Date 31 August 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 1/93 to 12/93

Anticipated Date of Project Completion/Final Report January 1994

Individual(s) Conducting Project:

(List Project Leader First)

Dr. John P. Sanderson - Title Asst. Prof. of Entomology

Telephone Number (607) 255-5419

K. C. Bennett - Title Technician

Plant Resistance as part of IPM for Whiteflies on Floral Crops

John P. Sanderson and K. C. Bennett

Cornell University

Progress Report to the American Floral Endowment, 8/31/93

A. Project Objectives:

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

2. Investigate the degree to which crop fatilizing 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.

Results from previous tests have suggested that poinsettia trichome (leaf hair)

characteristics are important to adult whitefly leaf choice and egg production. We suspect

that adult females will spend the most time and lay the most eggs on the cultivars with the

most trichomes. We have ranked poinsettia cultivars with respect to their trichome

densities on both young and mature leaves. We are now in the midst of a series of

experiments designed to examine sweetpotato whitefly (B strain) egg production in choice

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

densities. This work is currently 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. A scientific publication and a complete report to the

Endowment is in preparation. Within the range of nitrogen fertilizer rates that are

commercially typicaL she found no statistically significant affects on whitefly egg

production and egg-to-adult developmental time, although the plant growth responses to the

nitrogen treatments were dramatic. Nitrogen level eventually affected whitefly numbers to

a small extent, but only after the whiteflies were allowed access to the plants for at least six

weeks (more than one whitefly generation). We conclude that the level of nitrogen fertilizer

provided to poinsettia does not substantially affect sweetpotato whitefly numbers.

Objective 3. 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. This is particularly

important for insecticides that kill by contact action.

Objective 4. Leaf trichome density may affect parasitoid performance as well as

whitefly numbers. Studies related to those in Objective 1 are underway to evaluate the

extent to which trichome density can affect parasitoid effectiveness. Included in these

studies are new parasitoid species for sweetpotato whitefly.

C. Future Plans Covered by the Endowment Grant:

Objective 1. We will complete our studies to evaluate the importance of leaf trichome

density (”leaf hairiness”), and possibly other plant characterisitics (e.g., sap content), on

SPWF numbers on poinsettia.

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 will examine the effect of leaf characteristics on parasitoid

performance experimentally in conjunction with Objective 1, as well as with small scale

field tests.

D. Anticipated Benefits for Floral Industry:

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 potentially 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 will 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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