Uracils, substituted ureas and other long-term residual herbicides are used to obtain total vegetation control usually for long periods of time. These products are persistent in the soil for one or more growing seasons and are taken up by plant roots. Damage occurs when the material is applied over the root zone of nontarget plants. An upward spiral pattern of healthy foliage may appear on some conifers. Some long-term residuals may cause veinal chlorosis (yellowing of veins and adjacent tissues), particularly the uracils and substituted ureas which are photosynthesis inhibitors. However, they rarely cause marginal or interveinal necrosis, which instead may be caused by triazine herbicide injury.