This is turning out to be a later planting season than hoped for, and growers have many obligations in a late spring. Scouting fields often falls to the bottom of the priority list. But if a weed or insect problem arises, it's better to fix it before it gets out of control and hurts the yield potential of a newly planted crop. Taking an afternoon to walk fields is the best way to identify and react to challenges involving insect pests, weeds or diseases. Driving by the field is not an effective way to scout for pests!
The 2012 drought weakened herbicide performance. Weed escapes and the resulting increased weed seed banks will put greater pressure on crops this season. That's compounded by substantial moisture and cool temperatures this spring, which prevented many growers from getting into the fields at the normal time.
As soil continues to warm, farmers will be running strong and may forego scouting. That gives winter annuals the opportunity to flourish to the point where control options may be minimal.
Don't shortcut your program, apply the full rate of residual herbicide
Don't be "pennywise and a pound foolish" by skimping on residual herbicides, says Mike Owen, Extension weed specialist at Iowa State University. "Go with the full rate," he says. "You think you may be saving money, but in reality, you're probably setting yourself up for bigger issues that will actually cost you more than if you spent the money upfront for the residual herbicide."
Early control of weeds is important, emphasizes Scott Ditmarsen, a Dow AgroSciences field scientist. In corn for example, SureStart herbicide offers flexible application timing and can be applied from preplant up to early postemergence. "It offers six weeks of residual control, which can help overcome unexpected delays," he notes.~~~PAGE_BREAK_HERE~~~
Early control is even more critical in beans because of limited postemergence options, says Ditmarsen. Sonic herbicide delivers two unique modes of action preemergence and enhances the performance of a second herbicide treatment by keeping weeds smaller and easier to control.
Plant to the recommended depth for corn and beans -- that's another thing you can do to help get the crop up and growing ahead of the weeds. In fields that have not undergone tillage, consider including a burndown, an early application of 2,4-D. It's worth the time to avoid coming back later to clean up a mess. "Do it right," Owen says. "Even though it might be a little more time-consuming, do it right."
Use good evaluation methods; scout fields early and often to avoid problems later
Scouting provides the information needed to make sound management decisions. As the growing season starts, pests will make themselves known. The agronomists offer some tips for making the most of your scouting trips.
"The first thing a grower should do is mentally review any issues from the field last year," says Ditmarsen. "Generally, there will be one or two problems that stand out from the previous year. Keep those in mind while scouting."
For an accurate overview, collect samples of pests and weeds from multiple areas of each field. Note and diagnose any pest pressures and crop injury. Compare them with recommended economic injury levels or thresholds, and decide whether you need to take action.
Know what to look for; weeds that germinate early can be harder to identify
Common lambsquarters is a primary weed that can germinate early and warrants consideration for many northern Iowa producers.
Giant ragweed is "one of the first up and can grow very, very quickly, and must be addressed when it's small or it'll pose a problem to growers," Owen says.
Henbit, shepherds purse, field pennycress and marestail/horseweed also are common culprits in southern Iowa.~~~PAGE_BREAK_HERE~~~
Another resistant weed to watch for is Palmer amaranth. Similar to common waterhemp, Palmer pigweed as it is often called has been confirmed resistant to several herbicides including ALS inhibitors and glyphosate. Confirmed infestations have spread rapidly in Wisconsin, Illinois, Missouri and Nebraska. Proper identification and removal of Palmer amaranth before seed production is critical, to keep this threat out of Iowa fields. Scout and remove any pigweed by hand if necessary before they flower.
Monitor your corn and soybean stand for consistency at early emergence, advises Jeff Ellis, Dow AgroSciences field scientist. "Work to make accurate diagnoses based on carefully examined growth stages and plant health," he adds. "This is also a good time to see how well the foundation herbicide is performing and what weeds are emerging. If a foundation herbicide has not been used, then it is a critical time to determine when to pull the trigger on 2,4-D or glyphosate."
Weeds harbor insect pressure and damage. Rely on university trapping reports and be aware of environmental conditions that can boost insect populations.
Make return trips -- scouting fields on a regular schedule helps catch problems
Scouting a field once a season is not enough. Ditmarsen and Ellis recommend regular scouting to catch issues early before they become a problem. "I suggest establishing a routine and scouting every seven to 10 days. If you go out to scout on a Tuesday, then do the same thing the next week," Ditmarsen says.
Ellis especially emphasizes monitoring herbicide performance. "To check a postemergence application, go back into the field five to 10 days after spraying to determine whether an additional application is necessary," Ellis says. "Before the crop canopies, again go back into the field and note any unusual weed escapes and determine whether they are due to a spray coverage issue or something more serious like herbicide resistance."~~~PAGE_BREAK_HERE~~~
The final crop check of the season comes at harvest. Note any lasting weed, insect or disease issues while driving the combine. That final scouting trip will offer a head start when scouting the following spring.
In summary, here are key points to help get weed scouting off to a good start:
* Resistant marestail/horseweed, giant ragweed, common waterhemp and Palmer amaranth are expected to be tough this spring in addition to henbit, shepherd's purse and lambsquarters.
* Plan for success by planting at the correct depth, using full label rates of soil residual herbicides that will control the target weeds and consider a burndown in no-till fields, again being sure to choose an herbicide that will control the emerged weeds.
* Get into corn and bean fields once every seven to 10 days for early weed identification before they have competed for potential crop yield and become too large for effective management.
Tools of the trade: When scouting, take along a notebook and pen to record notes on location and species. Bring a small shovel, a tape measure and plastic baggies for specimen collection to make the task easier. Take pictures with a digital camera, smartphone or tablet to accurately capture pest symptoms and plant irregularities. This allows you to get second opinions and proper diagnoses.
Bring along the latest scouting guides, which are valuable resources for pest identification, disease symptoms and crop staging information. Some of our favorites are:
* Common Weed Seedlings of the North Central States — Michigan State University Extension
* Weeds of the North Central States — Iowa State University Extension and Outreach
* Early, mid- and late-season corn & soybean scouting cards — ISU Extension
* Identification of the weedy pigweeds and waterhemps of Iowa — ISU Extension
In addition, find other tips for weed management in the 2013 Herbicide Guide for Iowa Corn and Soybean Production, available from ISU Extension.