Care should be used in applying pesticides. Spiders are more susceptible to chemical pesticides, even some organic pesticides than many garden insects.
Methods of conserving spider populations in your garden include application of mulch, particularly straw, growing living mulches (cover crops) among your plants, and even allowing weeds to grow around the edges of the garden. These provide a diversity of environments and encourage the increase of spider populations. No-till gardening also increases spider populations, as conservation of spider populations is enhanced by reducing both chemical and physical disturbance of spider habitat. Read more about spiders in your garden in a research paper from the University of Maine.