generally wet climate, irrigation is often used in the slightly drier Upper Hunter where the winter and early growing seasons are prone to drought. Hazards The chief viticultural hazard in the Hunter Valley is the threat posed by vintage season rains. Site selection on well drained soils are considered of vital importance and much effort is put into ensuring the canopy is open so air flow can help dry the grapes off. Of particular concern is bunch rot often caused by the fungus Botrytis cinerea. In the production of late harvest wines, such as Semillon, Botrytis can be desirable and is known as noble rot. But for other grape varieties, particularly red wine grapes, the fungus is unwelcome with its infection described as grey rot. In the late 1990s, research in Hunter Valley vineyards discovered that a wide range of pathogens caused various occurrences of bunch rot in the vineyards. These other pathogens included Colletotrichum acutatum (ripe rot), Greeneria uvicola (bitter rot) and other fungi from the genera of Aspergillus, Penicillium and Alternaria. Susceptibility of certain wine grape varieties were found to increase as the grapes reached higher Brix sugar levels. Further research in the 2000s, showed that some of the open canopy techniques used to prevent Botrytis grey rot may actually promote the development of some of these other types of rot. Ripe rot, in particular, seemed to thrive at the higher ultraviolet B (280–320 nm) light exposure that open canopies allow. To compound the potential problem for Hunter Valley wine growers is that, as of 2010, there wasn't any fungicides registered for use for this disease. Other concerns The unique environmental pressures of the Hunter Valley also conspire to give growers problem with "dieback diseases" that damage the wood parts of the vine and eventually lead to death. While the fungus Eutypa lata is present in the Hunter, research in the 2000s indicated that another pathogenic species related to Botryosphaeria is also present in the area. Semillon vines, in particular seem to be susceptible to Botryosphaeria (also known as bot canker) while, conversely, Eutypa dieback is rarely observed in the variety. Vines suffering from Eutypa die-back and bot canker exhibit similar wood symptoms and similarly experiences reduce growth and yields. A major difference between the two is that bot canker do not exhibit the same outward foliage symptoms that Eutypa die-back leave on the leaves and buds of