Northern Corn Rootworm
Authors: Ron Hammond, Bruce Eisley
Last week we visited a cornfield in southern Wood County that had been in soybeans the previous year. There was substantial plant lodging in many parts of the field. Pulling and washing roots revealed moderate to heavy rootworm injury. Root ratings of the pulled roots ranged from 3 to 6 on the 1-6 scale, with the majority of ratings being 4. These ratings indicated an economic problem in this field from rootworms. Our immediate thought was that this was from the first year western corn rootworm biotype because it was first year corn following soybeans. However, we also knew that this area of the state (along with most of Ohio) had relatively few western corn rootworm adults sampled from soybean fields in 2003. Additionally, we are not receiving many reports of rootworm damage this summer. It wasn’t until we noticed extremely high numbers of adult northern corn rootworms (NCR) that we began to understand what might be happening. Not only were adult NCR flying like flies as we walked through the field, but also almost every ear tip of corn we examined had two to three NCR emerge from feeding. The population density of this insect in this single corn field was tremendous. As mentioned, the previous crop was soybeans, and on asking the grower about weed control in the soybeans in 2003, we were informed it was excellent. Although we will need to monitor this field throughout this summer and over the next few years, the probability exists that this is an example of the biotype of the NCR that has what we call “extended diapause”.
The problem in this field may have occurred because not all of the NCR rootworm eggs hatched last year. Under normal conditions, NCR adults laid their eggs in this field when it was in corn two years ago. All the eggs in this field would have hatched last year when the field was in soybeans, the larvae would have died from lack of food, and the rootworm cycle would have been broken. However, under certain circumstances not all of the NCR eggs hatch the year after the field has been in corn leaving enough eggs to hatch the next year to cause problems when the field is planted to corn the second year. This phenomenon in this insect is called “ extended diapause” and has been documented in NCR and is a problem occasionally in several states including Minnesota and South Dakota.
We have suspected that this problem may be in some fields in Ohio, especially those fields that have a large number of NCR adults, but have never been able to document the problem because only a limited number of corn fields have a predominance of NCR adults. While we cannot be certain that extended diapause from NCR is the cause in this field, the large number of NCR beetles in this field does look suspicious. There is nothing that can be done in this field this year but the field should be noted and if it goes to corn in two years, treatment for rootworm might be warranted at that time.
If you have problems in first year corn and you are seeing a lot of NCR adults in the field then this extended diapause problem might be considered and the field noted and watched.
Authors: Ron Hammond, Bruce Eisley
As mentioned in the C.O.R.N. newsletter two weeks ago, defoliators were beginning to appear in soybeans. This past week, observations have indicated insect numbers have been increasing, and the level of defoliation in some fields is on the rise. Growers are advised to visit their fields to make sure leaf feeding is not getting out of hand. Although most fields will not have economic problems (>15-20%), only a visit to each field will determine whether or not there is a concern. See the C.O.R.N. newsletter from July 12-19, 2004-22, for information on information on controlling soybean defoliators. Also, further reports of twospotted spider mites from dry areas have been received; so keep a watch for them.
New Soybean Leaves Chlorotic
Authors: Robert Mullen
Several soybean fields are showing chlorosis (yellowing) of new growth, and many want to know why. The first thought may be manganese (Mn) deficiency especially in Western Ohio, but this may not be the case. If the chlorosis occurs shortly after heavy rains or on areas of the field that are poorly drained and soil pH is at or below 6.5, then Mn is probably not the problem. As alluded to in previous newsletter articles, early-season moisture has caused poor root development of most crops. Dry conditions the past several weeks have resulted in somewhat slower development which has been followed by significant rainfall. After these rains, the new growth is chlorotic probably due to a flush of growth and the crop’s inability to uptake nutrients rapidly. The problem may be worse on fields that have received enough rain to saturate the soil or in low spots that hold water. Portions of roots in these areas may be dying as a result of excess moisture increasing demand on poorly developed root systems. Unfortunately nothing can be done to improve the condition. With time, the areas or fields should improve in appearance.
Weed Management in Wheat Stubble
With all of the recent rains in most of the state, there is still time to mow wheat stubble to help reduce summer annual seed production and allow for better herbicide coverage. Despite there still being time, I would get the mowing finished by the end of this week. The reason for this is to allow enough time for regrowth of perennial weed species in order to maximize herbicide translocation and control. Perennial weeds should be at least 10 inches tall, but preferably 12 to 18 inches tall for maximum control. Later in the month we will discuss when and what to apply to get the perennial weeds controlled.
Results of 2004 Wheat Performance Trials Now Available
Authors: Jim Beuerlein
Results of the 2004 Wheat Performance Trial are on the Internet at: http://www.oardc.ohio-state.edu/wheat2004/ and hard copies are available at County Extension offices. Fifty nine soft red winter wheat varieties and five soft white winter varieties were tested. Yields ranged from 51 to 93 bushels per acre and test weights fell between 54 and 61 pounds per bushel depending on test site and variety. The wet weather brought on lots of different diseases, so varieties were rated for their reaction to the diseases present. The test results will be are very useful to producers trying to select the best varieties to grow in 2005.
Deep Tillage Field Day August 11
Authors: Glen Arnold
A deep tillage field day is set in Putnam County for Wednesday, August 11th (rain date is August 18th) at 7:00pm at Dan Gerdeman’s Farm. The farm is located two miles north of US 224 on Twp Road 13 and is approximately two miles west of Glandorf. Local equipment manufacturers and dealers will be demonstrating their equipment and Natural Resource Conservation Service scientist Frank Gibbs will be on hand evaluating soil profiles after the tillage equipment is demonstrated.
Farmers with 5000 gallons or more of on-farm fertilizer storage will be required to construct a containment facility. The field day is located next to Glandorf Warehouse where farmers can see a fertilizer containment facility. For more information contact the Putnam County Extension office at 419-523-6294 or the Putnam County SWCD at 419-523-5159
State Specialists: Robert Mullen (Soil Fertility), Jeff Stachler (Weed Science), Bruce Eisley and Ron Hammond (Entomology), and Jim Beuerlein (Soybean & Wheat Specialist). Extension Agents and Associates: Harold Watters (Miami), Alan Sundermeier (Wood), Glen Arnold (Putnam), Roger Bender (Shelby), Steve Foster (Darke), Howard Siegrist (Licking), Ray Wells (Ross) and Dusty Sonnenberg (Henry), and Jim Skeeles (Lorain).