Corn is the most vulnerable early in the season right after planting. Even before the seed goes in the ground, producers want to do everything possible to ensure it is off to the best start to make the highest yields. However, the first couple of weeks following planting can be stressful if insects get in the way.
Alabama does have some consistent corn pests, but for the most part, many are opportunistic and will take advantage of high risk fields. Those include soil pests that feed underground and aboveground pests that will feed on the plant right at the soil line. Wireworms, white grubs, cutworms, and armyworms can all threaten corn crops early in the season.
Assessing Risk
A field’s history can tell you a lot about how much risk there is for pests, especially early in the season. Problems can arise in fields that were previously in pasture or CRP. Similarly, fields that are next to pastures can also be at higher risk. Conservation tillage systems can help enable the survival of overwintering insects which can lead to early season damage. Fields with heavy residue can also have increased insect problems. The residue will help maintain soil moisture levels, as well as temperatures that lead to increased insect survival.
Reducing Risk
The first step to starting the season off right is with proper varietal selection. Growers should select a variety that is well-adapted to their area and contains a good yield and disease package. Aboveground and belowground insect traits are also available in Bt varieties if needed.
If planting Bt corn, it’s crucial to pay attention to refuge requirements. The best way to preserve the current genes we have—both in corn and cotton—is to plant a non-Bt refuge in corn. Here in the south, the majority of the corn earworm/cotton bollworm moths going into cotton are coming from corn. Ignoring refuge requirements can lead to increase resistant populations of moths and eventually complete resistance. Maintaining a refuge ensures that non-resistant populations are kept in the field to avoid selection of resistant genes.
Requirements vary based on the exact Bt gene used. In general, at least 20 percent of corn acres must be planted with non-Bt corn. When planting corn with a single Bt trait, 50 percent of the planted corn must be a non-Bt refuge. There are multiple options for refuge configurations. The minimum refuge requirement can be planted within, adjacent to, or as a separate block within a half-mile of each Bt corn field.
There are also other strategies producers can employ to reduce risk in our fields and help to preserve the effectiveness of Bt traits in both corn and cotton. Rotation is a crucial component of risk reduction and a strong integrated pest management plan. Rotating crops and Bt traits, as well as rotating insecticide seed treatments and applications will help to preserve our current and future technologies.
Timeliness
Timely planting is crucial so that the seed germinates at optimal temperatures in the beginning of the season. Planting in a timely manner also helps fields avoid ear-feeding pests later in the season. It is rare to see yield loss from late season ear-feeding pests like corn earworm with corn planted on time. In south Alabama, the planting window is from late February to early March. This is followed by mid-March to late April planting for central Alabama, and late March through mid-May planting in the northernmost parts of the state. These dates are important because producers want to make sure that soil temperatures at a depth of two inches are at least 55°F.
Seedbeds should be clean prior to planting. Extension professionals like to see burndown herbicides applied at least 30 days before planting crops. It’s important to control weeds both in the field and on field borders to eliminate alternate hosts for insect pests. If producers are unable to clear the winter weeds or cover crop prior to planting, the field may be at risk for cutworms. Broadcast applications of any pyrethroid can be applied at planting to control cutworms.
Seed Treatments
Seed treatments like Cruiser and Poncho are standard these days and can serve as insurance to get your corn out of the most vulnerable growth stages. They will ensure optimal seedling development and reduce risk from insects or diseases. At label rates, seed treatments have enough residual for corn to develop past the high-risk period for both below- and aboveground insects.
It’s most common to run into issues when insect pressures are high, or there are suboptimal conditions around planting. For example, in fields that are not rotated, insect pressure may be high enough to overcome seed treatments and higher rates may be necessary. Cooler temperatures during germination can delay plant development and lead to uneven stand emergence. This can increase the corn’s susceptibility to pests.
For information on seed treatments or other at-plant insecticides, read the ACES Corn IPM Guide for 2021. To stay up to date on current crop information, check out the Alabama Crops Report Newsletter or our new Alabama Crops Report Podcast.
Source : aces.edu