SWEETPOTATO INSECT MANAGEMENT

Objective

To lessen the impact of pests and pest control costs:

1. Scout fields regularly, and make careful counts of insect pest
2. Use all available, practical noninsecticidal IPM
3. Apply insecticides promptly when
4. Use the most cost-efficient insecticide recommended for the target pest, and target applications against the most susceptible stage of
5. Follow recommended guidelines for practicing insecticide-resistance

 

Before deciding to treat and before choosing the insecticide, consider such factors as the potential to intensify secondary pest problems and insecticide resistance.

Warning

Information in this guide is provided for educational and planning purposes only. When using agricultural chemicals, you, the user, are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Before applying any insecticide, be sure to obtain current information about usage, and read and follow the product label.

Precautions

Before using a pesticide, read the label carefully. Follow the directions, and heed all precautions on the pesticide container label. Observe all regulations on worker protection and pesticide record-keeping. Store pesticides in original containers, safely away from livestock, pets, and children. Store pesticides in an area where they will not contaminate food or feed.

Integrated Pest Management

Successful, economical control of insect pests requires using a variety of control methods rather than relying just on one method of control, such as scheduled insecticide use. Integrated pest management (IPM) refers to this multi-tactic approach to in- sect control. Current insect control recommendations are based on the IPM concept.

Insecticides are a key part of sweetpotato IPM, but sustained economical insect control relying solely on insecticides is not possible in Mississippi.

The objective of sweetpotato IPM is to use all available, practical nonchemical methods of suppressing insect populations; to monitor pest populations closely; and when scouting indicates that pest populations are greater than economic THRESHOLDS, to integrate insecticides into the system to optimize crop production and minimize ecosystem disruption.

Management tactics applied against one pest may be favorable or unfavorable to the development of other pests in the system.

Thus, an overall IPM program must consider these types of long-term effects, because they greatly influence the ability of Mississippi growers to maintain economical production.

Many IPM components must be used to manage insect pests effectively. These include managing for early crop maturity, various cultural practices, insecticide resistance management, using economic THRESHOLDS, thorough scouting, and timely application of insecticides when needed.

Scouting

Proper scouting is the backbone of an effective insect management program. The goal of any scouting program should be to minimize insecticide use and insect control costs by avoiding unnecessary treatments and by properly timing required treatments. Effective scouting requires spending adequate time in the field and taking enough samples to make an accurate decision on whether or not treatment is required. Frequency of scouting is critical. During most of the growing season, scout fields thoroughly every 3 to 4 days, and allow enough time in the scouting schedule to allow spot checks more often when necessary.

Sampling equipment

Bugvac: You can use a shredder, vacuum, or leaf blower as a bugvac. Insert a 4.75-inch diameter plastic cup with the bottom replaced by a fine mesh (100 mesh) nylon screen into the end of the vacuum tube. Move the suction opening back and forth within the plant canopy to vacuum plants as you walk briskly along. Count the insects every 25 feet of row, but THRESHOLDS are expressed as numbers of insects per 100 feet of row.

Sweep net: We recommend a standard 15-inch diameter sweep net of heavy construction. Sweep nets are available from commercial sources. Count the insects every 25 sweeps, but THRESHOLDs are expressed as numbers of insects per 100 sweeps.

 

THRESHOLDS

Making insect management decisions based on established treatment THRESHOLDS rather than applying treatments based on schedules or presence or absence of pests is a proven method of reducing insect management costs. Effective use of THRESHOLDS requires frequent, intensive scouting to obtain accurate estimates of populations of various pest species that may be in a field.

The treatment THRESHOLD is the pest population level at which you must treat to avoid economic loss that would be greater than the cost of the treatment. THRESHOLDS can vary, depending on species of pest present, stage of crop development, yield potential of crop, cost of the treatment, price of crop, populations of other pests present, number of beneficial insects, potential for flaring secondary pests, ability to control secondary pests, and a variety of other factors. While the THRESHOLDS recommended in this guide vary according to pest species and stage of crop development, fixed THRESHOLDS cannot fully consider the many other factors that can influence a treatment decision. Although the THRESHOLDS recommended in this guide are generally somewhat conservative (quick to treat), factors such as multiple pest species could indicate a need to reduce THRESHOLDS. Likewise, factors such as high beneficial in- sect populations, risk of flaring difficult to control secondary pests, high treatment costs, and low price potential could indicate a need to use higher THRESHOLDS.

General Practices

Conduct tillage or herbicide operations to destroy vegetation at least 4 weeks before planting.

Preplant insecticides do not control the entire growing season but may significantly protect from some soil insects much of the season. Apply preplant insecticides as close to the time of planting as the preharvest interval (PHI) allows.

Make layby applications before canopy closure, preferably at last cultivation. Rotating foliar products helps manage insecticide resistance.

Adequate coverage can be difficult but is essential with most products. Best results from contact insecticides are with application volumes of 5 to 10 gpa, using hollow-cone nozzles. Do not use herbicide nozzles (low-drift nozzles or other types that produce large droplets) to apply insecticides.

Sweetpotato fields near pastures or hay fields appear to be more at risk for sugarcane beetle infestations. Planting more productive fields (fields with higher yield potential) first and harvesting them as soon as possible may allow these fields to be harvested be- fore sugarcane beetle infestations get severe.

Biological Control

Mississippi producers are fortunate to have a wide array of naturally occurring biological control agents that play an important role in managing pest populations. Together, these biological control agents are the primary method of controlling insect pests in Mississippi. Often the full economic value of these biological agents is not recognized or appreciated. Severe outbreaks resulting in high levels of crop loss or unusually high control costs seldom occur unless natural control has been disrupted. Profitable production would not be possible in Mississippi without these biological control agents that include predators such as big-eyed bugs, lady beetles, spiders, minute pirate bugs; and parasites. To gain the maximum economic benefit from the control provided by these natural control agents, growers need to know which species are beneficial, how to identify these species, which pests they attack, what factors enhance their usefulness, when they are most useful, and when they may not provide effective control.

Predators and parasites can often prevent a pest population from reaching treatable levels, and the control they provide is often cheaper, better, and longer-lasting than insecticides. Scouts and producers should be aware of population levels of naturally occur- ring predators and parasites and should recognize that treatment THRESHOLDS can often be increased when predator and population levels are high. Certain cultural practices may favor populations of specific predators (for example, fire ants and reduced tillage).

When insecticide treatment is necessary, it is often possible to select treatments that have little impact on populations of certain beneficial insects while still providing control of the target pest.

Insecticide Resistance and Resistance Management

Insecticide resistance is the increased tolerance to a particular insecticide by a pest population to the point the insecticide no longer controls effectively.

Resistance develops as a result of repeated or continuous exposure of a pest population to a particular insecticide or class of insecticides. Following an insecticide application, the death rate for susceptible insects is considerably higher than the death rate of resistant insects. Thus the numbers of resistant insects increase, and the frequency of resistance genes is increased in the next generation. If the same insecticide or class of insecticide is used against the next generation of pests, the level of resistance increases even more. At first the number of resistant individuals within a population may be extremely low, one individual in every 10,000 or more, and loss in efficiency is very small. But with repeated use of the same insecticide or class of insecticides, the percent of the population composed of resistant insects becomes great enough that efficacy declines and field control fails.

Resistance is costly to producers because it results in the need to increase insecticide rates, shorten treatment intervals, use expensive mixtures of insecticides, or use more costly alternative insecticides to keep effective control. Reduced control means in- creased yield losses, which can further reduce profits. In the absence of effective treatment alternatives, outbreaks of resistant pests can result in disastrous levels of crop destruction.

 

Insecticide resistance management is a plan of insecticide use that limits exposure of a pest population to a particular class of insecticide chemistry to prolong the useful life of that insecticide or class of insecticides. It is important to note that the goal of resistance management is not necessarily to prevent resistance from ever occurring, but to slow the development of resistance.

To be most effective, resistance management must be started before resistance is evident (while the frequency of resistant genes is very low) rather than waiting until resistance is evident in the field (frequency of resistance is high). Because many insects can readily move from farm to farm, resistance management efforts are most effective when all producers in a large geographic area practice them.

With foliar insecticides, selection for resistance may occur whenever an insecticide is used, simply because the pests that survive exposure to the treatment are more likely to be resistant. Thus, the proportion of the pest population that carries genes for resistance to a particular insecticide is higher after that insecticide has been applied. With foliar insecticides, resistance can be delayed by not exposing successive generations of pests to insecticides from the same class. Rotating different classes of insecticides against different generations of pests is an effective resistance management tool because insects resistant to one class of chemistry are often susceptible to insecticides from a different class. This provides immediate benefits in terms of improved control as well as long-term benefits in terms of reduced selection for resistance.

Responding to Control Failures

Key considerations and responses following suspected insecticide failures:

1. Don’t panic! Do not automatically assume that the presence of live insects following an insecticide application is the result of an insecticide
2. Examine the possible reasons unsatisfactory control may have Control decisions should consider a wide range of variables that influence insecticide efficacy and damage potential: species complex, population density and age structure, application timing, insecticide dosage rate, application methods and carriers, treatment evaluation timing, need for multiple applications, environmental conditions, and levels of insecticide resistance.
3. Under continuous pressure, multiple insecticide applications are required to reduce crop Against high, sustained infestations, multiple close-interval (3 to 5 days) applications of recommended economical treatments are often more effective than applications of expensive mixtures at high rates applied at longer intervals.
4. If you suspect a field failure is due to insecticide resistance, do not reapply the same insecticide at any Change to another class of insecticides, or use mixtures of insecticides from different classes.

 

Caution: Recommendations of specific insecticides are based on information on the manufacturer’s label and performance in a limited number of efficacy trials. Because levels of insecticide resistance, environmental conditions, and methods of application by growers may vary widely, insecticide performance does not always conform to the safety and pest control standards indicated by experimental data.

Insecticides are not listed in order of their effectiveness. Effectiveness of a particular insecticide can vary greatly from field to field, depending on previous insecticide use, pest species, levels of resistance, and many other factors. Within a group of insecticides recommended for control of a specific pest, there often will be considerable variability in cost, effectiveness against the primary target pest, and secondary pests controlled. Growers must consider each of these factors as well as the need to rotate among different insecticide classes (for resistance management purposes) when selecting insecticides.

Insecticides with the same trade name may be available in many different formulations. Please be aware of the product formulations listed in these guidelines and know that they may differ from the formulated product on hand.

Classes of insecticides: Effective resistance management requires rotation among the various classes of available insecticide chemistry. Often when one insecticide in a class fails because of insecticide resistance, other insecticides in the same class will also be ineffective, and selection of an insecticide from a different class will improve the chances of obtaining control. Growers need to be very aware of the type of insecticide chemistry being used. Classes of insecticides recommended in this guide are identified by the following abbreviations:

 

 

Supplemental Information

Based on historical data, the following pests could be expected at different stages of plant development. This is a generalized statement; conditions may be different on specific farms or in specific seasons.

Stages of Plant Development                                                   

Plant Beds

Sweetpotato weevils, flea beetles, aphids, whiteflies

Planting to runner development

Wireworms, white grubs, rootworms, flea beetles adult and larvae, whitefringed beetle larvae, cutworms, thrips

Canopy closure to full root development

Wireworms, rootworms, white grubs, flea beetle larvae, sugarcane beetles, caterpillars

Root maturity to harvest

Wireworms, rootworms, white grubs, flea beetle larvae, sugarcane beetles, caterpillars

Post-harvest storage

Sweetpotatoe weevils, sugarcane beetles, fruit flies

Foliar Insecticide Application Recommendations

Adequate coverage can be difficult but is essential with most products. Best results from contact insecticides will be with application volumes of 5 to 10 gallons per acre. Apply foliar insecticides with hollow cone nozzles and do not exceed 12 gallons per acre application volume.