Warm soil temperatures and minimal moisture are creating the perfect storm for heightened weed pressure this spring. As a result, annual weeds are likely to emerge earlier than the past few years because soil temperatures are already warming up, says Kent Bennis, market development specialist, Dow AgroSciences.
"Lambsquarters is germinating in some fields and will come up quickly with giant ragweed soon to follow," Bennis says. "Growers should continue to be vigilant and have a management plan in place to stay ahead of early germinating weeds."
The threat of winter annual weeds is much larger this year compared with the last few years, Bennis says. The probability of both increased weed pressure and larger weeds earlier in the season increases the need for a strong burndown herbicide program and a preemergence herbicide application, Bennis says. Left uncontrolled, species such as marestail, chickweed and waterhemp can compete with soybean crops for vital nutrients and moisture during early germination.
"If growers incorporate preemergence herbicides, such as Sonic or Surveil, it is recommended to run the tillage equipment a maximum of 4 inches deep to keep the herbicide in the top inch or two of soil," Bennis says.
There are several advantages to managing early season weeds this spring - including the opportunity to plant into a cleaner seedbed, which can result in timelier planting under dry weather conditions, Bennis says.
Weather permitting, corn and soybean grower Jay Wilburn of Laddonia, Mo., plans to plant soybeans toward the end of April. Even with untimely spring rain in 2015 that delayed soybean planting, Wilburn was able to keep his fields free of weeds due to the performance of his preemergence herbicide program.
"We have been using pre's for the past four to five years," Wilburn says. "When glyphosate quit working, we had to find a different way to control weeds. Pre's were the answer for our area."
Since soil temperatures have also warmed quickly this spring, weeds are likely to emerge early. For optimized weed control, scout for winter weed species such as chickweed and marestail, and early germinating annual weeds, such as lambsquarters and waterhemp. Follow up with a preemergence herbicide to control them early so they do not become a larger issue later in the season.
"There's a good amount of resistant waterhemp across Iowa," Bennis says. "The best way to manage waterhemp and other yield-robbing weeds is to use soil-applied herbicides before the weed is out of the ground."
When it comes to early season weeds, Wilburn says, if there are weeds in the field, yield potential is being robbed.
"If you don't control them early, especially waterhemp, it's almost impossible to control them at all," Wilburn says. "You need to control weeds to have a successful crop."