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, and in the evergreen system is primarily present during late fall and winter months. On susceptible varieties, rust can prematurely defoliate plants. Where leaves are not dropped in winter (such as in the evergreen system), 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 Ask IFAS publication PP348, “Florida Blueberry Leaf Disease Guide” (https://edis.ifas.ufl.edu/publication/PP348). Resistance is known to occur in anthracnose pathogens in Florida. Follow product recommendations for resistance management including observing total fungicide active ingredient limits per season (total of all products with any particular a.i.), limiting consecutive applications of the same a.i., practicing rotation of products with different mode of action groups, and using label recommended rates.

BACTERIAL SCORCH (XYLELLA)

Bacterial leaf scorch is caused by Xylella fastidiosa in the southeastern United States. Symptoms begin as a marginal-irregular leaf scorch (browning or necrosis), 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. Research into the management is lacking, but the disease 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 blight, 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 their salts to help protect surrounding plants or any replants from infection. Anecdotally, this practice has helped, but only in preventing new infections, and additional research is needed. See Table 1 and Ask IFAS publication PP332, “Bacterial Wilt of Southern Highbush Blueberry Caused by Ralstonia solanacearum” (https://edis.ifas.ufl.edu/publication/PP332).

BLUEBERRY BUD MITE

The blueberry bud mite is an eriophyid mite so tiny (i.e., 1/125 inch long) that it cannot be seen without magnification. Blueberry bud mite is an occasional pest in well-established blueberries in Florida. Bud mite injury is often confused with frost damage and may become more visible in late spring. In early spring, infested plants exhibit stunted, succulent, fleshy, closely packed, reddish and rosetted buds, which may dry up and often fail to open. Bloom on infested plants is reduced. Affected berries are small and rough and may have small, reddish pimples or blisters on the fruit surface. Sanitation by aggressive, timely pruning of infested branches can be helpful. Mechanical topping (i.e., hedging old fruiting twigs) immediately after harvest greatly reduces bud mite incidence the following year. Bushes that may be infested with blueberry bud mite should never be used for propagation. The application of horticultural oil immediately after harvest can help in the control of blueberry bud mite. New miticides, Magister® (fenazaquin), Portal® (fenpyroximate), and Kanemite (Acequinocyl) were recently registered in blueberries and should provide some protection against eriophyids (blueberry bud mites belong to this group). The insecticide Apta® (tolfenpyrad) should also provide protection against eriophyids. Conventional insecticides such as pyrethroids have miticidal effects and can be used to help reduce bud mite infestation. See Table 2 and Ask IFAS publication ENY-858, “Blueberry Bud Mite (Acalitus vaccini (Keifer) on Southern Highbush Blueberry in Florida” (https://edis.ifas.ufl.edu/publication/IN844).

BLUEBERRY GALL MIDGE

The blueberry gall midge (BGM) is a tiny fly whose larvae feed on vegetative and floral buds. Typically, gall midge will attack young developing floral and leaf buds, which will cause floral buds to abort or fall off the bush, resulting in poor flowering and “fruit set.” With heavy gall midge injury to floral buds, there would be a lighter bloom. Instead of the usual 5 to 6 buds producing several flowers, only 2 may reach maturity, resulting in poor fruit clusters. Blueberry gall midge will also feed on leaf or vegetative buds, leaving young leaves deformed and misshaped. Gall midges lay eggs on warm winter days and at any time during the growing season when the plants are making new flushes of growth. Delegate® (Spinetoram), Exirel® (Cyantraniliprole), diazinon, Apta® (Tolfenpyrad), and Movento® (Spirotetramat) can be applied for gall midge control between flower bud stages 2 and 3 (Figures 2 and 3). Application should take place when the most mature buds first show slight scale separation. Sprays may need to be repeated during warm spells. Bud scale separation may occur as early as December 15th in north Florida. Among rabbiteye cultivars, 'Premier' is often particularly attractive to the gall midge and is a good sentinel variety to monitor. Gall midge sprays can also suppress a prebloom thrips population. See Table 2 and Ask IFAS publications ENY-2105, “Management of the Blueberry Gall Midge on Southern Highbush Blueberry in Florida” (https://edis.ifas.ufl.edu/publication/in1414) and ENY-997, “Blueberry Gall Midge on Southern Highbush Blueberry in Florida” (https://edis.ifas.ufl.edu/publication/IN1239).

BOTRYTIS BLOSSOM BLIGHT

Botrytis blossom blight, caused by the fungus Botrytis cinerea, most commonly infects and blights wounded or senescent plant tissues. As a blueberry bush blooms, corollas (the fused petal of the flowers) senesce and become quite susceptible to infection. Ideally the corolla should drop from the flower after pollination but before senescence occurs. Frost damage on tender new growth may wound the plant, delay petal drop, and facilitate infection by the fungus. The development of Botrytis blight, like many other foliar fungal diseases, is highly dependent on environmental conditions. During bloom, periods of low temperatures combined with extended periods of high relative humidity result in more than 24 hours of leaf wetness and increase likelihood of significant disease development. If the blight continues, an entire cluster of berries can be aborted. When disease is severe, berry reduction can become economically important. Infected berries are sometimes deformed and may develop further rot if environmental conditions later become favorable for disease. After pollination of a flower and drop of the corolla, the risk of infection of the developing fruit is reduced. Economic loss due to Botrytis can be minimized by limited use of irrigation for freeze protection and judicious fungicide applications. See Table 1 and Ask IFAS publication PP198, “Botrytis Blossom Blight on Southern Highbush Blueberry” (https://edis.ifas.ufl.edu/publication/PP119).

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 Ask IFAS 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. Peak adult activity for Chrysobothris species in north-central Florida is between April and May depending on spring temperatures. There is evidence that beetles are moving from adjacent woodlands into blueberry plantings. 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.

FLOWER THRIPS

These are small insects (i.e., 1/16 of an inch in length), yellowish to orange in color with fringed wings. Flower thrips damage blueberry flowers in two ways. Larvae and adults feed on all parts of the flowers, including ovaries, styles, petals, and developing fruit. This feeding damage can reduce the quality and quantity of the fruit produced. Females damage the fruit when they lay their eggs inside flower tissues. The newly hatched larvae bore holes in the flower tissues when they emerge. Flower thrips can be very damaging to flower buds and blooms. Thrips numbers typically increase dramatically as corollas open and bloom progresses. Determining when or if blueberries should be treated for thrips is difficult. Blueberries are a pollination-sensitive crop, and misuse use of insecticides and subsequent bee kill can easily impair pollination and ruin fruit set. Only selected insecticides (such as Delegate®) should be used during bloom. If Delegate® is used, the insecticide should be applied in the early morning or late evening and be given 3 hours of drying time before bees are allowed to forage on the crop. To measure treatment thresholds for southern highbush and rabbiteye blueberries, begin sampling bloom clusters as soon as the flower begins to open. Sample four to five areas in a 1-acre block by placing a white sheet under a flower cluster and tapping lightly. Count the number of flowers and count the number of thrips dislodged from the flower cluster. If you average more than four thrips (southern highbush) or three thrips (rabbiteye) per flower, some type of management is recommended. Alternatively, two white sticky traps could be used to monitor a 5-acre block (one on the border and one in the center). If you have more than 80–100 thrips (southern highbush) or 60–70 thrips (rabbiteye), then some type of management tactics are needed. Assail® and Apta® are the material of choice until 5 days prebloom. See Table 2.

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.

PHOMOPSIS CANE AND TWIG BLIGHT

Phomopsis cane and twig blight is a fungal disease caused by Phomopsis vaccinii, which is spread to uninfected plants by wind and rain. Characteristic symptoms are dark-brown lesions on fruiting twigs (often surrounding floral buds), dieback of young twigs, and shriveling of flower and fruit clusters on diseased stems. Dying tissue may spread down the twig until most of the flower buds on an individual twig die. Shriveling of flowers and fruit clusters may appear similar to Botrytis damage. Control measures include fungicide applications and pruning out infected twigs. See Table 1.

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. A new fungicide (within the FRAC group 49) with reported Phytophthora efficacy is available for use on blueberry. Oxathiapiprolin is available in the product Orondis® Gold 200, or as premix with mefenoxam in the product Orondis® Gold (Premix). These products have not been evaluated on SHB in Florida; thus, look for additional information on these products as data becomes available. See Table 1 and Ask IFAS Publication PP374, Phytophthora Root Rot on Southern Highbush Blueberry in Florida (https://ask.ifas.ufl.edu/publication/PP374).

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)) and Florida wax scale (Ceroplastes floridensis), are the most prolific on blueberries in Florida. See Table 2 and Ask IFAS publication ENY-2094, “Wax Scale on Southern Highbush Blueberry in Florida” (https://edis.ifas.ufl.edu/publication/IN1387).

SPIDER MITES

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 produce a protective web over the infested surface to protect them from predators. The underside of leaves should be closely examined with a 10x hand lens for adults, white shed skins, and webbing. Tapping foliage onto a sheet of white paper can also be used to find adult mites. A few miticides, including Magister® (fenazaquin), Portal® (fenpyroximate), and Kanemite® (acequinocyl) have recently been labelled for spider mites. See Table 2 and Ask IFAS 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.

POLLINATOR PROTECTION 

Before making pesticide applications, monitor insect populations and signs of plant disease to determine if treatment is needed. If pesticide (fungicide, insecticide, or miticide/acaricide) application is necessary, please do the following: 

1. Use selective pesticides to reduce risk to pollinators especially when applied during bloom. Look for pesticides with low toxicity to bees and with short residual activity if the pesticide needs to be applied during the crop bloom.

2. If applying a pesticide during bloom, apply in the evening to allow for maximum residue degradation before bees return to forage the next morning. If renting honey bee hives, be sure to follow up with your contract with your beekeeper and inform them of pesticide applications made during bloom.

3. When applying pesticides shortly before the arrival of bees, pay attention to the length of the residual period to minimize risk to bees. Note that systemic products have long residual activity and can be present in the nectar and pollen after application.    

4. Read and follow all pesticide label directions and precautions. The Label is the Law! The EPA now requires the addition of a “Protection of Pollinators” advisory box on certain pesticide labels. Look for the bee hazard icon in the “Directions for Use” and within crop specific sections for instructions on how to protect bees and other insect pollinators. 

5. Follow label directions to minimize off target movement of pesticides. Do not make pesticide applications when the wind is blowing towards beehives or off-site pollinator habitats. 

For additional information relative to pesticide hazards to pollinators, see UF EDIS Publication ENY-2110, A Guide to Selecting and Using Pesticides During the Blueberry Pollination Period: How Can We Reduce Risk to Pollinators? (https://ask.ifas.ufl.edu/publication/IN1429).

Table 1. Disease Management Options

This table(s) lists registered pesticides that should be integrated with other pest management methods. Additional information on integrated pest management methods can be requested from UF/IFAS Extension horticulture or agriculture Extension agents. A list of local UF/IFAS Extension county offices is at available at https://ifas.ufl.edu/.

Table 2. Insect and Mite Pest Management Options

This table(s) lists registered pesticides that should be integrated with other pest management methods. Additional information on integrated pest management methods can be requested from UF/IFAS Extension horticulture or agriculture Extension agents. A list of local UF/IFAS Extension county offices is at available at https://ifas.ufl.edu/.