Micrometeorology in the potato crop

One of the problems involved in the study of potato virus diseases and of blight [Phytophthora infestans] is the accurate determination of the microclimate around the plants as it affects the aphid vectors of the viruses, and the conditions under which condensation can occur on the leaves to form a film of water favourable for blight [R.A.M., 34, p. 56]. In work on the aphid problem [cf. 29, p. 379] it has been shown that with an 8 m.p.h. wind at 2 metres, ventilation in the crop rarely exceeded 4 m.p.h., while with a 3 m.p.h. wind it was rarely more than -1/2 m.p.h. Thus weather inside the crop often favours aphid activity when that outside does not, but occasional aphids flying in the crop might be carried considerable distances to form new foci of infection.