• Arriving moths are looking for egg laying sites (e.g., weedy fields, fields with extensive groud cover, etc.), and there are many to choose from.
  
• Light frosts have little effect on eggs.
  
• Larvae need to "grow up" before they can damage corn.
  
• Accumulations of approximately 300 heat units (base 50°F) needed after egg hatch before crop damage will be noted.
  

Black cutworm moth catches in pheromone traps throughout the state have varied over the last week (see “Black Cutworm Adult Pheromone Trap Report”), but more importantly we know that from the previous week’s captures, significant egg-laying has occurred. Also, consider that the moths continue to arrive; that will be the case for weeks to come. That is why we continue to monitor until most corn is not only planted, but up to and including the 3-leaf stage to cover the vulnerable part of the growing season.

It is too early to scout for black cutworm. For one, very little corn has been planted in the state (1% according to Indiana Ag Statistics) and that has certainly not emerged. Secondly, the black cutworm eggs have not hatched because of the cool temperatures – egg hatch is temperature driven in this and most other insects.Light frosts (e.g., morning of April 23 and 24 in many areas) will not freeze-kill black cutworm eggs. Hatched larvae (“worms”) grow and feed anytime it is above 50°F, likely on the plant they were laid on or near, e.g., winter annual weeds. Black cutworms are generalists and feed on a wide variety of hosts. Corn is not a preferred food but larvae will switch their diet to corn as weeds are killed by herbicide application and the emerging crop is the only food. Before we can detect their presence in corn, they must develop to a size that allows them to feed on corn leaves. Refer to the following map (“Heat Units Base 50”), where we are tracking black cutworm development from the date of significant arrival (intensive capture of adults in pheromone traps), to when we expect first cutting/damage. Based on the growth development model, it takes approximately 300 heat units (50°F base) from egg hatch to early 4th instar; this is the life stage when black cutworm larvae begin to cut plants. As you can see, from April 13 (intensive captures) to April 22 (map created), 100 heat units (base 50) have accumulated in the extreme southern counties of Indiana – y’all in the south are a third of the way there! These maps will be updated and posted weekly in the Pest&Crop.

Happy Scouting!

Black cutworm larval development

Black cutworm eggs on leaf, next to a penny

Newly hatched black cutworm larvae feeding on corn

 

Wk 1 = 4/2/15 - 4/8/15; Wk 2 = 4/9/15 - 4/15/15; Wk 3 - 4/16/15 - 4/22/15