Taking Out The Top Five Pests

What do mites, aphids, thrips, whiteflies and leafminers have in common? Aside from being a royal pain in the neck, they’re a motley crew that’s undoubtedly called one of your plants home at one time or another.

On a recent visit to the offices of Greenhouse Grower, Bert Wagemans, the ornamental business lead for the lawn and garden team at Syngenta Professional Products, mentioned these infamous five are the top five ornamental pests globally.

“Any pest insect or mite that appears on a top five or 10 listing did not get there by accident,” says Richard Lindquist, senior technical manager for OHP. According to Lindquist, a broad range of host plants can actually have a negative effect on the active ingredients in chemical pesticides that growers use, but a positive one on the pest.

This wide range can give pests exposure to a number of pesticides, giving them an opportunity to develop some toughness, he adds.

The Short Of It

“Early detection is key,” Lindquist says. “This is simple mathematics. I cannot think of any insect or mite control product that will eliminate 100 percent of an insect or mite infestation.” The most effective products will kill most of the problem, but not all of it, so when it comes to starting treatment, the fewer pests the better.

Many growers bypass preventative applications, so scouting and monitoring for pests are of utmost importance.

Along with early detection, Lindquist says many growers need to keep in mind pesticide resistance. “Somewhere in the world there probably is an insect or mite population that is resistant to each of the current active ingredients,” he says. Fortunately, there doesn’t appear to be a pest population resistant to all active ingredients. With that being said, the goal of any control program should be to rotate or alternate products in several mode of action groups.


When it comes to treating a mite infestation, being under the assumption that the plant canopy is getting thorough coverage is a common mistake for some growers.

“Growers need to utilize more water-sensitive paper or fluorescent dye to check their spray coverage,” says Nancy Rechcigl, Syngenta’s field technical manager who specializes in ornamentals. “It will allow them to see where they are getting the sprays and where they’re not. It will also let them look at the disposition of the spray particles.”

Sampling is another important step in eradicating this pest. Be sure to take leaves from the lower part of the canopy and look at those with a hand lens, says Rechcigl. Because that’s where the mites will typically start out, in the lower canopy first and then they tend to move up. “So when a grower sees them higher up on the plant, it means they already have a pretty good infestation.”

The many life stages of mites are also important to take into account says Keith Santner, technical services manager for Scotts. It’s important to make reapplications for the various stages. Also make the effort to identify the mites properly, because a miticide that works well on two-spotted mites might not have the same desired effect on eriophyid or broad mites, Santner adds.

Lastly, enforce strict sanitation to minimize weeds, which tend to become a preferred safe harbor for mites.


Rechcigl says aphids are usually a fairly easy pest to control. Be sure to monitor your crops with yellow cards, she adds.
Marla Faver, field development scientist at BioWorks, Inc., says some growers may not understand that aphids do not have to mate to reproduce and produce live young. Different aphid species feed on different plant parts and may be missed until the population has exploded.

Santner from Scotts adds many insecticides labeled for aphid control work quite well. “If the crop cycle is over eight weeks, then a good choice is to apply one of the systemic neonicotinoids followed by supplemental applications (on an as-needed basis) of a product that contains the active ingredient acephate and/or a synthetic pyrethroid such as bifenthrin.”


Santner says first and foremost, growers rely too heavily on one active ingredient to kill thrips (like Spinosad). “In greenhouses, growers could be using insect screen to exclude thrips from entering through ventilation equipment. These screens are not necessarily a cheap investment, but it is one that will exclude virtually all other insect pests and weed seed from entering your greenhouses.

Rechcigl agrees a thrip screen is an investment, but growers can recoup their costs over time by having fewer problems and making fewer applications. Consider a quarantine phase, too, for all incoming plants to help fish out any bad apples.

“It’s important to change your application approach and differentiate between flowering and non-flowering crops,” she says. “Flowering crops require a slightly closer spray in order to get good penetration into the flowers. Total annihilation of this pest can take three to six weeks.


For whiteflies, the common mistakes growers make are not starting pest control practices early enough in the production cycle and not continuing them throughout the cycle, Faver says. The correct control is often not timed for the stage in the whitefly lifecycle that the control is effective on.”

Whitefly can sneak up on you Rechcigl says. The adult lays quite a few eggs. If you’re not monitoring with sticky cards, the immature stage can build up quickly. It’s important not to rely on nicotinyl compounds as the only management tool. It should be saved, using it as an application at the proper time, after the crop is fully rooted in, she says.


As mentioned with whiteflies, growers are not starting with preventative measures early enough when it comes to leafminers, Rechcigl says. It’s important to do your homework and understand what crops are susceptible to leafminers.

In regard to leafminer treatment, a common mistake some growers may make is not using block treatments of a product, she says. For leafminers, it’s best to make applications for one generation of leafminer before rotating to another product.

Wetting Your Plant

Kathy Conard, marketing manager of Aquatrols, wants growers to get the most out of their pesticides, and wetting agents are a great place to start.

But before you place that order, read the labels on your pesticides to find out if a wetting agent will work in harmony with your pesticide, advises Rechcigl. “Avoid using adjuvants that are labeled as a ‘spreader-sticker,’ particularly for products that have translaminar activity. It prevents the translaminar activity from working properly.”

Conard says wetting agents (media surfactants) can actually help you stretch your applications of soil-directed pesticide drenches. Pesticides are a costly necessity. Research has shown that wetting agents improve the efficacy of soil-drenches by guaranteeing precise placement throughout the soil profile, which means more pesticide solution is distributed uniformly into and throughout the rootzone profile and not running out the bottom of the pot. 

“When complete, uniform leaf coverage is important for foliar pesticide performance, it is recommended that you add a foliar surfactant (spray adjuvant). Foliar surfactants, when added to the spray solution, significantly improve spreading, coverage and penetration of foliar pesticides, even on hard-to-wet leaf surfaces,” Conard adds. “Complete coverage increases performance and reduces the need for follow-up sprays.”

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