MANAGEMENT OF WHITEFLY ON POINSETTIA 



Stanley R. Swier 



=.anagement of whitefly is com- 

 plicated because rarely will one simple 

 technique provide the total solution. 

 The whitefly population erupts quickly. 

 The selection of insecticides is limited 

 either due to government regulations, 

 phytotoxicity, or resistance. Lastly, 

 there is a low tolerance for whitefly on 

 poinsettia. Customers complain when 

 too many whiteflies abound in the 

 home. I will briefly summarize the cur- 

 rent knowledge on whitefly manage- 

 ment. All of the following pest man- 

 agement techniques should be consid- 

 ered carefully. 



■^o EXCLUSION 

 Inspect plants before acceptance. Qua- 

 rantine plants in a separate area, if 

 necessary. It is much easier to prevent 

 an infestation than to control it. Learn 

 to identify the life stages of whitefly 

 and search lower leaf surfaces. Screen 

 vents whenever possible and keep 

 doors closed. 



-c^ SANITATION 

 Control weeds inside and outside of the 

 greenhouse. Eliminate nearby crops 

 outside of the greenhouse which act as 

 a source of infestation. Or, at the very 

 least, spray these crops for whitefly. 



-cTd DETECTION 



Use yellow sticky boards at a rate of 1-4 

 per 1000 sq ft. Place traps at the top of 

 the canopy and around vents and 

 doors. Traps will not control whiteflies 

 but will indicate population trends, 

 detect "hotspots", and indicate the 

 effectiveness of chemical controls. It is 

 very important to make weekly counts 

 of whitefly and change traps often be- 

 fore they lose their effectiveness. 

 Without this record keeping, traps are 

 of much less value. Don't forget to 

 check the plants for whitefly in order 

 to develop a sense of the relationship 

 between trap and plant counts. 



^D CHEMICAL CONTROL 

 Whitefly populations vary in their 

 susceptibility to chemicals. What 

 works for one grower may not work for 

 another. Now, without Temik 

 chemical control is more difficult. 

 Chemical control can begin on a 

 preventative basis with a systemic such 

 as Oxamyl lOG. Systemics only work 

 on young, actively growing plants and 

 are only a partial solution. At the first 



sign of whitefly on the sticky traps, 

 begin a preventative spray program. 

 Increase plant spacing to get better 

 spray coverage and penetration, 

 especially as plants get larger. Small 

 droplets penetrate better than large 

 droplets. Whitefly nymphs do not 

 crawl around and contact insecticides. 

 Spray droplets must hit them directly. 

 Use a spraying system designed to apply 

 pesticides to the undersides of leaves, 

 where the whitefly feeds. Sprays are 

 more effective if applied early in the 

 morning when adults are less active. 

 Make sure the proper rate is applied. 

 Errors are very frequent. Proper 

 application technique is as important 

 as proper chemical selection. Even the 

 bestof chemicals will network if 

 misapplied. 



An application every 10-14 days 

 would be adequate on a preventative 

 basis. However, once whiteflies are 

 detected, reduce that interval to every 

 4-5 days for at least a month. Spray 

 every 3 days if whiteflies are numerous. 

 However, despite what I say, never 

 violate label directions. My comments 

 are guidelines only. 



The whitefly completes its life cycle 

 in about a month and all stages are 

 found at the same time. Not every 

 stage (egg, nymph, pupa, adult) is 

 equally susceptible to cover sprays. 

 Frequent applications are necessary to 

 disrupt this life cycle. Don't get 

 discouraged and keep repeating sprays. 

 Treat the entire production area; 

 otherwise you chase them around from 

 spot to spot. Change chemical classes 

 from month to month to avoid 

 developing resistance. Remember, your 

 goal is to get excellent whitefly control 

 before the bracts show color. Watch for 

 signs of phytotoxicity. Although any 

 insecticide has the potential to cause 

 phytotoxicity, be very careful with 

 rates and frequency of applications 

 with insecticidal soaps, horticultural 

 oils, Orthene, Thiodan, and Dibrom. 

 Other registered chemicals are 

 Resmethnn, Mavnk, Sumithnn, 

 Talstar, and Tempo. 



Once the bracts show color, 

 phytoxicity and residues are a more 

 serious problem. Avoid sprays unless 

 certain no problem will occur on your 

 varieties. Test the chemical on a few 

 plants first. When bracts turn color, 

 rely mostly on aerosols, fogs and 



smokes. However, these materials only 

 control adult whiteflies. If many 

 nymphs are present, complete control 

 is difficult. Use aerosols, fogs, and 

 smokes late in the day when adults are 

 flying for better control. Refer to the 

 New England Greenhouse Pest Control 

 and Growth Regulator Recommend- 

 ations for more chemical control 

 information. Be sure to follow label 

 directions. 



c?o BIOLOGICAL CONTROL 

 The use of Encarsia formosa, a parasitic 

 wasp, in commercial production is rare 

 in New Hampshire. There are several 

 problems. Large numbers of wasps must 

 be released weekly for 4-5 weeks or 

 more before it becomes established. 

 Encarsia is effective only against the 

 greenhouse whitefly and not the sweet 

 potato whitefly. Chemicals harmful to 

 the parasites can't be used. The grower 

 must spend significant energy 

 monitoring the Encarsia/Whitefly 

 interaction to keep the whitefly 

 population under control. However, 

 the proper use of Encarsia can reduce 

 pesticide applications. Few growers are 

 willing to spend the time, money, and 

 make the personal commitment it 

 takes to make biological control work. 

 This is understandable, as the risks of 

 failure are great, and the consequences 

 disastrous. For this reason, the UNH 

 Cooperative Extension IPM program 

 hopes to provide practical 

 demonstrations of biological control 

 and use of biorational pesticides in 

 greenhouses. More will be reported on 

 this effort in future articles. 



c?D SUMMARY 

 With proper knowledge of biology, 

 chemical and cultural control, 

 whiteflies can be managed. Forget 

 about 100% control. Complete control 

 will require the overuse of pesticides. 

 Choose a low level that you can live 

 with, for example 5 adults per week, 

 per trap, and try to maintain that level. 

 There is no magic to whitefly 

 management, just hard work. For 

 further information contact me or your 

 County Extension Educator. Good 

 luck. 



Dr. Stanley Swier is an Extension 

 Specialist in Entomology . For further 

 information, \ou can lurite Dr. Swier at 

 Nesmith Had, UNH. Durham, NH C 

 03824, oTcallhtmat (603) 862- J 159'^ 



October/November 1991 15 



