Insecticide and Miticide Guide
H.W. Browning and B. Cartwright*
Using a pesticide wisely requires forethought and analysis of a particular pest problem or situation to determine the best choice under those particular conditions. Often, more than one choice exists for a particular pest. Factors that should be considered in selecting one pesticide over another include:
- Product efficacy or effectiveness;
- Application frequency needed or amount of residual control provided;
- Cost per acre, factoring in the number of applications required to achieve control;
- Potential hazards to applicator, mixer and grove workers; signal words on the product label are a good indication of this hazard;
- Hazard to beneficials and other non-target organisms and
- Use restriction, including re-entry intervals, preharvest intervals, number of allowable applications, time required between applications and restriction on mixing with other products, particularly oils.
Water sources used for pesticide applications in the Lower Rio Grande Valley are alkaline with pH readings typically ranging from 7.8 to 8.2. Use of high pH water, particularly above 8.0, may affect the performance of many pesticides, particularly organophosphates and carbamates. Degradation of certain pesticides is more rapid at higher pH, especially at higher temperatures (>95oF). Little information is available on the degradation rate of specific pesticides in high pH water; some pesticides are relatively unaffected. Generally, it is a good idea to check pH levels with a pH meter on a regular basis and buffer spray water with suitable acid buffer down to a range of 6-7 pH. When tank mixes of more than one pesticide or when fertilizer is combined with a pesticide, the final sprav solution should be checked to determine pH.
Adjuvants or spray additives are intended to enhance product performance or coverage. Surfactants or spreading agents lower the spray particle surface tension allowing droplets to spread out on plant surfaces instead of combining to form large droplets subject to run-off. They are especially useful when spraying hard-to-wet surfaces such as waxy citrus leaves, armored scale insects, mite colonies with webbing or hairy-surfaced weeds. Some pesticide products are formulated with surfactant included.
Stickers and extenders function to lengthen pesticide performance life by increasing product tenacity or weathering qualities of materials sprayed on plant surfaces. These frequently are combined with surfactants and are available as "spreader-stickers." Other adjuvants available for special applications include anti-foam agents and suspending agents that improve performance and enhance application of pesticide suspensions. In general, adjuvants properly used increase product performance, reduce waste and help minimize non-target contamination.
The key to using pesticides safely is to be aware of potential hazards and take adequate precautions before and during use to prevent any unwanted effects. Before using any pesticide, read the label. Besides application instructions, the label provides information on re-entry intervals, hazards to the environment and non-target organisms, a statement of practical treatment or first-aid in case of exposure, storage and disposal procedures for containers, pre-harvest intervals to avoid excessive residues and the symptoms of poisoning. Users also should consult Texas Pesticide Laws and Regulations for state provisions that affect the application of pesticides to citrus.
With the exception of some tangerines and tangelos, most citrus cultivars do not require honeybee pollination. However, blooming citrus is highly attractive to honeybees as a food Source and may provide a good nectar source for a high quality honey sought by beekeepers. Although insecticides are not routinely applied during bloom, it is important to recognize that many pesticides applied to citrus are toxic to honeybees. The insecticides may cause significant bee death while they are foraging in sprayed orchards or through contamination of water or pollen brought back to the hive. The grower and beekeeper should cooperate closely to minimize bee losses. The following guidelines will reduce bee losses:
- If at all possible, avoid spraying during bloom. If applications are needed, apply when the fewest bees are foraging. Applications in the evening are least hazardous, early morning sprays are second best and mid-day sprays are the worst relative to bee hazards.
- To prevent heavy losses of bees, don't allow pesticides to drift onto colonies. Bees often cluster on the front of their hives on hot evenings. Pesticide drift or direct spray at this time generally results in high levels of mortality.
- Where insecticides are needed, consider their toxicity. "Highly toxic" pesticides present an extreme hazard to bees and should be used during bloom only if no other alternative exists. Insecticides categorized as "Moderately toxic" or "Relatively non-toxic" pose a much reduced hazard to bees and may be applied with relative safety in the evening or morning hours. For specific hazard ratings of pesticides to honeybees, refer to the pesticide recommendation table.
Many pesticides have special precautions listed on the label that should be considered prior to their use. Failure to completely follow label guidelines may resuIt in excessive residues at harvest, plant injury, poor pest control or undue hazards to non-target organisms including the applicator. The following are some of the major precautions for some of the most commonly used citrus pesticides:
Petroleum oil sprays. When applied properly, oils provide a very useful tool for controlling some citrus pests without damage to beneficial organisms but the sprays require careful use to avoid plant Injury. Soil moisture, humidity, temperatures, growth stage of leaves and fruit and the type of oil used can influence whether or not tree injury occurs. Spray oils should not be applied when soil moisture is low or when relative humidity is below 30 percent and daytime temperatures are likely to exceed 95o F. Effective use of oils for pest control requires that the oil persist on the tree long enough to kill the pest but not long enough to cause tree injury. Persistence of oil film on foliage beyond the tree's tolerance can interfere with photosynthesis and transpiration. Such damage can result in twig dieback, leaf drop, reduced yield and the reduction in amount of fruit sugars (soluble solids).
Table 1. Effectiveness of selected pesticides against major citrus pests.