A Multifaceted Approach For Control Of Blueberry Pests in SoutheasternUnited States: Project Summary
Blueberries are an important small fruit crop in the Southeastern United States with Mississippi, Georgia and Florida as key blueberry production states. The development of early ripening southern highbush Vaccinium corymbosum L. X Vaccinium darrowi Camp blueberry cultivars have created a niche for growers in the southeast. Blueberry growers in Florida can produce high quality berries as early as late March when prices are extremely high and other key blueberry producing states cannot compete for market shares. However, further growth and development of the blueberry industry in Florida is limited due to the high incidence and spread of blueberry gall midge Dasineura oxycoccana (Johnson), flower thrips Frankliniella spp., and blueberry bud mites Acalitus vaccinii (Keifer). In Florida, blueberry gall midge has almost completely eliminated the Rabbitteye V. ashei Reade blueberry industry. The blueberry bud mite is imposing an increasing threat especially to well established plantings of southern highbush varieties.
Another emerging pest of great concern in the southeast is blueberry maggot Rhagoletis mendax Curran. During 2000 and 2001, several cases of blueberry maggot infestations have been recorded throughout Mississippi, Georgia, and northeast Florida. The overall goal of this project is to develop a multifaceted approach for managing key pests in blueberries.
1. To develop monitoring / sampling techniques for blueberry gall midge and flower thrips in southeastern blueberry plantings
2. To determine correlation between blueberry gall midge and thrips densities and injury / damage caused by these pests in southern highbush and Rabbiteye blueberries
3. To investigate the potential for biological control of blueberry gall midge and thrips by parasitoids and predators
4. To develop and refine monitoring protocol for blueberry maggot fly in the southeast
5. To evaluate “reduced-risk” insecticides for control of blueberry gall midge and thrips
6. To disseminate research information via on-farm demonstrations, grower meetings, web-sites and other extension channels
7. To determine the life cycle of the blueberry bud mite in Florida and include their management into the blueberry IPM guide.
* Dr. Oscar E. Liburd, Fruit & Vegetable Entomologist, Univ. of Florida, Gainesville, FL
* Dr. Blair Sampson, Small Fruit Entomologist, USDA-ARS, Poplarville, MS
* Dr. Elke Weibelzahl, Nematologist / Entomologist Univ. of Florida, Gainesville, FL
* Dr. Jeffrey Williamson, Small Fruit Ext., Univ. of Florida, Gainesville, FL
* Dr. Paul Lyrene, Horticulturalist, Univ. of Florida, Gainesville, FL
* Dr. Gerard Krewer, Univ. of Georgia, Tifton, GA
Thrips Population and Management during the 2007 Blueberry Production Season
This year flower thrips caused considerable damage to southern highbush and Rabbiteye blueberry plantings in Florida and Georgia. Flower thrips cause injury mainly by feeding on the floral tissues including pollen, styles, ovaries and petals. When thrips populations are high, they feed on the developing berries resulting in scarred and sunken fruits; consequently, reducing the quality and quantity of marketable berries. Flower thrips begin to appear in blueberry plantings as soon as flowering starts. Thrips tend to emigrate from adjacent flowering plants, including citrus, as well as flowering weeds such as cutleaf evening primose, Oenothera laciniata Hill and white clover, Trifolium repens L. New arrivals into blueberry fields aggregate into ‘hot spots’. However, as the flowers develop thrips population increases and move into uninhabited areas. Their populations will continue to increase until shortly after peak bloom when they begin to decline. Their life cycle last approximately 18-24 days under ideal conditions but late flowering varieties can result in multiple generations of thrips, which may cause the population to linger in the field for a very long time. During periods of high pressure, thrips population can remain in the field well after fruit set and damage the developing fruit.
The dominant blueberry thrips in Florida is the ‘Florida flower thrips’, Frankliniella bispinosa (Morgan), accounting for 83.6% of the thrips captured on white sticky traps. However, in Georgia, F. tritici (Fitch) is the most abundant species representing 94.0% of the thrips captured on sticky traps. Flower thrips are small insects, approximately 0.05 inches long (smaller than a pinhead) with yellowish-orange coloration. They reproduce quickly and thrive under hot, dry conditions, which occurred during the 2007 blueberry production season in Florida and Georgia.
One of the best ways to sample for thrips is by collecting flowers randomly from both field borders and from the center of the field. Flowers should be cut open with a pocket knife and inspected for thrips with a hand lens. If the number of thrips exceeds a 1:5 ratios (1 flower to 5 thrips) it may be appropriate to consider some type of management action. Sticky traps and floral tapping can also be used to determine the presence of thrips inside a blueberry planting, although these methods are not as reliable as flower inspection. Thrips hide inside the flower, which makes them extremely difficult to control with pesticides. Repeated chemical treatments are necessary in order to achieve effective control because thrips continuously move in from adjacent hosts. To date, inundative biological control for thrips in blueberries has not proved successful, probably due to the relatively short period of time that thrips spend on the blueberry plant. For chemical control, SpinTor (Spinosad) is a good choice because this chemical conserves beneficial insects and other pollinators, which are important during bloom. Organic blueberry growers can use Entrust in place of SpinTor. During peak bloom extra precautions need to be taken when using chemical control to avoid interfering with pollinators. Any insecticides used should be applied either early in the morning or late in the evening when pollinators are less active.
Evaluation of conventional and reduced-risk insecticides for control of flower thrips in blueberries
During the 2003 blueberry growing season, researchers from the University of Florida Fruit and Vegetable IPM Laboratory in Gainesville conducted field trials to evaluate various conventional and reduced-risk insecticides for control of flower thrips, Frankliniella spp., in commercial blueberry plantings. Trials were conducted at two sites: a high-density southern highbush planting in central Florida, and a rabbiteye planting in South Georgia. All insecticides were applied at the recommended rates. In Florida, the following insecticides were evaluated: 1) Imidan 70W, 2) Provado 1.6F, 3) SpinTor 2SC, 4) Ecozin 3% EC, 5) Garlic Extract, and 6) Surround WP. In Georgia, six insecticides were evaluated: 1) Diazinon AG500, 2) Malathion 5 EC, 3) Actara 25 WG, 4) SpinTor 2SC, 5) Ecozin 3% EC, and 6) Surround WP. Insecticides were applied every 10 – 14 days at each site. Insecticide effectiveness for suppressing thrips was evaluated using white sticky traps and by collecting 40 blueberry flower clusters from treated areas (per insecticide). In Florida, Surround was the only insecticide that significantly reduced flower thrips population. It is uncertain how Surround reduced thrips populations, but one possibility is that it restricted thrips accessibility to blueberry flowers. In Georgia, Malathion and Ecozin were the most promising compounds for suppressing flower thrips population. Unfortunately, the structure of the blueberry flower allows thrips to feed in a protected environment, and many insecticides only reach the external surface of the flower. It is possible that some of the newer neonicotinoid insecticides (Provado and Actara) with systemic or trans-laminar mode of action may demonstrate more effectiveness against thrips in future studies. The quick movement of thrips within blueberry plantings and from adjacent hosts may hinder the potential to evaluate the effectiveness of selected insecticides. Future studies will include laboratory studies to provide additional information regarding thrips behavior as it relates to various classes of insecticides.