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Commercial Horticulture > Comm Hort Blog > Posts > Crucifer Crop IPM Scouting Report: Watch For Yellowmargined Leaf Beetles And Caterpillars

​This information is based on crop scouting on commercial farms and research stations in Central and South Alabama. A nice-looking Cole Crop Insect Pest Scouting Guide (ANR-2241) is available online for using in the field. When in doubt – call Extension for site-specific IPM questions!

 

Harlequin bugs:  At one location in Southeast Alabama, there was a large aggregation of harlequin bugs present on collards. These insects damage the plants by excessive sucking at the terminals or leaf bases that can result in severely weak crops. Nymphs and adult bugs may feed together in large masses causing major problem. Eggs look like tiny white barrels and are laid in the underside of leaves. Economic threshold is one adult per 10 plants which is very low and assumes uniform population across fields; use your own experience for best judgement. Keep good records and prevent buildup with pest exclusion systems or by using insecticides. Several synthetic pyrethroids, neonicotinoid (e.g., dinotefuran), and some organic insecticides (pyrethrin, spinosad or a mixture) may provide relief to producers. Being the spring time of year, don't over-spray with synthetic or organic insecticides as it may kill off beneficial insects that are trying to colonize crops.

 harlequin bugs1.jpg

Yellowmargined leaf beetle (YMLB): This insect has been active statewide for many years, yet, it has been misdiagnosed or undiagnosed by many. YMLB was first detected in Mobile, AL, in 1947; it has since expanded its geographic range to almost all parts of Alabama. Just look at the napa cabbage photo – those plants had about 80 larvae per plant. YMLB adults are 5 mm-long beetles with dark brown forewings that cover the soft hind-wings (these insects are good flyers). The hard forewing is lined with yellow border giving it the name. Although the eggs may be hard to detect, you can't miss the aggressive black larvae that can destroy produce at an amazing speed. Crop damage can happen in the open or inside high tunnels (see below), so all producers should watch out!

YMLB napacabbage1.jpg 

Larvae can skeletonize the leaves while adult beetles create notches on the leaf margins (working their way to the center of the crop). In other words, crop loss happens by direct feeding AND contamination that can cause over 50 percent crop loss if unchecked.  Control methods for conventional producers include a number of short-residual synthetic pyrethroid with various pre-harvest intervals. Organic producers can use natural pyrethrin or spinosad – try reducing the spray applications to the shortest according to label in case you have a heavy population. Application timing and insecticide rotation are important points for all producers for maximum kill. Trap cropping with turnips is a great way to protect main crops like cabbages – more on this in the next article.

 YMLB feeding on cabbage.jpg

Caterpillar issues: A number of caterpillars are usually active around in late spring, so crop damage can happen fast with high numbers and overlapping generations. In the IPM research plots, there were plenty of diamondback moth and imported cabbageworm larvae feeding alongside YMLB. Refer to the Cole Crop Insect Pest Scouting Guide (ANR-2241) for caterpillar identification and scouting tips. Controlling caterpillars is easy when they are small and low in numbers. Bt-based products do a good job along with synthetic or natural pyrethrins – producers have to apply materials timely before an outbreak. If you have one caterpillar on every other plant, you know you have too many!

 YMLB ICW pic1.jpg

Physical exclusion for gardeners: Pest exclusion is a great way to provide a barrier between insect pests and host plants. According to research done in Alabama, covering plants with insect barrier fabric using low-tunnels or hoops at early seedling stage can provide good pest protection and promote plant growth. 

 pest exclusion1.jpg

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