Hi Susanna,

Thank you for submitting your question to the UVM Extension Master Gardener Helpline.

It sounds as though you have the pest ID already, but I will include a general description and some comments about their life cycle.

Onion and garlic thrips are tiny insects that range in color from yellow to black and are only 1/16” in length. Onion thrips overwinter in legume and grain  fields, in weedy areas, and in onion or garlic bulbs that were not removed. Adults lay eggs in the outer layer of the plant, nymphs feed on leaves, and pupation occurs in the soil. Feeding causes whitish blotches that may appear as silvery streaking on leaves. As feeding continues, affected tissue may turn dry and yellow, and may eventually brown and die. The tips are often affected first. There are at least two generations per year in the Northeast. Populations are favored by hot, dry weather.
Blue and yellow sticky traps can help trap adult lacewings and help you monitor how severe your infestation is. Scouting for thrips should be done in July, August, and early September.

Control: Thank for your interest in the organic control techniques!

-Heavy rain or overhead irrigation can lower populations. 

-Thrips have some natural predators, such as lacewings and ladybugs. Lacewing larvae and ladybugs can be ordered on-line.

-Remove plant debris from gardens after harvest to decrease the chance of overwintering thrips.

-Practice crop rotation.

-Planting marigolds and/or carrots between rows of garlic and onions can reduce thrip populations.

-Do not plant onions or garlic near alfalfa , wheat or clover since these crops may have large populations of thrips and thrips can migrate to onions/garlic when these crops are cut.

-Straw mulch can deter thrips.

-Avoid using prior year onion sets and garlic cloves.

Here are some references:

https://ag.umass.edu/vegetable/fact-sheets/thrips-onion

https://hort.extension.wisc.edu/articles/onion-thrips/

I hope this is helpful. Good luck!

Hello Susanna:

Betsy has given you some great information on thrips. 

I do want to mention that without seeing some images of your plants, we cannot be certain that this is an accurate diagnosis.  Therefore, I wanted to provide some additional information and resources so you can be sure you provide the correct treatment methods for your plants.

We are seeing a lot of leek  moth damage in garlic this season.  Here is some information on this issue so you can do further research - https://www.uvm.edu/extension/leek-moth-information-center

And here are some resources on growing garlic in general:

https://extension.unh.edu/sites/default/files/migrated_unmanaged_files/Resource006097_Rep8611.pdf

https://njaes.rutgers.edu/fs1233/