Which is better?

Imagine a situation where your customer has a pest problem—not tough to do, as it’s a daily occurrence for most turf managers. The common-sense approach of integrated pest management (IPM) will guide you through the control process.

First, identify the pest. Next, consider threshold: the number of pests present that could possibly cause unacceptable damage. If the threshold is exceeded, then consideration of the control method or combination of methods is next. For best results, it’s wise to utilize more than one. For example, if a crabapple tree is infected with apple scab, these cultural and chemical practices should be implemented, or at least considered:

  • selection of a disease-resistant cultivar
  • frequent inspection to monitor the development of the disease
  • locating the tree in an area where moderate airflow exists
  • locating the tree in a landscape bed, rather than in the middle of a turf area
  • avoidance of overhead irrigation
  • inspection for, and possible removal of, crossing limbs, closely parallel limbs and sucker shoots
  • judicious and timely applications of a fungicide

Then what? If it comes to applying a pest control agent, should it be contact or systemic? The answer is: it depends. Both have pros and con, and each area should be analyzed individually, and the type of control chosen based on the conditions and goals of the site.

Photos by John Fech.
Slopes present special challenges to the turf manager. Plantings with a limited root system canbe tricky, especially in public places.

A systemic control product is absorbed by the leaves, stems or roots and moves within the sap inside the plant to untreated tissues. Systemic herbicides, such as Trimec, are absorbed by the leaves and move in the plant to kill the leaves, stems and roots. They may kill weeds with only partial spray coverage. Some systemic agents move only in one direction within the plant, either up or down. Knowing which direction the pesticide moves will help guide in the selection process. Some pesticides are considered to be locally systemic, and will move only a short distance from the point of contact.

A contact control product is neither absorbed into the plant nor moved through the plant in the sap. As the name implies, it functions on the outside leaf, bark or stem tissues by direct contact with the insect, weed or disease. To be effective, the control agent must completely cover the pest. A uniform application technique will increase the chances of success. Control with contact pesticides can be difficult. Applications of a contact pesticide to aphids, thrips or spider mites on roses often fail because the pest feeds either under the leaf or in tight locations of the flower or nodes.

In addition to pest identification, threshold establishment and following the IPM protocol, several other factors are helpful to consider.

Location

Location is just as important for landscape management as it is for real estate. As a turf/landscape manager, you don’t always get to choose the location of various ornamental plants in the landscape. They may be on a slope, near a parking lot, along a sidewalk or driveway; all of which make a difference in which action you choose.

On a slope, the first concern is runoff, especially if a large volume of spray tank material is necessary. Though both contact and systemic pesticides have potential to move to nontarget areas, systemics may have a greater capacity for damage due to root absorption by adjacent plants on the downward side of the slope. On the other hand, because it’s usually necessary to obtain complete coverage with a contact pesticide, the stability and footing for the applicator may become a problem.

Another location where this choice is pertinent is when the suckers of a small tree have become objectionable or when weeds are growing near other desirable plants. In these scenarios, a contact control agent may be the better choice because of the lack of off-target foliage and root absorption. Obviously, extreme caution must be taken to avoid uptake by the photosynthetic portions of the tree bark or the foliage of nearby plants, yet this remains an advantage nonetheless.

Systemic herbicides pose more damagethreat to a tree with suckers than contactherbicides.

Limited root system

When trees, shrubs or flowers are growing in a limited or stressed root system, a contact might be better because of the decreased capacity for root uptake. This is common in both residential and commercial landscapes.

Contacts may also be more favorable for trees that have been scarred or have damaged bark and stems, due to the limited capacity for movement in the phloem and xylem. In certain situations, for example, if the plant is located in a parking lot island planting near nontarget objects, such as cars, root-applied systemics should be considered to avoid drift.

Price

In some situations, several product choices of each type may be available and work equally as well, but one might be less expensive. For example, when controlling a wide variety of weeds on noncritical areas, such as an alley or between pavers, a contact, nonselective burn-it-off type product might be a better choice than the latest four-way combination controlled-release systemic. Of course, the other often forgotten aspect of price is the component of the cost of labor to apply a pesticide. Time spent mixing, calibrating, cleaning equipment after application and reapplication to take care of skips and gaps in coverage should also be considered. Price should be thought of as one piece of a jigsaw puzzle of factors that lead to a pesticide choice.

Finally, the selection of a product may be limited by availability.

In the long run, the choice of systemic or contact should be thought of as one of many other factors to take into account to achieve good pest control. Considering all available forms of control, plant choices and site factors will lead to customer satisfaction and profitability for turf and landscape managers.

John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln.