AUBURN, Ala. – Yellowmargined leaf beetle,Microtheca ochroloma, is a major pest of brassicas across the Southeast. Crops like turnips, napa cabbage, mustard, radish and cabbages among others are vulnerable. Dr. Ayanava Majumdar, an Alabama Extension entomologist, said the pest can destroy winter crops.
“It doesn’t matter whether those crops are grown in open field or under high tunnels,” he said. “YMLB can move in rapidly and devastate a crop.”
Majumdar added that YLMB pressure in new production areas may increase within two growing cycles. In Alabama trials on new ground, research documented complete devastation of turnips from high YMLB populations within two years.
In the past few months, monitoring shows YMLB numbers exploding. This December, sightings of yellowmargined leaf beetle attacks on turnips, a trap crop at research plots in Clanton, Alabama are widespread.
“Watch for the black hairy larvae of this leaf beetle that feed in large masses,” Majumdar said. “Unhindered feeding can lead to rapid defoliation and massive crop failures.
“Check the Alabama Vegetable IPM website for more information on this insect pest. Producers can call Alabama Extension commercial horticulture agents for proper diagnosis of multiple pest species before an outbreak.”
Native to South America, first reports identified yellowmargined leaf beetle in south Alabama in the late 1940s. Outbreaks are common throughout Alabama, Georgia and Florida where mild winters are common and brassica crops are abundant in fall and spring. While older literature calls it a home garden problem, YLMB is now also a major pest on commercial farms.
In Alabama, leaf feeding from the beetle is often misdiagnosed caterpillar activity. Identify the insect correctly. Take pictures and share with your Alabama Extension commercial horticulture agent for proper identification. YMLB eggs and larvae may resemble those of the lady beetle, a beneficial insect. YMLB lay their eggs loosely at base of plants while lady beetles lay eggs close together on leaves. Lady beetle larvae have spines on their back, but YMLB larvae do not.
Important to Know
- Watch for rapid defoliation from larvae that feed in masses along with the adult beetles. Research shows YLMB control should begin when there is one insect per plant.
- Larvae have been found feeding on leaves, stems and turnip roots planted as a trap crop on warm days even in mid-December. In other places, spring YLMB populations can destroy crops like cabbages if left unprotected by insecticides or the use of a trap crop.
- These insects are easy to kill on small crops with conventional insecticides like synthetic pyrethroids (e.g., zeta-cypermethrin and bifenthrin based insecticides) that also can reduce caterpillars.
- Watch for insecticide resistance in caterpillars and adjust control methods accordingly.
- Achieve best organic control when turnips leaves are small and erect so they are easy to spray. Some effective organic insecticides include Pyganic, spinosad-containing products and premixed products such as Azera. Do not use Bt products for YMLB control.
- Additionally, large or densely planted turnips and other crops with large droopy leaves provide hiding spaces for beetles and may be difficult to spray. It can be very difficult to control the YMLB adults on cabbages, which have large outer leaves that shield the inside from insecticide applications.
- Look for beneficial insects like spined soldier bugs and lacewings. University of Florida researchers confirm both are active YLMB predators. Protect beneficials, and reduce insecticide spraying when they are most active.
- For Extension articles and YMLB videos, visit the Alabama Vegetable IPM website.