come in and take over and you'll have a huge problem.

What to do: Leave the natural vegetation untouched—don’t bulldoze—until you are ready to utilize the land. Eliminate albizia seedlings and small trees before they become a problem.

Methods of control:  

After trees are cut down, immediately apply herbicide to cut stumps. Triclopyr amine is effective at concentrations of 7-10%.  For larger trees near buildings it may be advisable to first contact an arborist to determine the safest and most effective course of action to take in removing the tree.

The US Forestry Service in Hilo has an excellent publication entitled “Albizia – The Tree That Ate Puna” authored by C. Sumida, F. Hughes and Kathleen Friday.   For a copy write to USDA Forest Service, Institute of Pacific Islands Forestry at 60 Nowelo St, Hilo, HI 96720; or call at (808) 933-8121       

Parasitic Plants

Cassytha filiformis is a parasitic, leafless, flowering plant fairly common in the beach environment. It is often noticed as yellow blotches growing near the sea coasts. There is also another group of parasitic plants in the genus Cuscuta, known as dodder. These parasites infest a broad range of plants throughout Hawaii as well as tropical areas worldwide.  They appear as small orange colored strands growing over the host plant.

Although these parasites have some green coloration (often masked by the orange color), which indicates that photosynthesis does occur, they are entirely dependent on other plants for their nutrition, water and even physical support.  They vine around their host and produce adhesive structures called haustoria which penetrate the outer layer of cells of the host and extract water and nutrients from the plants phloem and xylem tissue. The host is slowly being depleted of its nutrients and water, while the parasite garnishes nutrients to grow, flower and produce seed.

Some common names for this parasitic plant in Hawaiian are kauna’oa pehu, malolo and pololo. It can often be seen parasitizing tree heliotrope, beach naupaka, ohi’a, noni and screw pine as well as fruit producing trees like citrus, mango, avocado and nutmeg. The seeds can be transported great distances by ocean currents, tidal waves, birds, strong winds, even hurricanes, and by humans.

Heavy infestations can smother host plants causing a decline and even death of the host. C. filiformis is a threat to lowland reforestation projects. It is damaging and capable of killing native, endemic and naturalized coastal and woody plants.

There are some benefits to this group of plants.  Traditionally it has been used in Hawaiian ceremonies - worn as ornamentation and in decorative garlands or lei. It is valued for its diverse healing applications; in Fiji it is used to treat jellyfish stings and as a food source.

Control:

·        Manually remove parasitic plants, especially before seed production.

·        Fire has been used to rid an area of the parasite, but will of course kill or at least damage the host also. The same is true for herbicides which may be effective, but can also damage the host.

·        C. filiformis is intolerant of shade.

·         Grazing sheep will feed on this pest.

Photos by Forest and Kim Starr

Control of Maile Pilau, a Weedy Vine

The weedy vine, Paederia foetida, or in Hawaiian maile piau, is able to grow 30 feet in length, climbing up into tree canopies or crawling along the ground. The vines can engulf and cover trees and shrubs. The weight of the vine climbing over vegetation can cause branches or entire trees to break or collapse. Crawling vines can form a dense layer of vegetation that smothers other plants. This leafy vine is pervasive in vacant lots and forests on the Hawaiian Islands.

Since broken stems of maile pilau are able to root readily in soil, care must be taken when disposing of the plant. When crushed, the leaves release a foul odor. The species, foetida, is Latin for stinky.

Chemical control is one of the most effective means for controlling maile pilau.  Yet, because of resprouting, single applications usually do not provide complete control; follow-up applications are necessary.  The herbicide recommended is one with the active ingredient, triclopyr, sold as Crossbow, Garlon, Pathfinder; unfortunately, they are rather expensive. Along with the herbicide, a non-ionic surfactant at 2 teaspoons per gallon of spray solution is suggested.  A 2% to 3% solution of glyphosate (Roundup, etc.) may also be effective, although some report it is not.  If you have Roundup, you may want to try it first before purchasing triclopyr.  

Presently biological control agents are being collected in Japan and Nepal.  It is hoped that these  ‘good guys’ which include a leaf and root feeding chrysomelid beetle will be able to help control the spread of this weed pest.

Photos by Forest and Kim Starr 

Controlling Bamboo

Bamboo is one of the most difficult plants to control. In fact, one of the best methods of control is prevention: do your homework before planting, learn about the different types and varieties and encourage your neighbors to do the same.

Homeowners with unwanted bamboo must be patient, as it requires an intensive control program which may last several years. Start with physically removing as much of the rhizome and root mass as possible, either by hand or with power equipment for larger areas.  If total removal is not possible, cut down the bamboo, wait for new growth to sprout, and then cut it down again, and again. Continue until no more shoots come up. Using this procedure, you are eventually exhausting the energy stored in the underground rhizomes. By constantly removing the foliage, you deny the plant the ability to photosynthesize and produce new energy so the rhizomes can no longer send up new shoots. If feasible, regular mowing will also work in this same manner, and over time the mowing will deplete the plant of energy.  Because bamboo is a grass, it can tolerate occasional mowing but does not tolerate frequent mowing. As much as two to three years of regular mowing may be needed in order to see results.

When controlling bamboo, it is often necessary to use herbicides.  Roundup (glyphosate) is one option for homeowners. It does not have residual soil activity and will kill only those plants that receive direct contact. First the bamboo must be cut, and then allowed to regrow until the new leaves expand.  Apply the herbicide at this point. Since Roundup does not translocate well to the rhizomes (i.e. transported from the leaves back down into the rhizome), the bamboo will likely re-sprout. Reapply Roundup whenever new growth is present.  It could easily take two years or more of this regime to attain control. Persistence is key.  

Another herbicide, Arsenal (imazapyr) is actually more effective than Roundup against bamboo.  The drawback is that unlike Roundup, imazapyr is soil active and will potentially kill other trees and shrubs and all grasses if their roots extend into the vicinity of the application. Therefore, if the bamboo is growing near any desirable plant species, Arsenal should not be used. As with all pesticides, the entire label ought to be read to make sure the material is being used in a safe manner, according to all label instructions.

If the bamboo in your yard has come from your neighbor’s yard, separate your ‘grove’ of bamboo from his by cutting the connecting rhizomes. They are usually quite shallow. If you don’t, your neighbor’s bamboo will continue to be a food source, providing energy to your bamboo and your efforts of cutting, mowing or spraying will be in vain. In addition, if not separated, any herbicide you apply has the potential of affecting your neighbor’s bamboo. To prevent a running bamboo from spreading, a barrier placed two to three feet deep in the soil can be effective. Barriers should be made of concrete, metal, or high density plastic. 

 In defense of this plant, bamboo can be a beautiful addition to a landscape. There are varieties of bamboo that do not spread out of control. Some varieties are even used for building, for furniture and for food.