SA Graan Maart 2016

populations were established in the fields at the time of plant-

ing, than in fields where maize followed on other crops, but de-

pending on wastage that had occurred at the previous harvests.

In maize following maize plantings, where harvest wastage in the

form of cobs and kernels was evident, relatively large established

colonies that increased after planting, were noted (

Photo 3a

and

Photo 3 b

). High populated areas severely affected maize at plant-

ing, necessitating replant.

Large gerbil colonies in fallow land following on maize dwindled

to negligible numbers at the start of the new planting season. A

maize trial planted in a fallow field had no gerbil damage in the

2014/2015 season.

To determine gerbil diet through stomach content analysis, High-

veld and Bushveld gerbils were collected in new maize fields

where groundnuts were planted the previous season, in new

groundnut fields following on maize, and in natural vegetation

adjacent to crop fields, for a period of one year.

The Highveld gerbil mainly fed on seeds at the planting, the veg-

etative growth stage of the crop, and at harvesting, while those

gerbils collected from natural vegetation included insects in their

diet in mid and late summer. The Bushveld gerbil’s diet in the

maize and groundnut crop fields at planting consisted of seed and

herbage, and included insects during high summer. The diet of

gerbils in the new groundnut fields, consisted of seeds through-

out the season until harvest.

Maize fields where livestock grazed after harvest had lower gerbil

populations and smaller gerbil colonies at the start of the new

planting season, than fields adjacent not used for grazing.

Maize fields where fallen cobs were collected by hand before and/

or after harvest, had lower incidences of gerbil activity at the start

of the new planting season.

At the Ottosdal study site, research on the effectiveness of barn

owls in the control of rodents, ten breeding pairs of barn owls

in nest boxes were monitored for a period of nine months. The

ten pairs constantly occupied the nests and most bred twice in

the study period. It was estimated that the ten pairs were able to

consume 14 600 rodents in a year.

Conclusion and suggestions

The Highveld gerbil and the Bushveld gerbil are indigenous and

common to most of the summer rainfall region of South Africa.

Food availability during winter determined the gerbil colony size

at the start of the new planting season. The food abundance in

field at this stage, whether maize or groundnuts, is determined

by the amount of wastage that occurred during harvest. The re-

striction of wastage, removal of fallen maize cobs, and grazing

reduces the food available for gerbils to sustain large populations

and limits the extension of the breeding season.

Encourage predators of gerbils by allowing for areas of natural

vegetation, and providing breeding sites and raptor perches.

Although maize seed treatment with zinc phosphide was effec-

tive in reducing the impact of gerbil damage on maize at planting

(

SA Graan/Grain

, October 2014), zinc phosphide cannot be used

pending registration. The only alternative for gerbil control is ro-

denticide bait registered for the use against gerbils in crop fields.

Rodenticide as burrow baiting must be applied to infested fields

and headlands over a three week period with three

applications at seven day intervals, preferably

three to four weeks before planting, with follow-up

baiting where activity persists.

ONS TOEKOMS!

Boere is gebore versorgers van gewasse en diere,

rentmeesters van natuurlike hulpbronne en produsente

van voedsel vir gesinne buiten hul eie. Met ons

uitgebreide kennis van gewasverbouing en plaaslike

toestande is PANNAR jou vennoot om voort te bou op

hierdie sterkpunte, en jou meer kostedoeltreffend te

help boer om ’n suksesvolle boerdery vir toekomstige

geslagte na te laat.

2016/CORP/A/016A

GEWASSE VIR ’N

VOLHOUBARE

TOEKOMS.

www.pannar.com infoserve@pannar.co.za

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vir die toekoms

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