ALGAL STEM BLOTCH

Algal stem blotch is a blueberry disease caused by the parasitic green alga Cephaleuros virescens Kunze, and it has become a significant disease on southern highbush blueberries in Florida. The alga is thought to enter the plant through natural wounds and openings, through pruning cuts, or by direct penetration of the cuticle. Early symptoms include small red blotches or lesions on green juvenile stems, with lesions expanding to form irregular cankers that can encircle canes. Bright-orange felt-like mats or tufts of algal growth appear from the lesions on young stems and older cane surfaces during summer and early fall when conditions are hot and humid. Leaves on symptomatic canes bleach white to pale yellow, and growth of the entire plant can be severely stunted as the disease advances. Leaf yellowing tends to occur on a few canes of each plant and is less uniform and blotchier than symptoms of nutritional deficiency. Algal stem blotch can lead to increased susceptibility to Botryosphaeria stem blight, in some cases leading to plant death. Plants that are stressed by abiotic or biotic factors are more susceptible to infection and subsequent disease development. To date, no systemic pesticide products have been found that will kill the algae living underneath the plant epidermis. Spray applications of copper-containing fungicides can help to reduce algal sporulation and protect healthy canes from infection for a few days after application. However, these applications do not impact existing symptoms or eradicate the disease. See Table 1 and EDIS publication PP344, “Algal Stem Blotch in Southern Highbush Blueberry in Florida” (https://edis.ifas.ufl.edu/publication/PP344).

ANTHRACNOSE LEAF SPOT, RUST, SEPTORIA, AND TARGET SPOT

Anthracnose, Septoria, rust, and target spot can cause premature defoliation, resulting in poor bud development and subsequent loss of yield. Fungicide timing for leaf spots varies across the state and by specific disease. Septoria can occur prior to harvest through late spring. Anthracnose leaf spots and target spots generally start postharvest and persist through summer. Rust is a problem in all Florida production areas. On susceptible varieties, rust can prematurely defoliate plants. Where leaves are not dropped in winter, rust can carry over on the previous year's foliage and can cause rust problems in early spring as well. Bravo Weather Stik® is labeled for control of both rust and Septoria leaf spots; this chlorothalonil product makes an excellent rotation partner for the strobilurin-containing products Abound® or Pristine®. However, Bravo Weather Stik® can only be used after harvest because chlorothalonil will damage fruit. See Table 1 and EDIS publication PP348, “Florida Blueberry Leaf Disease Guide” (https://edis.ifas.ufl.edu/publication/PP348).

AZALEA CATERPILLAR

The azalea caterpillar, Datana major, can be found in Florida from late summer to early fall on blueberries. Immature caterpillars are around 1/2 inch long and reddish to brownish-black with yellow and white stripes. Mature caterpillars are about 2 inches long and black with yellow to white stripes and a reddish head and legs. If left uncontrolled, a significant infestation can defoliate much of a plant. Although these caterpillars seldom kill the plants they feed on, the stress caused by defoliation can reduce flowering or fruiting the following spring. See Table 2.

BACTERIAL SCORCH (XYLELLA)

Bacterial leaf scorch, caused by Xylella fastidiosa, was first identified on blueberry in 2006 in the southeastern United States. Symptoms begin as a marginal-irregular leaf scorch, which may appear similar to symptoms of bacterial wilt or drought stress. Symptoms are initially observed on leaves attached to individual stems or groups of stems on one side of a plant. Plant vigor is reduced, stems and twigs of some varieties such as 'Meadowlark' turn a distinctive yellow color, and the plants eventually die. Diseased plants are typically observed randomly scattered throughout a field, rather than in distinct circles or groups within a row. Infected plants should be removed and destroyed. This bacterial pathogen is vectored by insects called sharpshooters and spittle bugs, including the glassy-winged sharpshooter. Infection levels may be reduced by controlling the vector with suggested insecticides.

BACTERIAL WILT (RALSTONIA)

Symptoms of bacterial wilt are similar to those of bacterial scorch, exhibiting signs of drought stress such as wilting and marginal leaf burn. Infected plants may also be more susceptible to developing severe symptoms of other stress diseases, such as Botryosphaeria stem blight, and therefore may show symptoms of both diseases. Crowns of plants with bacterial wilt have a mottled discoloration or light-brown to silvery purple blotches with poorly defined borders (distinct from the discoloration associated with stem, which is typically pie-piece-shaped and pecan brown in color). Wood chips floated in water from the crowns of plants with bacterial wilt will stream bacterial ooze (unlike plants with bacterial scorch or stem blight). Ralstonia can be spread easily in water, in soil, or through infected plant material, and infected plants may not initially show symptoms. Ralstonia can survive for years in soil, slowly spreading down and across rows of blueberry, leaving large circular patches of dead and dying plants. Where the bacterium is detected, remove and burn or deep-bury infected plants. Then, use soil drenches of products with phosphorous acids or salts to help protect surrounding plants or any replants from infection. See Table 1 and EDIS publication PP332, “Bacterial Wilt of Southern Highbush Blueberry Caused by Ralstonia solanacearum” (https://edis.ifas.ufl.edu/publication/PP332).

BLUEBERRY GALL MIDGE

The blueberry gall midge (BGM) is a tiny fly whose larvae feed on vegetative and floral buds. Blueberry gall midge will feed on leaf or vegetative buds, leaving young leaves deformed and misshaped. Gall midges lay eggs at any time during the growing season when the plants are making new flushes of growth. See Table 2 and EDIS publication ENY-997, “Blueberry Gall Midge on Southern Highbush Blueberry in Florida” (https://edis.ifas.ufl.edu/publication/IN1239).

CHILLI THRIPS

Chilli thrips are becoming a more pronounced problem in blueberry. Adults feed on blueberries in late spring to early summer shortly after the bushes are pruned. Chilli thrips feed primarily on young leaves, causing leaf bronzing and shoot dieback. During heavy infestation, the edges around younger leaves and stems are eaten and leaf curling occurs. The chilli thrips are smaller than the flower thrips and are approximately 0.04 inches long with dark fringed wings and dark spots across the back of the abdomen. Insecticides that can be used to manage chilli thrips include Delegate® (spinetoram), Assail® (acetamiprid), Sivanto® (flupyradifurone), and Apta® (tolfenpyrad). Conventional products that can be used to manage chilli thrips include Malathion and Sevin® (carbaryl). See Table 2 and EDIS publication ENY-2053, “Chilli Thrips on Blueberries in Florida” (https://edis.ifas.ufl.edu/publication/IN1298).

DIAPREPES (CITRUS ROOT WEEVIL)

Diaprepes larvae damage blueberry plants by feeding on the roots, including channeling and holes in the roots and feeding injury and girdling near the crown of the plant. Note that this damage is frequently observed some period of time after the larvae begin to feed on the roots, and at that point damage near the crown can appear similar to the effects of root girdling or mechanical wounding and abrasion. These injuries can kill or cause serious decline in blueberry plants and may also create an entry point for Phytophthora, causing a root rot infection. Management and control should target both the adult and larval stages. Control for adults consists of foliar insecticide sprays every 10–14 days when adults are active, beginning when 3 or more adults are found within 1-acre blocks. Larvae can be managed with insecticides either by directly drenching the soil area beneath the plant canopy or by applying them through drip or microjet irrigation systems. In addition, entomopathogenic nematodes may have potential for controlling root weevil larvae in blueberry. See Table 2 and EDIS publication ENY-999, “Diaprepes Root Weevil on Southern Highbush Blueberry in Florida” (https://edis.ifas.ufl.edu/publication/IN1241).

FLATHEADED BORERS

Flatheaded borers are a species of beetle in the Chrysobothris genus. The larvae tunnel through plant canes, ultimately killing the cane and acting as an entry point for disease. It is possible that adult beetles are attracted to stressed or damaged blueberry canes, with adult females laying eggs on the injured area, and larvae excavating tunnels just beneath the bark. This is a relatively new pest in blueberry, and research is ongoing regarding its life cycle, monitoring and trapping protocols, and control measures. See Table 2.

FLEA BEETLES

The blueberry flea beetle can cause serious damage during the summer months. Blueberry flea beetle eggs, and possibly adults, overwinter in the leaf litter of blueberry fields. Eggs are very small and orange-yellow in color, and hatching coincides with leaf bud opening. Larvae migrate to the foliage and feed on blossoms and leaf margins, giving the leaves a notched appearance. The larval stage takes 9–20 days to complete. Fully-grown larvae fall to the soil and pupate, with adults emerging approximately 15–28 days later. Adults are less than 0.25 inches in length, oval shaped, and a shiny copper bronze or metallic blue in color, and they chew small holes in the foliage. Adults mate and lay up to 200 eggs per female. The blueberry flea beetle has several generations per year in the southern United States. See Table 2 and EDIS publication ENY-411, “Insect Management in Blueberries in the Eastern United States” (https://journals.flvc.org/edis/article/view/116379).

IMPORTED FIRE ANTS

Ant baits employed in early spring as a broadcast treatment usually eliminate most but not all fire ant mounds within treated areas. Under high ant pressure, treating a second time in the fall provides better fire ant control. Most ant baits are slow acting and require up to 8 weeks to control active mounds because they interfere with reproduction, causing a gradual colony die-off. Extinguish® Professional Fire Ant Bait (0.5% methoprene) is labeled for use on all crop land sites. It is effective but somewhat slower acting than Esteem® Ant Bait (0.5% pyriproxyfen). In order for the bait to be effective, active ant foraging is essential. Worker ants must be attracted to baits so that they will carry the baits back to their colonies. Ideally, temperatures should be warm and sunny. Ant baits work best when the soil is moist but not wet. Avoid applying ant baits when conditions are expected to be cold, overcast, rainy, or very hot. Individual mound treatments are most effective when used as needed for the occasional colony that survives broadcast treatments. Mound treatments using insecticide baits should be applied in a circle 3–4 feet from the mound. Baits should not be placed directly on top of mounds so that mounds remain undisturbed. The colony will move the queen to safety if mounds are disturbed. See Table 2.

PHYTOPHTHORA ROOT ROT

Phytophthora root rot (PRR) is considered the most serious soilborne disease that affects southern highbush blueberries (SHB). Some SHB cultivars are considered tolerant and others highly susceptible, while rabbiteye cultivars are less affected by the disease. PRR is caused by the oomycete pathogen Phytophthora cinnamomi. Common aboveground symptoms associated with Phytophthora infections are reductions in plant vigor and premature fall discoloration. Symptoms at ground level and belowground include crown and root rots. Disease on susceptible hosts occurs when certain environmental conditions (primarily a saturated root zone and root wounding) trigger Phytophthora reproduction, infection and symptom development. PRR is typically more severe in low and poorly drained areas of a farm. The pathogen causes root discoloration (dark brown to black, instead of the normal cinnamon brown) and decay. Advanced stages of infection cause plant stunting, wilting, an abnormal or reduced root system, root rot, and plant dieback. Leaf discoloration also typically occurs, including yellowing, reddening with or without marginal burn, abnormal growth of new leaves, and defoliation. Plants affected by PRR may also be more susceptible to other dieback diseases including stem blight. Fungicides with the active ingredient mefenoxam, such as Ridomil Gold SL, are recommended where PRR occurs and are applied twice yearly (typically in January and June) through drip irrigation or as a band application directly to the bed. In addition to the phenylamide fungicide mefenoxam, which is applied to the soil, Aliette (Fosetyl-Al 80%) and numerous phosphorous acid products, referred to as “phites” or phosphonates, provide some control when applied as summer foliar sprays. See Table 1.

SCALE

Scale insects injure blueberries by sucking plant sap, inserting their mouthparts into a plant and remaining immobile throughout their lives. Signs of infestation are leaf yellowing (chlorosis), defoliation, fruit drop, sooty mold, branch dieback, or plant death. Soft scales, Coccidae, secrete a waxy covering over the body. They also secrete a large amount of sugary waste (honeydew) resulting in sooty mold, which can interfere with photosynthesis and slow plant growth. Of the soft scales, Indian Wax scale, Ceroplastes ceriferus (Fabricius), is the most prolific on blueberries in Florida. See Table 2 and EDIS publication ENY-2094, “Wax Scale on Southern Highbush Blueberries in Florida” (https://edis.ifas.ufl.edu/publication/IN1387).

SOUTHERN RED MITE

The southern red mite is the key spider mite pest attacking blueberry plants in Florida. Southern red mites primarily infest the lower side of the leaf, giving the leaf a bronzing appearance when the population is high. Southern red mites also produce a protective web made of silk over the infested surface to protect them from predators. The underside of leaves should be closely examined with a 10x hand lens for adults, shed skins, and webbing. Tapping foliage onto a sheet of white paper can also be used to find adult mites. A few miticides, including fenazaquin (Magister®), fenpyroximate (Portal®) and acequinocyl (Kanemite®), have recently been labelled for spider mites. See Table 2 and EDIS publication ENY-1006, “Mite Pests of Southern Highbush Blueberry in Florida” (https://edis.ifas.ufl.edu/publication/IN1284).

WHITE GRUBS (GRUBS OF ASIATIC GARDEN BEETLE, EUROPEAN AND MASKED CHAFER, AND ORIENTAL BEETLE)

White grubs are the larval form of certain beetle species, such as the masked chafer. They feed on blueberry roots, and damaged plants have the appearance of drought stress. It may take a number of years for larvae numbers to increase to a damaging level, although feeding injury on young plants can quickly result in symptoms and plant death. Masked chafer larvae are up to one inch long, with whitish bodies and brown head and legs. See Table 2.

YELLOW-NECKED CATERPILLAR

Yellow-necked caterpillars feed on the foliage of blueberry plants. Their bodies are covered with long, fine whitish hairs. The head is black, the area behind the head is yellow, and the body is covered with fine white hairs. Feeding by newly hatched caterpillars can skeletonize the foliage, leaving only the large leaf veins. In significant infestations, plant defoliation can occur. This can be minimized by pruning out infested stems. See Table 2.

Table 1. Disease Management Options 

Table 2. Insect and Mite Management Options