Spider Mites in Drought Years: Plan to Manage
Managing spider mites can be difficult. Because this tiny bug is extremely tough to see from the road or standing in the field, we often miss the initial stages of infestation. Once the first symptoms appear on the lower soybean canopy, the effects are much easier to see, forcing you to take a closer look.
Severe example of the stippling injury on an infested plant.
Spider mites are more common in drier climates, but they can appear in any field in the Midwest under the right conditions. What are the “right conditions” for spider mites? Simply put, they are undesirable: drought years with high temperatures (like in 2021 and 2023).
The two-spotted spider mite will wreak havoc on your soybeans and do it very efficiently. Once they have established themselves in your field, they “hide” on the underside of soybean leaves, making them difficult to spy.
Despite the difficulty, I have found a few methods to help identify the pest. The first method involves a sheet of paper. Take a plain white piece of paper and place it on the ground. Shake the plant over the paper and get down to ground level. Without picking up the paper, look for insects (a hand lens is especially helpful). You will be surprised by what you see, as it might be more than just spider mites! Another way to recognize spider mites is to use a small macro lens, either on a camera or as an attachment to the back of your phone (the above image was taken with an added macro phone lens).
From my experience, it’s best to control spider mites as soon as you see visible damage to the lower one-third of the leaves. If they infest and damage the center of the plant, they become more difficult to control. Available pesticides can work well, but they certainly are not bulletproof.
The most successful methods I’ve found are switching products and using products with multiple modes of action a week apart. One serious challenge we may have for the 2024 season is the availability of Lorsban or not. After talking with many in the industry and various soybean groups, it appears we will have some of the chemistry we need to control spider mites but may not have any state registrations. Only time will tell.
Spider mites will damage your crop until R6.5 – meaning it is important to keep an eye on your crop throughout the entire growing season, especially in those dry, hot years that favor spider mites.
Key Takeaways:
- In dry years, plan your management as if you WILL have spider mites.
- They are hard to see, but with a hand lens or a macro lens they can quickly be identified.
- Simply using a white sheet of paper is a valuable tool when scouting for infestation.
- Once colonized, they are hard to get rid of. Many times, a second application will be needed, so stay on top of them early.
