Date 28 February 1992

Title of Project Plant Resistance as Part of IPM for Whiteflies on Floral Crops

Institution where work is being conducted Cornell University

Amount of Endowment Grant$ 27,000
Covering Period 1/92 to 12/92

Anticipated Date of Project Completion/Final Report 2 years hence

Individual(s) Conducting Project:

(List Project Leader First)

John P. Sanderson - Title Asst. Professor of Entomology

Telephone Number (607) 255-5419

Plant Resistance as part of IPM for Whiteflies on Floral Crops

John P. Sanderson

Cornell University

Progress Report to the American Floral Endowment, 2/28/92

A. Project Objectives:

1. Screen cultivars of several important floral crops for resistance to whiteflies.

2. Investigate the degree to which crop fertilizing practices affect whitefly biology (and

perhaps that of other pests), and determine if pest problems can be reduced by modifying

crop fertilizer programs without sacrificing crop quality.

3. Compare the efficacy of insecticides against whiteflies on resistant and susceptible

cultivars.

4. Compare the effectiveness of the whitefly parasitoids on selected crop cultivars.

B. Summary of Work Conducted/Results to Date:

[Note: A recent paper published in the SAF 8th Conf. on Insect & Disease Mgt. (Feb.,

1992, in Orlando, FL) presents an overview of much of our progress to date.]

Objective 1. We have used the poinsettia cultivars ‘Celebrate’ and ‘Celebrate 2′ as

standard varieties for comparison with sweetpotato whitefly (SPWF) numbers on other

cultivars. In choice tests among nine cultivars, we consistently find the most SPWF

nymphs on ‘Annette Hegg Dark Red’, ‘V 14 Glory’, ‘Angelika’, ‘Lilo’, and ‘Annette Hegg

Lady’, compared to the numbers on ‘Celebrate’. However, all cultivars in all tests thus far

readily become infested with unacceptable numbers of whiteflies.

Objective 2. My graduate student, Dorothy Boorse, has been evaluating the effect of

the amount and form of nitrogen fertilizer on the biology of SPWF on several popular red

poinsettia cultivars. Through a series of studies, we are examining how N levels affect

SPWF egg production, egg to adult developmental time, survival, and plant choice,

including how nutrient levels affect the whitefly’s choice of cultivar. No significant

difference in egg production was observed among plants fertilized with either 100, 200, or

400 ppm of nitrogen. However, egg to adult developmental time was significantly slower

on plants fertilized with 200 ppm. Female SPWF laid more eggs on plants fertilized with

ammonium nitrate than with calcium nitrate, but no difference in egg to adult developmental

time was observed among the two fertilizer treatments. We have frequently noted that 4th

instar nymphs tend to be smaller on plants that are given low N. Small nymphal size may

result in low egg production by emerging adults.

Objective 3. Screening work with “biorational” insecticides, including several neem-

based chemicals, is continuing, as well as work with certain insect growth regulators.

Poinsettia cultivar had no effect on the degree of control by a mixture of Orthene plus

Tame, but mortality by horticultural oil was affected, probably due to differences in spray

coverage. Work with Miles Corporation’s insecticide, imidacloprid, is also continuing,

with excellent results. We recently treated stock poinsettia plants with a granular

application of imidacloprid, took cuttings two weeks later, rooted the cuttings for 5-6

weeks, potted them, and placed them into our SPWF colony, and the plants remained

whitefly-free for at least 3 weeks. Obviously there was enough insecticide in the cuttings

to maintain control under very heavy SPWF pressure, 11 weeks after the stock plants were

treated. It is doubtful that poinsettia cultivar will strongly affect control by this insecticide.

We have reviewed the proposed label for this product, and label submission is expected in

Winter/Spring 1992.

Objective 4. Weekly, inundative releases of Encarsia formosa (currently the only

commercially-available whitefly parasitoid) were evaluated for control of both greenhouse

and sweetpotato whitefly on Christmas poinsettia crops at four greenhouse operations in

New York. The crops at three of these operations (two had primarily greenhouse whitefly,

one had primarily SPWF) were sold without the need for any insecticide applications.

Initial SPWF numbers at the fourth location were too high and the sower failed to reduce

the whitefly infestation to a level that the parasitoids could control. This underscores the

importance of starting biological control efforts with low pest levels, at least until a better

parasite for sweetpotato whitefly is commercially available. Lastly, we evaluated the

influence of 7 red poinsettia cultivars on the performance of E. formosa releases against

SPWF under Christmas crop conditions. The pattern of percent parasitism differed

significantly among the poinsettia cultivars, indicating a potential cultivar effect on the

effectiveness of the wasps.

C. Future Plans Covered by the Endowment Grant:

Objective 1. We will continue to evaluate poinsettias and other floral crops for

resistance to whiteflies. We plan to evaluate the sap content and leaf trichome density of

selected poinsettia cultivars to determine factors that seem to influence SPWF numbers on

poinsettia.

Objective 2. We will evaluate whether the form or the amount of nitrogen affects

SPWF choice of poinsettia cultivar. We are also trying to determine the sap nitrogen

content of poinsettias fertilized with different amounts of nitrogen, to confirm that the

results we have observed were indeed caused by the amount of nitrogen that the whiteflies

were ingesting.

Objective 3. We will continue our screening of potential insecticides for whitefly

control, including an analysis of cultivar effect on insecticide performance.

Objective 4. We suspect that leaf trichome density (”leaf hairiness”) influences

parasitoid searching efficiency. We plan to examine this experimentally.

D. Anticipated Benefits:

This research will aid in whitefly control with less pesticides, provide

growers with more “least toxic” pest control strategies, and avoid problems associated with

the overuse of insecticides. Knowledge of plant resistance factors to whiteflies in

floricultural crops can be a valuable tool in breeding programs, and would make a

significant contribution toward the biology and control of this major pest. Screening

popular cultivars for plant resistance can give growers information on which cultivars

should be carefully inspected and monitored for pest populations. If we can identify plant

factors that affect whiteflies, we may be able to modify these factors for better whitefly

control. Resistant crop varieties might be integrated with insecticides for better chemical

control, or with biological control organisms for better non-chemical pest control.

A side benefit of this work is our ability at Cornell to incorporate pertinent results into

our New York State Greenhouse IPM effort, thereby testing it in the hands of growers and

eventually implementing it. From a scientific standpoint, these studies may be useful to

other scientists involved in plant breeding, chemical control, biological control, and IPM.

For example, our work with the influence of cultivar on whitefly parasites win complement

biological control studies underway by other entomologists. Our results may also be

directly applicable to plant resistance studies of other greenhouse pests, or be directly

applicable for whitefly control on other floral crops.

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