|After heavy rains, the sappy residue is quite rusty red.|
Birch (Betula sp) tend to be riddled with pests and disease in their latter life span. I've seen so many things plaguing birches lately. Including: bronze birch borer, stink bug, leafhopper bugs and aphids attacks. It's unfortunate they get so riddled with pests and disease when they are stressed.
Betula's (birch) are only one of many trees that can be infected by Phytophthora cankers. They start with lesions and wounds, either from insect damage, frost cracks, mechanical damage...etc. Usually the cankers develop after the tree has had a season of stress or drought. This summer has been unusually hot and dry, so this didn't come as a surprise.
Left untreated, the vascular flow of the tree will be inhibited, further stressing and weakening the tree.
The spores that cause the cankers germinate when water from puddles near the base of the tree splash onto wounded areas of the bark. This is evident, since the lesions are so close to the base of the trunk. Phytophthora spores thrive in wet soil conditions, where water puddles. Under this birch, there is a gravel path along one side, and when irrigated, water pools. There is frequent traffic on this path, which has compacted the soil beneath.
Treatment: Thankfully, trees can seal off wounds by compartmentally growing new rings of growth over the lesions. This takes time and several cultural measures need to be practiced in order to manage this disease.
A balance of moisture is necessary. Too much or little moisture plays a significant role with this disease. Birch trees like moist, well drained soils. Where birch trees grow in drought laden areas, the cankers are more common. However, if provided with adequate soaking and proper drainage of the root zone during dry periods, the trees can overcome the disease. In drought periods, soak the area to insure moisture penetrats down to at least 6 inches below the soil surface.
Aeration of the soil around the tree's drip-line will help moisture penetrate down to deeper roots. Alleviate soil compaction by aerating the soil. Take a gardeners fork and poke holes around the drip line of the tree, after a good rain fall. Over time, this provides more drainage, avoiding puddles forming too close to the base of the tree. In addition, provide several inches of composted bark mulch or a ground cover around the tree's drip-line. This prevents water from evaporating during the heat of the summer.
Avoid any heavy walking traffic after aeration and avoid wounding of the trunk or branches.
Following these cultural practices, will help the tree to seal itself and prevent further cankers from developing.