Highest Threat Remains in Most Southern and Coastal Regions
Situation
A brief warm spell pushed late season corn development this week, but more cool weather on the way should slow growth and pest pressure over the next few days. Crop quality continues to be very good, and insect pressure continues to be fairly moderate as we begin to wrap up another corn season. Next week’s newsletter will be the last issue planned for this season.
European corn borer: Most trapping sites caught corn borer moths this week, but numbers vary greatly by location. These moths will continue to threaten any fresh silking corn remaining in fields that are not on a spray schedule for corn earworm. Farmington, New Gloucester, Nobleboro, Oxford, Poland Spring, Sabattus, Wales and Warren were over the threshold of 5 moths per week in silking corn. The New Gloucester, Oxford, Poland Spring and Sabattus sites were not on spray regimes for corn earworm, so silk sprays were recommended. European corn borer feeding damage in pre-tassel corn was not over the 15% threshold in the few locations with young corn remaining.
European Corn Borer Larva on Ear, photo by David Handley
Corn earworm: Corn earworm moth counts were lower in most sites this week. Cool evening weather will probably keep activity low over the next few days. A 4-day spray interval was recommended for corn earworm on silking fields in Cape Elizabeth and one Lewiston site. A 5-day spray interval was recommended in Levant, Wales, Warren and one Dayton site. A 6-day spray interval was recommended in Charleston, Nobleboro and Palmyra.
Fall armyworm: Moth captures were erratic this week; with many sites catching no moths while others had very high counts. Feeding damage from larvae was also not as prevalent this week, although there are only a few fields left that are not yet in silk. Fields in Cape Elizabeth, Dayton, Monmouth, New Gloucester, Nobleboro, and Wales exceeded the threshold of 3 moths per week in silking corn. However, only the Monmouth and New Gloucester sites were not on a spray regime for corn earworm. Fall armyworm feeding damage did not exceed the 15% threshold in any of the sites with pre-silking corn remaining.
Corn Rust: We found several fields showing symptoms of corn rust this week. This fungus disease causes reddish-brown pustules to form on the leaves, stalks and husks. When the spores get spread over the husks, it can diminish the visual quality of the ears. A fungicide spray for rust is only recommended when infection occurs prior to tassel. Later infections are unlikely to cause enough damage to justify control measures.
Rust on Corn, photo by David Handley
When Should You Stop Spraying?
When a silking cornfield is under a recommended spray interval for corn earworm, spraying may be stopped once the silks have become thoroughly dried and brown. However, if earworm pressure is very high (e.g. 91+ moths/week) and/or fall armyworm moths are over threshold (3+ moths per week), then spraying should continue until either the moth counts drop, or you reach the required days before harvest (dh) for the product being used.
Source : umain.edu
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