Found in a rainbow of North American plants from avocados to beans, onions, citrus trees and market flowers, thrips are tiny insects,(fringed-winged individuals are hard to see without a magnifying glass)and those species that are plant feeders can scar leaf, flower or fruit surfaces with silvery speckling when they puncture and suck out the cell's content. Conversely, heavy pest populations can severely distort flowers and damage fruit. Other thrip species function as beneficial insects by eating mites, fungal spores and pollen.
Pest prevention in the home garden should always marry tried and true cultural practices that have been proven effective locally with general gardening rules-of thumb like these:
Do not plant susceptible plants near weedy areas or grasslands that are beginning to dry in spring or summer.
Vigorously growing plants stand a good chance of outgrowing thrip damage so keep plants well irrigated, but avoid excessive applications of nitrogen fertilizer, which may promote higher populations of thrips.
Plant resistant flower cultivars and promptly remove and dispose of old, spent flowers.
Regularly prune any injured and infested growth tips above branch crotches and nodes (rather than clipping just terminal growth)and destroy. Do not clip dense foliage on formal hedges to maintain an even surface as this will stimulate susceptible new growth. Fruit-scarring of citrus by thrips can be moderated by pruning the interior of citrus trees to increase predaceous mite populations in the exterior canopy.
Thrips can be physically barred by placing row covers of woven fabric or mesh at planting and while plants are young and most susceptible to insect damage. The covers can be removed once the plants are large enough to require more space.
Although trip damage to leaves is unsightly, thrip activity does not warrant spraying with pesticides and mild infestations may be dislodged with a hearty spray of water. Otherwise, use insecticidal soap, pyrethrins or neem per instructions, hang blue or yellow sticky traps or encourage/release native predators such as pirate bugs, lacewings and lady beetles.