Newsletters

Print this newsletter (pdf)
water use/GDD tables

INSECT UPDATE

There has been quite a variety of insects out in the crop fields but the good news is no major outbreaks or economic damage has been reported. Here are some general outlooks.

WESTERN BEAN CUTWORM

We continue to catch moths in our light trap, but with very low numbers (about 1 per night). Continue to scout for egg masses as emergence may be a bit later this year. Females will look for pre-tassel corn to lay eggs on.

CORN LEAF APHIDS

Some corn leaf aphids have been reported in the area. These bluish-green aphids will sometimes cover the tassels of individual plants, but they are not considered an economic threat. Usually predators remove them a week or so after tasseling.

SOYBEAN APHIDS

Soybean aphids are present in soybeans in very low numbers which is typical at this time of the year. The hot temperatures will slow their reproductive rate but will not entirely remove them. Continue to monitor soybeans for aphids.

CORN ROOTWORM DAMAGE

Corn rootworm beetles are emerging in the northeast, indicating that rootworm larval feeding is ending. Now is a good time to dig roots to evaluate the efficacy of your rootworm management program. The presence of adult beetles or rootworms in a field is not necessarily an indication of product failure. Soil insecticides are applied in a narrow band or infurrow to the soil, or as a seed treatment, and corn roots grow beyond the treated zone where rootworm larvae may survive. Some rootworm beetles will emerge from Bt corn hybrids labeled for corn rootworm control.

Also, plant lodging may occur without significant rootworm feeding. The most common problem that is confused with corn rootworm injury is shallow planting. Especially this year, when farmers planted into wet conditions and may have experienced sidewall compaction among other wet soil planting effects, it would not be unusual to have many fields with lodging corn mostly due to poor root development. Also, early heavy rains may have brought some seed near the soil surface, limiting the development of the root system. Washing and rating roots is the only way to confirm if rootworm damage is the cause of plant lodging.

Rootworm efficacy can only be evaluated reliably if replicated, untreated check strips are left in the same field as the treatment. Without check strips, you won't know whether the absence of injury is due to product efficacy or the absence of rootworms. Before corn plants can be rated for injury they need to be at a growth stage where at least three nodes of roots are clearly visible. Dig at least 10 randomly selected plants from several areas of a field. Leave a 9-inch cube of soil surrounding the root system, wash the roots to remove soil and rate each plant for injury using the rating scale. If several weeks have passed between the end of rootworm injury and the time of root rating, new root growth may hide the injury. Examine roots carefully to accurately rate them.

The most widely used method to evaluate root injury has been developed at Iowa State University . It is based on a 0-3 scale. In this scale 0 = no damage, 1 = one complete node of roots is pruned within 1 ½ inches of the stalk, 2 = two complete nodes of roots are pruned, and 3 = 3 nodes of roots are pruned. Fractional ratings are possible, e.g. 1.5 = equivalent of 1.5 nodes of roots pruned. A visual aid is description of the 0-3 rating system available on an Iowa State University Web site, http://www.ent.iastate.edu/pest/rootworm/nodeinjury/nodeinjury.html

The relationship between root injury rating and yield loss is complex, but usually a root injury rating of 0.25 or more on the 0-3 scale is needed to cause economic yield loss. The corn plant has the capacity to regrow roots and compensate for some early season injury, especially if soil moisture and fertility are adequate during the regrowth period.

MONITORING ET, SOIL MOISTURE SAVES FARMERS WATER, ENERGY, TIME AND MONEY

High energy costs mean farmers are looking for ways to reduce irrigation costs this summer. Using newer technologies such as evapotranspiration, or ET, gauges and soil moisture sensors along with crop growth stages can help farmers achieve that, a University of Nebraska-Lincoln Extension educator says.

It costs farmers an estimated $1,000 to $2,000 each time their center pivots make a revolution in a field.

"With the high cost of energy, we need to make sure we use it efficiently in our irrigation," said Gary Zoubek, extension educator in York County. "Using these tools not only saves energy, but protects our precious water resources."

An ET gauge costs approximately $250, and soil moisture sensors and a hand-held meter or data logger costs between $300 and $500. Producers have reported the past two years that these two tools used together can save 2 to 3 inches of irrigation water per season, he said. If a pivot puts on an inch of water for each revolution, that amounts to $3,000 to $6,000 in savings.

"These tools can more than pay for themselves in the first year," Zoubek said.

Water is evaporated off leaf and soil surfaces due to current climatic conditions. The ET gauge is a way to estimate what the crop water use should be based upon the crop growth stage.

An ET gauge is a tube filled with distilled water where water evaporates through a ceramic top covered with canvas. This provides a reference ET value. Farmers are encouraged to monitor ET gauges weekly. This information along with crop stage of growth can provide an estimate of crop water use.

The ET gauge should be located in a site representative of the field conditions and can be used for irrigation management decisions for more than one field within a radius of a few miles.

Soil water sensors can be used to estimate water in the soil. Combine it with ET, soil type, crop stage and rainfall, and farmers can make informed decisions on when and how much to irrigate.

"This saves water and allows farmers to put water on at the time it is needed," Zoubek said.

For more information, visit the Nebraska Agricultural Water Management Demonstration Network Web page at http://water.unl.edu/cropswater/nawmdn.

David P. Shelton
Extension Agricultural Engineer

Newsletters

ipm052808
ipm060508
ipm061108
ipm061808
ipm062508
ipm070208
ipm070908