Army worm Outbreak Necessitates Emergency Operation in Tigray
Dr. Wolfgang Meinzingen, UN-EUE Consultant and Dr. Robert Shank, UN-EUE Field Officer August 1994
Biology and Epidemiology
The African armyworm is the larval stage of the night flying moth, Spodoptera exempta. The larvae or caterpillar, when occurring in large numbers, can consume rangeland grasses or wheat, barley, teff, maize, sorghum or finger millet crops faster than 400 head of cattle per hectare. After molting through six stages or instars over 14-22 days, the larvae pupate in the soil to emerge as moths which reinfest at the same place or several hundred kilometers downwind.
The seasonal cycle of the armyworm begins with the low density breeding of dry-season populations in the cool, coastal highlands of Kenya and Tanzania. These small populations of the solitary phase, which do little crop damage, occurr in scattered grassy areas where it is not economical to spray or control them. As the Intertropical Convergence Zone begins moving northward causing the annual onset of the Meher rains, the strong winds accompanying the thunderstorms carry some moths to the interior highlands where primary outbreaks occur. Although not fully understood, it is here that the biological mechanism whereby a solitary pest transforms into the 40 times more active gregarious form takes place. It is thought that climatic changes at the onset of the rainy season, particularly when following a drought season, result in production of abundant forage which may trigger some response in the females laying the eggs. Because each female can lay 800-1000 eggs, as few as 30 moths could cause a serious outbreak of 15 million armyworms within two generations or two months.
During 1994 there were medium to large outbreaks in late March to early May in the Coastal, Nyanza and Rift valley provinces of Kenya which were monitored by the Desert Locust Control Organization (DLCO) and sprayed by the Kenya Plant Protection Department. By mid-April major secondary outbreaks were causing serious damage in Eastern and Northern Uganda and Southeast Sudan. The first outbreaks in Ethiopia were recorded in Borena on April 18 but not until mid-May did the movement encompass all of the Southern, Southwest, Ogaden and East/West Hararge areas. By June 17 it was evident that a major control operation was needed as 240,000 hectares were affected and 170,000 liters/kilograms of pesticides were being distributed to the zonal capitols of the appropiate Regions (Table 1).
Developments leading to the Northern Campaign
The MoA-Plant Protection in Dessie reported low moth numbers in light/pheromone traps at Kamisa, Kombolcha, and Dessie but were prepared with 6,600 liters/kg of insecticide and 124 hand sprayers. On May 24, 7,065 hectares (1066 hectares being grassland) were 10-20% infested and 1,314 hectares were already sprayed. However the Meher rains were delayed in the eastern escarpment areas and most maize and sorghum plantings were severely moisture stressed, thus providing little forage for the armyworms. Planting of short season crops had not yet begun so there would not have been substantial crop damage from armyworm even if outbreaks occurred.
On June 15 Dr. Robert Shank of the EUE began a forecasting survey of South and North Wollo and Tigray as reports were already being recieved of heavy infestations affecting about 40,000 hectares on the Gojam-Gonder side.
In North Wollo, the agronomist at Weldiya reported 5,559 hectares affected with 2,500 already sprayed. At hand were 32 sprayers and 5,900 liters/kg of pesticide. At Robit and Kobo, in North Wollo, moth traps were being neglected and numbers were not being recorded. Again sorghum and maize crops were nearly beyond hope of recovering even if rain would come. Farmers expected to use the stalks as forage and replant teff or pulses when rainfall came.
In Region 1 (Tigray), there were moth counts of 831 on June 3 from the Western zone (Shire)and reports of 24,500 hectares affected (7,000 being cropland). A radio call on June 24 of an additional 5,000 hectares of affected cropland signaled an impending severe outbreak.
In the Central zone, in Axum, a total of 3,500 hectares were affected. Five thousand liters of pesticide were sent to the zonal offices (2,200 to the western zone) and requests for additional assistance to the MoA-Addis brought the dispatch of 2,000 liters of pesticides. The DLCO spray plane arrived around June 21. Ten drums of AvGas and 2,000 liters of pesticide were dispatched by DLCO to Mekele and Humera on June 17.
Supplies Diminishing and Outbreaks Expanding
On June 17, at the regular FAO/DLCO/MoA meeting, it was reported that the outbreak of armyworm covered large areas of Borena, southern Bale, practically all of Hararge and Jigiga, Sidamo and the Omo area and parts of Jima and Welega. It was feared that pesticides of the MoA would be exhausted and an appeal was made to FAO and the donors for $897,000, $500,000 of which was for the purchase of chemicals, the rest for sprayers and safety equipment. The FAO agreed to contact Rome on an emergency basis but no donors were found. On June 30, at a specially called FAO meeting on the armyworm control campaign, while the spraying operations were known to be diminishing in the Hararge, South and Southwest, the report of 2,392 hectares affected by June 17 in Region 1 had grown to more than 40,000 hectares and was expected to reach 75,000 hectares by July 4. Chemical supplies of the MoA-Plant Protection Department were said to be exhausted. The government had allocated 1 million Birr for spraying expenses. A recent donation of about 32,000 liters/kg of pesticides from the Government of South Korea had already been cleared through customs and allocated to the areas being sprayed. It appeared that all resources had been exhausted and the campaign would soon end for lack of donors support for additional pesticide purchase. Shortly after the meeting, SIDA donated 1 million birr for the purchase from AISCO of 32,800 liters of pesticides.
Airlift and Aerial Spraying Operations Organized by EUE
With the knowledge of the strain already being placed on the single DLCO spray plane and an understanding of the historic food shortages in Region 1, it became apparent that help would be needed to transfer pesticides to Tigray and apply them in time to prevent severe crop damage. The window of time for application of pesticides in the case of armyworm is 7-10 days depending upon whether the infestation is spotted in the early instar stage and the air temperature where the larve are developing. Dr. Meinzingen, the former head of the FAO regional migratory pest control project, was requested by FAO and the UN/EUE to come to Addis on June 30 for a 17 day consultancy to assist in forecasting and verification of outbreaks, coordination of aerial control operations, donor awareness and solicitation, and training of local personnel in forecasting and control operations.
Based on the report that 8-10,000 hectares were affected in the Humera area where UN-HCR is resettling refugees, an emergency appeal was made to the Swiss Government to hire an additional spray aircraft from Ethiopian Airlines Spraying Service Unit (EA-SSU) and to transport fuel/pesticides to the area. The grant was recieved by Friday, July 1, the spray plane contracted on July 2 and moved to Axum July 3 for spraying July 4. By that time the infestation in Humera has pupated and the area affected around Axum and Shire had expanded; so it was decided to deploy the EA-SSU there. Specifications of the DLCO and EA-SSU planes are as follows:
DLCO EA-SSU Fuel capacity 100 ltr 250 ltr
Fuel consumption 80 ltr/hr(Avgas) 180 ltr/hr(Jet A-1) Chemical capacity 400 ltr 1200 ltr
Application rate .5 ltr/ha .5 ltr/ha
Area Sprayed 500 ha/hour 1000ha/hour1 (ave 5 hr day)Gross support supplies 1.6 MT/day 3.4 MT/day 1 The area sprayed is larger due to air speed and the larger chemical tank necessitating fewer returns for refilling.
The rates charged by the EA-SSU are as follows: -Spraying- 5208 birr/hr -Ferry (to and from refilling site) 2435 birr/hr
-Idle 1826 birr/hr -Guaranteed equivalent of two hours spraying/day unless weather/mechanical restrictions
The area sprayed by the two aerial applicators is given in Table 2. With stocks of fuel and pesticide low in the area being sprayed, it was necessary to assist the MoA logistically in support of deliveries. The Ethiopian Airlined DHC-5 cargo aircraft was chartered by the UN-EUE for the following flights/cargo:
Friday, July 8, 1994Schedule: Addis - Shire - Axum - Mikele - Axum - AddisCargo: Shire - 800 lts Avgas & 1000 lts ULV pesticide Axum - 1600 lts ULV & 2600 lts Jet A-1 Saturday, July 9, 1994Schedule: Addis - Shire - Mikele - AddisCargo: 2400 lts ULV & 800 lts Avgas
Sunday July 10, 1994Schedule: Addis - Shire - Mikele - Shire - AddisCargo: 800 lts ULV & 1400 lts EC (cargo from Mekele not known)
On Thursday July 7 two trucks were dispached from Addis, one by the MoA with 6 drums (1200 ltr) of Avgas and one by UN-EUE with 17 drums of ULV, 32 drums of malathion EC insecticide and 3,100 kgs of Carbaryl insecticide (the latter two being for ground application).
On Saturday July 9 an Ethiopian Airlines Hercules was chartered to airlift 6000 lts of ULV, 3200 lts of Avgas and 532 backpack sprayers from Addis to Mikele. Transport and distribution from Mikele to Axum, Shire and other places needed will be by truck. Table 2. Aerial spraying operations in West and Central Zones of Region 1 (Tigray) from June 28-July 10, 1994.
Axum Zone Shire Zone Date DLCO ESS DLCO ESS 6/28 2400 6/29 1200 3200 1200 En Route 6/30 1200 Rainy 1200 1600 7/1 1400 4000 pilot sick 1600 7/2 2000 " " 7/3 600 7/4 600 7/5 Fog-Rain 7/6 2000 7/7 2000 7/8 7/9 7/10
Current situation, Forecasting and the Farmers response
All remaining stocks of ULV in possession of the MoA and the AISCO have been moved to the aerial operation sites. An additional 30,000 liters donated by the Government of Japan is in process of port entry and clearance. Table 2 records the areas that have been surveyed for spraying as of July 8 in the Axum and Shire areas. Hand sprayers and EC pesticides will be distributed from the stocks transferred to Mikele. There remains about 20,000 hectares to be hand sprayed in the Axum area and 26,000 hectares plus the 9,065 in the Shire area. Further increases in the area infested can be expected though the worst is thought to be over since moth numbers are going down (discussed below) and moderate rainfall will be benificial to crop growth but not for small armyworm larvae.
However since rainfall has just begun in the Eastern and Southern Zones of Tigray as well as North and South Wello, outbreaks should be monitored through moth trappings and field observations. In fact an outbreak has recently been reported in the Timbien area west of Mikele. Also in the Humera area there was 8000 hectares of 1st generation larvae that was not sprayed so the larve pupated in the ground and upon emergence may infest locally or move on to more northern areas.
Table 3. Areas Surveyed for Aerial Armyworm Spraying in the Central and Western Zones of Region 1 (Tigray) as of July 8.
Central Zone (Axum) Western Zone (Shire)
Wereda Area (Hectares) Wereda Area (Hectares)
Chila 3000 Adinebred 6118Adi Arbaete 3301 Ade Hageray 4929Adi Abun 1476 Ade Daero 4379Edamariam 756 Medebai 2556Maikintel 500 Asgede 7901Endaba Tsahma 1600 L/Koraro 1925Enticho 2711 T/Koraro 1710 MaiTsebri 3710 Adi Wasla 1270 Tsimbla 243Already sprayed 12,000 Adi Remetz 324 Total 24,400 35,065Sprayed to date 12,000 11,200Allocated 12,000 14,800 Area infested suitable for aerial 400but ULV exhausted 9,065Pheromone moth traps are the simplest and least expensive method of predicting armyworm outbreaks. The synthetic female hormone attracts the male moth of only the armyworm, whereas light traps in addition to requiring electricity, attract many other species. When the number of male moths reaches 30 or more per day a light outbreak is eminent in 7-10 days and second generation outbreaks can be severe. During severe outbreaks moth counts in the hundreds per day are common.
Limited data on moth counts in several areas have been graphed in Figure 1. Some trapping stations aggregate several days counts when emptying or reporting data (See Mekele graph). This makes it impossible to accureately predict when outbreaks are likely to occur. Also it distorts the pattern of a normal cycle of an outbreak which is evident from the Shire data. Although moths usually arrive with the winds of strong thunderstorms, those storms may occurr over several days, the breeding and egg laying may be spread over several days, and the rate of larval/pupal growth is temperrature and food-source dependent. All these factors tend to spread out moth counts for the second ands subsequent generations. All the outbreaks occurred within a few days of the sharp rise in moth counts and could have been forecast based that data. The only exception is that of Addis Ababa, where moths arrived but mating, egg laying and larval development were retarded by low temperatures.
The knowledge and activities on the part of the local farmer is remarkable. Farmers were warned of possible outbreaks by radio but one farmer reported he knew what was coming by the number of moths flying into the light of his evening coffee ceremony fire.When the author was scouting fields near Adidaero in Shire Zone, the small farmers boy called "Ferenge" and showed the newly hatched 1/2 centimeter larvae hanging on the thread they spin to facilitate wind dispersal.
It is interesting to note from Table 4 the control proceedures practiced by the farmers in comparison to the area covered by the airplanes in Table 2. Cultural control is practiced mainly on grassland outbreaks and consists of collecting larvae by hand (sometimes fed to chickens), thrashing the area with thornbushes or trampling with cattle. The area covered by either cultural control or ground spraying is small probably due to the early stage of the outbreak in Region 1 at this time. When comparing to Table 1 and looking at the bold figures up to July 10, there was coverage of 10-25% of the affected area in spite of aerial spraying in East Hararge and Jijiga areas. One farmer who was very encouraged to see the spray airplane remarked, "Always before airplanes came to kill us; this time it was good to hear the airplane coming to kill our enemy."
Economics of Armyworm Control and Lessons to be Learned
Armyworm control will be another one of those expendatures that the new government had not planned on and could have done without. The loss has not only been the several hundred thousand liters/kg of chemicals, the costs of aerial and ground application and the millions of hours of labor directed toward saving crops rather than increasing production. Close to 1 million hectares will have reduced production due to complete or partial loss of crop leaf synthesizing area. CARE,Int alone was looking for short season crop seeds to replant 12,000 hectares of devastated crops, a 12,000 birr added cost let alone the expected 50% reduction in yield due to shorter season crops. Many areas which normally have poor weed control will experience drastic broadleaf weed growth (not affected by armyworms) because of reduced cereal crop stands.
To the UN and donors it must have seemed an expensive operation, airlifting chemicals and fuel into areas that could just as well been supplied over land by timely prepositioning. Also the utilization of both aircraft potential was dissappointingly low. However when comparing the overall cost of the operation to the number of hectares of crop saved, the cost comes to about $4. per hectare. Assuming that the mixture of maize,sorghum and finger millet will average 10 quintals or 1 ton per hectare, the cost to the food program of replacing that ton on site would be about $130. so it is not a bad investment not to mention the devastation that Eritrea was spared.
This brings us to lessons that we should recognize intellectually if not financially. It was after the drought of 1888-92, and again 1984, now again 1993 that armyworm exercised its devastating march across East Africa. Experts were fully aware of the problems in Kenya, Uganda and Sudan long before it reached Ethiopia. Possibly because of our reluctance to become involved in matters involving hazardous chemicals, due to our environmental awareness, we did not encourage endemic organizations to preposition chemicals because of already expired materials in the countryside. In the words of one of the 1993 crop assessment experts, Africa is going to have to become familiar with the agrichemical era in order to assure reliability of its much needed food supply.
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Editor: Ali B. Dinar, (firstname.lastname@example.org)