ISSUE 11 July 24, 2008
SUNFLOWER BUD MOTH DAMAGING TO SUNFLOWER BUDS
Larvae of the sunflower bud moth, Suleima helianthana (Riley), have been observed damaging sunflower buds in R1-R3 sunflowers. Typically, most of damage occurs mostly in the stalk. However, this year sunflower bud moth emergence is delayed and larvae are feeding in the bud causing injury to the developing head (see photograph).
The only time yield loss is noticeable is when larvae burrow into unopen buds, preventing proper head development. The larvae normally do not feed on developing seeds but confine feeding activities to the fleshy part of the head. The larva has a dark head capsule with a smooth, cream-colored body and is 0.31 to 0.43 inch (8 to 11 mm) at maturity (see photograph).
There are two generations of sunflower bud moth in North Dakota. Adults emerge from overwintering pupae between the last week of May to mid-June. A few days after adult emergence, eggs are deposited on the terminals of immature sunflower or on the receptacle of mature sunflower. Eggs also are deposited in leaf axils. The hatched larvae begin tunneling into the sunflower plant. The initial infestation in mid-June is characterized by an entrance hole surrounded by black frass, or insect excrement. Mature larvae pupate within the sunflower plant. Pupae move to the opening of the entrance holes formed in the stem or head tissue so that adults can emerge easily. The second generation adults appear in August. Infestation by the second generation larvae is not economically important.
A field monitoring scheme and economic threshold has not been established for this insect since it is not of economic significance most years. Insecticide use is NOT recommended for control of sunflower bud moth, because the larvae are protected when feeding within the sunflower plants. As a result, insecticides will have limited efficacy.
BANDED SUNFLOWER MOTH EGG LAYING UNDERWAY
Eggs of banded sunflower moth have been found on R3 stage sunflower fields. Fields should be scouted now for egg laying activity, especially R3 sunflower fields. Please refer to Issue 10 of the Crop & Pest Report for more information on scouting. The map from the pheromone trapping in North Dakota indicate increasing populations of adult moths, especially in the northern tier along the Canadian border.
NEW FORMULATION OF LORSBAN® FOR 2009
Dow AgroSciences will be releasing a new formulation of chlorpyrifos called "Lorsban Advanced®" in 2009. It features: lower odor than Lorsban-4E®, comparable efficacy, water-based formulation, and fewer VOCs (carbon-containing substances that, when exposed to air, volatilize into gases that contribute to ground-level ozone formulation). Lorsban Advanced® will be registered on the same crops as Lorsban-4E®, and listed in the North Dakota Field Crop Insect Management Guide for 2009.
SOYBEAN APHIDS INCREASING IN RED RIVER VALLEY
Soybean aphid numbers are increasing in the Red River Valley area and eastern counties of North Dakota. Most fields still have low numbers, but a few fields are approaching threshold. This is the time to scout and monitor your fields for soybean aphid. The economic threshold for soybean aphid in the upper Midwest is:
250 aphids/plant in 80% of the field and with soybean aphid numbers increasing.
The economic threshold of 250 aphids/plant was arrived at through research conducted over a three year period at 19 locations in the northern US including North Dakota. The economic threshold was established to give growers a seven-day lead time for insecticide application before aphid populations reach a level where economic loss actually begins. Even though soybean market prices are high, the 250 aphid/plant threshold is still valid. This is because 250 aphids/plant is lower than the population at which yield loss can be measured and attributed to aphid injury. What this means in practical terms is that the lead time for insecticide application is reduced from seven days to three or four days. Therefore it is critical that growers monitor their fields closely.
NDSU Extension Entomology has received a few calls from growers asking whether they should tank-mix an insecticide with their last glyphosate application even though soybean aphid numbers are not at threshold. We do NOT recommend this practice, nor do we recommend any insecticide application when the economic threshold has not been reached. Applying insecticides too early to control soybean aphid may result in a second aphid invasion, which will require a second insecticide application. Insecticides also kill natural enemies of soybean aphid (such as lady beetles and damsel bugs), and re-invading aphid populations can increase very rapidly in the absence of natural enemies. Some vendors are offering guarantees on second insecticide applications. While the guarantee covers the chemical, it may not cover application costs. There is also the risk of spider mite flare-up in fields that have been treated twice with pyrethroid insecticides because beneficial mites have also been killed. This may require a third application using an organophosphate insecticide (such as Lorsban) to control the spider mites. Natural enemies keep aphid populations from growing rapidly and may even keep aphid populations from reaching threshold. Conservation of natural enemies is of paramount importance in controlling soybean aphid - don’t spray unless and until you have to!
Most fields are currently in the R1 growth stage (beginning flowering), though some are still in late vegetative (V) stages. The 250 aphid/plant threshold is valid from late vegetative through the R5 (early seed development) growth stage. Research has shown that insecticide applications at R6 (full seed) and beyond do not give a yield benefit. Therefore, insecticide applications for soybean aphid are not recommended after the R5 growth stage. Pyrethroid insecticides (such as Warrior) offer good control of soybean aphid. Several pyrethroids are labeled for soybean in North Dakota. Be sure to read and follow the label for application rates and pre-harvest interval restrictions.
Extension Entomology Research Specialist