Sunflower enters critical reproductive stages

Sunflower at the R-3 stage, prior to flowering and pollination. (Photos by Bill Booker)

Pollination is also a critical time to scout for insects. The sunflower head moth and seed weevil are active and reproduce during this period by feeding on the pollen – it stimulates egg laying. By controlling the adults, egg-laying can be controlled. Once egg laying starts it is almost impossible to control the larva protected within the sunflower head. The R5 pollination stage lasts about 10 days so preparation and efficiency are crucial.

The sunflower head moth (at left) is a concern for all sunflower producers. They can be found on the pollen laden head in the evenings or early mornings or even at night if you use a flashlight. It is cigar-shaped and grayish, about 5/8 inch long and comes in on the southerly winds. The economic threshold is one to two adults per five plants. Spraying, if needed, should be done when 10-20% of the plants in the field are in bloom. The rule of thumb is to call the sprayer when 10% of the plants show the bloom (yellow ray petals). By the time the plane gets there 20% should be showing blooms. Each head moth larva can eat all the meat from 10-15 seeds which means the remaining light shell goes out the back of the combine. Head moth damage is a quantity issue.

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

The sunflower red seed weevil is about 1/8 inch long and will surface anytime you rub the top of the head with your hand or spray it with insect repellent. The economic threshold for confection sunflower is one to two per plant. Red seed weevil larvae produce a quality issue because only a portion of the meat within the seed is eaten. The seed will be heavy enough to stay in the combine and thus make it into the bag at the store. Current confection contracts specify control and spraying at least once. Spraying once using the head moth criteria listed above will usually suffice. Some contracts require spraying twice -- then spray at or just before first bloom and again about a week later. Check the product label for the chemical’s residual. The residual could be a day per ounce so seven ounces could be resprayed seven days later.

Each red seed weevil larva affects only the seed it is in so quantity is not usually an issue; however, 10-15 seed weevil per oil sunflower head would be an issue. With the red seed weevil, quality is usually the issue. There is also a gray seed weevil and it is like the red seed weevil except the larva eat the whole seed and the shell goes out the back of the combine. These would be a concern if the scouting revealed head moth numbers.

Uniform stands allow for better treatments

Good uniform stands are key to good yields in any crop. Part of a good sunflower yield is spraying at the proper time — when as many plants as possible are in the same stage. A uniform stands will allow more consistent insect control. Plants in different stages could harbor another round of meat eating larvae.

Automatic spraying clauses in confection contracts almost eliminate the need for scouting — unless you spray just once. Then you would need to monitor. A key benefit here is that spraying at the correct times controls both the head moth and seed weevil.

Bill Booker
Extension Educator in Box Butte County

Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.

Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.

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