Blueberry Cane Diseases

One approach to help sort this out is to closely compare canes on plants that are growing well with canes of the same age on plants that aren't. If they look the same, what you are seeing is probably normal.

Young canes (grown in the current year and into spring of the next year) should be smooth and the surface should be even, though lengthwise cracks will form as bark replaces the younger surface. Cut crosswise, young canes should be light green while older ones may show less color, but still be light. Color should be the same across the cane, except for slight variation from growth rings. Variation in surface color may be present, but as long as the discoloration doesn't extend into the cane, growth is likely normal.

If disease is present, fairly drastic color changes occur on random canes. If you run your fingers along the canes you may feel sunken areas. Often colors change within the infected area. Disease symptoms may progress from fungal entry points which can be buds, leaf scars, lenticels (raised pores on stems), pruning cuts (especially if wet conditions follow soon after cuts were made), and physical injury or burndown herbicide damage. Brown or tan discoloration in the cane indicates disease or possibly winter injury.

Symptoms to Watch For: Summer

During the summer, you can prune out infected tissue to prevent disease progression, so this is a good time to nip problems in the proverbial bud. If you find areas on the canes that appear to be diseased, cut progressively lower and far enough below the infected tissue to ensure that only healthy tissue remains.

Here are some common diseases and their symptoms.

Phomopsis cane blight, Botryosphaeria stem blight, and Anthracnose

The cane tip in Figure 1 was infected by Phomopsis; with this disease, infected tissue often "bleaches" as it ages. Note the "water-soaked" appearance at the invasion zone, which in this case is a very narrow area delineating healthy and infected tissue.

Figure 1. Phomopsis cane blight. Figure 2. Botryosphaeria stem blight on a one-year-old blueberry cane. Figure 3. Anthracnose on blueberry cane. Lesion tissue is flattened. Photos: K. Demchak, Penn State

Cankers in Figure 2 and Figure 3 show other symptoms to watch for—various shades of brown within the affected tissue, sunken or flattened areas, and reddening of tissue in the invasion zone. Botryosphaeria stem blight was isolated from the cane in Figure 2, and anthracnose from the one in Figure 3. Infections appear to have occurred through a bud or leaf scar.

The plant in Figure 4 was severely infected by Botryosphaeria stem blight. Lesions are visible on young canes where color changes from green to yellow to chocolate brown. Botryosphaeria stem blight is more deadly to young plants. The variety 'Duke' is very susceptible.

Figure 4. Plant from which Botryosphaeria stem blight was isolated. Note chocolate brown lesions on young canes and the dying young cane to the left. Photo: K. Demchak, Penn State

If infections from any of these diseases are not caught quickly, they can result in rapid cane death in summer during heat or drought stress. Leaves die and remain attached, referred to as "flagging", as no abscission zone is formed that would allow the leaves to fall off (as would normally happen in the fall). These canes should be removed and closely examined, as should other canes on the plant. It is difficult to find lesions on dead canes, as the entire cane surface may be darker than usual, so the lesion blends in.

Symptoms to Watch for: Dormant Pruning

Dormant pruning in late winter provides a good opportunity to look for disease symptoms in the canes that you remove in addition to pruning during the summer.

Botryosphaeria stem blight causes characteristic wedges of tan or taupe-colored wood in the cut stems. The cane on the left in Figure 5 shows a young cane that is only a little over a year old and that was recently infected with Botryosphaeria stem blight. Uninfected canes would be light green all the way through. In the cane on the right, the cane has been infected for longer and is nearly dead or completely killed.

Figure 5. Wedges of tissue affected by Botryosphaeria stem blight to varying degrees. Photos: K. Demchak, Penn State

Phomopsis cane blight causes a browning of the pith (Figure 6), often progressing far below the location of other cane symptoms such as those occurring at the tip. Be careful not to mistake this symptom for a borer, which will tunnel downward through the cane center and leave frass behind.

Figure 6. Phomopsis canker symptoms in stem. Photo: K. Demchak, Penn State

When pruning out infected canes, keep cutting until you reach healthy tissue with no discoloration. The entire cane may need to be removed in some situations. If diseases reach the crown area, the entire plant may be killed. Lime sulfur in spring and possibly fall (for Phomopsis) helps decrease disease incidence.

Things That Can Be Mistaken for Cane Diseases

Winter injury

Tips may die and are desiccated. Cut through buds in the spring to check for browning.

Herbicide injury

Cane surfaces may be injured and discolored by burndown herbicides. This injury provides entry points for fungi, so can increase disease incidence.

Road salt injury

Plantings near roads may experience salt burn from salt spray drifting onto canes. Salt injury is more obvious in the areas that are closest to the road. Elevated salt levels may not be detectable in the soil by the time injury is observed in the spring due to salts being flushed out by melting snow or spring rains.