Sunflowers

Sunflower Information:

To jump to insect information, click here. Weed and fungicide information is below.

Fungicides:
A June, 2008, article in Sunflower magazine suggests that Headline fungicide, when applied at early bloom, can significantly improve sunflower yields. Increases of over 500 pounds per acre are cited, and a three average of 205 pounds per acre is claimed.

Plant health is improved, according to the article, so that disease prevention is likely not the only reason for increased yield.

According to Vince Ulstad, BASF Ag Products, Headline suppresses the amount of nighttime respiration going on within the green plant cells, and this increases the concentration of an enzyme called nitrate reductase, which is the enzyme responsible for helping the plant convert nitrate-nitrogen — the form the roots take up from the soil — into the amino form, which is the one laid down in amino acid and proteins. The result is a smoother transition in the plant’s nitrogen conversion process.

Since the fungicide treatment occurs at early bloom, it can almost always be tank-mixed with a regular insecticide treatment, thereby saving the cost of application.

Sunflower growers should read the entire Sunflower magazine article.

Weeds: Sunflowers emit natural toxins which reduce weed competition, so the main strategy for weed control is get a clean stand established.  After that, there are few concerns about weed pressure. 

Normally, a pre-emergence herbicide will accomplish this task, with the normal caution that post-application moisture is required to activate the herbicide.  In addition, some sunflower herbicides require immediate mechanical soil incorporation to mitigate the damaging effects of sunlight: photodecomposition.

A secondary concern is that flowers sometimes create intense volunteer pressure in succeeding crops.  These volunteer flushes can normally be controlled with herbicides, but in some cases, two applications will be required to control secondary flushes.

Insects: Insects in sunflowers are generally controlled with the same strategy: control the adult to prevent egg laying, since the larvae are generally difficult or impossible to control.  (The exception to this rule are the defoliators: see below.) This means that careful scouting and timely applications are required, since a delay can result in unwanted egg laying.  The problem is complicated by the fact that flowers often host a very large number of insects, of which only a portion are harmful to crop production.  

There are four basic types of insects: those that attack the planted seed, defoliators, stem borers, and bloom insects.

Seed treatments can help on the first category, and defoliators, such as the sunflower beetle and painted lady butterfly (see above photo) are not common in our area.

Stem weevils are increasingly a problem in the tri-state area.  In 2008, we treated more fields than ever before, partially because of elevated prices, but also because growers reported yield losses in the previous year. Careful scouting is required, as the insects can be difficult to find, and will "hide" when disturbed by the scouting process. If you don't move carefully, they will drop onto the soil and become very difficult to spot. If you can't scout them yourself, it might pay to hire a consultant: yield losses can be in the hundreds of pounds per acre in severe infestations.

The eggs, which are generally laid at the base of the stalk, hatch larvae which bore into the stalk and cause yield loss from girdling and as disease vectors. Yield loss occurs from disease, loss of plant vigor, and most significantly, lodging prior to harvest. Stalk breakage often occurs very close to the ground.

Colorado State University says that adult weevils should be scouted when as early as 600 degree-days. They recommend treatment if 8 weevils are found on 25 scouted plants--five groups of five plants. The adult female can lay as many as 20 eggs per plant.  These recommendations were based upon prices much less than the 30 cent price which was available in 2008.

The most significant yield loss is due to lodging before harvest, especially if high winds occur. Early harvest can help, and defoliants can dry the crop early, allowing an earlier harvest.  But the best treatment is a timely insecticide application to control the adults. Click here to see a picture of the stem weevil.

Head moths and seed weevils are the most commonly treated bloom insects in the tri-state area.

Head moths adults are grayish moths which roll up their wings upon landing, resulting in a distinctive cigar shaped insect.  The moths lay eggs which hatch into larvae which initially consume pollen and florets, then bore into the seeds where treatment is much less effective. The larvae pupate in the soil, and in a warm winter, it is possible for them to over-winter in our area, but it is not common.

The moths are about 1/2 inch long. To see a pop-up picture, click here. Head moth is the most serious insect in sunflowers, since left untreated, they can cause a complete yield loss, and because "larval feeding provide(s) multiple infection sites for Rhizopus fungi that can quickly rot the entire head. Rhizopus infections also invade vascular tissues and can seriously impede seed fill." (Quote is from J.P. Michaud.)

Moths are best scouted in light winds, walking carefully through the field. Scouting just after sunset, with a flashlight, is also recommended by KSU. Normally, two moths per five plants is considered economic. At higher prices, such as we had in 2008, one moth per five is probably enough. Moth activity can also be monitored with commercially available pheromone traps that attract and capture male moths. If the traps exceed four moths per trap, immediate scouting is indicated.  Treatment should be ordered when the flowers begin to bloom, and one treatment is normally enough, although scouting should not cease after treatment.  Late treatments can allow larval escapes: timely treatment is critical.

The moths arrive from the south, carried on the winds, and they find the blooming flowers by smell. Earlier planted flowers may have greater infestations, but even late plantings can be affected. Moths can complete a life cycle in 30 days, so a second generation might infest late plantings. 

Seed weevils are easier to find: simply spray the head with a insect repellent, and you will find about 60-70 percent of the 1/10 inch long weevils as they move quickly out of the head.  CSU recommends you allow for this 30-40% error when counting insects. 

For confectionary flowers, one weevil per head is considered economic, because of the dockage penalties.  For oilseed flowers, ten weevils per head requires treatment for !2 cent flowers.

Treatment is at early bloom, and scouting can begin as soon as ray petals develop. To see a red seed weevil, click here.  

To download the 2008 KSU Sunflower Insect Management Guide, click here. (PDF, 276Kb).