Sweet Corn Report: July 31st 2014

Full Sweet Corn Report, July 31st, 2014

Hudson Valley: The full complex of sweet corn lepidopteran insects, including European corn borer (ECB), Corn earworm (CEW), Fall armyworm (FAW) and Western Bean Cutworm (WBC) adults were captured in New Paltz traps this week. Generally, fewer insects were captured throughout the season in Warwick sweet corn fields. CEW captures in the Hudson Valley (New Paltz) are averaging 0.57 per day, requiring growers to be on a 5-day schedule.

We began captures of the western bean cutworm, Striacosta albicosta, (WBC) in both Warwick and New Paltz last week with 0.4 and 0.3 captures of WBC per day respectively in green bucket traps. No treatment is required for this insect, HOWEVER, scouting for eggs should begin now that flight has begun in the upper 4 leaves of late whorl and early tassel-emergence as these fields during this stage of development are most at risk. Egg masses can be found even if no trap captures are observed. Cumulative trap catches of 100 moths should signal intensified scouting in fields nearing silk. Threshold set in Ohio for fresh market sweet corn is 1%. Upon hatch, larvae will spend a few days feeding on the tassel before moving down to the ear. Most insecticide sprays used to control ECB will also control WBC.

Western NY: The second flight of European corn borer has started, with higher ECB-E strain captures then Z strain. Relatively low CEW captures have been reported with two WNY sites over threshold. FAW emergence is also increasing across the region, predominately along Lake Erie. Highest state captures of WBC are occurring along central Lake Erie with over 13 per day in Eden, NY.

Eastern Long Island: E. LI. has very high FAW populations of 12 adults per day in Riverhead, and 9 per day in Mattituck using green bucket traps. CEW are below threshold averaging between <1.0 and 7.3 per day with Baiting Hollow on a 4-day schedule. Across the region: Highest captures of CEW are in west central PA with daily trap captures at 7.71 per day in Blair County, Curryville, PA.

Scouting should be ongoing in fields that are in the whorl and silk stage for the presence of all three major insect pests. Once the CEW adults are observed, a five day spray interval is recommended when the weekly trap catch is not greater than seven CEW’s (see chart below).

Field scouting: Check plants in a V or X pattern across the field in groups of 10. Avoid checking only field edges, and start at random, not only where you can see damage. A plant is infested if at least one caterpillar is found. Sometimes feeding damage is old and no larvae are found; this usually means that the larvae have left the plants to pupate in the soil.

Whorl and tassel stage: Typical examples of ECB feeding damage in the whorl stage are straight line pinholes as well as “window pane” damage. CEW and FAW larvae will leave ragged feeding holes in the leaves with large dark frass pellets (see photo below). ECB feeding on the tassel is usually accompanied by white or light brown frass the size of fine sand.

Silk Stage: When scouting silk stage, look for signs of larvae feeding and frass on the silk, around the ear, and in between the ear and the stalk. Pull the ear just slightly away from the stalk to look for signs of feeding or entry. Egg masses can be found in the ear zone area on the underside of the leaves, the flag leaves on the ear, and on the husk. ECB egg masses are white when first laid and then turn cream colored after a few days. The ECB egg mass will develop “black heads” just before the larvae hatch. FAW egg masses will be covered with gray scales and have the appearance of a small (about ¼”) piece of lint. CEW adults lay their eggs individually on the silk and are very difficult spot. Using the CEW pheromone trap chart below will help in determining the spray schedule.