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1. Late blight occurrence and LB severity by major production area in the country or countries in the region. What crops were affected (tomato, potato, others)? Disease sources (seed, cull piles, volunteer plants, soil)?

Prior to 2003, late blight was not known to occur in PNG. In 2003, PNG suffered a late blight epidemic similar in many ways to that which occurred when the pathogen was first introduced into Europe in 1845. The combination of susceptible plants and favorable environment led to almost complete crop destruction. According to Pitt and Wicks (2003) there was no marketable yield in many cases. The burgeoning potato industry in PNG came to an immediate halt in 2003.

Most of the potatoes in PNG are grown in the highlands in the areas around Wabag, Mt. Hagen and Goroka. Late blight swept through this area in a matter of months after it was first noticed in early 2003. The movement of the pathogen was basically from west to east. Researches in PNG assume that the pathogen came from the Irian Jaya, on the western side of the island.

Following is a description of the onset of the disease in 2003 and possible origins of the pathogen from the report by Pitt and Wicks (2003).

“The first confirmation of the presence of late blight of potato in PNG was in Enga Province in January 2003. Prior to this the disease was not known to occur within PNG. There was initially some uncertainty as to the reason for rapid haulm death and defoliation of the crops in Enga Province but the presence of Phytophthora infestans was confirmed by the pathology services of the National Agricultural Research Institute (report form P Kokoa, January 2003). The disease spread quickly from west to east across the highlands with the first reported cases in the Western Highlands Province in late February 2003, in Simbu Province by March 2003 and in Eastern Highlands Province by the end of April 2003. The disease may not yet be present in some of the more isolated valleys of the highlands region but it could now be considered to be endemic having undergone an extremely rapid migration through all the major potato production areas.

There is anecdotal evidence that the disease may have been present in the Upper Sepik areas prior to 2003. Reports obtained from farmers in the Telefomin and Oksapmin areas indicate that their potato crops died from a mystery illness or sickness in mid 2002. This technical assistance visit has been unable to visit this region. Late blight has been reported by David Minemba, NARI, as present in these far western areas of the PNG highlands. It seems logical that the disease may have been present in this area for some time and has taken a little time to find a path across the Strickland Gorge and establish the major epidemic that has been experienced in 2003.”

There is little evidence that tomato is infected. After repeated questioning nobody gave an account of tomato late blight being a problem. We visited a field in June 2004, and there was no blight, although the field had been heavily treated with copper-based fungicide. There are no other known hosts in the area.

Fungicide use is going up, causing increased cost of production, environmental problems and risk to human health. Business is hurting as there is less cash and reduced business activity. Many smallholders have probably pulled out of potato production, which was their primary source of income in the past.

Potential late blight severity. Weather data collected and kindly provided by Martin Gunther were used with a late blight disease simulation model to compare potential late blight severity in two locations in PNG (Mt. Hagen and Taluma) with severity in two other locations (Figure 1).

Potential severity at Mt Hagen (1700 masl) is similar to that of Toluca, Mexico (a location known for severe late blight epidemics). Potential severity in Taluma is somewhat less than in Toluca, but greater than in Huancayo, Peru (3300 masl), where late blight is not considered very severe. Overall, this indicates that severity at the PNG sites is about as expected for those altitudes in the highland tropics. Toluca is subtropical and gets a heat boost in the summer. Epidemics in PNG were simulated for the months of February, March and April 2003: in Toluca for July to September 1998: and Huancayo for January to March 2001, which correspond to primary production periods for each location. The reduction in disease severity at Mt. Hagan at 25 days after Emergence is due to 3 very dry days that occured about 1 week earlier. The simulator probably exaggerates the effect of the dry days.

2. LB impact (foliar damage, yield losses, tuber rot occurrences)?

It is very difficult to measure the complete impact of this disease. As NARI officials and other potato workers indicated, a 15 million Kina industry was abruptly halted in 2003 when late blight hit. Therefore, the immediate effects were catastrophic and went well beyond the producers, wholesalers and shippers. Much higher prices for potatoes in urban markets meant that consumers also suffered. Often, potatoes were not available in urban markets.

About 800,000 people live in the highlands of PNG that may be involved in potato farming. About 500 families (personal comm. M. Gunther) are involved in commercial production. When LB hit in 2003 it literally halted all potato production. Commercial growers are moving back into production with 3-4 day sprays of copper fungicide (Cuprous Oxide or Copper hydroxide). In 2004, some chlorothalonil was available but not widely used. Very small farmers had not yet found a solution to the problem as of June 2004. NGO’s and government officials are seeking ways to help small farmers get access to fungicides and spraying equipment.

Farm gate prices and commercial prices have increased between 300 and 400 percent after late blight was introduced and were still this high as of June 2004.

3. Fungicide use (amounts, types, etc.)?

In June of 2004 potato workers consistently mentioned that the primary fungicides in used were copper based (Cuprous Oxide or Copper hydroxide). We visited two agricultural supply stores in Goroka and found only these two fungicides and two formulations of cholorthalonil. The cholothalonil was much more expensive. The costs at the time of our visit were:

Nordox (58% cuprous oxide) 17.60 K per kg.

Kocide (50 % cupric hydroxide) 33.50 K per kg.

Barrack (72% chlorothalonil) 88.14 K per liter.

Bannis (40% chlorothalonil) 45 K per liter.

Prices in PNG Kina.

4. Other LB control measures (resistant cultivars, forecast systems, none)?

As of June 2004 there were no control measures beyond fungicides. All local varieties appear to be susceptible.

5. LB control effectiveness (fungicide or host resistance failures)?

The principle cultivar in PNG is Sequoia, which is highly susceptible. Other cultivars also exist but most appear to be susceptible. Most of these were probably introduced over the years by missionaries.

NARI began fungicide efficacy trials in 2003 and 2004. We do not have these data as of yet. Based on previous experience and conversations with workers in PNG, chlorothalonil works better and is more expensive than the copper-based fungicides.

6. Pathogen strains (mating type, fungicide resistance, virulence factors, etc)?

A collection of isolates was made in June 2004 and will be analyzed. At the time of this writing, nothing is known about the pathogen other than it is assumed to have come from Indonesia.

7. Disease risks and/or major needs?

Environmental conditions in the highlands of PNG are favorable for disease. In some areas (west) rainfall is relatively uniform throughout the year and risk of late blight is probably also year-round. In dryer areas, there may be periods when rainfall is not severe. Access to effective fungicides and spray equipment is a major need for all who wish to produce potatoes in PNG. There is also a need to introduce resistant varieties.

8.Any publications on late blight in the country?

There are no refereed journal articles that describe late blight in the country, but there are several reports commissioned by different organizations that focus directly or indirectly on blight.

Anonymous. (2004). Management of Potato Late blight in Papua New Guinea. National Agricultural Research Institute Research Project Proposal: 8. pp

Pitt, A.J. and T. Wicks. (2003). Late Blight of Potato, Phytophthora infestans. Ag Challenge pty ltd, South Australian Research and Development Institute Technical Assistance: 32.

9.Is tuber blight a problem?

Tuber blight does not appear to be a problem.

10. Other comments

Please send any comments to GILB(at)cgiar.org