Which Chemicals Can be Used with Minimal Impact on the Good Guys?

It is hard to think of bugs as good or bad, but as humans our brains process information by putting things in logical groups. If a group of bugs damages your cut flowers and cuts into your profit margin, the bug is labeled by most growers as “bad”. If an insect attacks and chows down on plant-feeding insects it is labeled “good”.  Japanese beetles and cucumber beetles would be labeled “bad bugs”. Ladybugs, spiders, lacewings, and syrphid flies are labeled “good bugs”.
A number of good insects and mites are active in your cut flower fields. These beneficial bugs are often attracted by pollen which is needed to sustain flight activity. Once they find your cut flowers, they search out and feast on plant-feeding insects and mites. (A guest that keeps on giving and hangs around until it runs out of prey or you kill it with chemical sprays.)  Even with this free biological control, sometimes the plant-damaging insects get out of control and have to be treated with chemicals to prevent economic loss. Ideally, we want to be able to control pests but preserve as many beneficial organisms as possible.  
It would be a wonderful world if we could just rely on beneficial organisms to control the entire pest population in a cut flower field. This doesn’t always happen and often you have to treat for one or more pests in your plantings. The best course of action is to avoid scheduled cover sprays that take out beneficial bugs as well as plant-damaging insects.  This means you will need to walk among your flowers on a regular basis to scout them for bug outbreaks, then treat these outbreaks with the most effective material that will have the least detrimental impact on the good bugs.

In March we held a conference entitled “Advanced IPM Methods” at Brookside Gardens. During this conference we had a lively discussion on what beneficial organisms can be used safely with which chemical applications. I thought I would share some of the observations of the various speakers.
One of the points brought up in the discussion was that some pesticides are very toxic to beneficial organisms when the chemicals make direct contact at spraying time, but the pesticide may be relatively non-harmful to beneficials once it dries.  An example is the insecticide Conserve, which is used to control thrips and caterpillars. A spray application will impact some beneficials on contact, but within 24 hours it is essentially non-toxic to most beneficials commonly found in cut flower fields. Other examples are horticultural oils and insecticidal soaps. These two materials, when applied as direct sprays on beneficial nymphs or larval stages, have a negative impact. Once horticultural oils and insecticidal soaps dry on the foliage the impact on beneficials is not detectable.
How can you use this information? If you had a thrips population building to damaging levels in your lisianthus and snapdragon plants, you might choose to use an application of Conserve insecticide to bring the level down below damaging levels. To have minimal impact on beneficials in the rest of your field, spray only the lisianthus and snapdragon plants. Don’t spray zinnias, celosia, or other cut flowers also growing in your field but not being damaged by the thrips. The spray application may kill some beneficial organisms in the snapdragons and lisianthus, but you are preserving the beneficial organism in the adjacent zinnia and celosia planting. The beneficials can then move back in to the lisianthus and snapdragons after 24 hours with little or no detrimental impact.

How are Impacts of Insecticides on Beneficials Rated?

First off, not all beneficial organisms have been evaluated for all chemicals on the market. Several companies see the benefit of understanding the impact on beneficial organisms and are taking proactive approaches in funding research.  We will see the list of chemicals evaluated grow over the next several years.
The International Organization of Biological Control ( IOBC) has classified chemical impact on beneficial organism into four classes, determined by how much of the beneficial organism population they kill. The following is the IOBC rating system:

Class 1    non-toxic    
Class 2    slightly toxic
Class 3    moderately toxic
Class 4    toxic              

How does this rating system work? One of the most commonly used insecticides used by cut flower growers is Acephate (Orthene). This is used to control aphids, caterpillars, Japanese beetles and many more chewing and sucking insects. Acephate is listed by IOBC ratings as “slightly harmful” to some beneficials organisms, a class 2 rating causing 25 -50% mortality. It has not been rated for all beneficial organisms but is slightly harmful to mealybug-destroying ladybugs and beneficial nematodes. Once Acephate is dried and taken into the plant foliage and stems, its impact on most beneficial organisms is minimal.

How about Pyrethroids?

Pyrethroids are effective in controlling several insects and mites that feed on cut flowers and they are usually comparatively cheap when priced against some narrow-spectrum pesticides. Pyrethroids include materials such as Mavrik®, Talstar®, Discus™ (Talstar and imidacloprid combination). The pyrethroids, as a group, tend to be very hard on beneficials when applied as a spray. Most fall into class 4 for several beneficial organisms such as lacewings and predatory mites. Chemicals in this class will affect most beneficials for 60 – 90 days after spray was applied. If you are trying to increase activity of beneficials in your cut flower fields, these would not be preferred materials to use.  You could use them to spot-treat plants with an established pest population, but they could impact beneficials that make contact with the treated plants for a fairly long time.
What about Carbaryl?

Carbaryl has been around a long time and is commonly used to control Japanese beetles, caterpillars, cucumber beetle, and several chewing insects. Plants prone to spider mites will often have an outbreak shortly after an application of Carbaryl. Carbaryl (Sevin®, etc.) will have an impact on the predaceous mite Phytoseiulus persimilis with the spray being toxic to both nymph and adults. It has a persistence of 2 weeks. Sevin is also toxic to lacewings with 4-week persistence . The spray is slightly toxic to the larva of the lady beetle, Cryptolaemus montrouzieri, but the direct spray will kill 75% of adult beetles.

Does Application Make a Difference?

Insecticides labeled for soil application generally have less impact on beneficial organism since you avoid a direct spray that could make contact with the immature stage which cannot fly out of the area. Systemic material such as imidacloprid (Marathon and Merit) and dinotefuron (Safari) are labeled for soil applications. These two materials are very effective in controlling sucking insects. They do not, however, control mites. There are no systemic miticides labeled as soil drenches.

How About Mites?

Certain cut flowers, such as crocosmia, are prone to mite infestation.  For a plant like this that you know will likely have a mite infestation, you may choose to release predaceous mites, such as Phytoseiulus persimilis. These can be obtained from a biological supply company. When making a biological release a grower may want the backup of knowing he can apply a chemical that reduces the population but not wipe out the beneficial mites just released. Two miticides fit this category: Vendex and Hexagon.  Hexagon is a mite growth regulator that kills the immature stages of plant-damaging mites. Vendex has been used for years in strawberry field to suppress plant-feeding mites; predaceous mites are released right afterwards. In some cases they have sprayed Vendex over Phytoseiulus with little impact on  survival.  The predaceous mite Amblyseius californicus is more tolerant of Vendex than Phytoseiulus persimilis.

For More Information

The University of Maryland just published a booklet entitled “Total Plant Management for Greenhouse Crops” in which we have information on controlling cut flower pests with a list of biological and chemical control options. The booklet is 289 pages and can be ordered from the University of Maryland for $25/copy and $5.00 for shipping. To order a copy send a check made out to the University of Maryland to CMREC, University of Maryland, 11975 Homewood Road, Ellicott City, MD 21042.

Come Visit This Summer

We will hold a summer field day for cut flower growers on July 14, 2005 from 3:00 p.m. to 8:30 p.m. at Triadelphia View Farm, in Howard County, Maryland. We will have a tour of the farm and several speakers on cut flower topics. Write to us for a complete schedule of topics and registration fee. Same address as above.