By Valent

The battle to control Palmer amaranth and waterhemp is a familiar one for many farmers, especially those growing soybeans in the Midwest US. With the tight supply of many inputs this season growers will need to have a well-thought-out approach to controlling these yield robbing weeds. 

What makes Palmer amaranth and waterhemp such an issue for growers?

Palmer amaranth and waterhemp are members of the pigweed family and share many characteristics that make them very difficult to control. Without the proper approach to season long control, these weeds can proliferate quickly causing economically significant yield loss. These traits include:

• Persistent emergence throughout the growing season 
• Rapid growth rates of up to1/2 inch per day
• Prolific seed production
• Dioecious reproduction systems (separate male and female plants) 

Because Palmer amaranth and waterhemp are prolific seed producers, selection for herbicide resistant individuals can be driven quickly when a non-diversified herbicide management approach is used. Both species have male and female plants, and the forced outcrossing can result in rapid spread of herbicide resistance traits. Resistance has been documented to multiple herbicide modes of action (MOA) in each species.

What is the best approach for a grower to use in managing Palmer Amaranth and Waterhemp?

Due to their aggressive growth patterns, high level of proliferation and tendency to quickly develop herbicide resistance, growers seeking to maximize soybean yields this season need to start with a solid weed management strategy. So, what is the best approach to protecting crops from Palmer amaranth and waterhemp? Below are four basic steps for controlling these difficult to manage weed species:

1. Know Your Enemy

The first step in developing the correct strategy is properly identifying the weeds you are targeting. Knowing the weed species in your fields will enable you to make the best decision on the approach that you should take. Although Palmer amaranth and waterhemp share many attributes, they can be identified by some of the physical characteristics outlined in the following table.

2. Have a Proactive Approach

Given the aggressive growth characteristics of Palmer amaranth and waterhemp, using a preemergent herbicide early is the best way to start the season with clean fields. When choosing a preemergent herbicide always look for a product that ideally can provide 6 to 8 weeks of residual activity. Such herbicides eliminate the need to make multiple passes prior to canopy closure. This is of particular importance this season as many herbicides are in short supply, making multiple postemergence applications an uncertainty and putting yields at risk. In addition, when combating Palmer amaranth and waterhemp always look for a pre or pre/post herbicide approach with multiple modes of actions to ensure good control and improved resistance management. 

3. Stay In It for the Long-Haul

This step can make or break your weed management program due to the extended emergence window of Palmer amaranth and waterhemp. Depending on the season, a preemergence residual herbicide alone may not provide enough control to get you through to canopy closure. Adding a post-applied residual, such as Perpetuo™ Herbicide from Valent, is one of the best approaches to ensuring extended weed control until full canopy. When choosing a post-applied residual herbicide, always look for one that has both residual and foliar activity and contains multiple MOA’s to help manage resistance.

4. Go All In!

Ensuring the right amount of product gets applied is critical for achieving good control of Palmer amaranth and waterhemp. The best way to ensure good performance is by applying the labeled herbicide rate, using the proper spray volume and adding an adjuvant that improves active ingredient uptake and coverage. Poor coverage or applying lower than recommended rates can result in poor in-season performance and lead to the development of herbicide resistance in future seasons. 

In summary, Palmer amaranth and waterhemp can dramatically reduce yields in soybean fields if left unchecked. By proactively developing a weed control strategy based on the four steps recommended above growers can reduce the impact of these yield robbing weeds and make the most of their crops. 

To learn more about developing an effective weed management strategy for controlling Palmer amaranth and waterhemp or on Perpetuo™ Herbicide, contact your local retailer representative, Valent representative or visit the Valent website.