February 2004
Controlling Pests in Retail Greenhouses By Rick Yates

If you have plants, you're eventually going to have pests. The key to minimalizing infestations is being vigilant.

The last thing a busy retail greenhouse needs is to be dealing with pest problems. Unfortunately, we have no choice in the matter because pests “come with the territory.” The challenge is stiff, but we are not defenseless.

Why is it so much harder to control pests in a retail greenhouse compared to a production facility? Most retail greenhouses are receiving plant material from many different sources. During the spring blitz, hardly a day goes by that new plant material isn’t being delivered. There are plenty of opportunities for pest problems to hitchhike into the greenhouse. You may get thrips under control just in time to unload more of the troublemakers with the next shipment. To make matters worse, retail garden centers operate long hours and some are open seven days a week.

When are you supposed to spray? If retail pest control wasn’t complicated enough already, consider the widely different types of plant material present at any one time — from alyssum to zebra plants, many of which boast beautiful but delicate blooms. All together, it’s the perfect pest environment. .

Enough complaining, though, lets get to work!

Input Controls

A wise person once said, “An ounce of prevention is worth a pound of cure.” Sage advice for the retail greenhouse operator. A good place to start is by communicating your reasonable expectations to your plant material suppliers. Even top-notch suppliers will occasionally have problems, but that is no excuse for your greenhouse to become a repository for their pest control failures. If a production greenhouse cannot achieve a high level of pest control, how are you supposed to put the fire out with the limitations a retail greenhouse faces? Your suppliers need to know that you inspect incoming shipments and that you will have to reject those with significant pest problems. .

The commitment to inspect incoming plant material when things are going crazy in the spring is a substantial one, but the payback is huge. Problems discovered after the shipment is unloaded will require much more time and resources than inspecting deliveries requires. Picture yourself spraying at 10 o’clock Saturday night after a 14-hour day. Catch my drift? .

Scouting Basics

I would like to make the argument that all greenhouse and nursery operations would be wise to establish a formal scouting program. Some operations already have employees who are capable of inspecting crops for pest problems. In this instance, the challenge is to dedicate this employee so that his first calling is to be a scout. All too often, when the busy times are upon us, the scout spends all day holding a hose or helping customers, but the busiest times are when you need your scout the most due to the increased plant shipments, heat and humidity, hours and traffic, all of which increase the probability of infestation.

During spring, you suffer from the tyranny of the urgent, and it is hard to break that pattern. Consider hiring a professional scout. In some parts of the country, this concept is beginning to take hold, and the results are very encouraging. In Maryland, Pennsylvania and New Jersey, I have observed programs through universities or cooperative extensions that train scouts. I am sure that other states have also developed similar programs. This is the beginning of a very positive concept. Professional scouts inspect your greenhouses at an interval that you agree upon and give you a full report based on their observations. Some scouts make control recommendations, and others refer you to crop advisors. One of the keys to success is that since their only job is to scout crops, there is no chance they will be loading a truck on Mother’s Day weekend!

Scouting crops leads to discovering problems early enough to make control easier and less expensive. Often a “softer” approach to pest control can be adopted when the pest populations are lower — no small benefit for the retail greenhouse. If a professional scout is not in your immediate future, take advantage of training opportunities for all of your employees who handle plant material.

Pest identification and control seminars are held in conjunction with many industry trade shows and extension meetings. With a little training, an employee restocking benches and watering plants can help scout your operation on a daily basis. The Internet is a good place to find pictures of common insect and disease problems. Add a color printer, and it is not hard to put together a manual for identifying the “bad guys” lurking in your crops. Even if you have a scout, you can’t have too many trained eyes working for you!

Chemical Controls

What if you’ve done everything recommended: You’ve worked with suppliers to purchase cleaner plant material, your crops are being scouted regularly, you even trained all of your employees to help, but the day still comes when you have pests that have to be controlled. Now what?

Before we talk about pesticide options, we should talk about the best way to deliver pesticides. For a number of reasons, retail greenhouses pose challenges when it comes to spraying pesticides. I have already mentioned the long hours of operation. In addition, retail displays are designed for eye-catching appeal and not necessarily for ease of pesticide application.

Low-volume applicators may be an option worth investigating. These machines are designed to deliver the same amount of active ingredient but with substantially less water than traditional hydraulic spraying equipment. Some low-volume applicators are automated, include timers and can fog your greenhouse without you ever setting foot in the greenhouse during the application. Low-volume applicators can do a better job of penetrating dense foliage at a fraction of the time required for traditional spraying, solid benefits for the retail greenhouse. Aerosol pesticide cans and smoke generators are also low-volume applicators. However, strong odor and long re-entry intervals would make smoke generators a treatment of last resort.

Pesticide selection in the retail greenhouse can cause you to reach for your favorite headache remedy! The ideal pesticide will have a short re-entry interval (REI) (no longer than 12 hours), does not produce a strong odor, has good bloom safety and, if you are lucky, will have some residual control so you don’t have to re-treat as often. Impossible, you say? Consider the following options, bearing in mind that this list is not exhaustive because of space limitations and that no slight is intended to products not mentioned.

INSECTICIDES/MITICIDES.

Akari SC. Has 21- to 28-day residual mite control and 12-hour REI.

Azatin XL (OrnazinEC). Neem-based IGR for thrips, whiteflies and others. Labeled for vegetables and herbs. Four-hour REI.

BotaniGard ES. Controls aphids, thrips and whiteflies. Requires multiple applications. Labeled for vegetables and herbs. Four-hour REI.

Conserve SC. Excellent thrips control, also labeled for leafminers and caterpillars. Four-hour REI.

Distance EC. Long residual IGR that controls whiteflies, scale, mealybugs and others. As a soil drench, it controls fungus gnat and shorefly larvae. Supplemental label available for tomatoes and peppers. Twelve-hour REI.

Endeavor 50 WDG. Excellent aphid control for up to two weeks. Twelve-hour REI.

Floramite SC. Up to 21 days of mite control. REI has been changed to 12 hours.

Marathon II. Excellent aphid control for up to three weeks. Labeled for whiteflies, mealybugs and others. Can be used on several vegetable transplants. Twelve-hour REI.

Pedestal SC. Long residual IGR for thrips, whiteflies and certain caterpillars. Not currently labeled for low volume applicators. Twelve-hour REI.

Ultra-Fine Oil. Controls mites, scale, mealybugs, powdery mildews and others. Labeled for vegetable and herb crops. Burns some open blooms. Four-hour REI.

FUNGICIDES. Cleary’s 3336 F (FungoFlo F, OHP 6672 F). Broad-spectrum control of foliar diseases, including Anthracnose, black spot of roses, Rhizoctonia and others. Also labeled as a soil drench for Rhizoctonia, Thielaviopsis and others. Twelve-hour REI.

Compass WDG. Long, residual, broad-spectrum control of foliar diseases, including Anthracnose, Botrytis, powdery mildews and rust diseases.

Decree WDG. Excellent Botrytis control for up to two weeks. Four-hour REI.

Medallion WP. Controls Alternaria, Botrytis, Cercospora, Rhizoctonia and others. Labeled as a soil drench for Rhizoctonia and Thielaviopsis. Twelve-hour REI.

Milstop SP. Quick knockdown of powdery mildews. Also labeled for Anthracnose, Botrytis and others. Labeled for several vegetable and herb crops. Four-hour REI.

Strike WDG. Controls black spot of roses, powdery mildews, rust diseases and others. Twelve-hour REI.

Terraguard WP. Controls Alternaria, Rhizoctonia, powdery mildews, rust diseases and others. As a soil drench, it is labeled for Rhizoctonia, Thielaviopsis and others. Twelve-hour REI.

Read and heed all of the information on pesticide labels!

Rick Yates

Rick Yates is technical support manager for Griffin Greenhouse and Nursery Supplies Inc. He can be reached by phone at (800) 732-3509 or E-mail at [email protected].