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 are using the highest recommended rate structure and achieve thorough weed coverage during the spray application.
Weather and Growing Conditions Herbicide performance may be influenced by weather conditions. For example, growth regulator herbicides create a hormonal imbalance resulting in erratic growth and eventual control of the weed being targeted. As a result, weather conditions have a large impact on the speed of control since the ability of the herbicide to move either upward or downward within a plant is influenced by its growth.
When annual grasses or broadleaf weeds 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, re-tillering or secondary growth may occur when application is made under adverse conditions. In addition if weeds are in advance stages and have initiated flowering or completed their life cycle control will be delayed due to size or reduced if the plant is no longer actively growing.
Good growing conditions such as high humidity, warm days and favourable soil moisture will encourages rapid absorption, translocation resulting in more complete weed 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 may increase 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.
II. Assessing Control
To help determine the level of performance with a herbicide, an untreated area that is representative of the weed pressure in the entire field helps provide a good measure. Untreated areas are a very important tool in assessing herbicide performance and weed control. An untreated area provides 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:
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).
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).
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.
