It appears to be a nutrient deficiency along with leaf scorch. Because the area between the veins is yellow, while the veins remain green, it is likely iron chlorosis (iron deficiency). The leaves scorch easily in hot weather when there is a nutrient issue.

Iron chlorosis refers to a yellowing caused by an iron deficiency in the leaf tissues.  The primary symptoms of iron deficiency include interveinal chlorosis, i.e., a general yellowing of leaves with veins remaining green. In severe cases, leaves may become pale yellow or whitish, but veins retain a greenish cast. Angular shaped brown spots may develop between veins and leaf margins may scorch (brown along the edge).

Iron chlorosis shows first and more severely on the newer growth at branch tips. Growing leaves may be smaller than normal. Leaves may eventually curl, dry up, and fall. Fruits may be small with a bitter flavor.  Mildly affected plants become unsightly and grow poorly.  In severe cases or if iron chlorosis persists over several years, individual limbs or the entire plant may die.

It is common for iron chlorosis to show on a single branch or on one side of a tree. This is particularly common for plant species with marginal winter hardiness and on the southwest side of the tree following winter injury. Plant species and varieties vary greatly in their susceptibility to iron deficiency.

Iron is necessary for the formation of chlorophyll, which is responsible for the green color in plants and necessary for photosynthesis (sugar production in plants). Any reduction in chlorophyll during the growing season reduces plant growth, vigor, and tolerance to stress conditions. Plants with reduced vigor from iron chlorosis are more prone to winter injury, and winter injury may aggravate an iron chlorosis problem. Weakened plants also are more susceptible to other diseases and insect infestations.

The factors leading to iron chlorosis are complex and not fully understood. A number of chemical reactions govern iron availability and contribute to the complexity of iron chemistry in soils.

Many environmental factors also create or contribute to iron deficiency. These factors need to be evaluated and alleviated to the extent possible.  In most situations, attention to watering and soil conditions will satisfactorily correct minor iron chlorosis problems.

Please refer to the CSU Fact Sheets at the links below for more information.

http://www.ext.colostate.edu/pubs/garden/02911.html
http://www.ext.colostate.edu/mg/gardennotes/223.html