Progress 10/01/02 to 09/30/06
Outputs
A new papaya disease caused by the fungus Asperisporium caricae was found first on the island of Maui in February 2001, then on the island of Hawaii and Oahu, and by September on Kauai. The fungus causes extensive leaf spots and fruit spots and can render the fruit unsaleable. Fruit and leaf lesions often are invaded by what appears to be a hyperparasitc fungus, tentatively identified as a Scopulariopsis sp. A field fungicide test for the control of Asperisporium black spot demonstrated that azoxystrobin (with either "Tactic" or "Latron B-1956") at 0.28 kg/ha applied at 2-week intervals for four sprays followed by mancozeb + copper hydroxide (2.8 kg/ha and 4.5 kg/ha) for three sprays at 2-week intervals resulted in 0% and 3.1% of fruit with new infections 1 and 3 weeks after the last spray with "Tactic"; 2.9% and 8.3% of fruit with "Latron B-1956"; 4.5% and 5.1% of fruit with new infections for mancozeb + copper hydroxide controls, and 49.2% and 63% for unsprayed
controls. Wettable sulfur applied at 4.47 kg/ha at 14 day interval was shown to be a commercially acceptable field control of this disease and is now standard practice by most papaya growers. A. caricae was successfully isolated and maintained on PDA and V-8 juice agar but growth was slow and sporulation limited. An inoculation technique using 2 to 3-month old papaya seedlings and utilizing fresh A. caricae conidia from naturally infected papaya leaves. Tiny yellow spots appeared in about 35 days and developed into typical lesions over the next 60 days. A 5 minute video was produced describing the cause and effects of the Asperisporium black spot disease on papayas for farmers. Several workshops on how to identify and manage the disease have been held.
Impacts
Growers were reassured that current registered fungicides were effective in controlling Asperisporium black spot when applied regularly. Based on earlier recommendations, papaya growers on the Big Island are incorporating wettable sulfur, an environmentally friendly fungicide, at the rate of 2.2 to 4.4 kg/ha into their fungicide sprays to control Asperisporium blackspot and getting very good control of Asperisporium black spot. An inoculation procedure can now be a tool for further research to study control strategies of this disease on papayas.
Publications
- Zhu, YJ, Agbayani, R, Nishijima, WT and Moore, PH (2005) Characterization of Disease Resistance to Phytophthora in Carica Papaya, First International Symposium on Papaya, Genting Highlands, Malaysia, Nov 22-24, 2005, Abstract S5-12, p96.
- Agbayani, R, Nishijima, WT, Moore, PH and Zhu, YJ (2006) Characterization and Improvement of Disease Response to Phytophthora palmivora in papaya. 18th CTAHR Student Research Symposium. April 10-11, 2006, Abstract #104, p63.
- Nishijima, W.T. 2002. A new disease hits papaya. Agriculture Hawaii, Vol 3:1:26. 2002
- Nishijima, W.T. 2004. Book Review (Diseases of Tropical Fruit Crops, Ed. R.E. Ploetz), Mycopathologia Vol 158:4:483
- Nishina, M. 2002. Asperisporium Black Spot of papaya. (Video), U of Hawaii, CTAHR, Komohana Video Center, Hilo, Hawaii.
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Progress 10/01/04 to 09/30/05
Outputs
Two to 3-month old papaya seedlings were successfully inoculated by utilizing fresh Asperisporium caricae conidia from naturally infected papaya leaves. Conidia were carefully brushed off and suspended in a 1:2000 Tween 20 solution. Seedlings were sprayed with a conidial suspension of approximately 5 x 10+5 conidia/ml to drip and placed in a moisture chamber for 24 hours at room temperature (25 C). After removal from the chamber, seedlings were placed in a greenhouse irrigated with sprinkler irrigated (3x a day). Lesions were first visible after about 35 days as tiny yellow spots that progressed over the next 60 days into typical Asperisporium black spot lesions. Most of the lesions developed on the lower leaf surface. The technique is being used to evaluate fungicides, and non-pesticidal chemicals such as benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) and other low-impact materials for disease control. Initial inoculation trials demonstrated that the
cultivar "Rainbow" is more susceptible than "Kapoho" to Asperisporium blackspot.
Impacts
Based on earlier recommendations, papaya growers on the Big Island are incorporating wettable sulfur at the rate of 2 to 4 lbs per acre into their fungicide (mancozeb) sprays to control Asperisporium blackspot and are getting very good control of Asperisporium black spot.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
Work continued in developing a culture medium for the axenic culture of Asperisporium caricae. This papaya pathogen is being successfully grown in culture on several non-defined, general purpose culture media such as PDA and V-8 juice agar but growth is slow and without conidia production. Trials on numerous other media have resulted in similar results. Tests with other media continues. Preliminary tests show that wettable sulfur applied at 4 lbs per acre at 14 day interval reduced incidence of black spot lesions on papaya fruit. Unfortunately, dry weather severely reduced overall disease pressure.
Impacts
The eventual goal is to control this disease with environmentally friendly materials to provide papaya farmers with an option in choice of materials for the control of papaya black spot and to minimize impact on non-target organisms at a lower cost.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Asperisporium black spot of papaya disease incidence and severity on fruit continues to decline in commercial and non-commercial plantings for unknown reasons. Incidence on foliage, however, continues to remain steady. Despite these observations, research was focused on the axenic culture of the fungus Asperisporium caricae for future experiments with environmentally friendly materials. Although A. caricae was successfully isolated and is being maintained on PDA and V-8 juice agar sporulation is limited and a better medium is being developed.
Impacts
The eventual goal is to control this disease with environmentally friendly materials to provide papaya farmers with an option in choice of materials for the control of papaya black spot and to minimize impact on non-target organisms at a lower cost.
Publications
- No publications reported this period
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Progress 10/01/01 to 09/30/02
Outputs
A field fungicide test for the control of Asperisporium caricae black spot on papaya demonstrated that azoxystrobin (with either the surfactant Tactic or Latron B-1956) at 0.28 kg/ha applied at 2-week intervals for four sprays followed by mancozeb + copper hydroxide (2.8 kg/ha and 7.4 kg/ha) for three sprays at 2-week intervals resulted in 0% and 3.1% of fruit with new infections 1 and 3 weeks after the last spray with the surfactant Tactic; 2.9% and 8.3% of fruit with new infections with the surfactant Latron B-1956; 4.5% and 5.1% of fruit with new infections for mancozeb and copper hydroxide controls, and 49.2% and 63.0% of fruit with new infections for unsprayed controls.
Impacts
Growers were reassured that current registered fungicides were effective in controlling Asperisporium black spot when applied regularly. Although Asperisporium black spot is still present, it does not appear to be as severe a problem as it used to be, possibly because of regular spraying by growers.
Publications
- Nishijima, W.T. 2002. A new disease hits papaya. Agriculture Hawaii. 3:1:26.
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Progress 10/01/00 to 09/30/01
Outputs
A new papaya disease caused by the fungus Asperisporium caricae was found first on the island of Maui in February, 2001, then on the island of Hawaii and Oahu and by September on Kauai. The fungus causes extensive leaf spots and fruit spots and can render the fruit unsaleable. Fruit and leaf lesions often are invaded by what appears to be a hyperparasitic fungus, tentatively identified as a Scopulariopsis sp. Because of industry concerns a fungicide test was initiated on August 15, 2001 to determine the efficacy of azoxystrobin at 1.125 l/ha (sprayed at 2-week intervals for a total of four sprays), then followed by mancozeb (2.8 kg/ha) + copper hydroxide (4.5 kg/ha) combination at 2-week intervals; and compared to the standard practice of mancozeb (2.8 kg/ha) + copper hydroxide (4.5 kg/ha) combination at 2-week intervals. Initial data appears to indicate that azoxystrobin and the "standard practice" mancozeb + copper hydroxide sprays significantly reduced foliar and
fruit lesions caused by A. caricae to an economically feasible level. Azoxystrobin also controlled Phytophthora blight on fruit and stems. A cooperative demonstration trial has been initiated with the Hawaii Department of Agriculture to create an area in the Puna District of Hawaii island in which PRSV susceptible cultivars of papaya will be grown. The area is surrounded by a buffer zone ca. 1.6 km wide in which only genetically engineered cultivars that are PRSV resistant will be allowed to be planted. The objective is to be able to grow non-engineered papaya for markets that do not allow GMO produce.
Impacts
Growers will be able to immediately utilize fungicides already registered to control the black spot disease to minimize losses. Azoxystrobin, which is soon to be registered, can be used to control this new disease as well as Phytophthora blight when registered. If the demonstration of utilizing a buffer zone to protect susceptible cultivars is successful, growers will have a management tool to grow non-GMO cultivars to satisfy that market.
Publications
- No publications reported this period
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Progress 10/01/99 to 09/30/00
Outputs
A papaya varietal test was conducted in Paauilo on the island of Hawaii using a split block test with Kapoho, Sunrise, Sunset and Waimanalo in half of the test and Rainbow, Rainbow cuttings, Sunup and female Kapoho in the other half. The field was planted in August 1997 and first harvested in July 1998 and weekly thereafter. Total production (kg/ha) for the first 12 months of production on a 1,977 trees/hectare basis was: Kapoho (24,503), Sunrise (48,087), Sunset (44,547), Waimanalo (50,342), Rainbow (36,569), Rainbow cuttings (51,008) and Sunup (51,636). At the elevation of the test site (207 meters) Brix (total soluble solids) was acceptable (11 or better) during the summer months for most cultivars but was not acceptable during the winter months. Sunrise had the most consistently highest Brix, followed by Sunset and Rainbow. Waimanalo had the lowest overall Brix. This reinforces the "rule of thumb" that commercial papayas should be grown at 152 meters elevation or
lower for best quality. The site was serviced by the Hamakua ditch but because of breaks in the ditch and connecting lines, overuse by users upstream, and other causes, the field frequently experienced no water. The field went without water for periods of 2 weeks many times. Water is essential for production of papayas in the Paauilo area. Rainbow cutting produced fruit at the lowest height, averaging 78.0 cm, followed by Waimanalo (82.8cm), Sunup (86.1cm), Sunset (90.9cm), Sunrise (91.4cm), Rainbow (94.4cm) and Kapoho (96.8cm). Rainbow cuttings were about 6 weeks ahead in fruit production than seeded Rainbow.
Impacts
Fields planted with cuttings can produce fruit about 6 weeks earlier and at a lower height than fields direct seeded. This added fruit production easily pays for the cost of producing the cuttings estimated at $1 per plant. Additional savings are realized by reduced fertilizer costs, and the time involved in sexing and eliminating non-hermaphroditic plants.
Publications
- No publications reported this period
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Progress 10/01/98 to 09/30/99
Outputs
A cultivar suitability trial was completed in the Kau District and data from a second planting in Paauilo in the Hamakua District were collected. The Solo cultivars Kapoho, Sunrise, Sunset and Waimanalo were included in both trials. In addition to these cultivars, the genetically engineered cultivars Sunup and Rainbow (by seed and rooted cuttings) were planted in Paauilo. The production potential of papayas in Kau is excellent. The production by cultivar, for the first 12 months of harvest (allowing for about 50% culls) was: Kapoho, 37,319 kg/ha; Sunrise, 56,680 kg/ha; Sunset, 47,606 kg/ha; and Waimanalo 53,298 kg/ha as compared to the industry average of about 26,070 kg/ha in Puna and 44,834 kg/ha for Sunrise on Kauai. Brix was consistent for all cultivars throughout the year, unlike papayas from the Paauilo trial where Brix dropped to between 7 to 10% total soluble solids during the winter months, but did not surpass 12.4 %. Monthly sprays of wettable sulfur
provided excellent control of powdery mildew and the papaya leafedge roller mite (Calacarus brionesae). Monthly sprays of mancozeb, directed to the flower and fruit column, provided excellent control of anthracnose and other fruit diseases. Fruit size averaged 304 g, 405 g, 390 g, and 568 g for Kapoho, Sunrise, Sunset and Waimanalo, respectively. The dry conditions in Kau are ideal for papaya production but the cost of domestic water was about $7,413/ha/year. Papaya ringspot virus (PRV) was effectively eradicated by the early removal of three infected trees early in the study despite an established reservoir of virus about 2 km up slope of the trial.
Impacts
Information derived from this project was used by the industry to relocate over 1100 acres of papaya from the PRV-ravaged Puna district to the Hamakua coast producing over $5 M/year. This allowed the industry to minimize market loss. Although many growers have returned to the Puna district using genetically engineered resistant cultivars, growers continue to grow about 300 acres of papayas along the Hamakua coast to supply West Hawaii hotels and Canada.
Publications
- No publications reported this period
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Progress 10/01/97 to 09/30/98
Outputs
Cultivar trials continued in Paauilo (Hamakua District) and Pahala (Kau District), Hawaii Island, both areas in which large areas of former sugarcane lands have become available for papaya production (PRSV). In each location, the cultivars Sunrise, Sunset, Kapoho, and Waimanalo were compared for commercial suitability. The cultivars Sunrise and Sunset appear to be the most suitable based on marketable yield, impact of pests, and Brix. Some of the signficant findings are: (1) It takes Kapoho about 2 months longer from planting to first harvest then the other three cultivars. The average first fruit height for Kapoho was 102 cm as compared to Sunrise (76 cm), Sunset (82 cm), and Waimanolo (71 cm). (2) Waimanalo is the most sensitive cultivar to powdery mildew and the papaya leafedge roller mite (Calacarus brionesae). These pests when occurring together can be so severe that they can cause extremely low Brix and even tree mortality. Kapoho was the most resistant. They
can be effectively controlled by monthly applications of wettable sulfur applied to the lower leaf surface. (3) Dependable irrigation is essential. (4) To minimize excessive tree height, a fertilizer with a 1:2:2 ration of N:P:K appears to be most suitable. Azoxystrobin at rates of up to 800 ppm for control of papaya postharvest diseases did not show any efficacy. Although commercial ELISA kits are capable of detecting (PRSV) from single "vein clearing" symptoms from 1 cm diameter leaf disks, the task of quickly finding these symptoms make it difficult to practically utilize this tool in large area surveys.
Impacts
(N/A)
Publications
- No publications reported this period
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Progress 10/01/96 to 09/30/97
Outputs
Papaya ringspot virus (PRSV) was successfully detected with commercial ELISA kits from 1 cm diameter leaf disks obtained from single "vein clearing" lesions in the early stages of symptom development. However, adjacent leaf tissue about 2 cm from these lesions were negative for PRSV. This technique has potential for early PRSV detection but sampling procedures will be important. A cultivar trial was completed in Paauilo and Hakalau, both PRSV-free areas on the island of Hawaii that have potential of supporting commercial papaya production. The trials demonstrated that Sunrise and Sunset were best suited for these areas based on yield, fruit size, and brix. Kapoho fruits were smaller than desirable and Waimanalo fruits were too large and brix was below commercial standards during winter months. The latter was also very susceptible to powdery mildew and the new papaya leaf edgeroller mite, Calacarus brionesae. Laboratory and field tests with thiram, tebuconazole,
azoxystrobin, and a potassium hydroxide-based fungicide for control of several field and postharvest diseases are in progress.
Impacts
(N/A)
Publications
- NISHIJIMA, W.T. 1996. Ethylene Thiourea: Hawaii Papaya Market Basket Study. Univ. of Hawaii. Coll. of Trop. Agric. and Human Resources Report No.: HWN-94-01. 56p.
- PAULL, R.E., NISHIJIMA, W.T., REYES, M. and CAVALETTO, C. 1997. Postharvest handling and losses during marketing of papaya (Carica papaya L.) Postharvest Biol. and Tech. 11:165-179.
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Progress 10/01/95 to 09/30/96
Outputs
A market basket study designed to determine the levels of ethylene thiourea (ETU) in Hawaii grown papayas found levels from non-detectable (0.005 ppm to a high of 0.0149 ppm. Thirty-seven and a half percent of fruit sampled had ETU levels below the detectable limit. These results suggest that an earlier "worst case" field residue study overestimated ETU levels by about 11 to 15 times. A papaya cultivar trial was planted in Paauilo in June, 1995 to determine the characteristics of the four commercial cultivars to assist growers who are trying to avoid the papaya ringspot virus. The cultivar Waimanalo (W) fruited first in the first week of July, 1996. Sunrise (SR) and Sunset (SS) followed 3 weeks later and Kapoho (K) after an additional 2 weeks. Fruit production was delayed by at least 2 months because of dry conditions. For the month of September, the cultivar W had fruit that averaged 676g with a Brix of 11.9; the values for SR were 386g and 12.9; SS were 376g and
12.5; and K were 356g and 12.8. A similar field is being planted in Pahala. Papaya fruit treated with the fungicide WECO-42894, vapor treated for fruit fly control, stored at 12 C for 14 days and ripened at 23 C showed no scalding or other injuries. Field efficacy trials have been started and data are being collected.
Impacts
(N/A)
Publications
- NISHIJIMA, W. T. 1996. Ethylene thiourea: Hawaii Papaya Market Basket Study, Col. Trop. Agric. and Human Resources Report. Pesticide Report HWN-94-01. Univer. Hawaii, Manoa. 56p.
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Progress 10/01/94 to 09/30/95
Outputs
The residue analyses for the year-long market basket study of fresh papayas in Hawaii's markets to determine the levels of ethylene thiourea (ETU), a breakdown product of ethylene bisdithiocarbamate (EBDC), present in the edible flesh has been completed. The final laboratory report has not been completed but preliminary results indicate ETU levels at lower than 15 ppb. A papaya cultivar trial planted in July 1994 in Hakalau (an alternative site for papayas to avoid papaya ringspot virus) on former sugar cane land has begun to fruit. This study was initiated to identify the different cultural requirements required to produce papayas commercially under different soil and environmental conditions. Summer fruit brix values ran from a high of 14.2% total soluble solids for Kapoho to a low of 12.6% for Sunset and Waimanalo. Sunset and Waimanalo were the first cultivars to set fruit and Kapoho the last. A larger cultivar trial with the same objectives as above was started in
Paauilo in June 1995. Concentrations of sucrose as high as 1.28% did not reduce the formation of appressoria by Colletotrichum gloeosporioides conidia. Papaya fruit treated with the fungicide thiram at .18 kg and .30 kg/100 l of water, vapor treated for fruit fly control, stored at 12 C for 14 days and ripened at 23 C showed no phytoxicity as a result of the thiram and/or vapor heat treatment.
Impacts
(N/A)
Publications
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Progress 10/01/93 to 09/30/94
Outputs
A market basket study of fresh papayas in Hawaii's markets was inititated in August, 1994 to determine whether ethylene thiourea (a breakdown product of ethylene bisdithiourea (EBDC) is present in the edible flesh. The protocol calls for sampling fruits grown on Hawaii, Kauai and Oahu islands once a quarter for one year. A calcium hypchlorite dip (1000 ppm) for 10 minutes reduced surface cane land on the Hamakua coast. The objective is to determine whether conditions are suitable for commercial papaya production. The papaya industry may be in need of alternative sites because of severe papaya ringspot virus disease pressure in the Puna district. Conducting cooperative study of metalaxyl-copper for registration for field use on papayas. Work continuing on the suppression of appressoria formation by Colletotrichum gloeosporiooides as a way of controlling fruit anthracnose.
Impacts
(N/A)
Publications
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Progress 10/01/92 to 09/30/93
Outputs
Fluazinam 85 SDG, a broad spectrum non-systematic fungicide, was less phytotoxicthan fluazinam 500F to papaya fruits at 1.12 kg a.i/ha. The former also showed excellent control of Phytophthora stem canker of papaya and significantly reduced incidence of fruit diseases. Treated fruits, however, became scalded upon being heat treated. In evaluations of heat treatments, the forced-air dry-heat (FADH) treatment showed little or no disease control properties; vapor heat (VH) significantly reduced postharvest diseases but not field initiated diseases such as anthracnose Thiabendazole used as a supplement to FADH or VH was effective in reducing postharvest diseases as well or better than a supplementary single hot- water dip.
Impacts
(N/A)
Publications
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Progress 10/01/91 to 09/30/92
Outputs
Field sprays of the broad spectrum fungicide, fluazinam 500F, was significantly phytotoxic to papaya fruit. Inert ingredients are suspected to be the cause. Because of phytotoxicity its efficacy on papaya fruit disease control could not by evaluated. Papaya fruit disease incidence was reduced by 10 - 20% over unsprayed controls by protecting thr fruit column from rain and fungal inoculum with a modified polyethylene banana bag over an 18 week period. Potassium sorbate, by itself or in a food grade wax applied as a postharvest treatment prior to vapor heat treatment resulted in no significant control of postharvest diseases over untreated vapor heat-treated fruit. Sodium hydroxide, calcium hypochlorite, sodium hypochlorite, EDTA, and sodium carbonate were not phytotoxic to papaya fruits in 5 minute dips at concentrations up to 8000 ppm.
Impacts
(N/A)
Publications
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Progress 10/01/90 to 09/30/91
Outputs
The fungicide chlorothalonil was previously demonstrated to cause scalding when papaya fruits from fields previously sprayed with the product were postharvest heat-treated to eliminate fruit fly infestations. This rendered chlorothalonil as an unacceptable replacement to mancozeb for exported Hawaiian papayas. In a test of two safeners, one increased the scalding damage and the other slightly reduced but did not eliminate the problem. The fungicide anilazine at 2.24 kg ai/ha was very effective in controlling anthracnose on papaya fruits when applied at 14-day intervals. Efficacy was reduced when applied at 1.12 kg ai/ha. However, fruits treated with anilazine became scaled when they underwent the vapor heat quarantine treatment. Fosetyl-Al showed efficacy in reducing blight of young seedlings caused by Phytophthora palmivora but only after three applications at weekly intervals prior to inoculation.
Impacts
(N/A)
Publications
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Progress 10/01/89 to 09/30/90
Outputs
A mancozeb residue trial using the cultivar Kapoho Solo was initiated on March 6, 1990 and completed on November 15, 1990. Mancozeb at 2.24 kg/ha was sprayed 13 times at 14 day intervals and fruits harvested 0, 1, 2 and 4 days after the last spray. Fruits were evaluated for ethylene bisdithiocarbamate (EBDC) and ethylene thiourea (ETU) in the edible flesh and in the whole fruit immediately after harvest; immediately after postharvest quarantine hot water treatments, and; after typical commercial postharvest treatments, handling and air shipment to the West Coast. The edible pulp portion of papayas had residues of EBDC from non-detectable to 0.33 ppm and ETU residues of 0.015 to 0.24 ppm (47 samples were less than 0.08 ppm, 5 were inexplicable high, up to 0.24 ppm). The PHI of 0 to 4 days postharvest treatment and handling did not appear to measurably affect EBDC and ETU residues in the flesh. Papayas appear to show a positive interference in the analytical procedure
for EBDC. Report submitted to the Environmental Protection Agency.
Impacts
(N/A)
Publications
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Progress 10/01/88 to 09/30/89
Outputs
A field test incorporating various combinations of "virgin soil" (VS) and soil amendments for the control of the "replant problem" that is primarily attributed to Phytophthora palmivora, at three times the recommended volume was significantly better, in terms of tree survival and height after 1 year, than any of the control or VS treatments at the recommended volume (4.3 liters of soil). Calcium carbonate and treble superphosphate at 2245 and 561 kg/ha consistently increased tree survival and tree height when used individually, in combination with each other, or in combination with VS or organic soil amendments. The optimum temperature for Rhizopus stolonifer development on stored papaya is 25C.Puncture wounds are more conducive to successful infection by Rhizopus than abrasion. Although hot-water treatments appear to induce a short-term resistance to Rhizopus when inoculation is within 2 hours of treatment, Rhizopus soft-rot development is enhanced in hot-water
treated fruits as compared to untreated fruits. Hot-water treatment of fruit significantly reduces Rhizopus incidence in commercial practice.
Impacts
(N/A)
Publications
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Progress 10/01/87 to 09/30/88
Outputs
Mancozeb applied at the label rate once every 2 weeks but substituted with metalaxyl + mancozeb (10% + 48%) at 1.1, 2.2, or 4.4 kg/ha every third spray for four times, showed excellent Phytophthora blight control of papaya fruit and stem. Metalaxyl + mancozeb at 2.2 kg/ha when applied four times once every 2 weeks followed by mancozeb once every 2 weeks also showed excellent control. Both schedules also caused remission of early stem infections of Phytophthora blight. Phomopsis soft rot of fruit is uncommon on fruits not receiving a postharvest hot-water treatment but is more common on double-dipped fruits and most prevalent when fruits are excessively heat treated. The standard hot-water treatment, when done as prescribed, will not result in Guignardia black spot but excessive treatment is a significant factor in its occurrence. A major factor in postharvest Rhizopus soft rot development has been shown to be a result of excessively high relative humidity (RH) during
forced ripening in storage. Reduction of RH with dehumidifiers reduced disease level. Field sprays also reduced Rhizopus soft rot from 9.8% to 2.3%. Rhizopus and Phomopsis (both require wounds for entry into the fruit) was shown to be capable of infecting through anthracnose and Cercospora blackspot lesions and causing soft rots.
Impacts
(N/A)
Publications
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Progress 10/01/86 to 09/30/87
Outputs
An analysis of the epidemiology of Phytophthora blight aerial cankers caused by Phytophthora palmivora over 16-month period show a strong linear correlation (f=0.86, a=0.63, b=0.64) between mean weekly rainfall and new incidence of cankers per week NIC). Mean weekly rainfall of 2.5, 5.0, 7.5 and 10.0 cm resulted in NIC of 0.1, 0.65, 1.29, and 2.0%, respectively. The data was developed in a commercial orchard in Puna that was sprayed on a 2-week cycle with mancozeb with a tractor powered mistblower. Insufficient coverage by mistblowers is suspected to be responsible for the lack of control. Preliminary results from a field test designed to identify control measures for the papaya replant problem caused by Phytophthora palmivora showed that the virgin-soil technique is the most effective. Preplant applications of calcium carbonate and treble super phosphate at 2245 and 561 kg/ha significantly reduced tree mortality 6 months after planting.
Impacts
(N/A)
Publications
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Progress 10/01/85 to 09/30/86
Outputs
Simulated shipping tests of commercially vapor heated papaya fruits showed a high incidence of stem-end decay. Botryodiplodia sp. which infrequently causes stem-end decay of untreated or hot-water dipped papaya fruits, was the most common cause of stem-end decay. Fusarium sp., Colletotrichum gloeosporiioides, Mycosphaerella sp., and Rhizopus sp. were less frequent causes of stem-end decay. Initial studies show that Botryodiplodia sp. is capable of surviving and growing at higher temperatures than the other less frequent fungi involved in stem-end decay of vapor heated fruits. Laboratory test confirm that the standard hot water treatment is very effective in controlling Rhizopus postharvest rots. However, Rhizopus begins to consistently appear in some packing houses whenever rainfall during the 14 days prior to harvest is 25 cm or more. Studies are continuing to determine whether inoculation takes place before or after hot water treatment.
Impacts
(N/A)
Publications
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Progress 01/01/85 to 09/30/85
Outputs
The combination product of metalaxyl 10% and mancozeb 48% applied at 1.2 and 2.4g/l (9353 1/ha) once every 2 weeks showed outstanding control of Phytophthora blight caused by Phytophthora palmivora while mancozeb and chlorothalonil applied at registered rates provided good but lesser control. Metalaxyl 2E drenches at 0.4, 0.8, and 1.6 ml/l applied at 1 1/site at seed sowing, 2 1/site at 3 months, and 4 1/site every 3 months threafter failed to control Pythium and Phytophthora root rot and Phytophthora blight in Puna. Under field conditions, however, metalaxyl 2E applied at 50,100, and 200 ppm for four times at 6 week intervals was effective in reducing seedling mortality caused by Pythium and Phytophthora root rots from transplanting to the start of harvest. Field tests of triadimefon 50WP at 0.15 and 0.31 g/l, biteranol 50WP at 0.31 and 0.61 g/l, metalaxyl 10% and mancozeb 48% combination at 1.2 and 2.4 g/l, chlorothalonil at 7.0 ml/l, and mancozeb 80WP at 2.9 g/l
all applied at 9353 1/ha for the control of anthracnose and Cercospora black spot demonstrated that the registered compounds (the latter two) were significantly better than any of the new fungicides.
Impacts
(N/A)
Publications
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Progress 01/01/84 to 12/30/84
Outputs
Disease monitoring studies suggest that approximately 2.5 cm of rain per week for several successive weeks is necessary to sustain a moderate level of infection by Phytophthora palmivora on the Sunrise Solo cultivar of papaya. Although primary Phytophthora blight infections in Kapoho Solo fields occur at random, most infection loci spread along the rows rather that in the direction of the prevailing winds. Field tests demonstrated that metalaxy1 drenches at 3,6, and 9 ml/1 applied once every 3 months beginning at seeding and Vapam soil fumigation at 467 1/ha were ineffective in controlling the replant problem. The standard virgin soil technique showed excellent control with tree growth only surpassed by a second virgin soil treatment utilizing three times the standard virgin soil volume. Preplant treatments of calcium carbonate and treble superphosphate at 1000 and 500 g/planting site resulted in significant reduction in tree mortality and increase in tree growth as
compared to standard planting practice. Colony characterizations of over 300 single ascospore and conidial cultures of Glomerella cingulata and Colletotrichum gloeosporioides from papaya petioles have failed to demonstrate any similarity between the petiole isolates and C. gloeosporioides from fruits. Inoculation studies with the petiole isolates also suggest that they are distinct from the fruit isolates .
Impacts
(N/A)
Publications
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Progress 01/01/83 to 12/30/83
Outputs
Metalaxyl 2E at 2 mg a.i./100 cmy soil drench provided excellent protection against root and collar rots of potted papaya seedlings caused by Phytophthora palmivora. Applied at 8 mg a.i./100 cmy soil drench, metalaxyl will also protect papaya against leaf and stem blights caused by P. palmivora, provided plants are approximately 20 cm or less in height. Protection of 30 cm plants and larger is marginal. At 8 mg/100 cmy, metalaxyl is marginally phytotoxic but usable. Laboratory evaluation of spray adjuvants for papaya field use identified significant differences among products. However, no single product excelled in both sticking and wetting abilities. Generally, those products that excelled in sticking ability performed relatively poorly as wetting agents and those that wetted well had poor sticking ability. Under relatively low rainfall conditions (about 2.5 cm of rain a week or less) surface coverage is more important than sticking ability, so spreaders are
more desirable. However, under higher rainfall conditions, sticking ability becomes an important factor and a combination spreader/stickers is more desirable.
Impacts
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Progress 01/01/82 to 12/30/82
Outputs
Field surveys, conducted in a 9-acre papaya orchard over a 7-week period averaging 4 inches of rain/week, showed that Phytophthora palmivora aerial canker incidence increased from .01 to .03% and 9.5 to 29.3% in lightly and heavily infected sections, respectively. Field observations have led to a reevaluation of the epidemiology of Phytophthora blight of papayas. Rather than direct inoculation of the fruit by airborne propagules, inoculation appears to usually take place by propagules that are deposited on leaf surfaces then carried in water droplets down the petioles and stem to the peduncles and fruits. Since mist blowers do not provide adequate coverage of the adaxial surface of the fruit and stem near the fruit column they would be less effective than hand-held hydraulic sprayers in controlling Phytophthora fruit rot and stem cankers. Papaya fruit surface area growth studies show that although fruits nearing maturity increase in surface area by about 7% a week,
the youngest fruits increase in surface area by about 33% a week. If no fungicide redistribution occurs, these percentages reflect the unprotected area as a result of fruit growth alone.
Impacts
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Progress 01/01/81 to 12/30/81
Outputs
Based on in vitro tests against Colletotrichum gloeosporioides and plant safety studies on 3-mos-old plants Baycor, Benlate, Vanguard, Daconil, and TBZ were the most effective fungicides. Mycosphaerella sp. has been repeatedly isolated from papaya trunks injured by Roundup, paraquat, and oxyflurofin. Greater susceptibility to this pathogen in 6-mos-old trees of cultivars Kapoho Solo, Sunrise Solo, and Waimanalo was demonstrated following herbicide injury as compared to mechanical injury or no wounding. Field tests over a 9-mos period have demonstrated that when disease pressure is low no significant differences in body rots occured when the maximum labeled rate of mancozeb was applied at 2- and 4-week intervals. These sprays with and without sanitation measures were ineffective in controlling stem end rots but the standard hot water treatment provided excellent control. This supports the hypothesis that inoculation occurs during or after harvesting. Disease
ratings continue to show that Kapoho Solo is the most resistant cultivar to powdery mildew of the seven being tested. Current data suggests resistance to powdery mildew involves one mechanism limiting the number of lesions and another suppressing sporulation. Sulfur applications reduced the total number of lesions formed however, spore production per lesion in treated plants was not uniformly reduced.
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Progress 01/01/80 to 12/30/80
Outputs
Acridine orange fluorochrome and safranin O diachrome methods were rapid and consistent for ascertaining nuclear numbers in Rhizoctonia solani-like fungi. R. solani (multinucleate) causes papaya root rots and damping off, whereas Rhizoctonia spp. (binucleate) obtained from papaya roots were non-pathogenic. Ridomil applied at 0.56, 1.12, and 2.24 kg (a.i.)/ha did not yield consistent results at 3 replant field sites, each test with 8 replications. Fourteen isolates of Stemphylium obtained from papaya were morphologically separable into two groups (species). Pathogenically, they caused 3 types of fruit spots on Sunrise Solo; i.e., (1) large (1-4 cm), dark, sporulating lesions that continue to expand; (2) gray to black depressed lesions, intermediate (1-3 cm) in size; and (3) reddish-brown lesions (chocolate spot-like), small (0.5-1 cm) and restricted. The latter two types are difficult to distinguish from similar lesions caused by Colletotrichum gloeosporioides. C.
gloeosporioides isolates from papaya fruit and petioles were culturally separable into seven groups; fruit isolates were highly conidial or perithecial and petiole isolates were more mycelial with sparse conidial production. Despite poor climatic conditions for powdery mildew development, differences in susceptibility/resistance, based on sporulation and number of lesions, was demonstrated in at least two of seven in-bred papaya lines.
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Progress 01/01/79 to 12/30/79
Outputs
Papaya yield responses to hole-size treatments and pre-plant Vapam applications to control Pythium and Phytophthora root rots were not significant after one year in tests at two locations. Ridomil at 1 lb. (a.i.)/acre effectively controlled these root rots in greenhouse pot tests. A severe outbreak of Phytophthora blight in February 1979 was accompanied by an unprecedentedly high incidence of Phytophthora rots developing on fruits which had been treated by the standard hot-water method. It was found that 24-hr. infections are eradicated by the hot-water treatment but there was approximately 30% survival of 48-hr. infections. Isolations from chocolate spots yielded only a Colletotrichum, indistinguishable from C. gloeosporioides, which causes common papaya anthracnose. Most isolates from chocolate spots and common anthracnose incited both lesion types in addition to a gray depressed fruit spot. Hot-water treatment of C. gloeosporioides colonies resulted in 60-90%
survival in each of 18 isolates. The findings on hot-water treatment of Colletotrichum as well as Phytophthora, indicate the difficulty of eradicating deep-seated infections, emphasizing the need for effective field control.
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Progress 01/01/78 to 12/30/78
Outputs
Pathogenicity for causal agents of three previously undescribed diseases were established: a) Purple-stain (Erwinia sp.), b) Stem-end rot (Mycosphaerella sp.), the perfect stage of Ascochyta caricae-papayae, and c) Stemphyllium fruit spot. The purple stain disease is sporadic and of little economic importance, whereas Mycosphaerella is important in stem-end rot, and Stempphyllium causes severe postharvest damage when fruits are stored for prolonged periods. Perithecia of Mycosphaerella were abundant in the orchard; numbers of ascospores increased abruptly immediately after rain. When no rain occurred numbers peaked at 3-5 AM. If hot water treatment was applied within 40 hours of inoculation, no symptoms developed. Field tests using Vapam at 100 gal/acre applied to 9 sq. ft/planting site was compared with non-fumigated as main plot treatments were installed at two locations to control papaya yield decline in replant fields caused by Pythium spendens and other
root-rotting fungi. As split-plot treatments, the standard virgin soil method (12" diameter multiplied by 4" deep holes) was compared with larger and deeper holes (12" multiplied by 12" multiplied by 12" and 17" multiplied by 17" multiplied by 12"). Growth response, was significant for fumigation at Pohoike, and highly significant for increased hole size at Keaau.
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Progress 01/01/77 to 12/30/77
Outputs
Field control of alternaria fruit spot, anthracnose, and to a lesser extent, stem-end rot of papaya were controlled by biweekly sprays of chlorothalonil (BRAVO) at 2 and 4 pts./acre. This fungicide is now cleared for use in orchard applications. Penduncle infection and subsequent stem-end rots are currently the most important post-harvest diseases of papaya in Hawaii. A monitoring program shows 90-100% of fruits of some growers may show disease only five days after removal from 7-day cold storage (50 degrees F). Other growers average 5-15% under the same conditions. Post-harvest handling practices (especially time and method of peduncle removal) are directly related to disease incidence. Disease is reduced by TBZ (thiabendazole), Benlate, Topsin M. or Guazatine used in addition to hot water. Control improved with addition of wax or spreader-stickers. Fungicides controlled disease 30-55% through two weeks of cold storage plus 5 days ambient temperature but not
after 3 weeks cold storage. Pythium splendens was the predominant fungus in a root rot survey of papaya showing yeild decline characteristics; Phytophthora palmivora, Fhizoctonia sp., and several other Pyghium spp. followed. A fumigation test utilizing Vapan to control root pathogens is in progress. Samples from leaf axils during rain revealed presence of P. palmivora in 2 of 100 axils.
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Progress 01/01/76 to 12/30/76
Outputs
Residue and efficacy tests for clearance of chlorothalonil (BRAVO) as orchard spray were completed at two test sites. A tolerance has been requested from EPAthrough the IR-4 program. When biweekly spray applications were discontinued, twenty weeks passed before an increase in disease was measurable, indicating that protection of fruits in early stages of development is critical. In post-harvest dip studies, benomyl (Benlate) gave best overall control of anthracnose, stem-end rot, fungal growth on the broken stem and internal blackening. Benlate is most effective when used in combination with hot water; it is effective applied in the host water tank or in cold water following hot-water treatment. It is more effective when applied just before packing (24 hours after harvest) than at harvest or four hours later. Benlate clearance awaits a federal hearing on its current registration. Phytophthora capsici isolates from papaya fruit rots were nearly equal in virulence
to P. palmivora when inoculated to mature papaya fruits. Other P. capsici isolates from pepper,tomato, and macadamia were significantly less virulent to papaya fruits. Rhizoctonia sp. from papaya seedling damping off and Pythium splendens from papaya root rot specimens were shown to cause root rot in papaya seedlings.
Impacts
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Progress 01/01/75 to 12/30/75
Outputs
Biweekly sprays of chlorothalonil (Bravo 6) 2 and 2 pts/A on field papaya plots in Maui, decreased the number of Alternaria lesions per fruit by 43 and 56% respectively as compared to the control. Benomyl (Benlate) (1 lb/A) was not effective in controlling Alternaria fruit rot on Maui, but did reduce fruit spots caused by Ascochyta caricae and Colletotrichum gloeosporioides, on Maui and in Pohiki on the island of Hawaii. Neither chemical was as effective as Dithane M-45 in reducing aerial Phytophthora infections. In greenhouse tests, 2formulations of pyroxychlor, (Dowco 269: M-3860 & M-4113) applied as a drench 120-x 1200 ppm to papaya seedlings, 15 ml/plants were most effective against Phytophthora root rot infections. Field tests for fungicidal control of papaya collar rot at Malama-ki were terminated for lack of uniform disease development.Studies are underway to induce high collar-rot incidence in the greenhouse so that controlled fungicidal tests can be
undertaken. Phytophthora capsici, obtained from rotted papaya fruit from Hana, Maui, was found to be virulent on papaya fruit; of approximately 30 trees in one field with fruit rots, 1/2 of isolates were P. capsici, the rest were P. palmivora. A laboratory method was developed for enumerating populations of Phytophthora palmivora in soil.
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