The=20 Affect of Insecticide Application Timing For Controlling Aphid Vectors = On Barley=20 Yellow Dwarf Incidence in Wheat Grown in Henderson Co., = KY.

(1998-99)

Doug=20 Johnson, Department of Entomology

University of=20 Kentucky =96 College of = Agriculture

Patterson=20 variety wheat was planted on Oct 16, 1998 in 4' by 15' plots on the = Alexander=20 Farm in Henderson Co. KY. The experiment was arranged in a randomized = complete=20 block design with four replications. The test area was most recently in = corn and=20 a conventional seed bed was prepared by moldboard plow followed by a = discing. Fertility was applied as 35 lbs N on Feb = 15, 1999=20 (Feekes GS 3) and 65 lbs. on March 22, 1999 = (Feekes GS: 5). Insecticide applications of = Warrior=AE=20 (lambda-Cyhalothrin) at 3.2 fl.oz. per acre were = made with a=20 backpack sprayer in 26 gal of spray per acre, on Nov 24, 1998 (Feekes GS: 2-3 ), Feb 16, 1999 (Feekes GS: 3), both dates or neither date. A = fungicide=20 application of Tilt=AE at 4 fl.oz. per acre = was made to=20 all plots on April 29, 1999 (Feekes = GS:10.3-5) using a=20 backpack sprayer delivering 25 gal of spray per acre. Plots were = observed for=20 BYD symptoms but pressure was too light to warrant rating. Regular aphid = counts=20 were not made but plots were observed at application times. Plots were = harvested=20 in June 1999 using a small plot combine. Harvested grain was weighed, = and check=20 for moisture content. Plot grain weights were corrected to a moisture = standard=20 of 13.5% and yields per acre were calculated based on a standard 60 lbs. = per=20 bushel. Yields and test weights were analyzed for differences using SAS, = Proc=20 GLM.

Plot=20 yields and test weights =B1 their Standard Errors (SE) are shown in = Table. 1. No=20 significant affect was detected on yields (F=3D1.13) or test weights = (F=3D1.47) for=20 any of the insecticide treatments. This was expected as BYD pressure was = very=20 light in these plots and could not account for any differences. Very few = aphids=20 were seen before the final insecticide application. However, aphids were = wide=20 spread and numerous during the spring.

TABLE=20 1. YIELD AND TEST WEIGHT OF WHEAT HARVESTED FROM PLOTS WITH = VARIOUS=20 INSECTICIDE TREATMENTS FOR CONTROL OF APHID VECTORS =20
OF=20 BARLEY YELLOW DWARF VIRUS.

Time=20 of Application

Yield=20 =B1 SE

Test=20 Weight =B1 SE

(Bu=20 / Acre)

(Lbs.=20 / Bu)

No=20 Insecticide

94.3=20 =B1 6.7

57.8=20 =B1 0.9

Nov=20 24, 1998

94.7=20 =B1 6.5

55.2=20 =B1 3.3

Nov=20 24, 1998 and Feb 16, 1999

102.3=20 =B1 2.3

62.9=20 =B1 5.3

Feb=20 16, 1999

100.8=20 =B1 2.1

55.8=20 =B1 2.5

Such=20 variations as did occur were largely due to lodging in some of the = plots. This=20 problem is partially illustrated (Table 2.) by the difference in yields = among=20 replications. If all the difference in yields were due to treatments (in = this=20 case the insecticide applications), we would expect that yields and test = weights=20 calculated for replications (since each replication contains all the = same=20 treatments) would be nearly equal. It is obvious that this is not the = case, so=20 something other than insecticide treatment is causing the differences in = yield=20 and test weight. A portion of this difference is random chance and a = portion is=20 likely to be due to the lodging.

TABLE=20 2. YIELD AND TEST WEIGHT BY REPLICATION OF WHEAT HARVESTED FROM = PLOTS WITH=20 VARIOUS INSECTICIDE TREATMENTS.

Replication*

Yield=20 =B1 SE

Test=20 Weight =B1 SE

(Bu=20 / Acre)

(Lbs.=20 / Bu)

91.4=20 =B1 5.6

57.8=20 =B1 3.1

95.5=20 =B1 6.7

57.8=20 =B1 0.8

101.3=20 =B1 1.6

55.6=20 =B1 2.4

103.9=20 =B1 2.0

63.7=20 =B1 5.1

* Each=20 replication contains all four insecticide treatments.

Because=20 the insecticide treatments did not produce any difference in yield at = this=20 location and year, using them would have reduced the producers profit. In general terms the fall = application is=20 often made as an "insecticide only" application, which would cost about = $ 11.00.=20 The spring application is often made in conjunction with other inputs so = the=20 application cost may be saved. Using this as the basis, in this location = in this=20 year, the insecticide applications would have returned the following: = Nov=20 (-$11.00), Feb (-$ 6.00) and Nov and Feb (- = $17.00).

Certainly=20 the circumstances on your farm will alter these figures. As prices and = yields=20 decline and treatment costs increase, the insecticide treatments will = look even=20 less appropriate. However, as prices and yields increase and treatment = costs=20 decrease the insecticide applications will look better. =

Deciding=20 whether or not to treat for control of aphid vectors of BYDV is a hard = decision=20 to make in KY. You do the best you can based = on the=20 information available at the time the decision has to be made. However, = it is=20 important to remember that spraying "just in case" is very often not = profitable=20 and even if you see symptoms in the spring that does not necessarily = mean that=20 you made the wrong decision by not spraying in the fall or winter.=20

The=20 author thanks Mr. Mike Smith for arranging for the location and Mr. = Alexander=20 for allowing the use of his farm, Dr. Lloyd Murdock and Ms. Dottie Call = for=20 making fertility applications, Dr. Don Hershman for=20 applying the fungicide, Mr. Charles Tutt for = harvesting the plots, and Ms. Call for coordinating the various efforts. =

From=20 University of=20 Kentucky, = Extension=20 Entomology Research Reports at: http://pest.ca.uky.e= du/EXT/Res/ResPubs.shtm