Field Performance Assessment

I. Performance Expectations
II. Assessing Control

I. Performance Expectations

If label directions and Dow AgroSciences recommended practices are followed, satisfactory control can be expected. If label rates and application instructions are not followed, control can diminish to unsatisfactory levels. Remember, an untreated area is the best measure for an objective evaluation of herbicide performance. Protect your herbicide investment by following label directions and Dow AgroSciences recommended practices. If you do not follow the label and Dow AgroSciences recommended practices, you should lower your expectations accordingly.

Infestation Levels
The number of weeds in a field will influence your visual expectations. If weed densities are low, for example, 10 per square foot, then 90% control would leave one weed per square foot. If weed densities are 100 per square foot, 90% control would leave 10 weeds per square foot and weed control would not look as effective. While a few escapes can have a visual impact on the look of the crop, they do not provide significant competition to a healthy crop. If you have high infestation levels, make sure you achieve thorough coverage of all the weed seedlings and be prepared to manage some areas with weed escapes.

Weather and Growing Conditions
Herbicide performance may be influenced by weather conditions. For example, growth regulator herbicides depend on the plants' ability to grow themselves to death. As a result, weather conditions have a large impact on the speed of control.

When annual grasses are stressed due to drought, heat, lack of fertility, flooding, or prolonged cool temperatures (5°C), control can be reduced or delayed. Therefore, when targeting both grassy and broadleaf weed control, grass escapes or re-tillering may occur when application is made under conditions of prolonged stress.

Good growing conditions such as high humidity, warm days and good soil moisture will encourage rapid absorption, translocation and more complete weed control. Weed control may be reduced during stress conditions, i.e., drought, heat or cold stress, or if weeds have initiated flowering. Prolonged cool temperatures of less than 5°C can reduce control since weeds are not actively growing. Weeds stressed longer than 20 days due to lack of moisture aren't growing well enough for satisfactory control.

You will get optimum weed control with your herbicide if you delay application until the stress conditions have ended and weeds are once again actively growing.

The risk of crop injury at all stages of growth could also be increased if the crop is already under stress.

Application Rates
Recommended label rates must be used for good weed control. Match your desired level of control with the recommended rate. If you reduce rates, you may receive inconsistent or lower levels of weed control. High than recommended rates may result in reduced crop safety.

Proper Application Equipment
Your herbicide should be applied through a well-maintained and calibrated ground sprayer that can apply the spray volume in a uniform spray pattern that covers all of the target weeds.

How Well the Label is Followed Affects Results
When you cut corners on the label, you assume the risk of non-performance. Product application (rates, timing, equipment) should be according to label directions, because years of research have proven that these directions give the most consistent weed control.

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II. Assessing Control

To help determine the level of performance with a herbicide, it is important to always leave an untreated area that is representative of the weed pressure in the entire field. Untreated areas are a very important tool in assessing herbicide performance and weed control. By leaving an untreated area, you'll have an objective way of measuring the level of control delivered.

To determine the level of control, compare weed control in the treated area with the number of weeds in the untreated area. The percentage of control can be determined as follows:

1. Place a one-foot square measure on the ground in a representative treated area of the field, and count the number of live weeds (i.e. weed escapes) in the square (Value A).
   
   
2. Place the one-foot square measure on the ground in a representative location of the untreated area and count the number of live weeds in the square (Value B).
   
   
3. Determine the level of control using the following formula:
   
   Percentage level of control = [1–(A/B)] x 100
   
   For example: if, in a square foot section, you counted eight live weeds (weed escapes) in the treated area and 96 live weeds in the untreated area, you would have the following level of control:
   
   8 weed escapes / 96 live weeds = 0.083
   
   (1 – 0.083) x 100 = 91.7% control
   Monitor fields starting 14 to 21 days after application and look for herbicide activity on labeled weeds. Look for the symptoms of control as described on the label or in the product information.

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