Has new plant tissue emerged or have treated leaves or fruit expanded substantially since the last application?
If so, these new tissues are probably not well protected since redistribution to fungicides is limited, particularly in dry weather. In addition, young tissues may be more susceptible to some diseases and therefore would need extra protection. Make sure to apply a fungicide if rain or heavy dews are in the forecast and pathogens are still active. Is residue still visible on plant surfaces? Depending on rainfall and the period of time since the last application, fungicide residues may remain visible on plant surfaces. The question is whether these residues are still active. Fungicides on exposed plant surfaces may not be present in high enough concentrations to be effective after two to three weeks, even in the absence of rain. Most fungicides are subject to natural breakdown, either by ultraviolet (UV) light or by microbes. Ziram, for instance, is known to be degraded by UV light as are many other fungicides and insecticides. Since sunlight has been intense in the last few weeks, fungi
