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Barley Thrips Increasing (06/15/17)

Barley thrips were observed in 55% of the fields surveyed by the IPM Scouts throughout the state, and ranged from 0-18 thrips per stems.

Barley Thrips Increasing

Barley thrips were observed in 55% of the fields surveyed by the IPM Scouts throughout the state, and ranged from 0-18 thrips per stems. High levels of barley thrips were observed in central and southwest North Dakota. Barley thrips prefer dry, hot weather conditions, which some areas of North Dakota are experiencing.

Scouting for barley thrips should begin when the flag leaf is visible and continue until the head is completely emergence from the boot. According to the USDA NASS, ND for June 12, 2017, the barley crop was 41% jointed, behind 59% from last year. Barley thrips can be found by unrolling the flag leaf away from the stem. Populations are usually higher at the field edges, so be sure to walk into the field using a W pattern, and check multiple plants and locations per field, such as 10 stems per site and 5 sites per field for a total of 50 plants.

The updated 2017 economic thresholds (E.T.) for barley thrips on feed and malting barley are:

 

  • Feed barley (low price range), the economic threshold is 16 to 21 barley thrips per stem.

Using the cost of control as $8-10/acre (insecticide + application cost) and $1.80/bu

 

  • Malting barley (high price range), the economic threshold is 13 to 18 barley thrips per stem.

Using the cost of control as $8-10/acre (insecticide + application cost) and $3.00/bu

  • Barley price may vary depending on contracts. Use the formula below to re-calculate the E.T. for barley thrips:

 

Economic Threshold:    

 Cost of control ÷ Expected value per bushel ($)

                                  0.4

Due to low barley prices and low yield potential in drought areas, spraying for barley thrips may not be economical in some situations.

knodel.1

Barley thrips are small dark brown to black insects about knodel.2 31 to 1.8 mm long. Females have feathery wings while males are wingless. Immature larvae are wingless, pale yellow, white or green with red eyespots. Larvae are difficult to see due to their light, almost transparent color and extremely small size. Adult and immature thrips have a long, narrow body shape.

Female thrips overwinter as adults in debris in fields and shelterbelts. Thrips emerge in late May and early June and move into winter wheat/rye and eventually to early seeded barley (preferred host). Occasional, barley thrips will feed on hard red spring wheat and durum. There is one generation per year.

Adult and immature thrips feed on succulent plant tissues by puncturing plant cells and sucking out the contents. Feeding injury symptoms are a whitened or bleached appearance (see photographs on right) with gooseneck-shaped stems and heads. Intensive feeding at the beginning of head formation produces small, shriveled grains. Often there is no seed development at the top and bottom of the head and intermediate grains are shriveled. When thrips feeding is severe on the flag leaf, kernels do not fill properly and seed weight is reduced.

Once the barley heads the insect damage is done and NO insecticide treatment is advised. Although many growers want to wait to tank-mix the insecticide with a fungicide for scab control at Feekes 10.5 (head fully emerged), I do NOT recommend waiting for the optimal timing of a fungicide application for scab control in barley. This is too late for effective barley thrips control and the damage/yield loss is already done by then.

Please consult the 2017 ND Field Crop Insect Management Guide for insecticides registered in barley in North Dakota.

Janet J. Knodel

Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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