By Katrina Vander Kooi
The first crops workshop in Rock County took place Tuesday near the new baseball diamonds, Luverne.
Weed science specialist Jeff Gonsolus and integrated pest management specialist Bruce Potter gave the audience information about current weed and insect problems in fields.
Watch out for weeds
Gonsolus encouraged rotating herbicides that are used on land. "If you use the same herbicide every year, you will select a certain type of weed," Gonsolus said. "We need to develop a more diverse weed management system."
Gonsolus used water hemp as an example. "Water hemp is a wimp," Gonsolus said. He said it is hard to grow in a lab because it is temperamental. In southwest Minnesota, however, it is thriving. "We could tell that something was up with our management strategies," Gonsolus said.
He characterized the problem, by comparing water hemp to a plant unknown to those attending the workshop, biannual wormwood.
Water hemp and biannual wormwood share a number of characteristics. First, they have a long emergence period, which means they take a long period of time to grow out of the ground. Second, they have a high seed production which helps them stay alive from year to year. Third, they have fast growth in open canopies, and fourth, they are the result of post weed management. This means that herbicides sprayed on the crops at the usual time will not kill them.
Adapted rootworms
Potter said that some populations of the northern corn rootworm have adapted to the corn-soybean rotation and now have a two-year life cycle.
This two-year life cycle is called "extended diapause" because the eggs remain dormant in the soil for almost two years before hatching.
"Spend some time looking at cornfields," Potter said. "Keep track where there are lots of beetles. That's where you're going to have problems in two years."
He suggests farmers scout weekly beginning one to two weeks after beetles first appear in the field and ending when silks are brown and dry. The best time for scouting is between 9 a.m. and 2 p.m.
According to Potter, if a plant is found to have four or more beetles per plant, there are three options for action.
"The first option is to do nothing," Potter wrote in his handout. "There is not certainty that you will have lodging and especially yield loss in 2001 or 2002. Given prospective corn prices, a low-cost strategy is simply to plant hybrids with good root scores.
"The second option is to change rotation and plant another non-host crop instead of corn, and the third option is the use of corn rootworm insecticide in rotated corn," Potter said.
For more information on material presented at the workshop, contact the Rock County Extension office at 507-283-8685, Ext.4.