Over the
past decade or so, wireworms have emerged as prominent pests in the Texas High
Plains and parts of the Rolling Plains. Wireworms are not a new pest. True
wireworms and false wireworms are larvae of click beetles and darkling beetles,
respectively. Multiple species of these groups of insects have been present in
these regions for a long time. Two primary factors likely contribute to the
rise in their numbers and pest status: the reduced use of at-planting
broad-spectrum insecticides like aldicarb and other products, and the increased
adoption of conservation practices such as cover crops, particularly those with
preferred hosts such as wheat and rye.
Field
research indicates that wireworm populations are significantly higher in fields
with cover crop residue compared to conventional fields. Cover crops provide
continuous food sources for wireworm larvae and shelter for adult beetles to
lay eggs. Such observations and experiences often lead to skepticism about the
practice of using cover crops. I come across many entomologists who frequently
express reservations, noting that cover crops can exacerbate pest issues,
including cutworms, pill bugs, wireworms, and slugs, particularly in regions
with higher moisture, humidity and insect abundance.
While
cover crops may harbor pests, they offer numerous ecological and agronomic
benefits. For example, in the Texas High Plains, where high wind speeds and
sandy soils are prevalent, cover crops play a crucial role in mitigating sand
damage to young seedlings. Sandblasting—caused by blowing sand—is a serious
issue in the region. Farmers often resort to a practice known as “sand
fighting,” which involves opening the soil crust to slow sand particles and
protect seedlings. On bare ground, sand burn can cause more damage to cotton
seedlings than wireworms. Cover crops can help reduce sand injury and soil
erosion, offering significant advantages. Rather than rejecting cover crops
outright due to increased wireworm presence, it is essential to adopt a
balanced view. The benefits of cover crops, such as protecting young plants
from sand damage, often outweigh the drawbacks in regions like the Texas High
Plains.
Sand damage to young cotton
To harness
the benefits of cover crops while minimizing pest buildup, proactive management
strategies are necessary. Applying preventative insecticide seed treatments to
cover crop seeds can help minimize wireworm numbers if they are present.
Terminating cover crops at the appropriate time (60 days prior to planting the
main crop) can help prevent them from serving as a bridge for pests to the main
crop. Although this may not help with wireworm larvae in the soil, it can be
beneficial if damaging beetles (e.g., Blaptinus) are present.
To manage
wireworms in cotton, we need to minimize exposure time by facilitating quicker
seed germination and emergence. Planting when conditions are good, such as
optimal soil temperature and moisture, is important. Similarly, the seeding
depth and rates are critical. In fields with a known history of wireworms,
increasing the seeding rate may help compensate for stand loss to some extent.
Other
measures to combat wireworm issues in cotton include preventative insecticide
seed treatments and at-planting in-furrow applications. When purchasing seeds, making
sure the seed treatment package selected has a commercial rate of insecticide
(e.g., imidacloprid, thiamethoxam) is critical. Although these products are not
a silver bullet against wireworms in cotton, they can help reduce injury to
young seedlings.
While
research into biological controls such as fungi and predatory nematodes has
been conducted, these methods have shown limited success against wireworms.
They are particularly challenging pests to study and manage because of their long-life
cycle (>5 years in some species), subterranean habitat, ability to move in
soil, wide host range, and patchy distribution within and among fields.
Finally,
though cover crops can favor the survival of pests such as wireworms, we also
need to weigh the agronomic and ecological benefits they provide before
excluding the idea completely. We need to understand the complexities of
agricultural landscapes and perform the balancing act of harnessing the
benefits of cover crops while minimizing the harm with proper management.
