July 4, 2003

"What a difference a year makes," is a phrase often heard in the farming community this year as farmers compare crop stands and remember last year's drought conditions.

Western bean cutworm moths in flight

Western bean cutworm

Farmers and crop consultants throughout Nebraska should begin to scout fields for the white dome-shaped western bean cutworm eggs. Female moths preferentially search out pre-tassel corn and later, if available, move to dry edible beans to lay their eggs. These eggs are laid in clusters of five to 200 on the top surface of the upper most leaf of a corn plant and on lower leaf surfaces of dry beans. The eggs require five to seven days to develop, during which time the egg color changes to tan and then to purple immediately before they hatch.

After the small, dark brown larvae hatch on corn plants, they move to the whorl or tassel to feed on the tender yellow leaf tissue or on the tassel itself. Once the tassel emerges or if it has already emerged when the eggs hatch, the larvae will move to the green silks. The developing larvae will feed on the green silks, moving down the silk channel until they reach the ear tip. The larvae will feed in the ear tip until they are fully developed. If the infestation on one ear tip is so great that the larvae become crowded, a few individuals may move outside the ear and begin to feed on the side of the ear. They will chew through the husks and eventually begin to feed on the developing kernels, causing extensive damage.

Western bean cutworm that hatch on dry bean plants, feed on blossoms and young, tender leaf material. The larvae will attack bean pods as they develop, eventually feeding on the developing seeds.

In corn

Even though field scouting for western bean cutworm in field corn should begin when the first moths are caught, control decisions should be made shortly after the moth flight peaks. The moth flight usually peaks between July 10 and July 24.

When scouting for western bean cutworms in corn, check 20 plants in at least five areas of each field. Look for eggs on the top surface of the upper most leaf or look for larvae in the tassel. If 8% of field corn plants, 5% of seed corn plants or 5% of popcorn plants have egg masses or larvae, consider applying an insecticide.

Western bean cutworm eggs

Western bean cutworm moths prefer to lay eggs in corn plants that are in the late whorl stage compared to those that have completely tasseled. Pay particular attention to later planted fields or those with uneven development. Western bean cutworm eggs that hatch when corn plants are in the whorl stage of growth have a high rate of survival. The larvae are well protected in the whorl or tassel.

If an insecticide treatment is warranted in corn fields, it should be made when 95% of the plants in a field have tasseled. This timing of the application increases the chance that the worms will be exposed to the insecticide resulting in better control. It is also important to make insecticide applications before the larvae reach the silks. Once the larvae reach the silk zone they quickly move to areas under the husks where they are more protected from insecticide treatments.

In dry edible beans

You can harvest seeding year alfalfa as early as 40 days after seedlings emerge. Note that this is 40 days after emergence, not planting. Usually it takes 6 to 14 days for plants to emerge and 40 days for plants to develop their ability to regrow from the crown after cutting. If alfalfa is cut before this development occurs, at least one set of leaves must remain on the plant for it to regrow.

While alfalfa seedlings can be harvested 40 days after emerging, often it may be better to wait until 60 to 70 days after emergence, around early flowering, and before first cut. Total yield often will be higher, roots will be better developed, and plants will withstand weather stress easier with a little extra growth. This is especially true for early planted alfalfa.

This first harvest recommendation is earlier than many folks like to cut. But by cutting early, regrowth of seedling alfalfa soon will become similar to established alfalfa, possibly providing two or three cuts the first year.

However, with seeding year alfalfa, avoid cutting if soils are wet and give extra time between cuts for young plants to recover. Also, never cut alfalfa during the four-week period before a killing freeze. Winter injury can be severe due to the smaller root systems.

Not surprisingly, herbicide resistant soybeans constitute the majority of soybeans planted in Nebraska this year at 86%, a slight increase from 85% in 2002.

Nebraska ranked fifth nationally in its planting of biotech varieties as a percent of all soybeans planted, behind South Dakota (91%), Mississippi (89%), Indiana (88%) and Kansas (87%). Other top users were: Arkansas (84%), Iowa (84%), Wisconsin (84%), Missouri (83%), Minnesota (79%), Illinois (77%), Ohio (74%), North Dakota (74%), and Michigan (73%). The U.S. average of soybean acres planted to biotech varieties was expected to be approximately 81%, up from 75% last year.

With corn, Nebraska producers planted 52% of this year's crop to a biotech hybrid, an increase of 6% from last year's 46%. Thirty-six percent of all Nebraska corn was planted to insect resistant (Bt) corn, a slight increase from the 34% in 2002. The use of Bt corn constituted the majority of the biotech use in corn for all states and increased or stayed the same from 2002 for all states. In Nebraska herbicide resistant corn accounted for 11% of the total, compared to 9% last year, equal to the national averages. The top 11 reporting states all increased their use of herbicide-resistant corn slightly, with the largest increase in Minnesota where use increased form 8% to 14%. The survey also indicated that 5% of Nebraska's crop had been planted in corn with a stacked gene, up from 4% in 2002.

Nebraska biotech corn plantings (52%) placed it third in the nation behind South Dakota at 75% and Minnesota at 53%. The percentages of the total corn planted to a biotech hybrid ranged from a low of 9% to 75%, a significantly broader range than with soybeans.

Percent of all corn planted to biotech hybrids for other states included: Kansas (47%), Iowa (45%); Missouri (42%), Wisconsin (32%), Illinois (28%), Michigan (35%), Indiana (16%) and Ohio (9%). In the United States, a total of 40% of the corn was planted to biotech hybrids, up from 34% in 2002.

The states represented 81% of all corn acres and 89% of all soybean acres. Regarding corn production, the insect resistant varieties include only those containing bacillus thuringiensis (Bt) and the stacked gene varieties included those with both herbicide and insect resistance. The states for which these statistics were reported represent 81% of all corn planted acres and 89% of all soybean planted acres.

Vegetative growth stage

Drought stress during the vegetative stage prior to tassel and silk appearance may result in small ear size. From the 10-leaf to the 12-leaf stage (a leaf stage is indicated by the presence of the exposed leaf collar), potential kernel row number is determined in the corn plant. From the 12-leaf to the 17-leaf stage, potential kernel number per row is determined. Moisture stress during these vegetative periods may reduce both ear length and the number of potential kernels on each ear. If ear size is reduced during this period, it cannot be corrected by relieving the moisture stress later in the season. Research has shown that four consecutive days of visible wilting during the vegetative growth stage can reduce potential corn yield by 5% to 10%.

Reproductive stage

Moisture stress during pollination can result in a lack of synchronization between silking and pollen shed. Silking may be delayed in moisture-stressed plants and pollen grains do not remain viable long under drought conditions, especially when temperatures are in the mid 90s. A common result is a lack of viable pollen late in the pollination period when the silks from the tip-end of the ear are emerging, resulting in barren ear tips. Corn under moisture stress during early grain fill often will abort the last kernels to be fertilized by pollen. This also results in barren ear tips and is known as "tipping back". During silking and pollination, after four consecutive days of wilting yield can be reduced by 40-50%.

Within one to three days after a silk is pollinated and fertilization is successful, the silk will detach from the developing kernel. A preliminary estimate of the degree of pollination can be conducted in the field by carefully removing the husk leaves from an ear shoot, shaking the cob, and observing how many silks easily shake loose from the cob.

Another method to determine whether drought-stressed corn plants have been pollinated and fertilized is to look for small white blisters on the ear seven to ten days after pollen shed. To identify the blisters, take ears from several areas in the field and break them in half. Using a knife, dig out several kernels on each ear. If you find kernels that resemble blisters on the ears, you can assume that kernel fertilization occurred. If you are unsure, observe corn ears again in five to seven days. If the kernels were fertilized, the blisters will have rapidly increased in size compared to the earlier observation. If fertilization did not occur, kernel size will not have increased. It is also possible to tell if fertilization has occurred by slicing the kernels longitudinally through the embryo side and looking for the young embryo. Only fertilized kernels will produce embryos. Most kernels that have been fertilized will continue to develop and mature if the plants get water.

If a plant has tasseled and shed pollen but no blisters have appeared on the ears, it will be barren. Drought stress after pollination and fertilization can result in aborted kernels or poor kernel fill, causing low test weight and reduced yield. It may also predispose the plants to development of stalk rots. Continue to assess the condition and health of the corn plants even if it appears that pollination was successful.

Alternative harvest options

This June has been exceptionally wet in comparison to June 2002 and temperatures are considerably cooler. Last June, much of the state failed to receive an inch of precipitation, with most locations receiving at least 15 days of temperatures over 90^oF. This year, most locations received at least 2 inches of precipitation, with some areas of central and eastern Nebraska receiving 6-12 inches. The number of days above 90^oF was 30-40% of the long-term average of seven days.

Even with the heavy bouts of rainfall and severe weather, western reservoirs are still suffering the impacts of multiple drought years and insufficient snowpack. Several reservoirs in southwestern Nebraska have failed to respond to the increase in precipitation. According to the Natural Resource and Conservation Service, inflows into reservoirs are not outpacing evaporation and lake levels continue to decline. Until soil profiles are sufficiently moist, a dramatic increase in streamflow rates is not expected until the conclusion of the agricultural season.

As of June 19, the level of Lake McConaughy was 14 feet lower than at the same time last year. Fortunately, planting delays coupled with normal to slightly below normal temperatures have tempered irrigation demands. Irrigation water is expected to be delivered through August and into September. In addition, there should be enough water in Lake McConaughy to make it through the 2004 irrigation season. Once again, future delivery will depend on the 2003-04 Wyoming and Colorado snowpack.

Crop water demands will increase significantly over the next few weeks. If temperatures are normal the next seven days, corn is expected to use 0.20-0.25 inches of water per day based on a May 17 emergence date. Subtract 0.05 inches per day if your corn emerged on May 26. By July 14, corn will require 0.30-0.35 inches per day, regardless of what day in May the crop emerged. This value is based on receiving normal temperatures and could increase by up to 0.10 inch if temperatures approach or exceed 100^oF coupled with low relative humidity.

If normal precipitation occurs during the next three weeks, there should be enough soil moisture to offset crop water demands of corn. This is especially important, since most of the corn crop is expected to be in the pollination stage during the last two weeks of July. The potential exists for a very respectable corn crop this year as long as the atmosphere cooperates. At this time last year, many eastern Nebraska dryland corn fields were exhibiting signs of severe drought stress. What a difference a year makes.

Nebraska corn growers planted 8.0 million acres in 2003, down 5% from last year and 1% below 2001. Soybean producers planted 4.7 million acres, unchanged from the previous year. The 2003 plantings are equal to the second highest of record, but 5% below the record high of 4.95 million set in 2001.

Last fall winter wheat was sown on 1.8 million acres, up 9% from a year earlier and the largest acreage in four years. Sorghum growers planted 650,000 acres, 44% more than 2002, up 18% from 2001, and the largest total in five years.

Alfalfa hay acreage for harvest, at 1.45 million, is up 7% from last year while other types of hay cut is down 3%. Oat seedings at 195,000 acres are up 11% from 2002. Dry edible bean producers planted 160,000 acres, down 14% from a year earlier. Sugarbeet plantings of 39,800 acres are down 30% from 2002. Sunflower acreage of 55,000 is down 5% from a year ago. Millet was being planted on 160,000 acres, up 23% from 2002.

What they've found may change how some of the more popular herbicides, such as glyphosates, are applied.

Table 1. In Roundup Ready corn plants, glyphosate applied with fine, medium, and coarse droplets. (Paul Feng, Monsanto) Droplet size % Retention(actual over calculated) % Total uptake % Root translocation Fine 47 + 2 30.1 9 Medium 37 + 7 35.1 10 Coarse 38 + 4 48.9 16

Doubling the spray particle size diameter -- for example, from 300 to 600 microns -- results in 1/8 as many spray droplets. Traditionally it was thought that a medium spray droplet (volume median diameter of 242-358 microns) should be used for maximum herbicide efficacy. The UNL research, however, suggests that different droplet sizes work better with different types of herbicides, depending on the mode of action.

For example, with a contact, nontranslocated herbicide such as paraquat, a medium spray droplet size provides for maximum plant coverage. Since damage is caused where the droplet lands, with more smaller droplets dispersed over a wider plant area provided greater herbicide efficacy. However, for translocated herbicides, such as glyphosate products, a coarse droplet size (volume median diameter of 359-451 microns) was found to work better. With the larger droplet, more material was available in a given location to disrupt the cuticle and enter the plant, helping facilitate translocation of the herbicide before it could evaporate. The bigger the spray droplet, the greater its persistence or longevity.

These results should be good news to producers using translocation herbicides and wanting the benefits of reduced pesticide drift and improved herbicide efficacy.

Purple loosestrife -- biology and control

Purple loosestrife

When purple loosestrife invades wetlands, the natural habitat is lost and the productivity of native plant and animal communities is severely reduced. Song birds will not feed on loosestrife seeds. Muskrats can not use roots for food or shelter. Waterfowl are affected when dense impenetrable stands eliminate nesting sites and open water. If there is no room for displaced wildlife and it can't move, it may be lost forever. Purple loosestrife will grow vigorously and clog irrigation canals, ditches, stream banks and reservoirs, resulting in less water available for crop production and recreation.

A perfect plant

Purple loosestrife can colonize and thrive easily because it is a prolific seed producer and has a strong perennial root system (rhizome). Each plant can produce up to 2 million seeds in one season. Seeds can be carried far away by water, wind, and birds and can remain viable for many years. The rhizome grows well in marshy soils and can help the spread the species if washed away by the river water.

Not many birds, fish or animals like to feed on purple loosestrife. They feed, however, on other plant species that grow around purple loosestrife. By doing this, indirectly, the wildlife population "eats themselves out of house and home". As native vegetation get consumed, more space is created for purple loosestrife to spread and produce new plants.

In general, purple loosestrife can grow 3-9 feet tall with several, square stalks per plant. Leaves are on opposite sides of stalk, thin and sharply pointed with the base rounded or heart shaped. In Nebraska, it will flower from July to September. Flowers, which range from red to rose-purple, are arranged on 1-3 foot spikes. The fruit is a small oblong capsule with two valves containing many small seeds. Each plant has several spikes and each spike can produce up to 100,000 tiny, light seeds that are readily moved by wind. Seeds are extremely viable and will easily germinate when exposed on bare soil. Root system is strong and when mature, the root branches become thick and woody.

Control

Purple loosestrife can quickly invade a natural habitat.

Purple loosestrife has no natural enemies or plant competitors here in North America, therefore its spreading is hard to stop. A single control measure can't provide long-term, sustainable, management; however, management practices integrated in a systematic manner can provide for improved control. Elements of an integrated plan include: