Sweet corn earworms are developing from eggs laid at night by moths

Chris Himmelwright
Pratt Tribune
Corn earworms seem to love sweet corn as much as people do.

Corn earworm tends to be a problem every year on sweet corn in Kansas. The earworm moth lays eggs on developing silks at night. When the egg hatches, the larva crawls down the silk and into the ear. Feeding starts at the tip of the ear and works down. Though several earworms may hatch and attack a single ear, only one is usually present at harvest due to the cannibalistic nature of the insect. Control is challenging as silks continue to grow over a period of time. This means that even if silks are treated, new silk will appear that hasn't been protected. Applications every two to three days are needed for insecticides to be effective, especially in early July when peak flight of these moths usually appear.

There is a three-week period from silking to harvest, but there is only a two-week period from when the silks appear to when they begin to dry. Since moths prefer juicy silks and shun those that have started to dry, insecticides are only needed the first two weeks of silking.

Homeowners can use cyfluthrin (Baythroid; BioAdvanced Vegetable and Garden Insect Killer) or spinosad (Captain Jack's Dead Bug Brew; Natural Guard Spinosad, Monterey Garden Insect Spray). Spinosad is an organic product. Commercial growers have additional choices including zeta-cypermethrin (Mustang Max), bifenthrin+zeta-cypermethrin (Hero), spinetoram (Radiant) and flubendiamide (Belt).

Though more time consuming, mineral or other light horticultural oils may also be used as an organic control. The oil is placed inside the silk end of the ear with a medicine dropper (½ to 3/4 of a dropper) when the tips of the silks begin to wilt and turn brown. This will coat the earworms already present and likely suffocate them and earworms that enter the ear after the mineral oil is applied will also be controlled. Applying the oil before the silk has begun to brown may interfere with pollination, leading to incompletely filled ears.

Dutch Elm Disease (DED)

People often assume that all of our American Elms have been killed by Dutch elm disease. Fortunately, such is not the case. Though many have survived thus far, the number diminishes each year. We are still seeing examples of Dutch elm disease on American elms. Though American elms are the species often associated with this disease, red and some hybrid elms are also susceptible. Siberian elm (sometimes referred to as Chinese elm) and the true Chinese elm (Lacebark elm) are considered resistant but not immune to the disease. However, we do have true American Elms that are naturally resistant..

Early diagnosis can help save recently infected trees. Look for branches with leaves that have wilted and suddenly turned yellow to brown. Remove a portion of the

branch and peel back an area of the bark. If you notice brown streaking in the sapwood, you may have Dutch elm disease. Healthy bark is more cream-colored and the streaking is absent. Suspect wood should be submitted to the diagnostic lab and control measures started immediately.

Dutch elm disease can often be controlled through the use of systemic fungicide injections, judicious pruning of affected trees and removal of nearby diseased elms. However, trees infected through root grafts with nearby infected elms or those in which the disease has reached the main stem cannot be saved. Therefore, preventative measures have a better chance of success and are preferred. Fungicides labeled for Dutch elm disease include Arbotect and Alamo. The Arbotect fungicide is preferred because it is the most persistent with a three-year interval between injections. Alamo may need to be applied every year in high risk areas with high value trees. A trained arborist should administer injections. These treatments are quite expensive. Check with your local arborist for current prices.

Adapted from the Kansas State Horticulture Newsletter