Thrips on Vegetables

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HOSTS

• Alfalfa
• Asparagus
• Bean
• Cabbage
• Cauliflower
• Cucumber
• Garlic
• Onion
• Potato
• Small Grains
• Tomato

DESCRIPTION

Adults are minute with elongated yellow or yellow-brown bodies and two pairs of fringed (hairy) wings. Larvae are a creamy-yellow color, and wingless.

BIOLOGY

Egg | Larva | Pupa | Adult
Thrips overwinter as adults plant debris and protected areas. In the spring, they become active and move into fields.  In Utah, females reproduce asexually (parthenogenesis) and insert eggs individually into leaves. Females will lay eggs for about 3 weeks. Larvae remain on the host plant before moving to the soil at the base of the plant for one prepupal stage and pupation. A complete generation requires 3 to 4 weeks during the summer months, and 5 to 8 generations may occur each year. Thrips populations increase rapidly under hot, arid conditions, leading to economic crop losses.

SYMPTOMS

• White flecks or silvery scars on foliage.
• Dark fecal spots on leaves.
• Distorted leaf growth.
• Reduced bulb size in onions.

SCOUTING

• Use a 10x hands lens when scouting fro thrips. 
• Onion thrips are commonly found in the neck of the onion.
• Look for silvery scars, bleached spots on foliage, and dark fecal spots. 

GENERAL MANAGEMENT

Serious infestations in cabbage make the crop unmarketable. Tomato spotted wilt virus may be vectored by thrips and can cause death in some host plants. Iris yellow spot virus vectored by onion thrips and can cause reduced bulb size and quality in allium crops.

• Plow plant debris under after harvest and remove volunteer host plants.
• Inspect transplants for thrips infestations (using a 10x hand lens) and discard or manage infested plants.
• Remove weeds within fields and around greenhouses.
• Place mulch to prevent larvae from reaching the soil to pupate.
• Plant crop varieties with resistance to thrips.

INSECTICIDES

• Thrips have rapidly developed resistance to several classes of insecticides. Insecticides will be most effective when used in conjunction with other non-pesticide management practices.
• For onions:
  – June to early July in highly susceptible onion varieties (e.g. red onions): 115 thrips per plant.
  – July and August in more tolerant onion varieties (many yellow and white varieties): 30 thrips per plant.

Click here to reference insecticide options for home use.
Click here to reference insecticide options for commercial use.