Twig blights, stem cankers, stem blights.  These diseases are caused by several fungi including species of Phomopsis, Fusicoccum, and Botryosphaeria.  The most visible symptoms of canker diseases are dieback of twigs, branches, or entire stems, often adjacent to healthy parts of the same plant.  Dead branches may have brown or reddish-brown leaves clinging to them (Figure 1).  Symptoms may begin on smaller twigs and then spread into larger branches and the crown.  Some lesions appearing on infected stems may be a red-maroon-brown color and be centered around a leaf scar, with a bulls-eye pattern.  Other lesions may appear as a broad brown or tan discoloration of the woody tissue, often on one side of the stem.  Main stem infections can quickly lead to flagging and dieback of the entire stem (Figure 2).


Image 1. Twig affected by blueberry canker disease.



Image 2. Phomopsis canker causing dieback of blueberry branches (APS photo).

Phytophthora Root Rot.  Root rot, caused by Phytophthora cinnamomi or other species of Phytophthora is usually associated with poorly-drained areas of a field where the fungus thrives and survives for long periods of time.  The very fine absorbing roots turn brown to black; larger diameter roots may also be discolored.  Above-ground symptoms include chlorosis and reddening of the leaves, small leaves, defoliation, branch dieback, death of entire stems, stunting, and death of the entire bush.  The disease may be present in a few infected plants scattered throughout the planting, but is more often localized in a group of plants in a low lying area of the field (Figure 3).  Heavy clay soils often favor root rot.

Mummy Berry.  This sometimes-devastating disease is caused by the fungus Monilinia vaccinii-corymbosi.  The fungus overwinters in mummified fruit on the ground.  Young shoot tissue infected in early spring may become blighted, resembling frost injury.  The fungus also infects the developing fruit causing it to become malformed, and turning salmon or grey by midsummer (Figure 4).  By fall, these fruit drop to the ground where they turn to mummies, ready to produce spores the next spring.

Botrytis Blight/Gray Mold.  The fungus Botrytis cinerea causes ripening fruit to rot with a typically gray, moldy cast (Figure 5).  The fungus also causes a stem canker which is similar to that caused by other fungi.  Cultivars with tight fruit clusters are more prone to gray mold.

Anthracnose.  Caused by the fungus Colletotrichum gloeosporioides, anthracnose primarily rots fruit, but also infects twigs and spurs.  The disease causes a soft, sunken berry rot, usually on the calyx end, which ruins fruit quality.  The fungus may produce a salmon or rust-colored mass of spores on the rotted berry.  Anthracnose can also cause a post-harvest fruit decay and is favored by warm, wet weather.

Iron Chlorosis.  This abiotic disease appears as chlorotic (yellow) and stunted plants (Figure 6).  The major cause of chlorosis is planting on a site with pH levels above 5.5.  The best soils for blueberries are well-drained sandy silt loam or silt loam, with a pH of 4.5 to 5.2, organic matter of 4 to 7% and adequate phosphorus and potassium.  Blueberries with iron deficiency will be growing under stress and be more susceptible to many of the canker diseases.


Image 6. Interveinal chlorosis of Blueberry leaves caused by iron deficiency.

Blueberry disease management.  With good crop management, most blueberry diseases can be avoided.  The following suggestions should be useful:

One can obtain some early warning of the presence of these pests by checking the UK-IPM web pages (http://www.uky.edu/Ag/IPM/ipm.htm). Corn earworm is one of the insects that we trap for at both Princeton and Lexington, KY.  (Those of you in the southern tier of counties, especially the purchase area, may want to check the University of Tennessee traps at Jackson and Milan. http://www.utextension.utk.edu/fieldCrops/cotton/cotton_insects/ipmnewsletters.htm).

 The Kentucky graphics will illustrate to you the presence of the adult moths as indexed by these traps. Remember the moths are not your target; it is the caterpillars that do the damage.  But the caterpillars will begin appearing sometime after the moth flight, depending upon temperature.  Also, our graphics provide you with a view of what this years’ population size as compared to previous years, and a rolling five year average.

You should be scouting from late bloom through maturity.  Late planted fields, especially those in which a closed canopy did not develop, and are located near maturing corn fields are at greatest risk.

Adults are buff to light green moths with a wingspan at rest of about 1/2". Eggs are white to pink, about 1/30" wide and laid singly.  Larvae (worms) are very small to 1 1/2" in length when full grown.  They are usually tan to pale green with several dark stripes down the back.  However, color may be quite variable, with some individuals almost black.

These insects feed almost exclusively on pods.  They eat away the pod wall and completely consume the seed.

If you are using a shake cloth in wide rows the threshold is greater than 2 worms per row foot. If you are using a sweep net in narrow rows the threshold is 9 worms per 25 sweeps on average. In both cases one should sample in at least five locations in each field and average the results.
So, just to review; factors for increasing risk from this pests are: late planting, late blooming, open canopy and nearness (especially during bloom and early pod set) to maturing corn. The greatest area of risk will be the Purchase Area and the southern tier of Pennyrile Area counties.