ISSUE 7 JUNE 18, 1998
DETERMINE BARLEY THRIPS LEVELS
Barley thrips can be found easily in barley fields. Normally, hot dry conditions increase risk of injury from barley thrips. Last week, 5 to 6-leaf stage plants from a barley field in northeast North Dakota were showing severe damage from thrips feeding which is bleached and whitened leaves or entire plants. Thrips numbered one to two adults on damaged plants. The level of damage found is not expected in barley of that age. However, interaction between thrips, cool weather, and an herbicide treatment are believed to have resulted in the higher than expected injury. Thrips generally have more impact on plants when they are growing slowly.
Initiate sampling for barley thrips now and continue through flag leaf and until the head is completely emerged from the boot. Most barley thrips can be found under the top two leaf sheaths.
To count the number of thrips on a stem, first break off the plant at the second node from the top. Run your thumbnail between the two edges of the sheaths at the collar and slowly unroll the sheath away from the stem. The adult thrips are only 1 to 2 mm. long, very slender and dark brown or black. The immature thrips resemble the adults but are smaller and white or green in color.
Treatments, when warranted, are only effective if applied before heading is complete. Treatment after heading has not demonstrated a yield increase according to NDSU trials.
To determine a field's threshold, know the cost of control (insecticide and application cost), the expected per bushel dollar value of the barley. The threshold is the cost of control divided by the expected bushel dollar value which is then divided by 0.4 (bushels lost due to one thrips/stem).Threshold = cost
of control ÷ expected dollar value per bushel
0.4
EUROPEAN CORN BORER ACTIVITY
With the many concerns about European corn borer throughout the region, NDSU, South Dakota State University, and Pioneer have initiated a black light trapping project. Moth flight is underway, but generally at low levels. The numbers are likely to increase very soon. The trapping results are being reported through a web site which is updated two times a week. This should provide insight into the kind of moth flight activity that is occurring. It won't tell people if they have a problem in fields, but it will help in recognizing flight trends.
You can access the trapping records and management information for corn borer at the web address:
http://www.ndsu.nodak.edu/entomology/ecb
The site can also be accessed through the NDSU Dept of Entomology home page at the address:
http://www.ndsu.nodak.edu/entomology
Some of you have asked about pictures of corn borer life stages (e. g., moth, eggs, larvae). The management information for North Dakota includes some pictures that illustrate what you are looking for in the field. Bookmark these sites and we hope you find them useful.
WHEAT MIDGE - Emergence Beginning
Locations in the southeast corner of the state have reached 1300 degree days, the time when female midge are emerging. It is important to begin watching fields that are heading to determine if treatable levels of midge, 1 per 4 to 5 wheat heads, are present in the field. Scouting must be done at dusk. When temperatures are below 60°F, midge adults will not be active. Refer to last weeks newsletter for midge management basics.
The following table updates the degree days. Sites in BOLD letters have or will exceed the degree days for female emergence shortly. Currently, daily degree day accumulations are averaging in the low to mid 20's, so only 4 to 5 days are needed to add 100 DD to location totals.
Wheat Midge DD Accumulations (Base 40°F)* |
|||||||
Location |
6/16/97 |
Location |
6/16/97 |
Location |
6/16/97 |
Location |
6/16/97 |
Baker |
1037 |
Fargo |
1275 |
Linton |
1123 |
Rolla |
855 |
Bismarck |
1018 |
Forest River |
1140 |
Mayville |
1029 |
Streeter |
1011 |
Bottineau |
958 |
Galesburg |
1173 |
McHenry |
1089 |
St. Thomas |
1140 |
Cando |
1066 |
Grand Forks |
1185 |
Minot |
1075 |
Towner |
935 |
Carrington |
1053 |
Harvey |
1000 |
Mohall |
951 |
Turtle Lake |
1036 |
Cavalier |
1072 |
Hillsboro |
1206 |
Northwood |
1114 |
Walhalla |
1081 |
Columbus |
861 |
Horace |
1219 |
Oakes |
1223 |
Williston |
1096 |
Dazey |
1135 |
Jamestown |
1104 |
Prosper |
1245 |
Wyndmere |
1260 |
Edgeley |
1120 |
Langdon |
941 |
Robinson |
1037 |
||
* Adult female midge
are present at 1300 DD
Phillip Glogoza
Extension Entomologist
SUGAR BEET ROOT MAGGOT
Last week’s cold spell occurred while a good majority of SBRM eggs were trying to hatch. At present, many first instar larvae can be found, and some wilted plants from heavy larval feeding can be found on untreated beets.
Sugar beets should be large enough at this point that larval damage should not be a significant threat. That does not mean there will not be damage from feeding. It means plant stands are not threatened. Some consistent sunny days would be the best remedy for beets, at least in the southern half of the valley.
SRINGTAILS FEEDING ON BEETS
Every year is different and brings new challenges in crop production, right! One of the challenges in sugar beets this year has been the presence of Collembola, better known as "springtails". These arthropods are one of the most primitive known to man. They have some very strange biology which unfortunately can’t be covered in this short article. They are broken down into two groups; above ground species and below ground species. The one causing plant stand loss in sugar beets this year (at least in three separate fields) has some interesting characteristics. It is a below ground species that is semi-aquatic, requiring a very moist soil for survival. This is why we have seen problems this season. This particular species, Folsomides parvulus, is from 1/32 to 1/16 inch in length which makes them very hard to find in soil.
Springtail injuring sugar beets (drawing by Dr. Gerald Fauske, NDSU Entomologist).
All life stages are solid white in color and very active. When you pull up soil around the base of a dying plant, you may see them move for only a second or two before they disappear back into the soil. Very good eye-sight is required for finding this insect.
Why are sprintails causing problems this year ? Because of the moist soil. Fields inspected where springtails have reduced sugar beet stands have two consistent factors in common. Very moist soil and high residue such as last years small grains straw. This springtail feeds on fungi and bacteria associated with rotting organic matter in the soil. When the springtail densities reach several thousand per square foot in moist soil and the fungi and bacteria happen to be in contact with the root surface, feeding injury occurs. In some instances, plant stand loss occurs to the point where beets have to be replanted. The use of granular insecticides at planting appears to control springtails. I have heard reports that granular insecticides are not effective in controlling springtails but personally have not seen significant injury in fields where a granular insecticide were used. Upon re-visiting the fields that have injury and no granular insecticide, I noticed that the problems seems to continue as long as soil moisture remains high. Sprintails continue to reproduce, although the number of generations they have is unknown.
Should you be interested in finding sprintails in the soil, take a shovel full of moist soil and throw it in a bucket of water. Sprintails will float to the surface. The next trick is to see them!
I have to include some other interesting facts about this strange arthropod attacking beets:
1. It never has wings
2. It has no eyes
3. Most springtails have a spring loaded device at the end of it’s tail to project it away from danger.
4. It has a very different reproductive life that we can’t go into here!
I did not make any of this up. If you have more questions call me at 231-7901.
Scott Armstrong
NDSU Entomologist
