A Song of Ice and Fire depicts medieval warfare as devastating the countryside, crop harvests, and peasant population with widespread abuses of non-combatants. Is this accurate of what warfare was really like during the War of Roses time period?

Yes, and for a much longer period than just the Wars of the Roses (ie. mid-to-late fifteenth-century). The encastellation of Europe in the eleventh- and twelfth-centuries made violent marches through enemy territory, known as the chevauchée, a highly popular and essential military tactic. The purpose of this form of warfare was to damage your opponent's financial income and their reputation - since one of the features of good lordship was the ability to protect and nothing demonstrated bad lordship like hiding in a castle while your land was ravaged. The treatment of non-combatants is a central topic to the study of chivalry (side-note: Gillingham has several fantastic papers available through Academia.edu, I highly recommend taking advantage of this and his other freely available articles), often romantacised by the idyllic imagination that noble warriors would spare those not explicitly involved in the combat, has been comprehensively demonstrated as untrue, see this post for more information.

In this Martin is accurate, but this does not mean, of course, that all knights were bloody sadistic torturers (ie. they were not all Mountains that Ride or the Bloody Mummers) but that such actions were a widely accepted part of warfare and only condemned within certain moral contexts or because they might contravene accepted norms or desired (quasi-idealised) standards but usually not explicit legal structures.

However, even the standards of chivalric conduct have been noted as being thrown out the window during periods of civil conflict. As Philip de Commynes, writing about the Battle of Towton (1461), noted King Edward 'shouted to his men that they must spare the common soldiers and kill the lords, of which none or few escaped'. As demonstrated by the violence of the Anarchy of the mid twelfth-century; the Baronial Movements of the thirteenth-century; the deposing of Edward II in the fourteenth-century; and the Wars of the Roses in the fifteenth-century, it is clear that chivalric conduct often did not withstand the force of civil strife (and these examples just restricting us to England and Normandy).

Traditional non-combatants usually lacked even this thin veil of protection, and when the aim was to better yourself at the expense of your enemy (and doubly so when you knew you would be unlikely to keep hold of any territory you might ride through) it was a fairly vicious time to not have a set of walls to hide behind.