New tools and off-season planning facilitate IPM for onion thrips

New insecticides effectively control onion thrips. Applying these as part of a planned rotation of threshold-based sprays can control thrips, save money and prolong the life of these effective chemistries.

New insecticides, including Movento and Radiant, can be used as part of an effective integrated pest management (IPM) program to control onion thrips, a damaging pest of Michigan onions. Off-season planning can help growers use these compounds effectively and prolong their useful life. Keys to success include planned rotation, appropriate application and the use of research-based thresholds.

Planning a rotation prior to the growing season can ensure that these new chemistries are applied at the right time and rotated with other chemical classes to reduce resistance. Planning a rotation involves sketching out a sequence of insecticide applications for the worst-case scenario, where thrips populations exceed threshold each week of the growing season. The key is to include a sequence of compounds with different modes of action, which should delay development of resistance.

Example of a rotation of insecticides with different modes of action;
at each week, thresholds can be used to decide if application is necessary.

Week

Insecticide

Chemical class

Threshold

1

Movento

Tetramic acid

1 thrips/leaf

2

Movento

Tetramic acid

1 thrips/leaf

3

Agrimek

Avermectin

1 thrips/leaf

4

Agrimek

Avermectin

1 thrips/leaf

5

Lannate

Carbamate

1 thrips/leaf

6

Lannate

Carbamate

1 thrips/leaf

7

Radiant

Spinosyn

3 thrips/leaf

8

Radiant

Spinosyn

3 thrips/leaf

When formulating a rotation, plan to apply the same compound in back-to-back weeks if threshold is exceeded after the first application; do not space applications of an individual product out across the growing season. This limits the application of a given insecticide to one thrips generation, which lasts two to three weeks, and avoids selecting multiple generations for resistance. Second, plan to use insecticides when they will be most effective. For example, Movento should only be applied at the start of the season, while compounds such as Radiant are effective at knocking back high populations that build later. (Final registration of Movento for onions is currently pending after a 2012 Section 18 exemption.)

Planning for effective application is also important. Work by Dr. Brian Nault of Cornell University recently presented at the Great Lakes Fruit and Vegetable Expo shows that using a penetrating surfactant is essential when applying insecticides in onions. Further, his work suggests it is important to avoid tank-mixing these products with chlorothalonil-based fungicides, as it compromises these insecticides’ effectiveness.

Once a rotation is planned, action thresholds can inform decisions about whether to apply an insecticide at a given point during the growing season. For example, Dr. Zsofia Szendrei of Michigan State University has observed that after applying back-to-back applications of Movento, it may be possible to skip one to two weeks of insecticide applications, as its systemic nature means it has longer residual activity. Dr. Szendrei’s ongoing work shows that using thresholds may reduce insecticide applications and save money while providing control as effective as calendar-based spray schedules.

Effective use of insecticides is only one component of an effective IPM program. To find out more about IPM, register for the 2013IPM Academy, hosted by Michigan State University Extension.

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