Look for these pests in 2008

As you start off the new year it is important to be mindful of the insects in your greenhouse. It is just as import to know how to properly manage them. This includes using the proper insecticides, correct rate and knowing the maximum number of applications the label allows.

Inspect incoming plant material

The number of new invasive pests increases every year. As a result, it is more important than ever to inspect plant material you purchase from other growers and the plants growing around your greenhouses. Look for both the presence of pests and signs of their damage. Chilli thrips (Scirtothrips dorsalis Hood) is a good example. Although it is small, its damage is easily detected on plants.

If you suspect you have an unusual pest or large pest population, immediately close up the shipping boxes. It is critical to have an area set aside where you can bring in new plant material and inspect it before you expose production areas to whatever pest may be lurking in the boxes.

With all the talk about chilli thrips, pink hibiscus mealybug and Q-biotype whitefly, don’t forget about traditional pests. Aphids, thrips, mites, fungus gnats, leaf miners and mealybugs are still out there and most likely will be the main pests you will encounter this year.

More on chilli thrips

Chilli thrips are on the move and they are likely to show up in other states this year. So far they have only been found in the landscape in Florida and Texas. Chilli thrips is a polyphagous species documented to attack more than 100 host plants from 40 families. As this pest expands its geographical coverage, plants are added to its host range.

Field identification of chilli thrips is extremely difficult and oftentimes impossible to differentiate from other thrips. Adults have a pale body with dark wings and are less than 2 millimeters long. Immature chilli thrips are pale in color as are the immatures of many other thrips species.

The main method a grower can use to identify these thrips is the damage they cause to host plants. Chilli thrips is mainly a foliage feeder and, unlike western flower thrips, does not feed on flower pollen. Young leaves, buds, flowers and fruits are preferred, but all aboveground parts of host plants may be attacked.

Feeding damage turns tender leaves, buds and fruits bronze. Damaged leaves curl upward and appear distorted. Feeding on buds may cause them to become brittle and drop. Infested plants become stunted or dwarfed, and leaves with petioles detach from the stem, causing defoliation.

Examine plants with these symptoms for thrips. Collect leaves or buds from symptomatic plants and place them in a sealed plastic bag to prevent the thrips from escaping. Label the bag with collection locality information, host plant, date collected and name of collector. Send samples next-day delivery to a diagnostic lab for identification.

Research conducted to date indicates that Orthene, Avid, Spinosad, Pylon (indoors), Safari (foliar), TriStar, Flagship (foliar), Aria and the predatory mite Amblyseius swirskii are effective treatments.

Pesticide-tolerant thrips

Growers were provided brief relief from western flower thrips when Conserve SC was labeled for ornamental crops. Unfortunately, there are reported cases of western flower thrips not responding to Conserve applications.

This developing tolerance may be a result of growers not following label instructions. The Conserve SC label states “no more than three consecutive applications should be used, nor should there be continuous use for more than 30 days. Consider rotating to a different active ingredient with a different mode of action or use no treatment for the next generation. ... Regardless of the crop or pest being treated (excluding leaf miners, spider mites and/or diamondback moths), do not apply Conserve SC more than 10 times in a 12-month period inside a greenhouse or a structure that can be altered to be closed or open.”

Some growers are exceeding the three consecutive applications and the 10 total applications per year. One common mistake growers make is applying Conserve repeatedly for thrips and then again for Lepidoptera pests. This causes them to exceed the number of applications that can be made in a year. It is critical to follow the label instructions to reduce resistance development in western flower thrips to Conserve.

The recent labeling of Pylon for western flower thrips control provides greenhouse growers (not labeled for outdoor use) a highly effective rotation partner to use with Conserve. As with Conserve SC it is important to follow the resistance management component of the Pylon label to lengthen the period of efficacy of this product.

Other insecticides can be used in rotation for thrips management. These include, but are not limited to, Avid, Azain XL, BotaniGard, Enstar II, Pedestal, Mesurol and Orthene. Some growers have found that the addition of a pyrethroid insecticide enhances control.

Pesticide-tolerant pests

Mites, leaf miners and aphids also have a history of developing resistance to pesticides. With this in mind, if you encounter problems trying to manage insects, it may not be a result of your spray program. The pests may have developed a tolerance to chemicals applied to nearby adjacent agriculture crops or in other ornamental production locations from where plant material (i.e., plugs and liners) is shipped to your facility.

New problems

Greenhouse employees should keep their eyes open for plant damage that doesn’t look normal and for insect pests, especially those that look different from commonly identified ones. You never know when you may be the first in your area to find a new pest or traditional pest that has developed resistance to your product of choice.

If you are concerned about a pest issue, it is best to ask an expert, such as your local cooperative extension agent. Asking for assistance to identify a potential problem could save you money and time since you will learn how to property manage the correctly identified pest problem.

Be aware of whiteflies year-round

Growers usually focus on whitefly control during poinsettia season. However, the increased tolerance observed to the neonicotinoid class of insecticides is not occurring solely during poinsettia season, but it is developing over the entire year. It is just as critical to properly manage whiteflies on bedding plants and pot plants as it is on poinsettia. For more information on whitefly management plans visit http://mrec.ifas.ufl.edu/lso/bemisia/bemisia.htm.

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- Scott Ludwig

Scott Ludwig is extension program specialist, IPM, Texas Cooperative Extension, (903) 834-6191; swludwig@tamu.edu.