A wide variety of insect and mite pests have been found in association with poinsettia production both in shade houses and in the greenhouse (Table 1). These pests can feed on many parts of the poinsettia plant or be associated with the production areas. Pests of poinsettia, as well as natural enemies of these species, should be monitored using appropriate methods. Direct observations of the undersides of a large sample of randomly selected leaves made on a regular weekly or semi-weekly schedule is the best method of early detection. Shaking or beating plant parts over an off-white cardboard sheet dislodges pests and can make small arthropods such as spider mites and thrips easier to detect. Yellow sticky traps (1 trap per 1,000 sq. ft. placed no closer that 150 ft. in the greenhouse) are useful for monitoring adult whiteflies, thrips, aphids, leafminers and fungus gnats. Pheromone traps and black light traps are also useful for monitoring populations of certain pests, particularly adult moths.
Natural enemies of insect/mite pests include insect pathogens (viruses, bacteria, fungi), parasites (those that develop on or inside their hosts) and predators. Every effort should be made to encourage populations of these beneficial organisms. Releases of certain natural enemies (Table 3) have proven to be effective in certain instances when other pests, such as aphids, requiring additional insecticide applications are not present. Products containing Bacillus thuingiensis (Dipel, Thuricide) have been shown to control certain exposed caterpillar outbreaks. Use of broad spectrum insecticides/ miticides eliminates these natural controls. If insecticide/ miticide treatments are required, use of target-specific products that preserve populations of natural enemies is encouraged.
Preventive treatment programs for pests such as spider mites and whiteflies are often conducted using soil-applied systemic insecticides such as Oxamyl 10G (oxamyl) or Temik 10G (aldicarb, removed from the market), and/or foliar sprays. However, even after preventative treatments are rountinely applied, plants should be monitored for secondary pest outbreaks and pest resurgence. Management tactics work best when implemented when infestations are detected early.
When pesticides are used, select the materials least toxic to the user and to natural enemies of pests, if possible. Materials should be applied in strict accordance to instructions provided on the product’s label.
Wear required protective clothing and heed all safety precautions and required reentry intervals specified on the label. Considerations for possible phytotoxic reactions (the ability for the pesticide to harm the plant) are very important in poinsettia production, particularly after the bracts show color (Tables 2 and 3). If the potential of phytotoxic reaction is not known, apply the material to a few plants and observe the plants for a few days before spraying the entire crop. Tables 2 presents common symptoms.
Foliar applied insecticides/ miticides can frequently be mixed with other pesticides (fungicides) and adjuvants (spreaders, stickers, buffers, etc.). When mixing materials together for the first time, do so in a clear container and observe any precipitation, settling or other reactions. Provided these materials go into solution, the mixtures may be phytotoxic or less active as a tank mixture. Again, a few plants should be sprayed and observed. Use of adjuvants is suggested only when warranted.
Managing Sweetpotato Whitefly
Bemesia tabaci (Gennadius), is a relatively new pest of greenhouse grown poinsettias in Texas. Although this species has occurred outdoors on other crops for some time, insecticide resistant/tolerant strains appeared in 1986 in Florida. In Fall, 1987, the first report of this stain was reported from greenhouses in Texas. Since then, it has spread to all greenhouse ornamental production areas of the state. This strain is difficult to control with “standard” materials used to control other species such as the greenhouse whitefly.
The sweetpotato whitefly can be identified by characteristics of the adult and the ‘pupal’ skin. The adult whitefly holds its wings ‘roof-like’ over its back, as compared to the greenhouse whitefly which holds its wings in one plane. The pupal skin, found on the undersides of older leaves is tear-drop shaped and is oval in cross section. On the small end of the tear drop are two prominent stiff hairs or setae. In contrast, the greenhouse whitefly pupal skin is oval, square in cross section and may or may not be spiny.
Management of the sweetpotato whitefly begins with good sanitation and cultural practices. Try to provide an interval in the greenhouse that is host free by removing and/or treating alternate hosts (they are known to attack over 50 plant species, including weeds!). Purchase cuttings or plants that are pest free and inspect plants carefully as they enter the production facility. Workers working in infested areas should avoid wearing yellow, which is attractive to the whiteflies, and thereby prevent movement into uninfested greenhouses.
Chemical control of the sweetpotato whitefly is difficult and may cause an explosion of the population after treatments are discontinued. Products that seem to be effective in one production area (presumably representing a select strain of sweetpotato whitefly) may not be effective in another area (presumably representing another strain).
For poinsettias under more than minimal pressure, apply pesticides twice weekly for adult control and twice weekly for nymphal control through a period of one whitefly generation (about 3 weeks). Subsequent weekly applications of pesticides detrimental to adults and nymphs may be sufficient to maintain control.
Resistance management is the practice of utilizing selected control tactics, such as insecticide use, in such a manner to prolong the effectiveness of available materials. Use of one ingredient over many generations leads to the development of resistant/tolerant pest strains. Using tank mixtures over successive generations could lead to the development of “multiple resistance”, pests that are resistant to a wide range of ingredients. Growers are encouraged to rotate between classes of nerve active pesticides used, as much as practical between whitefly generations (Table 3). Using the least toxic, most target specific material earlier in the production cycle may delay the need for nerve active insecticides.
Application methods should be scrutinized if control failures are detected. Use of any one method (smoke bombs, foggers, low or high volume sprays, soil-applied systemic) may prove to be inadequate to achieve thorough coverage of infested areas. Whole-house treatments, using several techniques may prove to be superior. Plants should be spaced to permit effective use of the proper pesticide application equipment. Under-the-leaf coverage is essential for successful sweetpotato whitefly control.