Pasture spelling as a control measure for cattle ticks in southern Queensland

Abstract

When two herds of cattle (A and B) grazed their paddocks continuously, tick infestations of the herds were similar. In the second phase of the experiment, lasting 18 months, when herd B grazed two halves of its paddock alternately, tick infestation of this herd was about one-fortieth of that on herd A, which grazed an undivided paddock throughout; during this period herd A was sprayed with DDT on four occasions to control excessive tick infestations, whereas herd B did not require spraying. The lightness of infestation of herd B was attributed to the first move of this herd taking place in May when engorged ticks would produce few or no progeny, and to subsequent moves at about 4-monthly intervals which prevented the tick population from rising to troublesome levels. In the third phase of the experiment the subdivision fence was removed from herd B's paddock, and herd A's paddock was divided into two, so that in this phase 'pasture spelling' and "continuous grazing" treatments were interchanged. There was then an intermittent decline in tick counts on herd A and an increase on herd B, over the following 2 years. During this phase, tick counts on herd A totalled about one-third of those on herd B. Throughout the experiment the rate of increase of ticks did not exceed five times per generation. During phase 2, herd B gained more weight than herd A. This lead was maintained during phase 3. After the cattle left the paddocks in January 1957 and 1958, randomized pasture sampling showed a rise in larval numbers, followed by a decline to negligible levels after 2-3 months. In winter, larvae persisted for longer and less predictable periods. Engorged ticks were placed out in a wide range of environments for observations on egg production, egg development periods, percentage hatch, and duration of larval survival. Results were similar to earlier published data, based on observations in a small enclosure at Brisbane. Larvae which had survived up to 13 weeks on grass succeeded in maturing to adults when placed on cattle.