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2015 Economic Thresholds for Barley Thrips (06/18/15)

Fifty-eight percent of the barley is in the jointing crop stage in North Dakota (USDA NASS, ND – June 15, 2015) and susceptible to damage from barley thrips.

2015 Economic Thresholds for Barley Thrips

Fifty-eight percent of the bent.knodel.4.adult barley thripsarley is in the jointing crop stage in North Dakota (USDA NASS, ND – June 15, 2015) and susceptible to damage from barley thrips. NDSU IPM scouts scouted 47 barley fields last week and only three fields were above the economic thresholds for barley thrips in McKenzie and Williams counties. Barley thrips prefer dry, hot weather conditions, so the recent wet cool weather will NOT promote development of barley thripsent.knodel.5.barley thrips feeding injury. I’m repeating this article from last year’s Crop & Pest Report on pest management of barley thrips with updated economic thresholds using the 2015 market prices for malting and feed barley.

Scouting for barley thrips should begin when the flag leaf is visible and continue until the head is completely emergence from the boot. Barley thrips can be found by unrolling the flag leaf away from the stem. Remember, populations will probably be higher at the field edges.

Barley thrips are small dark brown to black insects about 1 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.

The economic threshold (thrips per stem) for barley thrips is calculated by:

 

Economic Threshold:      Cost of control ÷ Expected value per bushel ($)

                                                                                                0.4

 

Using the cost of control as $8-10/acres (insecticide + application cost) and $2.25/bu for

Feed barley (low price range), the economic threshold is 9 to 11 barley thrips per stem.

 

Using the cost of control as $8-10/acres (insecticide + application cost) and $4.75/bu for

Malting barley (high price range), the economic threshold is 4-5 barley thrips per stem.

 

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.

Insecticides approved for use on barley but do NOT have barley thrips listed on the label include: Baythroid XL (beta-cyfluthrin), Warrior II & generics (lambda-cyhalothrin), and Malathion. It is legal to apply an insecticide if it is labeled for use in the crop; however, if the target pest is not listed for that crop on the label, efficacy is not implied by the manufacturer and growers who choose to use the product assume their own liability for any unsatisfactory performance.

In 2013, we tested an experimental insecticide and Baythroid XL for barley thrips control at Fargo (Table 1). While barley thrips numbers were below the economic threshold (typically 4 to 8 thrips per stem depending on crop value), these data suggest that the experimental insecticide and Baythroid XL at 2.4 fl oz per acre were effective in controlling barley thrips. This is important in light of the cancellation of methyl parathion, which was the most-used insecticide for barley thrips control in the past.

 

Table 1.  Treatment means (± SEM) for barley thrips count data.

Treatment

Number

Treatment

Name

Thrips per Stem

Pre-spray

Thrips per Stem

7 DAT

1

Untreated Check

1.21 ± 0.23a

0.90 ± 0.17a

2

Experimental insecticide

1.36 ± 0.25a

0.07 ± 0.04b

3

Baythroid XL

1.24 ± 0.24a

0.12 ± 0.06b

Means within a column that share the same letter are not significantly different (α = 0.05).

 

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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