![]() We’re going to look at common weeds with white, yellow, pink, purple, and blue flowers. Instead, let’s turn the beautiful flowers that some weeds produce into a means of identifying and attacking them before they get too far along. Now, by no means is that an endorsement of the notion that you should just allow them to bloom and take over your lawn. Heavy rainfall within 2 hours after application may wash the chemical off foliage and a repeat treatment may be required.Despite all the trouble that weeds bring to your lawn, some of them can be quite beautiful. after application may reduce effectiveness. *Rainfall will improve control from root uptake. Rainfast time for postemergence herbicides commonly used in New Jersey Specialty Crops. If you apply herbicide and it rains before it’s rainfast, herbicide performance will be reduced. For many herbicides, any amount of rainfall soon after spraying has the potential to reduce absorption, translocation, and subsequent weed control. Poor conditions may require a longer interval between application and any rainfall to ensure adequate herbicide translocation within the weed before the herbicide is washed off. Generally, herbicide rainfast ratings are based on good growing conditions (table 1). The rainfast period is the minimal period of time that must elapse between herbicide application and subsequent rainfall to ensure good postemergence herbicide performance. ![]() Remember that the efficacy pf postemergence applications is mainly dictated by weed size… spraying weeds beyond the size range recommended on the label will result in porr weed control. However, if weeds are at growth stage that require a rapid intervention, select a herbicide with excellent efficacy for controlling your target weeds. Ideally, you should be waiting for the right conditions to apply the herbicide. Use an oil additive if risk of crop injury is acceptable for those herbicides that allow use. Refer to each herbicide label for specific information on adjuvant use during stress conditions. Oil additives may increase risk of crop injury but may be necessary for greatest weed control. The use of such ester formulations should be restricted to fall, winter, and early spring because sensitive plants are not present and lower temperatures reduce vapor drift hazard.Īdjuvants may also affect crop safety and weed control. 2,4-D ester or dicamba will rapidly evaporate at temperatures above 80☏, causing. High temperatures increase the loss of volatile herbicides. Thus, it is best to avoid applications of postemergence herbicides during periods of cool temperatures (<40☏ at night <55☏ during the day). ![]() Reduced herbicide rate treatments are less likely to provide acceptable control under adverse conditions than when plants are actively growing. Weeds that have been damaged (by mechanical equipment for example) or that are under stress (drought, water excess) at the time of herbicide application or before herbicide has properly translocated will not be properly controlled. Also, slower herbicide uptake by the weeds will increase the required rainfast period and slows the development of herbicide symptoms on the plants. At lower temperature, weed control will be slower, especially with systemic herbicides such as glyphosate, Poast, Select, or Sandea that are more slowly absorbed and translocated by the weeds compared to applications at higher temperatures. The ideal air temperature for applying most post-emergence herbicides is between 65☏ and 85☏. Grass and broadleaf weeds are controlled more effectively when plants are actively growing. However, cool and wet weather can increase the potential for crop injury with preemergence herbicides because of slower herbicide metabolization by the crop. Of course, herbicides should never be applied on frozen ground. It is important for preemergence applications to be effective that residual herbicides are applied before soil reaches this optimum temperature range. Summer annual weeds such as lambsquarters or crabgrass require good soil moisture and soil temperatures between 60 and 70F to start the germination process. ![]() The effect of cool temperatures on weed control efficacy will depend on the type of herbicide application, the rate applied, and the physiological status of the target weed. With air temperatures remaining relatively low this spring, growers have asked about how temperature may affect the efficacy of herbicide applications.
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