Heat stress and too much water can cause yellowing of leaves. If the stems themselves are not getting enough oxygen due to too much rain (or because the soil drains poorly), the top of the stem may start to get mushy. Eventually, the top part of the stem may dry out (turns dark brown and then faded/light brown) or the whole stem may dry out. You can prune out the yellowed part of the stem. Another way this can occur is if the stem has winter injuries due to early frosts but this would be noticeable earlier in the year; July 2 is starting to "feel" to late in year to be noticing the extent of winter damage.