Citrus Industry Magazine CEU 2012 Articles Test Series: Article #3
Using integrated pest management principles
By Tim Gaver and
Stephen H. Futch
Posted Aug 1, 2012
(expires Jul 31, 2013)
The Florida citrus industry has battled a considerable number of pest species throughout its history. These pests include mites, insects, nematodes, weeds, fungi, viruses, citrus canker and, relatively recently, huanglongbing (HLB), commonly referred to as citrus greening, a bacterial disease. Growers have utilized a number of pest management tools, including biological, host resistance, cultural, sanitation and chemical controls to deal with these native and exotic pests.
THE INTEGRATED PEST MANAGEMENT STRATEGY
An integrated pest management (IPM) program utilizes all appropriate pest control methods in a plan to reduce the populations of targeted pests and their potential damage to an acceptable level. While chemical control is often utilized, consideration should routinely be given to other possible methods like biological and mechanical control.
The first step to a successful pest control program is proper identification of the pest. Effective pest control is often dependent on basic knowledge of the pest, including the life cycle stage where the pest is most likely to be controlled by the method chosen. Most pests are more easily controlled in their younger or immature stages, and become more difficult to manage as they reach maturity. A good example is targeting immature mealybug or scale insect crawlers before they settle under fruit buttons or form a protective shell as adults.
Knowledge of a particular pest will also include the action threshold, or the population level at which a crop is being damaged or will be damaged if pest populations continue to increase. In some cases, a small amount of damage may be less costly than the expense of treating an area to control or reduce the pest. Some citrus rust mite damage to the peel of processed citrus fruit is tolerated, while little or no damage is acceptable on fruit destined for the fresh market. Rust mite populations are managed according to the intended destination of the crop.
The goals of a pest control program can be divided into three broad categories or types of management, dependent on the pest present, environment, crop involved, and perhaps the potential value of the produced crop. The three pest control goals include prevention, suppression and eradication.
Prevention might be a goal when a citrus fungal disease such as melanose fungus on oranges and grapefruit intended for the fresh fruit market is involved. The grower might apply a protective fungicide to susceptible young fruit when a wetting period of sufficient length is expected that would result in infection of the fruit rind.
An example of a goal of pest suppression would be to apply a miticide spray to a low population of citrus rust mites when conditions are suitable for that population of mites to increase to damaging levels. Frequent scouting and knowledge of action thresholds and the behavior of mite populations would help the grower make the decision of when to treat, thereby avoiding future damage.
Eradication of a pest is rarely the goal of pest control programs when treating large areas, usually because it is so difficult and costly to achieve. An exception would be an instance where an invasive pest has been accidently introduced into an area, but has not yet become established. Examples would be unwanted introductions of the Oriental or Mediterranean fruit fly, and the necessary eradication effort would be planned and supported by government agencies. The canker eradication program in Florida that ended in 2006 is an example of an eradication effort to remove an unwanted bacterial disease that proved both costly and ultimately unsuccessful.
A number of biological agents have been introduced into Florida to combat citrus pests after careful research of the potential consequences from such introductions. Beneficial predators or parasites have been brought in from other parts of the world to suppress populations of brown citrus aphid, citrus leafminer, citrus blackfly, citrus whitefly, numerous scale insects and other pests. Until recently, a number of armored and soft scale pests that were once significant problems have successfully been controlled by the combined action of native and introduced exotic natural enemies. This balance has been upset in a number of areas as a result of intensive chemical management efforts to control the Asian citrus psyllid (ACP), the insect vector of HLB, or citrus greening disease. This psyllid found its way into Florida in 1998 and rapidly spread across the state, quickly building to huge populations in the absence of effective natural enemies. A parasitic wasp, Tamarixia radiata, has been introduced and become established across the state, but does not provide sufficient natural control of the psyllid populations to slow the spread of HLB.
Utilizing rootstocks or varieties that are tolerant or resistant to various insect or disease pests is a common practice in many fruit and vegetable production programs. When considering host resistance in a new citrus planting that may be in production for many years, the selection of a scion variety that can be grown and marketed profitably may be more important than its susceptibility to selected pest issues. Citrus rootstocks are available that are resistant to citrus tristeza virus (CTV) and offer some tolerance or resistance to Phytophthora foot rot and root rot. Resistance to nematodes and the Diaprepes root weevil may also be an important consideration in some areas where these pests are endemic.
Vegetable growers utilize sanitation as a pest management tool when they destroy plant residues after a crop is finished, depriving pests of a host to continue their life cycles. Citrus growers have used sanitation practices to prevent or reduce the spread of citrus canker bacterial disease. Utilizing canker spray stations at grove entrances and exits to sanitize vehicles, equipment and harvesting personnel has been shown to be beneficial. In groves where canker is an established problem, delaying hedging and topping operations and harvesting until the trees are dry has become a common practice. Some growers are finding that selective pruning of foliage that is heavily infected may also be beneficial. This practice is labor intensive and must be combined with fungicidal spray applications to be effective.
In many cases, even though IPM tactics are utilized, pest populations can reach action thresholds, and pesticides must be applied to manage those populations. The selection of a pesticide to manage a pest should consider efficacy, cost per acre, length of control, ease of use and the potential effects on beneficial organisms. Efficacy is the ability of a pesticide to control a pest population. The effectiveness of a chemical application can be dependent on many factors, including the pest to be controlled, weather conditions following the application, and if the pesticide was applied at the correct labeled rate by equipment that was accurately calibrated to apply the proper amount of finished spray per acre.
The length of control of a pesticide application will also depend on the pest, growth stage of the plant, weather and the pest population at the time of the application. Because no pesticide kills 100 percent of a pest population, applications that are made when pest numbers are very high can result in relatively short periods of control.
Pesticides that are easy to use can increase the productivity and safety of pesticide applicators. Although large package sizes of liquid and dry pesticide products may lower the unit cost, smaller packages of dry products that contain the proper amount of product for each tank mix may improve application accuracy and efficiency. Formulations such as dry flowable products may be easier to measure and be less dusty than wettable powder formulations, leading to less handler exposure to the pesticide. Handlers should be provided measuring containers that are properly marked for the correct amounts and have written mixing instructions posted at the mix/load site to ensure that the proper pesticide amounts are mixed and applied.
Selection of a pesticide product that has a low per acre cost often conflicts with the goal of using a product that is “soft” on beneficial insects. Planning a pest control program for the entire season can help to minimize costs while protecting populations of helpful organisms at certain times of the year. An example of this would be using organophosphate or pyrethroid pesticides to control minimal ACP populations during the dormant or cool season, and utilizing spray oils or other “soft” pesticides during the warm seasons for ACP control when beneficial populations are higher. Information on the potential for a product to affect friendly organisms can be found on the pesticide label or from other information from the manufacturer.
PESTICIDE RESISTANCE MANAGEMENT
In addition to the other factors involved in pesticide selection, the potential for pest resistance to a product should be considered. Pesticides are grouped according to their mode of action (MOA), which is the specific manner in which their chemistry affects a pest. Organizations devoted to managing pesticide resistance worldwide include the Insecticide Resistance Action Committee, Fungicide Resistance Action Committee and the Herbicide Resistance Action Committee.
Repeated applications of pesticides with the same MOA can result in insect, weed or fungal populations with resistance to that particular product or other products with that same MOA. Rotating pesticide applications using products with a different MOA is the best recommendation to avoid resistance. When practical, coordinating applications with a like MOA with your adjacent growers can help avoid developing pest resistance. This can be especially useful for managing an insect like whiteflies or ACP which can fly from one grove or field to another to avoid treated areas. Attempting to cut pesticide costs by using less than labeled rates can also contribute to the buildup of resistance when more pests survive the application. For citrus growers, the MOA of pesticides can be found in the Pesticides Registered for Use on Florida Citrus section of the 2012 Citrus Pest Management Guide SP43 or on the web at http://edis.ifas.ufl.edu/cg017.
Growers should utilize all of the appropriate IPM principles to reduce the number of pesticide applications as much as possible and actively contribute to a responsible environmental stewardship effort. Correctly identifying pests, choosing the appropriate pesticide and applying the product at the correct rate are all important factors in a successful and sound pest ma nagement program.
Tim Gaver is an Extension agent at the St. Lucie County Extension Service, Fort Pierce; Stephen H. Futch is an Extension agent at the Citrus Research and Education Center, Lake Alfred.