Develop a weed management system

Many of you will recall that I was trained as a plant pathologist in the university. Universities are great at training highly focused experts on narrow topics. The real world does not work that way! Fortunately for me, University of California-Berkeley was not highly focused.

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When I began extension work in Ohio, I quickly learned that I was mainly valued for my willingness to try and broadly solve growers’ problems in all aspects of plant health. I called myself a “plant health manager.” This is why I can write about weed management programs.

In March (Page 65), I reviewed the general parts of a weed management program. In this second of three columns, I will focus on the principles of using chemicals to control weeds.

The starting points

Did you ever wonder why weed-control products are called herbicides? After all, many weeds are woody perennials. The reason is because even woody weeds are best controlled when they are young -- for the most part.

Hundreds of herbicides are available. Most nurseries use only a few. This is because of five main reasons:

* Need. What weeds do you have? What plants are you trying to grow where this or that weed is bad? Why do other weed control methods not work well for you?

* Cost. This is cost per acre per application, including labor and equipment.

* Availability. Does your local pesticide supplier have the product? Do your local salespersons have any knowledge about the product? Can you contact them when you need to?

* Formulations. Can you get the product in a formulation that is easy to use? Are there any appropriate combination products that would be useful?

* The bottom line. It takes a lot of product knowledge to select a herbicide. In July, I’ll mention some products for you to consider.

Preparation for use

No types of pesticides are more demanding of following labeled use instructions than herbicides. This is simply because no herbicide (killer of plants) is “safe” on your plants if incorrectly used. Study, understand and follow the label. Here are the important points on a label:

Kinds of weeds controlled and crops the product can be used around. The manufacturers summarize expensive research around the regions of the country where their product will be sold to develop this information.

Dose. This is the amount of product to use when making an application. For herbicides, this is given in the amount of product to use over a given amount or area. It may be modified by several factors, most commonly the maturity of the weeds or the crop plants, soil types, temperatures and surface water runoff patterns.

Calibration. Figuring dose requires calibration of the equipment you’ll use for the application. These guides will usually be given on the labels. There are different calibration methods depending on the equipment used. They all start with filling the equipment with water, running the applicator over a known area, and seeing how much water was used up. Most also need some sort of measure of the different rate of delivery of the nozzles on the applicator at the speed you intend to go. All of this affects the evenness of the dose over the crop and weeds. Do not forget to set the nozzles to target the weeds.

In my July column on weed management, I will touch on safety for the handlers and mention a bit on the most popular products I see used. All of this is taken from my new book, “Healthy Plants: A Systems Approach.” It is available only from me for $30.

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- Charles C. Powell

May 2008