Traill County Ag Alert Newsletter

Traill County Ag Alert Newsletter

July 31, 2008

Issue #13 July 31, 2008

RAINFALL & GROWING DEGREE DAYS (GDD)
Location                                 Mayville                      Hillsboro                    Galesburg
Corn GDD                              1194                            1211                                1203
Compared to 2007                   -259                             -248                              -244
5 Year Average                        -129                             -115                                -79

Wheat GDD                           2595                            2607                             2616
Compared to 2007                   -383                             -372                              -344
5 Year Average                        -218                             -205                             -138

Rainfall Since June 1 8.50 inches 9.15 inches 7.84 inches

FIELD TOUR FOR RAGWEED
Glyphosate-resistant common ragweed may have been discovered in North Dakota. A field tour will be held August 5, 2008 near Mayville, North Dakota to demonstrate the possibility of glyphosate-resistant common ragweed and to gain a better understanding of glyphosate-resistance. Additional studies will show how to control the potential glyphosate-resistant common ragweed in sugarbeets, soybeans, and dry beans.

The tour of the research studies will begin at 9:30 a.m. and last approximately two hours. To get to the field, take exit 111 off Interstate 29. Go four miles west on North Dakota Highway 200. Turn north and go 2.5 miles on County Road 10 (158th Avenue). The research plot is in a wheat field on the east side of the road. Parking is available only along the side of the road. In case of inclement weather, the tour will be canceled or postponed. If inclement weather does occur, contact Jeff Stachler at (701) 231-8131, Mohamed Khan at (701) 231-8596 or Kendall Nichols at (701) 636-5665.

TIME TO SCOUT FOR RED SUNFLOWER SEED WEEVIL
Red sunflower seed weevil are emerging and can be found in R4 and early blooming sunflower fields in the major sunflower producing areas. Last year, populations were lower than 2006.

Identification: Adults are small, about 1/8 inch and reddish-brown in color. Newly emerged adults feed on the bracts, sunflower buds, and pollen. Peak emergence is usually in late July and early August. The female seed weevil must feed on pollen for fertile egg development.

Scouting: Sunflower normally reaches the bud stage in late July at which time only about 30 percent of the weevils in the soil have pupated and emerged. Most weevils emerge from the soil by the first week of August. Field scouting for adults should begin when plants are showing yellow ray petals (R5.0) to 30% of the head shedding pollen (R5.3), and should continue until most of the plants have reached 70% pollen shed (R5.7). A plant that has reached R5.7 has few seeds still suitable for red seed weevil egg laying and should no longer be susceptible to further significant damage.

Seed Weevil Damage: Research reveals that most seeds are only partially consumed or destroyed by the seed weevil larvae and that damaged seeds have lower oil content than undamaged seeds. The economic loss caused by larval feeding includes the loss of both seed weight and oil content.

Economic Threshold:

Oilseed Sunflower . . . The threshold can be calculated using the following formula:

Threshold (Weevils per head) = Cost of Insecticide Treatment
(Market Price x 21.5) (0.000022 x Plant Population + 0.18)

The current high prices for oilseed sunflowers has lowered thresholds for red sunflower seed weevil! Typically, we are at 6-8 weevils per head for the economic threshold; however, thresholds are only at 2-3 weevils per head this year!

CONFECTION: The economic threshold is only ONE WEEVIL PER HEAD.
Insecticide Spray Timing: Insecticide spraying is targeted at the adult weevil to prevent egg laying. The best time to treat is when more than half of the plants in a field are beginning to show yellow ray petals (R5.0) to 30% of the head shedding pollen (R5.3) and the rest of the plants in the field are still in the late bud stage. Although insecticides applied to sunflower at the bud stage will kill weevils, treatments at that stage are not economical or effective because (1) seeds have not developed to a stage suitable for oviposition, (2) eggs within the weevil are not mature, and (3) adult weevil emergence is still continuing. Considering treatment at the early bloom stage is the optimal insecticide timing for efficacy and should allow growers a sufficient time to have their fields treated.

Growers must be aware, however, that if weevil populations are high and/or spraying is done too early, a re-infestation may occur and a second insecticide application may be necessary. Banded sunflower moth and red sunflower seed weevil can both be controlled with one well-timed spray, usually near 10% of the head shedding pollen or R5.1 Fields should always be scouted for both insect pests.

UNIVOLTINE EUROPEAN CORN BORER EMERGENCE UNDERWAY!
It’s time to be scouting non-Bt corn fields for European corn borer eggs and larvae. Look for eggs masses on the underside of leaves focusing in on the 3 leaves above and 3 leaves below the ear leaf and early signs of larval feeding (irregular pinholes in corn leaves or whorl). According to the corn GDD about 75% of the moths should have emerged be laying eggs.

The best time to apply insecticide is when larvae are in the early instars, only a 7-day window, before it enter the corn stalk. Once the larvae are inside the corn plant, no insecticides can kill it.

Control should be considered in field corn when 45 - 50 percent of the plants in dryland corn or 25 - 35 percent of the plants in irrigated corn have shot-holing in the whorl, egg masses on the undersides of leaves or live borers visible in whorls. Specific economic thresholds (corn borer/plant) are available that factor the crop value and cost of insecticide. See the following weblink: http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/ecb/mngborer.htm

NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating, Duane Hauck, Director, Fargo, North Dakota. Distributed in furtherance of Acts of Congress of May 8 and June 30, 1914. We offer our programs and facilities to all persons regardless of race, color, national origin, religion, sex, handicap, age, Vietnam era veteran status, or sexual orientation; and are an equal opportunity employer.

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Traill County Extension Office

P.O. Box 730

Hillsboro, ND 58045

701-636-5665 or toll-free1-877-843-6383