• Corn planted into grass = armyworm risk
• Wheat in areas of dense growth = armyworm risk
• Corn where weedy growth existed = cutworm risk
• Soybean first emerging is at risk for bean leaf beetle.
Corn & Armyworm - Corn that has been no-tilled into an abandoned wheat stand or a grass cover crop should be inspected immediately for armyworm feeding in southern Indiana. Hatched larvae will move from the dying grasses to emerging/emerged corn. Armyworm feeding gives corn a ragged appearance, with feeding extending from the leaf margin toward the midrib. Damage may be so extensive that most of the plant, with the exception of the midrib and stalk, is consumed. A highly damaged plant may recover if the growing point has not been destroyed. If more than 50% of the plants show armyworm feeding and live larvae less than 1-1/4 inches long are numerous in the field, a control may be necessary. Larvae greater than 1-1/4 inches consume a large amount of leaf tissue and, as with any large insect, are more difficult to control. If armyworm are detected migrating from border areas or waterways within fields, spot treatments in these areas are possible if the problem is identified early enough.
Armyworm feeding on 1-leaf corn (Photo by Dan Childs)
Wheat/Grass Pasture & Armyworm - Examine plants in various areas of the field, especially where plant growth is dense. Look for flag leaf feeding, clipped heads, and armyworm droppings on the ground. Shake the plants and count the number of armyworm larvae on the ground and under plant debris. On sunny days, the armyworm will take shelter under crop residue or soil clods. If counts average approximately 5 or more per linear foot of row, the worms are less than 1-1/4 inches long, and leaf feeding is evident, control may be justified. If a significant number of these larvae are present and they are destroying the leaves or the heads, treat immediately.
Armyworm feeding on wheat heads
Corn & Black Cutworm – As outlined in previous Pest&Crop articles, the moth flight into the state has been heavier than ever this year. Trapping is over for this year, now it is time to wait and see what is found in terms of larval feeding. Generally the moths that arrived weeks ago were attracted to winter annual weeds for egg-laying. Those eggs have hatched, and caterpillars are out in those fields now, either feeding on dead/dying weeds or starting to move onto emerged corn. Insecticides, whether soil or seed-applied, should not lull producers into a false sense of security, as larger larvae are able to continue their feeding. Timed scouting, and careful assessment of damage can go a long way in preserving a stand of corn.
Cut plant pulled under soil surface by black cutworm
Soybean & Bean Leaf Beetle – These beetles awoke from their winter’s nap some time ago and have been feeding on forages and other legumes (e.g. clover) while waiting for soybean to be planted and emerge. Amazingly, they are able to “smell” and subsequently find first emerging soybean, whether near a wood’s edge or in the middle of a large field. Once plants have emerged throughout a field, beetles will typically dissipate to non-economic levels. First planted and/or first emerging soybean seedlings should be inspected for their feeding on cotyledons and unifoliate leaves. Although this initial leaf feeding may look serious, only extensive cotyledon damage is cause for serious concern - if cotyledons are being destroyed before the unifoliate leaves fully emerge or if the growing point is severely damaged, reduced yields are likely. However, once trifoliate leaves have unrolled, soybean can tolerate up to about 40% defoliation without yield loss. It may look ugly, but they can take a beating.
Bean leaf beetle feeding on cotyledon
Eye-catching, but non-economic unifoliate leaf feeding
There are a lot of yellow fields out there, especially in the southern half of Indiana. The weed species is cressleaf groundsel, aka, ragwort, butterweed, senecio, “that mustard thing” (Figure 1). See a related article for more information on the biology and identification of this weed.
Figure 1. Yellow fields in Indiana with cressleaf groundsel
Figure 2. Flowering cressleaf groundsel
Figure 3. Fall applications of glyphosate were applied on the left field, and the right field did not receive a fall application
Figure 4. Conventional tillage practiced in the field on the left.
Figure 5. Large clods from disking
Figure 6. Fall application of glyphosate + 2,4-D Canopy EX. Taken May 6, 2006.
Within the past several weeks the PPDL has received wheat samples with virus symptoms from Adams, Posey, and Tipton counties that have tested negative for virus but positive for Bacterial Mosaic. This is the first report for Bacterial Mosaic in Indiana however not the first report in the Midwest (first report from Illinois in 1990). Bacterial Mosaic, caused by Clavibacter michiganensis subsp. tessellarius (Cmt), produces symptoms resembling viral infections. Flecking and small yellow lesions that coalesce into streaks are typically uniformly distributed over the leaf blade resulting in a mosaic-like pattern. No bacterial exudates are produced. It appears that there may be degrees of resistance among cultivars. The PPDL uses a serological ELISA test kit from Agdia Inc. to test for the presence of Cmt in symptomatic leaf tissue and multiplex PCR analysis to test for the presence of WSSMV, WSMV, WSBMV and BYDV. The following fact sheet from Texas AgriLife Extension Service provides additional information on Bacterial Mosaic: <http://amarillo.tamu.edu/files/2010/11/BacterialMosaic.pdf>
Figure 1. Mosaic like symptoms spread over the entire leaf surface (Photo credit: Tom Isakeit)
Figure 2. Magnification of advanced foliar symptoms. Unlike other bactgerial infections, neither oozing nor water-soaking is present (Photo credit: Tom Isakeit)