Idaho                                         Aphid                                                         Flyer

James B. Johnson & Monica Wiebe
JULY 20, 2000                                                                                        Vol. 15  No.7

Suction Traps

    Suction trap counts from the July 7 samples did not show any significant changes from the preceding 
week. The July 14 samples reveal several changes. Overall aphid counts are up substantially in Moscow, Lewiston, Kimberly and Burley.  

    Russian wheat aphid numbers increased in Moscow, Lewiston, Kimberly, Burley and Soda Springs. Growers in these areas should monitor fields that are still vulnerable
 to RWA damage.  

Russian Wheat Aphid Thresholds

Season

 Plant growth stage Threshold
Fall Seedlings (l tiller) 10% plants infested
Fall Larger plants Treat if plants are stressed or there is danger of winter kill
Spring (Winter grain) green up to appearance of 1st   node 5% plants with reproducing populations and fresh damage
Spring (Winter grain)   appearance of  1st node to head emergence 10% tillers infested
Spring (Spring grain) Emergence to head emergence 10% of tillers infested
Spring Head emergence to soft dough.  (After the soft dough stage, insecticide treatment will have little to no benefit) Treat only if heavy populations (i.e. more than 20 aphid per plant) develop on 10-20% of flag leaves or stems
a/   After the soft dough stage, insecticide treatment will have little to no benefit.

 

 Cereal Aphids

     Bird cherry-oat aphid numbers are rising in Moscow, Lewiston, Kimberly and Burley. Barley yellow dwarf virus is transmitted by cereal aphids (principally bird cherry oat aphid and, in the southeast Idaho high country, the greenbug). Barley yellow dwarf virus can cause 50-75% crop loss if all the plants become infected. More importantly, we use these aphid numbers as an indicator of the presence of wheat curl mites, which spread wheat streak mosaic virus. This problem seems to occur with higher bird cherry oat aphid populations.

    English grain aphid collections are beginning to increase in northern Idaho. The threshold for these aphids is 100 per head in the soft dough stage. If irrigation has been shut off treatment is not usually beneficial.

     Rose-grass aphid samples show increased numbers in Moscow, Lewiston and Burley. Rose
 grass aphids do not inject a toxin as they feed and generally cause very little injury. Since they are easily confused with the more damaging greenbug, care should be taken in identification. If you are not sure of the species, contact your University County Faculty or Entomologist before any sprays are applied.
 
Green Peach Aphids

    Green peach aphid numbers are increasing in Lewiston. We have also collected GPA in several commercial fields in southern Idaho. The PLRV regulations were listed in Aphid Flyer # 3 on surveying and controls of this aphid.
Spotted alfalfa aphids

     Spotted alfalfa aphids are still increasing in the Parma area. The threshold for this aphid on seedlings is one per plant. If the crop becomes yellow and stressed treatment should be applied.

                       Funded by the University of Idaho Agricultural Experiment Stations and the Wheat & Barley Commissions.

IDAHO 
APHID   DATA

Samples collected July 14 & 21, 2000

Cereal Others

Total

Suction Trap Location

 Russian Wheat Aphid Green Bug Bird Cherry Oat Aphid English Grain Aphid Rose Grass Aphid Corn Leaf Aphid Apple Grain Aphid Green Peach Aphid Potato Aphid Pea Aphid Spotted Alfalfa Aphid Bean Aphid (All Aphids)

Moscow		 18
97		 - 34
39		 17
34		 93
239		 6
9		 3
5		 2
15		 - 33
42		 - - 250
523

Lewiston		 44
15		 - 110
91		 15
35		 444
534		 22
26		 2
5		 23
11		 - 44
31		 1
3		 - 837
1011

Parma		 62
27		 2
 14
16		 -
3		 91
119		 1
 - 1
1
3		 1
4		 17
45		 - 197
241

Picabo		 3
6		 2
 1
5		 - 2
12
1		 - - - 1
1		 - 29
143

Kimberly		 341
68		 2
1		 27
14		 - 12
3		 - 1
 - 1
 1
1		 - 405
100

Burley		 945
526		 8
14		 41
105		 - 47
41
16		 - -
1		 1
1		 - 1063
728

Aberdeen		 4
12		 1
9		 4
5		 - 1
4		   - -
2		 -
1		 - 24
40

Rockland		 72
204		 - 2
26		 1
7
8		 - - - - - - 76
248

Arbon		 32
88
5		 2
56
1		 2
55
10
7		 - - - - - 40
233
Soda Springs 40
2		 1
 11
8
1		 1
9		 2
1		 1
 - - 4
1		 - - 78
30

Ririe		 3
1		 - 9
5		 1
 9
6		 2
2		 - - - 5
 - - 43
30

Tetonia		 - - 3
 - 3
1		 - - - - - - - 18
6