CNGA Looseleaf Dec 2018 Jan 2019

19 colorad o nga.org LooseLeaf December 2018/January 2019 How to Make Pre-emergent Applications Effective THE ART & SCIENCE OF HORTICULTURE By Robert A. Garcia, Sales Representative Winfield Solutions, LLC When developing a pre-emergent weed control program or pest management strategy, we need to keep in mind a couple of things. All areas have residual weed seeds that given the proper conditions have the potential to germinate and create an issue in the fields. Proactive weed management is easier to schedule and accomplish with pre-emer- gents rather than curative applications. The products used are safer for the container stock, and the REI (re-entry interval or restricted entry interval) on these products is much shorter than with many post- emergent herbicides. Management of other pests is also easier and much more effective than curative applications. It is easier to schedule applications before an issue occurs, rather than to try and diagnose and determine a plan of attack after a pest problem has already begun. The potential damage to the crop is much greater in the latter scenario. To determine the cost effectiveness of a pre-emergent program, the grower needs to analyze the amount of time that was spent during past seasons on labor and materials when making post-emergent ap- plications, keeping in mind that those applications always require a greater level of safety. The grower also needs to consider the REI for the areas treated. Then, they should analyze the lost time when treated areas are closed during the growing season to see if the applications are cost effective. Many factors affect the percentage of control that a grower gets from a pre-emergent application. The timing of the application greatly effects the control. If we miss our window and weed seeds have already begun germinating, we will not get complete control. In this instance, a pre/post herbicide combination may be the choice. Most pre-emergents perform best when they get watered after application. If no irrigation cycles or natural precipitation can be used to water in the product, especially with granular applications, the control will not be maximized. Depending on the pre-emergent chosen, we could also see cases where the disturbing of the soil causes applications to fail. All pre-emergent herbicide labels have a list of the weeds and weed types that are controlled, such as grassy weeds or broadleaf weeds. If a certain weed is not typically controlled by a given herbicide, we may need to use a combination of two pre-emergents or change to a com- pletely different product. Here are a few tips to maximize pre-emergent herbicide applications: 1. Apply applications two to three weeks prior to having the opti- mum conditions for weed seed germination. 2. Apply products with the maximum amount of water that your equipment can carry. For instance, four gallons per 1,000 square feet will give better control than one gallon per 1,000 square feet. 3. Try to follow label recommendations for watering after the application. 4. If a pre/post combination is applied, allow plenty of time for the post-emergent herbicide to translocate, and then water in the pre-emergent. Ideally this would be 24 to 48 hours. Pre-emergent applications are not soil sterilants; they do not kill everything in the soil. They stop weed seed germination and estab- lishment. All pre-emergent herbicides have a finite time where they provide control, so pay attention to the labels, which provide a rate per time of control. “It is easier to schedule applications before an issue occurs, rather than to try and diagnose and determine a plan of attack after a pest problem has already begun. The potential damage to the crop is much greater in the latter scenario.”

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