At harvest is a good time to evaluate the effectiveness of your weed management plan. Evaluation is a critical component of an integrated weed management (IWM) system. The components of IWM include prevention, scouting, implementing a multiple-tactics weed management plan, preparing rescue treatments in case the plan fails, and evaluating the effectiveness of the weed management plan.
Evaluation should be done at least twice during the growing season: 1) during the growing seasons and 2) at harvest. An evaluation should be done earlier in the season, as well, at four weeks after herbicide application. This initial evaluation should a.) rate phytotoxicity (crop injury) and b.) determine which weeds are showing injury or susceptibility in response to herbicides. This can help assess if weeds present at harvest were treated with herbicide or emerged after herbicides were applied.
At harvest evaluation is especially important for a couple of reasons. First, it allows for determination of new weed species that may have invaded the field(s). It is easier to identify weed species after harvest when the weeds are larger and in flower versus earlier in the season when they are seedlings. Second, evaluation at harvest can determine which weeds are escaping management. This allows corrections to be made to management plans thereby preventing further escapes.
Weeds might escape management for several reasons. Selecting herbicides with low to marginal activity on the weeds present is the first potential problem. Herbicide resistance may also cause weeds to escape control. Repetitive use of herbicides with the same mode of action increases the risk of herbicide resistant weeds developing on your farm. Do not use herbicides with the same mode of action every year of crop production to control the same weed species. Lastly, environmental conditions can cause weed escapes. For example, a hailstorm could take out crops, thereby decreasing competition with weeds. Rain at the wrong time after an herbicide application or drought stress can help weeds escape management.
Rating the effectiveness of an IWM system at harvest allows for determination of which weeds are producing seed. This serves as a summation of the effectiveness of the IWM system. Secondly, rating at harvest will help determine which weed species are having the highest impact on crop yield. For example, are the impacts of wild oat on spring wheat greater than or less than the impacts of pennycress on spring wheat? This should help prioritize which weed species need to be targeted and help prepare for potential future weed problems.
This relates back to the importance of scouting. Walking or scouting fields for weeds will help determine if pre- or post-harvest weed management is needed for weeds, to either aid harvest or prevent seed set. Scouting and evaluation are two critical components of your integrated weed management system. Continuing to remain watchful of your weed problems will help prevent future weed escapes and yield loss.
Categories: Weed, Herbicide Resistance, Integrated Weed Management
Date: 04/15/2005