Rootworm larvae have been hatching for at least four weeks throughout the state and this process will continue for several more weeks. Peak hatch has occurred when about equal numbers of different size larvae can be found feeding on roots. It is also a time when few producers realize that root damage is occurring. Later in June or early July, when most rootworm feeding is complete and stormy weather hits, is when damage becomes apparent ... lodged corn.
First, the larvae are very small and live mostly within the roots. As they increase in size, so does their appetite. They will feed both inside and outside of the roots, causing tunnels, channels, and pruning. When rootworms weaken and/or remove nodal and brace roots, and when saturated soils and strong winds are present, severe plant lodging may occur. Though plants are often able to upright themselves (“goose necking”), there are physiological stresses (root regrowth and infection by soil pathogens) that may lead to yield loss. Losses can be substantial should lodging occur just before or during pollination. If soils become excessively dry and root regrowth is inhibited, grain yield tends to be reduced. If however moisture is adequate, some minor feeding can actually stimulate root growth and occasionally results in over-compensation of root masses producing in little or no loss.
Fields at high risk to rootworm damage should be sampled for rootworm and their feeding. Also, this would be a good time to compare rootworm control treatments (e.g., granular, seed-applied, liquid, transgenic) if producers have comparisons in their fields. To sample for rootworms, use a shovel and lift out the root mass and surrounding soil and place on a dark surface (black plastic garbage bags work well). Carefully break up the clods and sort through the soil. Look for 1/4 to 1/2 inch long, slender, creamy-white larvae with brownish-black heads and tails. Inspect the root mass for root scarring and pruning. You may find the larvae under the lower leaf collars that are close to nodal roots; tear these leaves away to check. Also, you may even observe the rootworms sticking out of roots. Repeat this process with several plants representing different areas of a field. A QuickTime movie of rootworm larval sampling can be viewed at www.entm.purdue.edu/entomology/ext/fieldcropsipm/videos.htm. Applying rescue insecticides where rootworm numbers are averaging over two per plant is still possible where high clearance sprayers can direct product to the base of the plant.
Recent heavy rains in areas of the state may have had a detrimental effect on larvae. Extended periods of flooded, or very wet soils cause larval death in one of two ways. Larvae can either drown from lack of oxygen (anaerobic conditions) or starve from lack of food because the corn plants have succumbed to flooding. What does this mean for the corn producer? Expect to see fewer adult beetles feeding on corn silk and tassels in areas where rain was extensive and prolonged. This occurrence was very obvious in some areas following extensive heavy rains in June of 1998 and in early July of 2003. In 2004, regional mortality of rootworm may be more pronounced than what was observed in either of these two previous episodes because of the greater extent of saturated soils across the State. Monitoring corn rootworm adults in soybean in 2004 will indicate which fields have reduced risk to rootworm in 2005 and pest management may be adjusted accordingly (See publication E-218, Monitoring and Decision Rules for Western Corn Rootworm Beetles in Soybean www.entm.purdue.edu/entomology/ext/targets/e-series/EseriesPDF/E-218.htm).
Reports of adult Japanese beetle sightings have been received from southern Indiana. Northern counties will begin seeing these notorious pests in the next few days.
This year’s adults are the result of eggs deposited in soil last summer. After these eggs hatched, the grubs immediately began to feed on roots and decaying organic matter. They continued feeding until cold temperatures prompted them to move deeper in the soil profile. Early this spring, the surviving grubs returned to near the soil surface to feed. Spring root feeding by the grubs can result in serious damage to early-planted crops, especially corn. Surprisingly very few calls have been received concerning grub feeding this spring, even with the early planting season. This could indicate that fewer grubs successfully overwintered and would result in fewer adults this summer.
Japanese beetles feed on more than 350 different species of plants, but are especially fond of roses, grapes, smartweed, soybeans, corn silks, flowers of all kinds, and overripe fruit. Beetle damage to cultivated crops is often minimal and defoliation (leaf removal) on soybean looks much worse than it is. The beetles often congregate in several areas of a soybean field, feeding and mating in the upper plant canopy. The beetles’ iridescent, metallic color catches the attention of those doing “windshield” field inspections. Closer inspections will often reveal that weeds such as smartweed have made fields even more attractive to the beetles. Look for more on this pest in future issues of Pest&Crop.
Recently, I have been asked to identify some mustards that I have not had to deal with in the past. Not surprising since I have only been in Indiana for just over three years. Over the span of three weeks, I have seen three specimens that have turned out to belong to the cress group of mustards. As I became acquainted with these plants I found that they were two different plants.
The two plants I have dealt with, according to An Illustrated Flora of the Northern United States and Canada (Britton and Brown, 1970), were creeping yellow-cress (Radicula sylvestris [L]), Figure 1, and yellow water-cress (Radicula palustris [L.] Moench.), Figure 2. However, in the USDA Plant Data Base, the same two plants are referred to as being in the Rorippa genus. Plants often are placed in new genera as the plant’s categorization changes through time, sometimes making identification and reference tricky.
The predominant difference between these two plants is that creeping yellow water-cress is a perennial and yellow water-cress is annual or biennial when the environment allows.
Both plants have small yellow flowers with four petals. Yellow water-cress flowers (4-6.4 mm* wide) are slightly smaller than creeping yellow water-cress (6.4-9 mm* wide). Both plants bloom from May to August. Both plants have leaves that are deeply lobed, ranging from 7.5 to 112 cm* in creeping yellow water-cress and 7.6 to18 cm* in yellow water-cress. Both plants have pods; however, creeping yellow water-cress generally has pods that are linear where yellow water-cress can have pods linear to oblong (Figure 3).
I don’t see many of these plants, because they generally don’t interfere with soybean and corn production. They tend to grow in wet places. In An Illustrated Flora of the Northern States and Canada, 1970, Britton and Brown report creeping yellow water-cress growing from Ontario, Canada, to Virgina. The USDA reported creeping yellow water-cress in most Eastern US states. Yellow water-cress can be found throughout the US. In 1940, C. Deam reported yellow water-cress being found in almost every county in Indiana. It appeared in 1940 to be fairly evenly distributed throughout Indiana. Dean also reported creeping yellow water-cress in 24 Indiana counties throughout Indiana. Yellow water-cress is native to the US, but creeping yellow water-cress is introduced.
The floods we experienced last year in certain areas may have deposited seed in areas that are not flooded out this year. This may have increased peoples awareness of these two plants this year.
*1 inch = 25.4 mm and 1 inch = 2.54 cm.
Deam, C.C. Flora of Indiana 1940. Department of Conservation, Division of Forestry Indianapolis, Indiana. 494 and 1052.
Britton N. and A. Brown. 1913. An Illustrated Flora of the Northern United States and Canada Vol. 2. Dover Publications, Inc., New York. 1970. 3 vols. 160-161.
Weed Scientists at the University of Wisconsin have developed an excellent publication that discusses potential sources of puckered soybean leaves. This issue is quite common in Indiana every year and information in this publication would be very pertinent to soybean grown in this state.
“Dicamba Injury to Soybeans” is a new publication that discusses the three most common sources of dicamba exposure to soybeans, symptoms of dicamba exposure on soybeans and the potential for yield loss. This publication contains a photo gallery of dicamba injury symptoms and dicamba injury mimics on soybean. It is available from the Nutrient and Pest Management Program at (608) 265-2660. Or you can check it out on the web at http://ipcm.wisc.edu/.
You are invited to attend the 2004 Purdue Weed Day sponsored by the Department of Botany & Plant Pathology, Purdue University. The 2004 Weed Day tour is scheduled for Tuesday, June 29, 2004. The program will begin at 8:30 AM Eastern Standard Time (Central Daylight Time) at the Purdue University Agronomy Research Center (located 7 miles NW of West Lafayette on US 52 W). Parking will be at the main entrance of the farm. Come a little early and have coffee and a doughnut with us. Water and soft drinks will be available during the tour.
Even with this being a wet spring we have everything planted and all the soybeans, popcorn and corn have emerged. Weed pressure is quite good and early post treatments will soon be applied.
The herbicide plots will give a look at “What’s Coming” and a comparison of some new herbicides. You will be able to compare new corn, popcorn and soybean herbicides with those commonly used, and evaluate the effects of adjuvants on herbicide performance. Graduate students will be available to discuss their research plots.
In the afternoon several of the Purdue staff will be around to visit and review in more detail the research plots seen during the morning tour. See the agenda for a look at the day’s activities www.btny.purdue.edu/weedscience/.
Several motels are available in the West Lafayette-Lafayette area. A few are listed for your convenience.
Please return the enclosed attendance form www.btny.purdue.edu/weedscience/2004/WeedDayAtt04 .pdf, if possible, to allow us to maintain a mailing list and to estimate coffee, doughnuts, and soft drinks needs for the Weed Day.
Crazy top gets its name from the symptoms produced in the tassel. Instead of producing tassels, infected plants produce a proliferation of small leaves. Other symptoms include excessive tillering and rolling or twisting of upper leaves. Ears may also develop masses of small leaves.
The recent heavy rains flooded many corn fields in Indiana. Some have been flooded long enough that corn will die or be severely injured by the long immersion in warm water. Other areas were evidently flooded for briefer periods, and aside from muddy leaves, the plants appear to be healthy. However, some of these plants might develop the top rot phase of bacterial stalk rot.
The rain storms of the past week left a lot of things floating or submerged throughout Indiana, including corn fields. Total rainfall over the several day period was greater than 10 inches for some areas in northern Indiana. The consequences of such extreme weather events on crops this late into the growing season are often severe, with few available remedies to recover lost yield potential. Here are a few thoughts to consider relative to water-damaged crops.
Hoeft, Robert. 2004. Predicting and Measuring Nitrogen Loss. Univ. of Illinois “the Bulletin”. Available online at www.ipm.uiuc.edu/bulletin/article.php?issueNumber=10&issueYear=2004&articleNumber=8 (URL verified 6/14/04).
Lipps, Patrick E. and Dennis R. Mills. 2000. Crazy Top of Corn. Ohio State Univ. Coop. Ext. Service publication AC-0034-01. Available online at http://ohioline.osu.edu/ac-fact/0034.html. (URL verified 6/14/04)
Nielsen, R.L. (Bob). 2003. Stalk Health Issues in Stressed Corn . Corny News Network, Purdue Univ. Available online at www.kingcorn.org/news/articles.03/StalkHealth-0813.html. (URL verified 6/14/04)
Nielsen, R.L. (Bob). 2004a. Effects of Flooding or Ponding on Young Corn. Corny News Network, Purdue Univ. Available online at www.kingcorn.org/news/articles.04/Flooding-0507.html. (URL verified 6/14/04)
Nielsen, R.L. (Bob). 2004b. Soggy Soils, N Loss, & Supplemental Nitrogen Fertilizer for Corn. Corny News Network, Purdue Univ. Available online at www.kingcorn.org/news/articles.04/Flooding-0507.html. (URL verified 6/14/04)
Nielsen, R.L. (Bob) and Peter Thomison. 2003. Delayed Planting & Hybrid Maturity Decisions. Purdue Univ. Cooperative Extension Publication AY-312-W. Available online at www.agry.purdue.edu/ext/pubs/AY-312-W.pdf. (URL verified 6/14/04).
For other Corny News Network articles, browse through the CNN Archives at www.kingcorn.org/news/index-cnn.html.
For other information about corn, take a look at the Corn Growers’ Guidebook at www.kingcorn.org.