Blueberry Pest Scouting Tips

More than a dozen arthropod pests and an equal number of diseases can attack highbush blueberries. The most important key pests are those that can be found in most areas where blueberries are produced. Some of these pests are discussed below in rough order of seasonal appearance.

Mummy Berry

This is one of the most common diseases that can occur in blueberry production. There are two phases of the disease — primary and secondary infections. Overwintering mummies near the soil surface produce miniature mushroom-like cups (apothecia) in the early spring in which ascospores are formed. During infection periods, ascospores shoot up from the ground and land on expanding leaf tissue. As these leaves wilt from the primary infection, conidia or secondary spores are formed.

Infection periods and pollinators, which land on infected leaves, can carry the conidia to open blossoms, thereby infecting the fruit. The infected fruit will “mummify” and over time looks like a little gray pumpkin. Upon cutting the fruit open, a white fungal mass can be seen developing in the fruit.

Scouting should start with ground examinations for mummies, especially in wet areas between the time green tissue first starts to show and half-inch of growth. An average of one or more cups per bush usually indicates moderate to severe disease pressure.

Primary shoot strikes should be scouted for prior to and during bloom. Look for flagged, necrotic leaves. A dark-brown to gray sporulation can often be seen on the leaf surface. The count can be based on 200 fruit clusters or approximately 2,000 fruit.

Nothing for that season can be done at this point, but the information can be used as an indicator of where disease pressure may be highest during the following season. This would be similar to monitoring mummified fruit on the ground during the dormant period.

Anthracnose

Usually considered a postharvest or even late season rot, the real problem occurs much earlier in the season. The fungus overwinters on twigs, especially on bud scales. Most infections occur during bloom and on young fruit. Therefore, good fungicide programs are most important during this period.

The infection cycle is highly dependent on variety. Bluecrop drops bud scales late, and is very susceptible to infection, and therefore needs a longer period of fungicide use. Post bloom sprays on other varieties have little value as long as the field is well managed and disease pressure is low.

The most easily recognized symptom during scouting is infected fruit. Field counts may be made using the 20 cluster times 10 bush sample method (approximately 2,000 fruit) and recording the percent of fruit showing anthracnose symptoms.

If infected fruit are seen during the early ripening phase, then additional fungicide applications should be made, and the presence noted for an improved disease control program the following year. Fruit infections first show up as sunken areas, then progress into masses of salmon-colored spores.

Fields may also be monitored prebloom and postharvest. During the dormant period, a field can be assessed for its approximate risk to anthracnose and judgments made for the potential use of fungicides in that field.

Depending on the number of fields being monitored, collect from 10 to 100 shoots, about 18 inches long, per field. Mist them well and enclose in a plastic bag. Maintain the shoots at room temperature for two to three weeks, then remove them and look for the presence of orange sporulation.

Count a branch as positive for anthracnose if there is at least one sporulating lesion, and record the number of branches that have one or more sporulating lesions. Heavy disease pressure is indicated if at least 20% of the shoots are positive.

During harvest, collect at least 1 pint per field per picking. Incubate at room temperature in plastic clamshell containers for seven days. Count the berries with anthracnose symptoms and calculate the percent of infested fruit.

Infected berries will have sunken areas with concentric rings of orange sporulation. The incubation method is more accurate, but both are used only as an indication of disease pressure for the following year, as well as an assessment of the current season’s spray program.

Blueberry Maggot (BBM)

BBM overwinters in a puparium in the soil, and adults emerge by early to mid June. Adults continue to emerge throughout the remainder of the season.

After seven to 10 days, eggs are deposited on green or ripening fruit just under the skin. Maggot larvae hatch in two to seven days, and develop inside the fruit for about three weeks.

Infested berries are soft and often have a depressed area at the point where the egg was laid. Infested fruit may drop, where the mature larvae emerges and pupates in the ground.

Monitor adult flies with baited yellow sticky boards hung in an inverted “V” in the top 6 inches of the bush canopy along field edges. Monitor at least once per week, preferably two times per week, and change the traps every two weeks.