Date 28 February 1993

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 One year hence

Individual(s) Conducting Project:

(List Project Leader First)

Dr. John P. Sanderson – Title Asst. Professor of Entomology

Telephone Number (607) 255-5419

Ms. Dorothy Boorse – Title Grad. Res. Asst.

Plant Resistance as part of IPM for Whiteflies on Floral Crops

John P. Sanderson

Cornell University

Progress Report to the American Floral Endowment, 3/1/93

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 whitefly parasitoids on selected crop cultivars.

B. Work Conducted/Results to Date:

Objective 1. We continue to investigate plant factors that influence whitefly numbers.

We are currently testing our suspicion that trichome (leaf hair) characteristics are important.

To test this hypothesis, we are looking at sweetpotato whitefly (B strain) egg production in

choice and no-choice tests within and between groups of cultivars that have similar

trichome densities. We predict that egg production will be greatest on the cultivars with the

most trichomes. This work is still in progress.

Objective 2. My graduate student, Dorothy Boorse, has completed her studies on the

interaction of nitrogen fertilizer level and poinsettia cultivar on sweetpotato whitefly (B

strain) biology for her M.S. thesis, and will defend her thesis in April. Scientific

publications and a complete report to the Endowment will be prepared shortly. Generally

speaking, within the range of nitrogen fertilizer rates that are commercially typical, she has

seen relatively minor affects on whitefly egg production and egg to adult developmental

time, although the plant growth responses were dramatic. The cultivars that were used

affected whitefly egg production and developmental time, but only to a small extent.

Cultivar and nitrogen level eventually affected whitefly numbers, but only after the

whiteflies were allowed access to the plants for at least six weeks (more than one whitefly

generation).

Objective 3. We evaluated the effect of two insecticide treatments (Tame+Orthene, and

fenoxycarb) delivered through three types of sprayers (electrostatic, hydraulic, and cold-fogger)

on sweetpotato whitefly numbers on different cultivars. Our results continue to

indicate that the most important effect that cultivar has on chemical effectiveness against

whitefly nymphs is whether a cultivar’s canopy architecture allows for effective coverage

and canopy penetration.

Objective 4. As noted in Objective 1, trichome density may affect parasitoid

performance as well as whitefly numbers. We are currently evaluating the extent to which

trichome density can affect parasitoid effectiveness. The pattern of percent parasitism by

Encarsia formosa differed significantly among seven poinsettia cultivars in a previous

study. We are also evaluating new parasitoid species for sweetpotato whitefly in these

studies.

Note: As a spin-off of our Endowment-funded work, we have recently developed

statistically-valid sampling plans for estimating whitefly numbers on poinsettia cuttings and

for use during the season for the Christmas crop. I presented this information at the SAF

9th Conference on Insect & Disease. Mgt. on Ornamentals in February, and provided

guidelines for the sampling plans in the Conference Proceedings. We anticipate a scientific

publication and a trade magazine article of our results, and plan to implement these

sampling plans in Cornell’s 1993 New York State Poinsettia IPM Program. I have also

received numerous requests for this information from extension personnel from several

other states. Much of the data that were used to develop the sampling plans were gathered

in the course of Endowment-funded experiments.

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 will evaluate the importance of leaf trichome density (“leaf

hairiness”) on SPWF numbers on poinsettia in the short term, and other plant

characterisitics (e.g., sap content) in the future.

Objective 2. This objective has been completed.

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

control, including an analysis of cultivar effect on insecticide performance. We are close to

completing this objective.

Objective 4. We suspect that leaf trichome density influences parasitoid searching

efficiency and effectiveness. We plan to examine this experimentally in conjunction with

Objective 1, as well as with small scale field tests.

D. Anticipated Benefits for Floral Industry:

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. For example, if trichomes

are important in plant resistance to whiteflies, this trait could be modified via breeding

programs. Screening popular cultivars for plant resistance can give growers information

on which cultivars should be carefully inspected and monitored for pest populations, or

those cultivars, on which chemical or biological control will be more effective. Our results

have now indicated that the level of nitrogen fertilizer does not greatly affect whitefly

levels, regardless of the cultivar. We now know that growers can apply as much or as little

nitrogen as the crop needs without concern about its effect on whitefly levels.

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 them. 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.

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