- Author: Nastaran Tofangsazi and Beth Grafton-Cardwell, Department of Entomology, UC Riverside
With the detection of Huanglongbing (HLB) in California in 2012 and 22 additional cases reported during 2015 through June 2016 there is a major concern among citrus growers about the spread of this incurable bacterial disease. The vector of the disease, the Asian citrus psyllid (ACP), is a hardy insect with good dispersal capabilities and can be found in many southern California citrus groves today. With no direct cure for HLB at present, the only option for growers to combat the disease is to control the psyllid. This can prove difficult for conventional citrus growers with broad spectrum insecticides, but for organic citrus growers, which grow an estimated 7% of citrus in California, the task is even more difficult with the currently available options.
Entrust (spinosad) + oil, Pyganic (pyrethrin) + oil, and oil alone are currently the recommended and most widely used insecticide options for organic growers (UC IPM Guidelines for Citrus). While these insecticides are fairly effective in killing ACP if they make direct contact, the residual life of these pesticides is very short (days) compared to conventional insecticides (weeks to months). For example, in our petri dish studies, 10 fl oz/acre Entrust SC + 0.25% Omni supreme spray oil caused 89% mortality, 17 fl oz/acre Pyganic 5.0 EC + 0.25% Omni supreme spray oil caused 73% mortality and 0.25% Omni supreme spray oil caused 42% mortality when 1st-2nd ACP nymphs were exposed to treated leaves one day after application. Nymphal mortality continued to decline for the Entrust + oil treatment (69% mortality) and even more severely declined for Pyganic + oil (27% mortality) 3 days after treatment. In contrast, one-day-old residues of a conventional insecticide, the neonicotinoid 5.5 oz Actara (thiamethoxam), resulted in more than 95% mortality of nymphs and mortality remained high for more than a month.
Studies of grower orchard treatments confirmed laboratory studies that showed a short residual effect of organic treatments (Entrust + oil and oil alone) compared to conventional insecticides (Actara). We monitored changes in population densities of ACP (adults by tap, nymphs and eggs by flush examinations) in the fall of 2015 before and after a grower sprayed separate orchards with one of three insecticides; 1) 1.25% 440 Supreme Spray Oil by ground application (400 gpa), or 2) 9 fl oz Entrust SC + 1% oil by air (50 gpa), or 3) 5.5 oz Actara by air (50 gpa). The oil treatment had little effect on the adult population, but significantly reduced psyllid nymph densities for 17-24 days. Entrust was completely ineffective in controlling psyllid nymphs, but suppressed adult and egg populations for about 14 days. Actara, a conventional insecticide, was the most effective treatment in the study and provided more than 5 weeks of both adult and nymph control. Because of the short residual effect of organic insecticides in citrus, repeat treatments are needed at a frequency of about every 2 weeks for ACP control.
Tamarixia radiata wasps released for biological control of ACP provide 20% to 88% parasitism depending on geographical location and time of year. If there were no disease to be concerned about, this level of parasitism by Tamarixia would be sufficient to protect citrus from the feeding damage of the psyllid. However, the disease spreads rapidly with just a few psyllids and so a greater level of control is needed. Generalist predators, such as lady beetles, lacewings and assassin bugs, also assist with control. Argentine ants can severely disrupt this parasitism by protecting psyllids from natural enemies. Unhappily, Entrust + oil, thought of as a very selective insecticide combination, was found to be highly toxic to adult Tamarixia wasps exposed to 3 day old residues. Thus, the organic insecticide that is the best for controlling the psyllid pest is not compatible with the parasitoid natural enemy, limiting our ability to use integrated strategies to control the psyllid.
At present, it is not mandatory, but is strongly recommended, that all southern California citrus growers treat their orchards in an area wide manner. The area wide program consists of coordinated treatments twice a year (winter and fall), and additional treatments in between. Due to the short residual nature of organic insecticides, organic applications should be applied twice within 10-14 days of each other for every single conventional insecticide application. This is especially important for younger groves as ACP nymphs thrive in new flush. Organic growers have a tough decision to make between treating frequently for ACP and the high cost associated with those treatments or transitioning into conventional management in order to more effectively control ACP. Additional solutions are needed for organic citrus.
UC IPM Guidelines for Citrus: Asian Citrus Psyllid. http://ipm.ucanr.edu/PMG/r107304411.html
- Author: kathy keatley garvey
Originally published on the Bug Squad Blog on January 19, 2015
What's killing the honey bees?
The email arrived in my UC Davis inbox at 9:10 a.m., Thursday, Jan. 8.
An employee from the UC Davis Plumbing Shop wondered what was happening in front of the Robert and Margrit Mondavi Center for the Performing Arts on the UC Davis campus. "There are dead bees everywhere," he wrote, adding that "There were some grounds workers waiting for the UC Davis bus in front of Mondavi, and they commented that they also saw dead bees everywhere in their grounds-keeping areas."
Did the cold spell have something to do with this? But why would honey bees be outside their colony? Honey bees don't fly until the temperature reaches around 55 degrees.
What was happening?
Super sleuth Extension apiculturist (retired) Eric Mussen of the UC Davis Department of Entomology and Nematology, arrived on the scene. He was appropriately dressed in a trenchcoat, a la Sherlock Holmes (Note that Sherlock Holmes, aka physician Sir Arthur Conan Doyle, was a beekeeper, too, according to Wikipedia).
Mussen, who retired last June after 38 years of service, picked up some of the dead bees and noticed that nearly half had small-to-large pollen loads on their legs. Their wings were not tattered. He quickly deduced that the bees had not worn themselves out foraging.
"However, this early in the season, many of the foraging bees are bees that survived since last fall," Mussen said. "Depending upon their overall health, they were working toward the ends of their lives."
Mondavi house manager Kerrilee Knights showed him dead bees on an upper outdoor patio. So the bees were not only dying at ground level but upper levels, Mussen realized.
He noticed some bees flying up over the roof and some live bees "resting" on various parts of the building.
"There's a colony up there somewhere," Mussen said, pointing toward the roof.
Mussen cupped some of the sluggish bees in his hands, and once warmed, off they flew. The other survivors? They were too cold to fly and they would die overnight as the temperature dropped.
Mystery solved. "Elementary, my dear Watson?" No, not really. It's a scene that non-beekeepers rarely see.
"So, it appears that an older population of bees from a colony nesting around the top of the building were foraging near the ends of their lives," Mussen said. "They could not adequately produce enough body heat to keep foraging and they could not adequately produce enough body heat to fly back to their colony and they were falling to the ground, basically exhausted."
"This is normal and no reason for alarm," Mussen said, "except that people usually are not that close to bee colonies to notice the normal demise of substantial numbers of overwintering bees."
So, it wasn't pesticides, pests, diseases, malnutrition or stress.
Old bees and a cold spell...
- Author: James A. Bethke
I often teach that there is a place for pesticides, especially when there are no effective alternatives. For instance, if you leave the aphids alone on your rose plants, they will eventually disappear due to the abundance of all the associated natural enemies like ladybird beetles. Some damage will occur, but the end result will be enjoyable roses in the landscape or in a vase. However, if you are going to show the rose - that first early season rose is the most brilliant - and not protect it, it will not be showable. Similarly, it is a shame if you own a 100-year old beautiful shade tree in your yard and you let a pest destroy it when you could have prevented it.
There is a concern by many that the systemic neonicotinoid insecticides are harming wildlife and the environment, and many folks are not willing to use them or purchase plants that have been treated with them. That is amazingly unfortunate because of all the benefits of this insecticide class, and much of the expressed concerns are scientifically unfounded.
The best example I can give of a fit or a need for insecticide use is presented in the case of the Emerald Ash Borer (EAB). EAB is a beetle as an adult, but the immature form, called a grub, is responsible for girdling ash trees and killing them within three years depending on the size of the tree and the extent of the infestation. EAB has been blamed for killing tens of millions of trees in about 22 states, and it is said, that the destruction of the ash in our forests and urban landscapes could rival the loss of elms due to the Dutch elm disease. That's significant. The benefits of ash trees in the landscape is clear, so the loss of all or nearly all of the landscape ash would be devastating, in my opinion.
There are those, however, that would not protect the trees with neonicotinoid insecticides at any cost. Unfortunately, there are grand examples of communities that refuse to protect their trees with systemic neonicotinoid insecticides, and I recommend that you take a look at the before and after pictures attached and check out the links to more information below. You will see that there is a place for insecticide use in this instance. Some may say that we can replace the landscape trees with alternatives that won't be affected. That's true, but it won't save our forests, and it will leave infected trees in our urban landscapes that will act as a reservoir for the beetle.
- Author: Andrew M. Sutherland
[From March 2014 issue of the Retail Nursery and Garden Center IPM News.]
A massive killing of bumblebees in Oregon, concerns about impacts on honey bees, and tight new regulations imposed by the European Union have kept neonicotinoid insecticides in the news. The neonicotinoid group includes imidacloprid, one of the most popular garden insecticides sold in stores.
First developed in the late 1980s, neonicotinoids represented the first new class of insecticides in over 50 years. They are insect nervous system toxins widely used in horticulture, agriculture, and structural settings for a broad range of pests. Desirable qualities such as reduced toxicity to people and pets (as compared to some organophosphates and carbamates) and systemic activity in plants, led to rapid and widespread use. Imidacloprid, the first neonicotinoid developed, is now the most widely used insecticide in the world (see Table 1 for other active ingredients and common product names).
The high water-solubility and environmental persistence of neonicotinoids meant they could be applied to the soil or tree trunks and taken up by the tree and translocated into leaves and stems where pest insects feed. When considering large trees or shrubs in an urban environment, this approach is clearly an efficient method of insecticide delivery. Garden neonicotinoid products are usually applied with soil drenches (Fig. 1), but professional products are often applied as soil injections, trunk injections, or bark treatments. Since leaves were not treated and pesticide drift was minimized, these types of nonfoliar applications were believed to reduce the risk to nontarget organisms.
From the beginning it was recognized that foliar applications of neonicotinoids, listed on some labels, are quite broad-spectrum in their effect and would negatively impact beneficial insects and bees. Now, however, after 20 years of use, soil and trunk applications of neonicotinoids have also been associated with serious nontarget effects and environmental contamination. Negative impacts due to neonicotinoids have been documented for earthworms, soil microorganisms, predatory beetles, bees, and parasitic wasps. Also, unexplained increases in spider mite reproductive rates in response to imidacloprid have been described.
The systemic action of neonicotinoids means that in some cases the active ingredients can be transported to a treated plant's pollen and nectar, potentially injuring pollinators and other beneficial insects. In fact, the widespread use of neonicotinoid insecticides has been cited as a possible contributor to the global honey bee decline phenomenon known as Colony Collapse Disorder.
In April 2013, European Union member states voted to forbid the application of three neonicotinoids --imidacloprid, clothianidin, and thiamethoxam-- to flowering plants. In June 2013, a mass die-off of native pollinators attributed to applications of neonicotinoid insecticides led Oregon authorities to adopt permanent restrictions on dinotefuran and imidacloprid. In August 2013, the United States Environmental Protection Agency unveiled new label language requirements and a new graphic, “Protection of Pollinators” (Fig. 2), on all products containing clothianidin, dinotefuran, imidacloprid, or thiamethoxam that are labeled for outdoor use.
Of special interest to retail nurseries and garden centers is a 2013 study conducted by environmental advocacy groups (Pesticide Research Institute and Friends of the Earth) that found more than half of the plants, including those labeled “bee-friendly”, sampled from garden centers at national retail chain stores contained neonicotinoid residues. The report recommended that garden retailers should voluntarily demand neonicotinoid-free stock from suppliers, remove home-use neonicotinoids from their shelves, and use the opportunity to market themselves as environmentally conscious and proactive.
The water-solubility qualities of neonicotinoids create another problem in urban settings. Runoff from improperly applied soil drenches or irrigation or rain can wash these long-lived materials into creeks and stormwater systems, where aquatic organisms may be injured or killed. A study published in 2012 by researchers with the California Department of Pesticide Regulation revealed that imidacloprid was found in about half of the urban creeks sampled.
Retail products containing imidacloprid or other neonicotinoids are very popular; many are combination products that deliver a fertilizer, herbicide, or fungicide in addition to the insecticide. Improper application and improper disposal of such products may be contributing to the contamination highlighted in this article. Consumers do have choices. Most applications are made for pests such as aphids or soft scales for which other safer, effective products, such as horticultural oils or soaps, are available.
Retailers have the ability and the opportunity to act as environmental stewards by advising customers to limit the use of neonicotinoids to pest situations where there are no effective alternative tactics, delay applications of systemic insecticides until after plants have flowered, take precautions to avoid insecticide runoff into aquatic ecosystems, and follow all pesticide label guidelines.
- Author: Kathy Keatley Garvey
"For many years, beekeepers and environmentally interested individuals have expressed the opinion that the use of neonicotinoid insecticides ("neonics") have interfered with the ability of honey bees and native bees to conduct their life activities properly," begins Extension apicuturist Eric Mussen of the UC Davis Department of Entomology in his latest edition of his newsletter, from the UC Apiaries.
"Since laboratory studies have detailed the disruptive effect on those insects, it was suggested that the same things were happening in the field. Unanticipated losses of formerly strong honey bee colonies, and easily observable decreases in bumble bee sightings, correlated well with increased use of neonics."
Mussen goes on to talk about the neonic situation in Europe and what the European Food Safety Agency (EFSA) has to say about the controversial issue. EFSA concluded that the neonicotinoid pesticides posed a “high acute risk” to pollinators, including honey bees, but that a definitive connection between the chemicals and loss of colonies in the field remained to be established, Mussen wrote.
Mussen, California's only Cooperative Extension apiculturist and a member of the UC Davis Department of Entomology faculty since 1976, says the situation is not that simple. Read why. His newsletter is available free on the UC Davis Department of Entomology website. Access his web page and then click on "March/April 2013."