Insect pests are one of the major limiting factors in vegetable production.

Continuous warm weather and high humidity in the Deep South favor multiple generations of insect pests resulting in high pest pressure during late summer.

Vegetables are affected by many species of chewing insect pests like caterpillars and sucking insect pests in mid- to late-season.

In recent years, sucking insect pests like the leaf-footed bugs and stink bugs have become major pests of tomatoes produced in open field and in high tunnels.

Sucking insect pests have needle-like mouthparts that penetrate the skin of fruits and inject toxic saliva resulting in off-colored and off-flavored fruits.

Although a number of insecticides are available for chewing insect pest control, there are major challenges to controlling sucking insect pests using an insecticide-only strategy.

Over-dependence on insecticides can result in insecticide resistance in the long-run. In other words, controlling leaf-footed bugs and stink bugs on a large scale will require ‘thinking out of the box’ and growers have to truly follow an ‘integrated pest management’ (IPM) approach.

One IPM tactic that has been researched in Alabama and other states is called trap cropping.

Trap cropping is based on the principle of host preference, that is, insect pests prefer an alternative plant than the one harvested as produce.

Trap crops is a new area of research and their use for leaf-footed bug control for tomato production has not been widely studied or utilized. Therefore, during the last three years, Alabama Cooperative Extension System has been evaluating trap crops in small and large plot research and demonstration projects scattered across the state.

Pertinent findings

Here are some of the pertinent findings from Alabama studies:

• Summer trap crops like silage sorghum variety NK300 and sunflower “Peredovik type” planted two weeks ahead of the main crop were highly attractive to leaf-footed bugs (Leptoglossus phyllopus was most common) and to some extent, stink bugs. The reproductive structures of these trap crops are the main attraction for these bugs.

• Leaf-footed bugs, being the critical sucking insect pest of tomatoes in July, August and September, were the primary insects recorded in Alabama studies with numbers reaching up to 23 bugs per head in high pest pressure areas of the Deep South.

• Multiple trap crops are better than one. In Alabama studies, it was evident that Peredovik sunflower planted early would mature (flower) first to become attractive to the leaf-footed bugs. The sunflower seed heads were increasingly attractive as the seeds matured. Sorghum seed heads emerged and matured slowly which allowed continuous source of alternative food for leaf-footed bugs.

• Leaf-footed bugs will feed and reproduce on trap crops like sunflower and silage sorghum as long as the trap crops were in good condition. It is desirable to know the migration pattern of these bugs so that the trap crops can be planted in the best possible manner. In large plot studies, only 12 to 15 percent land area with trap crop mixture around the border of tomato fields worked very well. It is not necessary to surround a tomato field with trap crops if logistics are a challenge. Planting perimeter trap crops along two to three sides of a tomato field may work as well and may be easy to maintain. Don’t plant trap crops in poor soil conditions because then they won’t work.

• It is possible to arrest the migratory behavior of leaf-footed bugs between crop fields using multiple rows of trap crops. In large field plot studies of 2012 at Cullman and Clanton, Ala., sunflower and sorghum trap crops were either planted one-behind-the-other or side-by-side in alternate rows on the same planting date.

Sunflowers were attractive initially and allowed early detection of leaf-footed bugs. As the sunflowers matured and desiccated (hastened by couple of storms that passed through Alabama), leaf-footed bugs migrated to sorghum panicles and stayed there for the rest of the season.

During this time, leaf-footed bugs were present in negligible numbers on tomatoes planted 6 to 10 feet away from the trap crops.

• Trap crops like sorghum can be treated with insecticides when the leaf-footed bugs are at peak activity (August to September). In our studies, one to two applications of synthetic pyrethroids spread out over a month provided 78 to 98 percent control of leaf-footed bugs at various test locations.

It is not recommended to treat sunflower trap crop with insecticides in order to protect the pollinators. In the tests, tomato main crop was treated minimally or none at all for protecting against leaf-footed bugs.

• On producers’ fields, sequential trap crops can be left untreated as long as the leaf-footed bugs have continuous availability of alternative host. Leaf-footed bugs will migrate out of a trap crop if they are past their prime. Organic producers should stagger trap crop planting to keep the pests busy and harvest their produce timely. In this way, trap cropping is an excellent cultural control tactic that does not need additional equipment but careful planning to make it successful.  

• Other benefits of trap cropping included wind protection from border rows and shelter to natural enemies. In other words, trap crops can harbor a substantial population of predators like syrphid flies, lady beetles and arachnids.

In short, trap crops have applications in conventional as well as reduced-input farming systems. The major benefit of trap crops is the significant reduction in pesticide usage for controlling leaf-footed bugs.

Trap crops can fit easily in current farming strategies without the need for specialized equipment.

Providing irrigation to trap crop rows during hot, dry summers improves trap crop performance.

In the absence of trap crops, producers need one or two weekly applications of synthetic pyrethroid to keep sucking insect pests at bay.

By using trap crops, producers can focus on caterpillar management as needed and worry less about their risk of leaf-footed bugs.

With only 12 to 15 percent area in trap crops and careful management of the trap crop, farmers can concentrate the insects away from main crop and bring more sustainability in their IPM plan.

If any vegetable producer is interested in trap cropping for leaf-footed bug control, please contact a Commercial Horticulture Regional Extension Agent in the county office or email [email protected].

For pictures of trap crops and farmers using trap crops, please subscribe to “Alabama Vegetable IPM” on Facebook and look through the albums. For videos about trap crops, please visit the “IPMNews” channel on YouTube.