The good rain cycle that started in the Karoo in early summer 2020 broke a long-standing drought in many parts of the Karoo and conditions favored an outbreak of the brown locust, Locustana pardalina.
Insect Ecology Division, ARC-PHP said the brown locust swarming continued well into the autumn and winter of 2021 with many hundreds of swarms laying eggbeds of a wide area of the Karoo before being controlled. Conditions were therefore set for a very large locust outbreak in the summer of 2021 once the rains fell.
ARC says the eggs lay dormant in the soil over winter, but the first hatchings were reported in September 2021 in the eastern Karoo (Graff Reinette and Cradock districts) and in the northern Namaqualand area of Springbok and Concordia, which was unusually early in the locust season. Some locusts hatched on as little as 10-15mm of rainfall, but others only hatched later when more widespread rains fell across the Karoo later in October and into November.
Swarms escaped control and laid eggs over a wider area, while later rains in November caused new hatchings from overwintering eggbeds in the Central and Upper Karoo. A second generation developed in November and December with widespread hopper outbreaks reported over the eastern Karoo, Bushmanland and Central Karoo, even into the Great Karoo.
The ARC continued to say a heavy locust campaign was waged across Bushmanland (Pofadder to Gamoep area) and the Central Karoo in December and thousands of hopper band targets were controlled. However, many other hopper bands escaped control and fledged in late December with numerous adult swarms now on the wing.
The fledging of the second generation often occurs over the Christmas period when many landowners are away on holiday, so there is always a significant drop in the efficacy of the locust reporting at this time, with farmers returning home in the New Year to see the veld full of locusts.
Current situation in Bushmanland, Central Upper Karoo and Great Karoo:
The intense hopper control campaign waged in this area throughout November and December has slowed down since Christmas, and adult swarms have vacated the area. Some swarms have been reported flying north from Bushmanland into the remote Kalahari towards Askam and farmers have been asked to report swarm sightings. These swarms will likely disappear into the Kalahari and their progeny will return to the Karoo as swarms later in the autumn.
The Central Karoo area of Carnarvon and surrounding Districts were busy controlling hoper bands before Christmas, but the situation is now a lot quieter as the remaining locusts have fledged and evacuated the area. Likewise, in the Great Karoo there was a large hopper control campaign before Christmas in the Prince Albert and Merweville areas, but there are now fewer reports of locust activity.
Current situation in the Eastern Karoo:
The second generation of hoper bands is now largely compete and the majority of the control effort is focussed on tracking and controlling the adults swarms in the area. The smaller swarms have coalesced into large swarm targets, some of which have been reported as being well over 30km long when in flight and roosting at night on the Karoo bushes as a dense blanket over and area of 2-3km2.
Large and fast-flying swarms are being reported over a large area between Middelburg, Colesburg Nouport, Hanover, De Aar and Prieska districts. Some of the swarms are flying east towards Philipollis in the Free State and will likely escape from the Karoo. Maize cropping areas outside of the Karoo could now be at risk from migrating swarms, but the maize is currently more mature and less vulnerable to damage than it was before Christmas. However, maize farmers should be advised to be aware of the threat of locust swarms.
The reports of fast-flying swarms flying high above the ground indicates that these swarms are already mature and will lay eggs immediately this week and for the next few weeks. A widespread 3rd generation of hatching hoppers can therefore be expected over large areas of the Karoo from late January into March 2022.
The brown locust control campaign is expected to continue over a wide area of the Karoo and Bushmanland well into the autumn months of 2022. The ongoing wetter rainfall cycle over South Africa, including many areas of the Karoo, is likely to support the intense swarming activity of the brown locust until drought conditions again break the outbreak cycle.
The Department of Agriculture’s locust management teams are highly motivated, but the control strategy and tactics need to be significantly modernised to improve the surveillance and reporting of outbreaks and the efficacy of the control response.
Current control conditions are difficult for the control teams in mid-summer as temperatures are high and the locusts leave their overnight roosting sites early in the morning due to the high light intensity and temperature, leaving only a limited window of opportunity in the morning to control the locusts while on their roosts. In addition, the flying swarms will only roost (sleep) late in the evening after dark, giving the control teams less time to prepare for the night spraying of the roosting swarms.
The socio-demographics in the Karoo have also changed a lot over the past 50 years, with perhaps a majority of farms in the remote Central Karoo and Bushmanland areas having non-resident farmers (absentee farmers), leaving huge gaps in the locust surveillance and reporting network. Locusts emanating from these vast unpopulated areas are now only reported when they are seen as late instar hoper bands crossing the main roads or as flying swarms when it is too late to mount an effective control campaign. An urgent re-think of brown locust control strategy in the remote Karoo and Bushmanland areas is urgently required.
ARC action to assist:
Contact has been made with the FAO office in Pretoria to try and implement a Technical Cooperation Project (TCP) to undertake a pilot trial of the FAOs eLocust3 electronic reporting and GIS mapping system in the Karoo. The ARC could assist with technical inputs on brown locust outbreak dynamics and campaign management expertise.