Pest Management Guidelines
L. Smith, H. W. Browning and B. Cartwright*
Field monitoring is the key to an integrated pest management program. When performed systematically on a quantitative basis, it provides the information needed to detect important changes in pest activity and disease incidence; evaluate pesticide performance; and establish seasonal records for evaluating and upgrading managerial decisions. When weather data and cultural practices that influence pest behavior are considered, pest behavior and populations can better be anticipated.
Monitoring systems may be limited to a single primary pest Such as the citrus rust mite, and to environmental conditions that influence rust mite behavior or they may include all major pests and beneficials. Monitoring techniques vary depending on individual preferences and management intensity, but should provide a consistent, repeatable means to numerically measure pest activity. Follow monitoring procedures upon which the control action thresholds were designed.
Monitoring frequency depends on the pests' reproductive capacities and time needed under optimum conditions for populations to reach economic damage thresholds. Because of the reproductive potential of citrus rust mite, biweekly monitoring of susceptible fruit is required from petal fall until harvest or arrival of cool weather. Other pests generally require less frequent monitoring. Outside of the petal-fall to harvest interval, monthly monitoring is adequate for the citrus mite complex and other potential pest or disease situations.
Sample size, location and selection are important to any sample program. Each citrus orchard is unique and requires individual monitoring; the first step in developing a monitoring system is to decide how many trees need to be examined and, within this parameter, how many fruit, leaf or soil samples need to be observed or collected for adequate representation and sampling reliability. Sampling may involve trees randomly selected for each monitoring period or permanently designated station trees. Trees should be dispersed sufficiently to achieve representative sampling of the entire orchard. This can be accomplished in most rectangular orchards by sampling in a diagonal direction. For square orchards, a Z-shaped pattern is appropriate.
The station tree concept involves selection of representative trees at the time of orchard establishment or at the beginning of each season. Selected trees are flagged, numbered and revisited each monitoring period throughout the season. Random samples provide information on a larger proportion of trees within an orchard over time. Station trees more closely follow pest or disease dynamics on a few individual trees. Both systems have merit and, depending on the desired result and amount of time to be invested, a combination of both methods may prove most useful.
Systematic recording of data in the field is time consuming but necessary for clarity in review and interpretation of results. If field counts are considered impractical and some form of rating scale is employed (e.g., trace, low, medium, high, very high), the assignment of numerical values from 1-5 is acceptable. Organization of the data in summary form following field sampling allows for id review and assessment of individual orchard situations. Information gathered during the monitoring process aids in planning future pest management strategies.
Control Action Criteria
Control action criteria can be defined as specific pest population levels or threshold levels that signal impending economic damage to the crop or trees. Ideally, each threshold value considers the pest's life cycle, its potential for rapid population increases under existing or anticipated environmental conditions, orchard history, the type of damage likely to occur in proportion to control costs, other stresses the trees are experiencing and other relevant factors.
Progress has been made in establishing threshold values for citrus rust mite, the major economic pest of Valley citrus, but standardized criteria for other common pests are lacking. Suggestions in this text for key pests are based on guidelines developed in other citrus production states and observational data recently accumulated by local IPM programs. Action criteria in any pest management program are flexible and should be altered to fit individual management conditions.
These guidelines provide information on how to monitor specific pests and offer insight on what constitutes reason for control action. Pre-season monitoring suggestions are provided to encourage early season inventory of pest populations and disease potential in advance of post-bloom control effects. Early monitoring provides information helpful in selecting the most appropriate and cost-effective pesticides. This early information may be useful in making volume purchases of pesticide materials and for determining which orchards merit immediate attention.
Citrus Mite Complex
Field studies of rust mite behavior have indicated that populations in excess of 50 mites per square centimeter (cm2) on fruit for 2 weeks or more are needed for rind damage to become visible. Also, rust mite populations on infested fruit may more than quadruple in a 2-week period under favorable conditions. These data support the need for a 2 week monitoring frequency for rust mite and are useful in establishing action thresholds.
As a general reference, a threshold value of 3 to 5 mites/cm2, depending on optimal or suboptimal mite reproductive conditions, has been used successfully for several years in the local TAEX-IPM program. Structured to allow the grower 2 weeks' lead time before significant damage Could occur, and provide a cushion for any sampling weakness, this threshold value applies to the following sampling regime:
To avoid rust mite management decisions being biased by two or three heavily infested fruits, consider the proportion of infested fruit. Also, consider mite distribution within trees or within orchards. Under this particular sampling regime, less than 20 percent incidence of infested fruit or of station trees would ameliorate average rust mite density values, and an incidence of more than 20 percent would substantiate or override them. The following criteria are utilized:
- Sampling is from selected station trees, one tree per two acres.
- Six fruits sampled per station tree; two fruits on each of east, north and west quandrants, selected at random from partial shade areas.
- Mite counts taken from shaded side of fruit using a 14X hand lens, counting all live unites present in four separate lens fields per fruit.
- Each lens field is roughly 1 /4 cm2 in area, for a total of 1 cm2 per fruit or 6 cm2 sample per station tree.
A sampling technique involving different action criteria has been used successfully by growers for several years. It involves random sampling of a single fruit per tree on 50 randomly selected trees within an orchard. Rust mite counts are expressed in numbers per cm2. Action criteria vary according to irrigation schedules and weather outlook, but generally action is indicated when average mite density exceeds 20 mites/cm2 and/or 25 percent of sample fruit are observed to be infested.
- Less than three mites /cm2 and less than 20 percent of sample fruit with mites-no action necessary.
- Three to five mites/cm2 and 20 percent of sample fruit with mites-borderline situation.
- More than five mites/cm2 and more than 20 percent of sample fruit with mites-control should be initiated.
Factors to consider when making control decisions regarding rust mites include:
Citrus red mites, first observed in 1980, are distributed throughout the Valley and have become a major citrus pest, particularly in the mid-Valley area between US 77 and US 281. Red mites feed on tender new leaves and populations increase with new growth flushes. Population levels decline during hot, dry July/August weather and resurge with the fall flush. Information about natural control agents in the Valley is not sufficient to determine when control action is most appropriate.
- Variety-given similar rust mite densities, oranges are downgraded less by mite damage than grapefruit.
- Lead time needed by producer to spray.
- Weather outlook and time of year-heaviest rainfall periods are May/June and August /September. Evaluate borderline mite densities during these periods in light of possible re-entry difficulties.
- Irrigation scheduling-orchards expected to need water within 10 to 14 days of an anticipated action threshold should be sprayed prior to irrigation.
- Miticide used in previous spray treatment-mite populations may rebound quickly following use of low residual materials.
- Orchard history-certain orchards, because of location, cultural practices, tree spacing or lack of uniformity in tree sizes and other reasons, consistently experience rapid re-infestation following control efforts.
Control action guidelines for red mite on Texas citrus are incomplete pending further research on natural control agents and tree tolerance levels. Factors to consider in evaluating need for red mite control include:
Texas citrus mites do not require specific control action in most seasons if trees and fruit are protected from other mite and insect pests. Threshold levels vary according to tree vigor and should be determined by period during which heavy feeding is sustained rather than by specific mite numbers. Numbers exceeding 10 adult mites per leaf over a period of 30 days have been associated with winter defoliation of crown leaves.
- General tree vigor.
- Mite reproductive potential and environmental conditions.
Major considerations in Texas citrus mite management include:
False spider mites' increase in the past was associated with the use of organophosphate pesticides to control other pests and situations involving use of zineb alone for control of rust mite. With the present trend to use specific miticides such as dicofol, chlorobenzilate and fenbutatin-oxide, primarily for rust mite control, recent false spider mite problems have been associated with orchards where aldicarb soil treatment replaced post-bloom and late spring sprays. In aldicarb-treated orchards where the need for rust mite control may not arise until late summer, start monitoring for false spider mite in July and continue through September.
- Tree vigor.
- Current and projected climatic conditions.
- Deleterious effect of fungicides applied for melanose or rust mite control on beneficial fungi.
- Effect of certain fall scalicide applications on over-wintering mite populations (azinphos-methyl and methidathion have been implicated with increased mite populations).
- Time of year-predisposition of mite-damaged leaves to defoliation by strong, dry winds greatest during fall/winter months.
California red scale is a major pest of citrus in the Rio Grande Valley. It attacks all parts of the tree aboveground and is a common cause of limb dieback and tree death in new trees. Populations usually are kept in check by natural enemies, but tend to reach damaging levels during abnormally dry seasons on trees adjacent to dusty roads. A small parasitic wasp, Aphytis lingnanensis, provides effective control in most seasons if not restricted by dust or by application of broadspectrum insecticides.
Begin monitoring for red scale in late spring to early summer to advantageously schedule a spray application during periods of high crawler activity or the early growth stages when scales are most susceptible to control. Orchards having a history of heavy red scale infestations the previous summer should be monitored early following warm winters. Monitoring always is required from July through October when colonization on fruit is easily seen and infestation levels are more easily determined.
To limit scale damage below tolerances set for federal grade standards, begin control action when 5 percent of the fruit examined have 10 or more live scales. Examine at least 10 outside fruits on both east and west quandrants of sample trees to calculate infestation levels. A hand lens will help distinguish live scale insects from dead or parasitized scales, which appear partially loosened from the peel or exhibit holes cut by adult parasites as they exited the scale body. Estimates of scale parasites from leaf samples are less reliable than those based on fruit samples because of the difficulty in determining leaf age and when parasitism occurred.
Consider the following for monitoring and control of California red scale:
Chaff scale is the most common widespread armored scale pest of Valley citrus. It attacks all aboveground parts of trees and can result in serious downgrading of fruit, but infestations rarely cause twig and limb dieback. Several species of parasites are known natural control agents.
- Monitor new tree plantings frequently as they are subject to relatively rapid infestation.
- Inspect every young tree in the planting at least twice during summer and fall months.
- Natural control by scale parasites often is reduced during the heat of July and August.
- Increased incidence of spherical yellow crawlers encountered when searching fruit for rust mites signals impending infestations in bearing orchards.
- Oil sprays are least injurious of all scalicides to scale parasite populations.
Monitoring for chaff scale is suggested during pre-season and biweekly scouting for rust mite. Grade standards for fruit are important in deciding if summer or early fall scalicide application is warranted. Control action criteria are the same as described for California red scale.
Various minor citrus pests capable of causing economic damage under favorable circumstances require consideration during monitoring of major pests. Secondary pest eruptions usually result from loss of natural enemies through improper pesticide use, exposure to off-target pesticide drift or weather extremes. The two most common secondary pests are brown soft scale and citrus mealybug. Outbreaks of these pests occur most frequently and persistently near fields traditionally planted close to cotton and vegetable crops.
Brown soft scale infestations generally develop during the summer and fall months. Early signs of infestation are easily overlooked during monitoring activities until blackening of leaves by sooty mold fungi becomes noticeable. Tree vigor is diminished by feeding activities and inhibition of photosynthesis by sooty mold growing on the leaves. When localized infestations are found, spot treatment of trees on an "as needed" basis may be appropriate to reduce costs and prevent possible deleterious effects on natural enemies.
Citrus mealybug is controlled most effectively with pesticides during early stages before protective wax secretions and sooty mold form. Monitoring activities must be concerned with identification and quantitative assessment of first and second stage larvae. Mature mealybugs are highly resistant to contact pesticides. Clusters of fruit-usually the higher quality, inner canopy fruit-are preferred by mealybugs. Heavy infestations interfere with fruit development and may cause fruit drop. Sooty mold is difficult to remove at the packing shed, often resulting in downgrading of fruit.
Mealybugs have several predatory and parasitic natural enemies. Severe outbreaks in orchards not normally affected by mealybugs usually are the result of pesticide-related reductions or other unfavorable circumstances affecting natural enemies.
Whitefly infestations (citrus whitefly, citrus blackfly, cloudy-winged whitefly or woolly whitefIy) occurring in isolated situations also can be associated with disruption of natural control agents.
Texas leafcutting ants can cause serious damage to citrus, particularly In young plantings, so monitoring notes on location and severity of infestations will facilitate control efforts. The leafcutting ant poses a special problem in well-drained sandy loam soils because it may nest some distance from the orchards Repeated defoliation of trees reduces tree vigor, eventually killing young trees. Locate the nest by tracking at dawn or dusk or during periods of cloudy weather because aboveground activity ceases during direct sunlight.
*Former Extension agent-pest management; former entomologist, Texas Agricutural Experiment Station; and former Extension entomologist; The Texas A&M University System.
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