• Armyworm should be scouted soon in high-risk crops in southern IN.
• Armyworm development table helps better scouting efforts.

Armyworm moth captures, see “Armyworm Pheromone Trap Report,” were quite impressive during the third and fourth week of April, especially in Northeastern Indiana. Granted, a large moth flight does not an outbreak make. But it increases the likelihood. It would be prudent to inspect high-risk situations (grassy weeds, rye cover crop etc.) when larvae are are expected to be about .5 to .75 inch long. Larger larvae not only consume a far larger proportion of leaf tissue, but will begin to move, a.k.a “march,” as plants are denuded. They are also a lot harder to kill with insecticides.

A look back at the literature reveals that in 1914 Indiana experienced a significant armyworm outbreak. Dr. John J. Davis, known to us as the father of Purdue entomology, was inspired to conduct some simple, yet valuable, life history development information on the armyworm that year. The chart below summarizes the approximate number of days for each of the life stages of the armyworm and body measurements. Because this table isn’t based on temperature, and the last of April/early May has been cool, you would expect a delay in armyworm development.

Stage	Approximate Days	Approximate Body Length (mm)	Approximate Head Capsule Width (mm)
Egg	6	-	--
Larva:
First instar	4	2-4	0.4
Second instar	3.5	3-6	0.6
Third instar	3	5-10	1.0
Fourth instar	3	11-15 (about .5 inch)	1.5
Fifth instar	3.5	14-21	2.4
Sixth instar	8	24-35 (about 1 to 1.5 inch)	3.4
Total larval stage	25
Pupa	21

When armyworms reach a length of about 1-1/2 inches they still have about 8 days to feed before pupating. During this time period they can consume a tremendous amount of foliage. If they consume all the food in an area, they can be seen “marching” from that field to another. Dr. Davis said, “The remarkable voracity of the armyworm during its last larval instar explains its sudden appearance in such enormous and destructive numbers when it is nearly full grown. The amount of foliage eaten in this (sixth) instar was nearly seven times as much as in the fifth instar, and more than 80 percent of all of the foliage eaten during the entire larval period.”

Mid-May would be a good time to scout wheat, grass pastures, and corn planted into a grass cover-crop for armyworm feeding, especially in southern Indiana. Noticeable armyworm activity in nothern Indiana probably won’t occur until the third week of May. Again, this changes dependent on temperatures. Their feeding on the edges of grassy plants give a ragged or notched appearance. The caterpillars are more difficult to find, especially when small, as they seek refuge during the day under residues, soil clods, etc. But a persistent searcher will find them every time. Occasionally on an overcast day, they will be found feeding on the leaves. The key is to catch them early during an infestation.

Chris DiFonzo, Michigan State University has revised the wonderfully helpful table of hybrid corn Bt traits. This is a great reference that summarizes the many combinations of Bt traits in the marketplace, including which insects they control and how they differ in terms of refuge area requirements. This one-page publication has gotten kudos from seed dealers and producers alike, and is worth a look. Check out this publication at: http://www.msuent.com/assets/pdf/28BtTraitTable2016.pdf

Wk 1 = 3/31/16 - 4/6/16; Wk 2 = 4/7/16 - 4/13/16; Wk 3 = 4/14/16 - 4/20/16; Wk 4 = 4/21/16 - 4/27/16; Wk 5 = 4/28/16 - 5/4/16

Wheat that will be flowering over the next few days in southern Indiana is at moderate to high risk for Fusarium head blight (FHB), or scab, development (Figure 1).

Last week’s Pest and Crop article discussed the symptoms of FHB and how farmers and crop advisors can monitor risk of FHB development using a risk assessment tool. The link to last week’s article can be found here: https://extension.entm.purdue.edu/pestcrop/2016/Issue4/. The FHB risk assessment tool (http://www.wheatscab.psu.edu/) is predicting that wheat that will soon flower (Feekes 10.5.1) in southern IN will be at moderate to high risk for FHB, depending on variety susceptibility.

If varieties susceptible to FHB have been planted, or farmers are worried about the risk of FHB development, they may want to consider a fungicide application at early flowering for suppression of FHB. Indiana research indicates that applications of the fungicides Prosaro and Caramba are most effective at managing FHB if they are applied at Feekes 10.5.1. Other products are available, but may not be as effective. Fungicides that have a strobilurin mode of action are not labeled for Fusarium head blight suppression.

The recent rains have delayed some fungicide applications, or may prevent applications from occurring precisely at Feekes 10.5.1. Research conducted at Purdue and other institutions indicates that fungicide applications can occur after flowering and still suppress FHB and the associated mycotoxin deoxynivalenol (DON; vomitoxin). For more information please see Purdue Extension Bulletin BP:145-W, Revised Fungicide Spray Recommendations for Fusarium Head Blight. https://mdc.itap.purdue.edu/item.asp?Item_Number=BP-145-W. Although some level of efficacy may be obtained for applications occurring a few days after flowering, fungicide applications should occur as close to Feekes 10.5.1 as possible for best results.