Incorporating nematodes into an insect control programs

Resistance management, restricted entry intervals and enhanced environmental awareness have caused many greenhouse growers to incorporate biological control agents (BCAs) as part of their integrated pest management programs. BCAs provide an opportunity to supplement or replace existing insecticides, reducing the likelihood of pesticide resistance development, while maintaining control of targeted insect pests.

Real world applications

Michael’s Greenhouse in Cheshire, Conn., and C. Raker & Sons in Litchfield, Mich., have developed BCA-based programs for control of western flower thrips, fungus gnats and shore flies. Foundation products in their pest management programs are insect parasitic nematodes. These microscopic, non-segmented, roundworms are released in their infective juvenile stage to search out, enter and kill insect pests. Once a juvenile nematode finds a suitable host, it enters through natural openings (i.e., mouth, anus and spiracles). Once inside, the nematodes release a symbiotic bacterium that quickly kills the host within 24-48 hours. Reproduction inside the insect releases new generations of infective juveniles that disperse in search of hosts.

Nematodes can be used as a stand-alone program or in rotation with conventional insecticides to limit development of pesticide resistance. Because insect parasitic nematodes have no adverse affects on beneficial insects or microorganisms, nematodes also can be used in conjunction with other BCAs to broaden the pest control spectrum.

Roger McGaughey, head grower at Michael’s Greenhouse, initiated a BCA program in spring 2008. He decided to ramp up the program in 2009 when he discovered western flower thrips on newly received perennials. He applied Steinernema feltiae nematodes (Nemasys) which controlled the thrips and fungus gnat larvae. McGaughey has fully integrated the nematodes, as well as other BCAs, into the weekly control schedule. He supplements with an occasional conventional pesticide application when pest populations exceed action thresholds.

Expanded nematode application

McGaughey also started spraying the nematodes on weed mats, floors, benches, hanging baskets and all other locations where thrips and fungus gnat larvae may hide. Plugs and cuttings shipped from plant suppliers also receive nematode treatments before being integrated into the greenhouse. With a desire to receive clean plants, McGaughey has requested that plant suppliers start nematode treatment programs. His goal is to receive plants with fewer pests and to eliminate chemical residues that might be harmful to the nematodes that he applies. One of McGaughey’s plant suppliers is C. Raker & Sons.

Trish Bills and Mary Giles are sectional growers at Raker. They started experimenting with BCAs prior to McGaughey’s encouragement, but never implemented a strict program.

"Roger was very rigid about having nematodes applied to the chrysanthemums he was getting,” said Trish Bills. “We started by just treating Roger’s crop. After a while we started to see fewer western flower thrips and fungus gnats. Once we realized how well Nemasys worked, we started to branch out, treating more areas of the greenhouse, which resulted in more widespread success.”

Bills and Giles also started using S. carpocapsae nematodes (Millenium) for shore fly control. Tank-mixes of the two nematodes are applied to control thrips, fungus gnats and shore flies.

Application tips

The biological control program at Michael’s and Raker didn’t come without initial trial and error. As the growers’ experience with the nematodes grew, they learned easier and cost-effective techniques.

They discovered that a higher level of control was achieved when regular, weekly applications were made to the entire greenhouse crop. The result of missed applications and untreated areas became evident as greater pest numbers appeared on sticky cards.

The three growers also realized the importance of applying nematodes at the right time of day and under the correct environmental conditions. Nematodes should be applied in the evening when temperatures are below 86ºF. Hot, dry conditions may limit the nematodes’ effectiveness. Cloudy and rainy days are favored for nematode applications because the cool, wet conditions maximize nematode activity. Pulling blackout curtains, increasing humidity, tank-mixing with spray adjuvants and increasing the application volume are all ways to preserve moisture and prolong the life of the nematodes on the plants.

Bills, Giles and McGaughey stress it is important to keep nematode solutions cool and to prevent settling in tanks during applications. Mixing nematode solutions is an important and often overlooked step in the application process. When nematodes are allowed to settle in spray or stock tanks during application, they consume oxygen at the bottom of the tanks and cause injector issues due to intake positioning. This causes uneven nematode applications and ultimately, uneven pest control. Nematode solutions can be kept cool by placing a cold pack in the solution.

Application equipment used for conventional insecticides can also be used to apply nematodes. Sprayer equipment should be clean and free of pesticide residues that can be harmful to the nematodes. When setting up equipment, verify that pump pressure is maintained below 300 psi, use nozzle apertures larger than 0.5 mm, remove filters of 50 mesh or finer and check compatibility of nematodes with tank-mixed chemicals and previously applied chemicals. These simple adjustments will assure that nematodes are viable and applied uniformly.

Source: Greenhouse management & Production