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Psidium guajava (tree, shrub)  |
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Management Information
Preventative measures: A Risk Assessment of
Psidium guajava for Hawai‘i and other Pacific islands was prepared by Dr. Curtis Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service. The alien plant screening system is derived from Pheloung et al. (1999) with minor modifications for use in Pacific islands (Daehler et al. 2004. The result is a score of 21 and a recommendation of: "Likely to cause significant ecological or economic harm in Hawai‘i and on other Pacific Islands as determined by a high WRA score, which is based on published sources describing species biology and behaviour in Hawai‘i and/or other parts of the world."Physical: Extensive stands of young trees can be controlled through burning, as cutting results in regrowth with multiple stems (Morton 1987). On the other hand, in the Galapagos, burning, manual cutting and even bulldozing have resulted in exacerbated invasion. Regeneration from underground parts by suckering limits the effectiveness of manual control (Cronk and Fuller 2001). Chemical: Guava is sensitive to foliar applications of triclopyr, dicamba and 2,4-D at 1 lb/acre, and to cut surface applications of concentrates of these herbicides; very sensitive to basal bark treatments of triclopyr ester and 2,4-D ester at 2% and 4% respectively, in diesel or crop oil; very sensitive to soil-applied tebuthiuron at 2 lb/acre. Very sensitive to very-low volume basal bark applications of 20% triclopyr ester product in oil. A small-leafed shrubby form of guava appears to be tolerant of foliar applied herbicides but sensitive to tebuthiuron (PIER). Biological: Goats and sheep can be used for control, as they graze leaves and strip the bark. Goats have been successfully used in Hawai‘i.
Location Specific Management InformationAscension Is. (Saint Helena)
Futile' attempts to control Psidium guajava were made around 1900 (Ashmole and Ashmole, 2000 in Varnham, 2006). Fiji
mechanical means have proven most successful Galapagos Islands (Ecuador)
Psidium guajava is controlled in the Galapagos, but eradication is not considered feasible at present. Queensland (Australia)
Targeted for eradication, despite this not being seen as feasible. Raoul Is. (New Zealand)
This species has been subject to an eradication programme on Raoul Island since 1972, and is ranked Category A(i) - known to have the potential to significantly alter the vegetation of Raoul Island. Raoul Island has been divided into 13 weeding blocks for the purpose of controlling and eradicating alien plants since 1972, which make up 64% of the vascular plant flora on Raoul Island. These are divided into active plots which are searched at least twice a year, and null plots which are searched at least once every two years. Grid searching is used to examine the areas with easier access, while steep cliffs are searched using binoculars or a telescope. This is carried out when plants such as Caesalpinia decapetala are in flower (June-November). Aerial surveillance is carried out periodically which has been useful in identifying flowering trees such as Senna septemtrionalis, mature vines of Passiflora edulis or trees of Olea europaea ssp. cuspidata. The initial knockdown phase involved for most species the cutting of mature individuals and painting of stumps with herbicides, or scattering herbicide granules around them. Blanket spraying was used to treat dense, inaccessible infestations. Subsequent searches involve the removal of any seedlings or young plants found. If a mature plant is found, the fruit is removed for burning, the stem is cut and herbicide applied. Information regarding the eradication programme is stored on an Access database. Psidium guajava can resprout vigorously from cut stumps, and may require many applications of herbicide. Less than 100 individuals have been removed since 1997, and all have been removed from Denham Bay. The importation of alien plants to Raoul Island is prohibited. San Cristobal Is. (Ecuador) (Ecuador)
45% of species introduced to the Galapagos Islands have been naturalized and of those, 32 are considered aggressive and have invaded extensive areas. The invaders affect the native vegetation negatively, changing the composition of the community and threatening populations of rare species. The majority of the introduced plants are found in the humid highlands where agriculture is the major activity and the conditions are better. The most noxious of these plants are the trees and shrubs that invade the native vegetation below the highest areas. The present methods of control are limited to removal by hand and by use of herbicides. Removal by hand requires continued effort since the plants may sprout from fragments of roots or branches. Few quantitative studies have been carried out to determine the type, concentration and method of application of herbicides. A 1999 study evaluated the effectiveness of three types of herbicide (glyphosate, picloram and triclopyr) in different concentrations to determine which method of application (“hacking and spraying”, spraying the bark and fumigation) is the most effective and the least damaging to the surrounding vegetation. These experiments were carried out on trees of Cestrum auriculatum, Cinchona pubescens, Cordia alliodora, Psidium guajava and Syzygium jambos and on the shrubs Kalanchoe pinnata, Lantana camara and Rubus niveus (Gardener et al., 1999).Please follow this link Rentería et al 2006 to An illustrated guide providing practical information for the effective control of the worst invasive plant species in Galapagos. Designed for farmers and other land managers, it describes manual and chemical control methods. Cedrela odorata is among 23 introduced species with descriptions and control options listed. Santa Cruz Is. (Ecuador) (Ecuador)
Galapagos National Park Service uses manual and chemical control in priority conservation areas
Management Resources/Links
1. Daehler, C.C; Denslow, J.S; Ansari, S and Huang-Chi, K., 2004. A Risk-Assessment System for Screening Out Invasive Pest Plants from Hawaii and Other Pacific Islands. Conservation Biology Volume 18 Issue 2 Page 360.
Summary: A study on the use of a screening system to assess proposed plant introductions to Hawaii or other Pacific Islands and to identify high-risk species used in horticulture and forestry which would greatly reduce future pest-plant problems and allow entry of most nonpests. Results Page: 1
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