106 Oktober 2014 emergent seedlings. newly and seeds maize germinating on forage gerbils when stage planting crop the Damage to is reported. usually restricted been had State Free West North the in soils damage to maize crops on sandy severe where Sandveld the of areas bron Wessels- and Hoopstad the in conducted were trials research and surveys Field 2013. of end the at started Council, Research Agricultural the and Trust Maize the by A KIRSTEN FRIKKIE MALTITZ, VON EMIL in maize Update on gerbil management Graph 2: Burrow baiting with two rodenticides in a maize field. amaize in rodenticides two with baiting 2:Burrow Graph (10 m). mx24 seed untreated to compared seed treated phosphide zinc of density plant 1: Maize Graph ON FARMLEVEL

regions of ”, funded funded Africa”, South of regions crop fieldsrodent management pest in maize in theproject called “Ecologically-based summer rainfall Integrated pestcontrol nagmuis, leucogaster ( gerbil Bushveld The vegetation. of irrespective soils sandy prefer but woodland, to savannah from distribution, geographical awide have They Africa. South central to common and indigenous are Two Background and control methods. chemical effective determining of objective term ashort with utilisation, food and ecology, breeding rodent utilisation, habitat surveys; rodent species identification, ecological of consist actions project The PHANUEL MALEBANA, MALEBANA, PHANUEL Gerbilliscus species (formerly (formerly species ARC-Plant Protection Research Institute Research Protection ARC-Plant Rodent pest management / Maize / Habitat utilisation /Habitat /Maize management pest Rodent Bosveldse ) occurs Tatera ) phosphide, the incidence of gerbil damage zinc with treated been had seed maize inresulting but bare in patches, where plots colonies, the around seed maize minating ger- the up dug gerbils maize, untreated ed out around gerbil In colonies. the mark- 10 mwere mx24 of Plots seed. maize phosphide was compared to untreated zinc with treated seed maize field, the In ed seed. untreat- and treated between development seedling and germination the in ference dif- significant no with laboratory, the in tested was seed maize of germination the on treatment phosphide zinc of effect The Seed treatment sites. untreated and treated both in chemicals the of applications after size were and monitored activity before and with ready-bait rodenticides. Gerbil colony baiting burrow and planting, at phosphide ametal with treatment aseed were They areas. Wesselsbron and Hoopstad the in farms producing maize commercial on tools aswas potential tested gerbil management control chemical of types two of effect The trials control Chemical area, but the Highveld gerbil ( gerbil Highveld the but area, study the in found were species these Both . and Limpopo, to Province, West North the and Gauteng the highveld of the Free State, Mpumalanga, G. brantsii The Highveld gerbil ( Africa. southern into north further and west the in Cape Northern the to east, the in KwaZulu-Natal northern from Cape. nagmuis ( gerbil Cape the species, A third enter buildings. not do and climb not do They ha. 0,5 to up of area range ahome have males and colonies in association social aloose in live burrows, dig They food. hoard not do and insects and herbage seeds, eat nocturnal, are They gerbil. Bushveld the than conditions drier tolerates gerbil Highveld the but habitat, and diet in similar are species two The fields. maize the in identified species the , G. afra ) occurs from the Eastern Cape, Cape, Eastern the from ) occurs ) is endemic to the Western Western the to endemic ) is Hoëveldse nagmuis, Photo 1 Kaapse Kaapse ) was ) was 1 2a

3

2b

1ThHih1: The Highveld ld gerbil. bil 2: Maize seedlings of zinc phosphide treated seed com- pared to untreated seed. (a) Gerbil digging marks are visible near treated seedlings; (b) untreated seed was removed by gerbils. 3: Burrow baiting in maize. to seedlings was reduced. Gerbil digging environment, thus zinc phosphide treated susceptible to the bait, as there was little marks in the soil near treated seedlings seed must be planted within 24 hours of food available on the soil surface (Photo 3). (Photo 2) were noted, and the conclusion treatment. The use of correct protective Two different ready-bait (wax block) was made that a sub-lethal dose caused clothing when mixing is important. rodenticides, namely coumatetralyl and aversion towards zinc phosphide treated flocoumafen, and an untreated control, seed by surviving gerbils. Information gathered from producers that were applied in 20 m x 20 m plots with terbufos and ammoniac gas may have a known gerbil colonies. Two months after planting, maize plants in repulsive effect on gerbils, was tested in the marked plots (10 m x 24 m) were counted trials where these chemicals were used as Burrows in the plots were closed, the active to determine the impact of gerbil colonies part of normal farming practices. In a trial burrows were baited on day 1, the process on maize plant density. Zinc phosphide with zinc phosphide treated seed, planted repeated a week later (day 7) and the treated maize had an average 530 plants per together with terbufos (as a soil applied active burrows counted again after 14 days plot, compared to the average of 349 plants insecticide/nematicide) and compared to (day 21). Both rodenticides reduced the in the untreated plots – a decrease of 34% in zinc phosphide treated seed only, the com- number of active burrows by more than plant density (Graph 1). bination did not add to the effect of the zinc 70% compared to the untreated control phosphide treated seed on gerbils. within the three week period (Graph 2). Although seed treatment with zinc phos- The trials were repeated in the same plots phide was effective at reducing the im- Where ammoniac gas was used as fertiliser, pact of gerbil damage on maize at planting with the same gerbil colonies during May the number of burrows in the colonies of where it was tested at sites in the Free State when maize was at the pre-harvest stage, both treated and untreated sites was re- Sandveld, it may not be as effective in areas with similar results in the reduction of gerbil duced, but differences between the sites with acidic (low pH) water or soil moisture. burrows. It must be noted that the gerbil were not significant. The reduction in colony colonies had recovered to more or less the size can be attributed to the soil disturbance Zinc phosphide (Zn P ) is used as a same numbers during March to May so that 3 2 during the tillage (rip) process and not to the rodenticide because it is claimed that its the trial could be repeated. “smell” of the chemical. pungent, garlic-like odour attracts , but repulses other . Birds are not Project trials are ongoing. We thank our sensitive to the smell. The acid in the Burrow baiting funders; the Maize Trust and the ARC digestive system of rodents reacts with Burrow baiting trials were conducted in a for their support, and Grain phosphide to generate the toxic phosphine maize field during February to March when SA and the produ cers in gas (PH3). Zinc phosphide breaks down maize was in the vegetative growth stage the Sandveld for their co- when exposed to water or moist soil in the and it was presumed that gerbils would be operation. October 2014 107