Abstract: An infestation of Peronosporales on plant leaves will only fully develop if the leaves experience a period of wetness of a duration sufficient to allow the penetration of zoospores into the stomata of the leaves. The duration of this period is temperature dependent. Apparatus is provided which includes a pulse generator arranged to generate pulses at a rate dependent on the ambient temperature, a signal gate controlled by a leaf wetness sensor to pass the pulses output from the generator only when the leaves are sufficiently wet to favor penetration of the zoospores, and a counter arranged to count the pulses passed by the gate to time a period the duration of which varies with temperature. Upon completion of timing, the counter outputs an infestation signal which causes a monitor counter to start counting the pulses output from the pulse generator whereby to provide an indication of the subsequent advance of the infestation.

Abstract: For an infestation of scab to develop through its initial stages requires the presence of prolonged periods of leaf surface wetness to enable the spores to germinate. Apparatus is provided which monitors the ambient temperature and humidity to detect the occurrence of periods of leaf wetness sufficient to permit the initial development of an infestation. When the occurrence of such a period of wetness is detected, the apparatus changes its operating state to indicate the progress of the infestation through its secondary stages, this progress being dependent on the ambient temperature but not the wetness of the leaves. The apparatus follows the progress of the infestation by means of a monitoring device which generates a pulsed signal whose frequency is dependent on the ambient temperature and humidity, the pulses of this signal being then counted in counter means and selectively displayed on a display.

Abstract: A braking device for controlling the torque transmitted to driving wheels via a differential gear, in which the speed and acceleration of each wheel is detected and the appropriate wheel is braked if its speed and/or acceleration exceeds respective predetermined thresholds if the speed and acceleration of the other wheel does not exceed these thresholds; the speed difference is detected between the two wheels for the purpose of controlling, with the speed and acceleration signals, a logic control circuit, preferably a ROM, which determines when the brakes of each wheel are to be applied and released.