Bacterial Spot is a key pest of Peach, Nectarine and Plum and in some years like 2019 can cause significant losses. It is caused by the bacterium Xanthomonas arbicola pv. pruni. During bloom overwintering cankers begin to appear. These cankers are very similar to other peach diseases and are often difficult to distinguish when they first appear. Other cankers that may appear during bloom are caused by the blossom blight phase of brown rot, and constriction canker. While scouting last week the first signs of tip die back where observed. Typical symptoms are a gradual blackening of the tip with dead tissue moving down the twig. This is typical of black tip from bacterial spot and was observed in blocks of highly susceptible cultivars (Fig. 1).

Fig. 1 Tip die back likely bacterial spot.

In some blocks the twig was healthy and the tip began growing only to die back after leafing out and flowering. This is often a symptom of late winter/early spring infections of constriction canker. Indeed this was observed in a block of old trees that has a history of constriction canker. This is often a symptom of late winter/early spring infections of constriction canker. Indeed this was observed in a block of old trees that has a history of constriction canker (Fig. 2).

Fig. 2 Tip die back possibly constriction canker.

In none of these cases were cankers observed on flower buds lower down the on the twig as is typical of blossom blight and constriction canker. Spring cankers of bacterial spot that form around flower buds are less commonly seen in our region. Only tip die back was observed suggesting the likelihood that bacterial spot cankers are forming. In cases like this its difficult to diagnose the disease early on. The only thing that can be done is to note the trouble blocks and watch to see what develops. Blossom blight and constriction canker will eventually develop unique symptoms. Bacterial spot lesions will eventually show on the leaves. If you see these cankers forming during bloom its not a bad idea to assume its bacterial spot and include copper or oxytetracycline with your blossom blight sprays.