2008 — Maui Invasive Species Committee (MISC)

Fast-growing ivy gourd threatens rare dryland ecosystem on Maui

Posted on August 23, 2012 by Lissa Strohecker Leave a Comment

Ivy gourd can be identified by the 5-petaled flowers and green fruit that turn red as they ripen, hanging like Christmas lights from the plant. Photo by MISC

On Maui, we are lucky to have so many open spaces. Our island is relatively undeveloped, though you may beg to differ when you’re stuck in traffic. The majority of the population lives along the coastlines. This distribution of island residents is nearly identical to the distribution of ivy gourd; a highly invasive vine found growing in central, south, and west Maui. And, as development expands, so does the population of ivy gourd. This is no coincidence.

Native to Africa, India, and Southeast Asia, ivy gourd was probably brought to the Hawaiian Islands by an immigrant from one of those areas. The immature fruit of the plant, as well as the young shoots, are used in cooking. Many recipes from Southeast Asia call for ivy gourd. While it may taste good in a stir fry, it’s in poor taste—illegal even—to have the plant growing in your yard.

Inevitably, the vine escapes cultivation. Humans—and their pesky rodent counterparts—have been the vectors for spreading ivy gourd. Rats scamper off with a stolen fruit spreading the seeds. In absence of the insect pests that limit ivy gourd’s growth in its native habitat, the plant grows unchecked. Roots form every time the branching vine touches the ground. Each root is enlarged, giving ivy gourd the ability to survive lengthy periods of drought.

Ivy gourd, Coccinia grandis, can be hard to identify without the flower or fruit present. The leaves are broad and flat, shaped like an angular heart, about 2.5 inches wide. They are arranged in an alternating pattern along the vine. The flower is white, with 5 petals curving out of a tube-like base. If the plant reaches the fruiting stage, the 3-inch long fruit, dangling like bright red Christmas lights, is a dead giveaway that the vine smothering your yard is ivy gourd.

Ivy gourd is fast-growing. While we don’t know the actual rate of growth on Maui, it is a member of the cucumber family of plants that may grow up to 4 inches a day. If we ignored this aggressive growing vine what would happen? “We’d be ivy gourdians” a 7^th grade student so aptly replied during a class visit by MISC. When people don’t consume ivy gourd, ivy gourd consumes the environment around us. Trees, power poles, fences, even cars disappear beneath a mountain of vines.

The fast-growing ivy gourd can easily smother trees, fences, and power lines. It could transform the native dryland ecosystem, choking out rare Hawaiian plants and leaving nothing but curtains of green. Photo by MISC

Ivy gourd is currently limited to residential areas on Maui. MISC’s successful control of the population depends entirely on the cooperation of property owners and residents. Because the vine grows so fast, and because the seeds germinate so quickly after a rain, monthly site visits may be necessary. A plant can go from seedling to seed-bearing within as little as a month, and once the plant produces seed, the seed bank can last for years. Field crews must find and apply a few drops of herbicide to every single root in order to kill the plant, no small task when the plant has covered several kiawe trees.

On the islands of O`ahu and Hawai’i, ivy gourd is invading natural areas. On Guam and Saipan, ivy gourd is so established that the only way to limit it may be through biocontrol. Insect pests have been released in these areas. On Maui, control efforts have reduced ivy gourd to a level that would no longer support a viable biocontrol population. The only way to eradicate it is to get rid of the remaining plants, monitor locations for new plants, and prevent new introductions.

If a plant nursery is infested with ivy gourd, it’s almost inevitable that seeds and plant material will be spread in contaminated soil. This may help explain why we find ivy gourd in golf courses. A huge infestation was discovered on Lāna‘i in 2006, and with continued effort the population is being knocked back.

And those open spaces on Maui? Above the development of Lahaina and Kīhei are the remnants of the native dryland forest ecosystem. The leeward slopes of Haleakalā, where this ecosystem was once predominant, still harbor stands of native trees. This is where ‘iliahi (sandelwood) grows. The wiliwili tree can be found here, as well as the naio trees that gave us the name for the area: Kanaio. These areas have been greatly altered by ranching and the introduction of goats and deer, yet they still include rare native plants and insects. There is no ivy gourd here. Ivy gourd would thrive here if introduced into these native forests. Ivy gourd would smother the existing vegetation, leaving curtains of green where there once were diverse and rare ecosystems.

Help us protect these rare ecosystems on by finding and reporting ivy gourd in Maui’s residential and rural areas. Do not grow ivy gourd. If you suspect you may have ivy gourd on your property, please call the Maui Invasive Species Committee at 573-MISC (6472) and we will remove it, free of charge.

Poisonous Rubber Vine Needs to be Controlled

Posted on December 8, 2011 by Lissa Strohecker Leave a Comment

The rubber vine may appear to be a beautiful plant but it is actually poisonous. The vines will also creep up trees and into their canopies and foul up streams. (Photo by MISC)

When the crew from the Maui Invasive Species Committee (MISC) arrived on Moloka‘i in February of 2005, they soon realized this was not going to be just another week at work. They were assisting the Moloka‘i/Maui Invasive Species Committee (MoMISC) in controlling a large infestation of rubber vine plaguing the Kamalō and ‘Ualapu‘e areas. The pest had invaded over five acres, forming impenetrable thickets that made it difficult to control. Just looking at the vast amount of area conquered by this one invasive plant made the MISC crew realize why the two-person MoMISC team called in reinforcements.

Controlling the large population was a daunting task and, at first, overwhelming. But one by one, vine by vine, the crew attacked the rubber vine as if they themselves were an invasive species, quickly devouring everything in their path. By the end of the week, the once dark forest of rubber vine blanketing the treetops was transformed into a more open area with sunlight. By helping to initially suppress the pest, MISC was making it manageable for MoMISC to monitor and treat it in the future.

Here on Maui, we are fortunate that we do not have such large rubber vine populations. Instead, we have limited infestations growing in residential areas. There is hope that we can eradicate this invader before it affects our natural and agricultural areas as well as quality of life.

Rubber vine (Cryptostegia grandiflora on Maui, C. madagascariensis on Moloka‘i) are vigorous climbing vines from Madagascar that can scramble their way 30 meters up a tall tree or grow as an unorganized shrub-like clump of vines one to two meters tall. The plant invades waterways forming dense, impenetrable thickets that smother riparian vegetation and decrease biodiversity. Rubber vine can also impact ranching operations by restricting livestock access and lowering pasture productivity.

This invasive plant is extremely poisonous; it contains cardiac glycosides, chemicals that interfere with heart function in humans and animals when the plant is ingested. Contact with the plant’s milky sap can cause burning rashes and blisters. When the vine is dry, a powdery dust emerges that can cause violent coughing, swelling of the nose, and painful blistering of the eyelids.

Rubber vine has large, showy pinkish-purple flowers with five petals arranged like a funnel. Its shiny, dark green leaves, directly opposite each other, range from two to four inches long. The distinctive triangular seed pods average three to four inches in length and grow in wing-like pairs. Approximately 200 days after formation, the seed pods dry out and split open. Seeds with silky hairs are released into the wind and waterways. Approximately 95% are viable – increasing the potential for rubber vine to rapidly spread.

In addition to natural dispersal, rubber vine can be introduced to an area by animals or humans. Livestock can carry seeds long distances through agricultural fields. Contaminated vehicles and machinery transport seeds from one worksite to another. Cultivation of rubber vine as an ornamental plant makes the problem much worse, especially since a plant may live for up to 80 years. Rubber vine is widely available to the public through Internet seed companies, few of which describe the plant’s noxious qualities.

In order to prevent the spread of rubber vine, areas downstream and downwind from known infestations must be inspected. Do not import, purchase, or plant this toxic species in your yard. If you have rubber vine on your property, call MISC and give permission to control it. If you see rubber vine growing or for sale, call MISC at 573-MISC. Encourage friends and family not to buy this or other pest plants so nurseries will stop selling them.

We are happy to report that since MISC assisted MoMISC in February 2005, the five-acre rubber vine population has been significantly reduced and eradication of this pest is within reach for the Friendly Isle. Inclusion of rubber vine on the Hawai‘i State Noxious Weed List is currently under consideration. Until it is listed, it is up to residents and visitors to protect Maui from this aggressive pest so that we can avoid dealing with large populations such as that once found on Moloka‘i.

By Joylnn Paman
Originally published in the Maui News, January 13, 2008 as part of the Kia‘i Moku Column. Check out all of the MISC articles in the Kia`i Moku series at: www.hear.org/misc/mauinews/

Biocontrol precision is weapon against invaders

Posted on September 6, 2011 by Lissa Strohecker Leave a Comment

Lloyd Loope

Last month I began to present my point of view as a conservation scientist relevant to current “controversy” over biocontrol of strawberry guava (Psidium cattleianum), Hawaii’s most damaging invasive plant species. I touched upon the generally accepted theory that many highly invasive plant species, held in check by insects and pathogens in their home range, become unbeatable competitors in their introduced range where those insects and pathogens are lacking. Strawberry guava exemplifies the “enemy release” theory; it is attacked by virtually no insects or pathogens wherever it invades on many tropical islands of the world.

Though I’ve always supported the concept of biocontrol as a potential tool for Hawaii’s most widespread and most invasive plants, I recall a personal pessimism in the 1980s that biocontrol success might be unlikely in this case because guava is in the myrtle family (same as Hawaii’s ‘ōhi‘a) and commercially important common guava (Psidium guajava) is such a closely related sister species.

A strawberry guava tree in Curtiba, Brazil is heavily infested with the galls of the scale insect Tectococcus ovatus. This is the typical effect of the insect on the plant. It was a result of a naturally developing infestation of the insect in the plant’s native range. U.S. Forest Service photo

But state and federal natural resource agencies in Hawaii have managed to cobble together a remarkably stellar program to address the rampant invader. In 1991, the National Park Service and the University of Hawaii began to collaborate with the Federal University in Curitiba, Brazil, to identify and evaluate potential biocontrol agents. After 10 years of field observations and other testing working within the native ranges of both strawberry guava and common guava in Brazil researchers found 133 insect species in 12 orders and 80 families that fed on strawberry guava. Thirty-one of those species fed only on plants in the myrtle family, and five species fed only on strawberry guava and not at all on common guava. The collaborative program zeroed in on Tectococcus ovatus, a scale insect that feeds on the new growth, creating galls on the leaves of strawberry guava. This scale insect was the choice for more intensive work based on the relative severity of damage inflicted on P. cattleianum and the ease of handling it.

Tectococcus ovatus was brought to containment facilities in Hawaii and Florida, where strawberry guava is also invasive, for intensive experimental testing to ensure its safety as a biocontrol agent. Many related native and non-native plants were tested as potential host species. Strawberry guava is the only plant in Hawaii that this insect is able to feed on. Dr. Tracy Johnson of the U.S. Forest Service in Hilo has brought the program close to fruition over the past eight years.

The insect reduces the plant’s energy and nutrients available for growth and reproduction. Heavy infestation is expected to accelerate leaf drop and reduce fruit and seed production. Some fruit will be produced and the plants are not expected to die. If the scale insect thrives, it will level the playing field between the invasive strawberry guava and native forest species.

What other species in the ecosystem will be affected by the expected decline in strawberry guava fruit production? Feral pigs and a few species of non-native birds will lose a seasonal carbohydrate diet supplement during the September-December fruiting season. These same species are fully able to thrive in areas where there is no strawberry guava.

Hawaii is confronted by intractable invasive species problems, but by integrating prevention, early detection, rapid response, and biocontrol we can begin to address these problems. Biocontrol is an essential part of invasive plant management strategies in New Zealand, Australia, and the U.S. mainland. Florida has become a leader in biocontrol in the past decade. For example I recently learned that thanks to two insects introduced about 10 years ago as classical biocontrol agents, the notorious Melaleuca, or paper bark tree is no longer invasive in the Florida Everglades! My scientific opinion is that biodiversity conservation in Hawaii will not succeed without the enlightened use of biological control.

Lloyd Loope is a research scientist with the U.S. Geological Survey stationed at the Haleakala Field Station. He holds a doctorate in botany from Duke University and is an active Maui Invasive Species Committee member.

Originally published in the Maui News, October 12, 2008 as part of the Kia‘i Moku Column.
You can see all the articles in the Kia‘i Moku series http://www.hear.org/misc/mauinews/

Strawberry guava sows seeds of infestation

Posted on August 30, 2011 by Lissa Strohecker 1 Comment

The fruit if strawberry guava are eaten by birds that spread the tiny seeds. Photo by Forest & Kim Starr

When I came to Maui 28 years ago to work as a research biologist at Haleakala National Park, one of the first things I learned was that strawberry guava (Psidium cattleianum) was regarded as the most damaging invasive plant in the state. A year later, I was in Kipahulu Valley and experiencing the amazing guava fruiting and dispersal season. The 10-30 foot tall trees left a sea of red fruits that still lurks in my memory. There were dense, extensive guava thickets of tens of acres at the 2,000-3,000 ft elevation level in the valley. One could scarcely walk through; there were literally no other species present. These devastated areas contrasted sharply with the rich biodiversity in nearby areas with intact native understory vegetation.

A dense infestation of strawberry guava, or waiawī , in the Makawao Forest Reserve. Photo by Forest and Kim Starr

At that time, C.H. Diong, a graduate student at UH-Manoa, was putting the final touches on his Ph.D. thesis. Diong showed that feral pigs had been the primary agent spreading strawberry guava from the mouth of the valley upslope for the past 30 years or so. The pigs fed almost exclusively on guava fruits during September-December. The seeds pass through the pigs’ digestive tracts with no loss of viability. Fruiting was occurring only below about 3000 ft elevation but the seeds could germinate and grow much higher, up to over 4000 ft in the valley.

Years later, my colleague Dr. Art Medeiros did his Ph.D. thesis on the biology of weeds in Kipahulu Valley and East Maui. Art estimated that strawberry guava already occupies over one-third, or 8900 acres, of its potential area of dominance on East Maui. Although feral pigs had been eliminated and fenced from Kipahulu Valley since the late1980s, Art found that non-native birds, primarily the red-billed leiothrix, were also spreading strawberry guava seeds. Strawberry guava plants were still not fruiting above 3000 ft, but seeds planted experimentally (or those carried by birds or pigs) germinate at much higher elevations. Strawberry guava now reaches as high as 5300 ft on East Maui in at least one location.

Strawberry guava has infested the outlined area on Mahana Ridge, just to the east of Honokahua Valley in West Maui. Photo by Randy Bartlett.

Newly established guava plants can spread vegetatively by root sprouts. On all the major islands, nearly monotypic guava stands infest thousands of acres of moderately wet (mesic) and very wet forest. Strawberry guava is considered a serious threat to native forests due to its ability to invade relatively undisturbed areas and form thickets with dense mats of feeder roots. Dense invasion allows only about 5% of sunlight into the understory. The guava at first invades under native canopy, then expands and closes the mid-level canopy position, preventing the establishment and regeneration of all other species, including the dominant native forest plants – ohia and koa. Although it continues to expand into relatively pristine native forest areas, strawberry guava is now so widespread in Hawaii that its future impacts are expected to consist mainly of filling in areas creating monotypic stands.

As one of the founding members of the Maui Invasive Species Committee, I never considered taking on strawberry guava as a MISC target given its wide distribution and abundance and MISC’s limited resources. We always hoped for the eventual possibility of identifying an effective biological control.

A generally accepted theory of biological invasions is that certain plant species, held in check by insects and pathogens in their home range, become invasive in their introduced range where those insects and pathogens are lacking. Strawberry guava seems to fit the “enemy release” theory perfectly. In Hawaii, it is currently attacked by no insects or pathogens.

The first biocontrol researcher for this species, Dr. Charles Hodges, traveled to coastal Brazil in 1988 and reported that strawberry guava occurs not in dense stands but as scattered trees and rarely in small clumps. He noted that “few trees were observed that had not been attacked by at least one kind of insect,” and “often four or five types of insect damage could be identified on the same tree.” After 20 years of research to determine the best potential biocontrol agent, the scale insect Tectococcus ovatus has jumped through all the hoops but one – public opinion.

Lloyd Loope is a research scientist with the U.S. Geological Survey stationed at the Haleakala Field Station. He holds a doctorate in botany from Duke University and is an active member of the Maui Invasive Species Committee.

Originally published in the Maui News, September 14, 2008 as part of the Kia‘i Moku Column.
You can find all the articles in the Kia‘i Moku series http://www.hear.org/misc/mauinews/

Fast-growing ivy gourd threatens rare dryland ecosystem on Maui

Poisonous Rubber Vine Needs to be Controlled

Biocontrol precision is weapon against invaders

Strawberry guava sows seeds of infestation

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