August 17, 2007

Sunflower head moths are about 5/8 inch long and feed on the pollen-laden head.

The major late season insect in confection sunflower is the red seed weevil, a particular pest during pollen shed (R5 stage). 2007 has brought a late "pollination season" infestation of sunflower head moth to the High Plains and in particular to all of the sunflower production areas of western Nebraska. This is another "pollen shed" insect — that is, egg laying occurs just during pollen shed.

Confection fields are normally sprayed for seed weevil at first bloom which would also control head moth. Some of the early fields are now in the R6 stage (pollination complete with petal drop) but are exhibiting head moth larva infestation readily visible under the bracts. It is unusual to occur this late and has caught many growers off guard. We have not had a serious head moth infestation in years. Pheromone traps at the High Plains Ag Lab at Sidney have measured 30 adults per night (with four being the threshold) with other trap sites also reporting high numbers.

Did spraying with pyrethroids not work? Pyrethroids have a residual which is a function of rate — a day per ounce, for example. The R5 stage usually lasts ten days to two weeks so a second spraying for seed weevil control is common for many confection producers with the current 23 to 25 cents per pound price. This usually makes head moth scouting a moot point. Also, later plantings (after June 1) usually avert head moth flights but this year any sunflower approaching or finishing pollination at this time should be monitored closely. This recommended renewal of scouting for the adult head moth may indicate that the second spraying should occur sooner rather than later. Once the initial insecticide spraying residual is gone, the head moth adults are right there. Egg laying occurs just during the pollination stage for these insects.

In two to three weeks the second generation of adults emerge to further infest other fields. These pests also are in wild sunflower in wheat stubble and road ditches. All of the conditions have presented a "perfect storm" scenario for head moth development.

Head moth adults are tan-colored, cigar-shaped and about 5/8 inch long. They fly at the slightest motion and are difficult to find during the day. At dusk or evenings they can be found on heads feeding on the pollen or at night with a flashlight.

Sometimes head moth larva can be found on the surface of the head but are more easily found around the bracts where they begin their task of depleting the meat out of 12-15 seeds per larva. This is a quantity issue for all sunflowers.

The seed weevil larva only eats part of the meat of one seed and that seed is heavy enough to stay in the combine bin and eventually moves to the consumer's supply. This is a quality issue and can mean rejection of the load.

Larva feeding can also lead to other damge. Any injury or opening to the head provides opportunity for the development of Rhizopus head rot with humid conditons. Extreme cases of Rhizopus will result in the head falling to the ground. Careful monitoring should continue through all bloom stages.

Sunflower Rust

To add to this, leaf rust is being reported in sunflower — mid-plant infection at completion of R5 stage begins the questionable area of return. Monitoring is needed.

Bill Booker
Extension Educator, Box Butte County