ISSUE 15 Autust 13, 1998
APHIDS IN SUNFLOWER
One of the most common calls this week concerns a build up of aphids in sunflower fields. It certainly isnt every field. The infested fields take on a wet or shiny appearance due to the buildup of honeydew on the foliage. Along with the honeydew, black sooty mold grows on the honeydew where the humidity is high, lower in the canopy.
Other items you see include the white cast skins of the growing aphids. In some cases, you may see off colored aphids that look swollen. These are the mummies of parasitized aphids that have been killed by the larvae of tiny wasps. You may also find aphids that are "fuzzy"; these are aphids that have been infected with a fungus and have died. These fungal outbreaks can cause a rapid decline in an aphid population.
Should we be concerned about aphids in sunflower? Normally, we would say no. Infestations have been observed by researchers before with no apparent impact on yield. BUT, we do not have any information that would indicate a level that might cause harm.
Some contacts this week have indicated that infested plants are taking on a wilted appearance. This may or may not be due to the aphids. It is more likely due to moisture stress that a rain shower would help correct. It was suggested that fields with aphids that are stressed be checked early in the day to see if they have recovered their turgid state during the night while it was cooler. If the plants have recovered, moisture is the likely problem, although this doesnt rule out aphids having some impact.
Should you treat for these aphids? If this is the only insect pest present at high levels, probably not. If flowers are beginning to bloom and seed weevils are present at levels just under the 7 weevils per head threshold, then it might be advisable to treat. Under this scenario, the treatment would be directed at multiple pests.
What product might you use? My experience with the pyrethroid (Asana, Baythroid, Scout, and Warrior) insecticides has taught me that these products are not the best choice where aphid control is desired in a field. In other crops I have worked (examples, cotton and pecans), aphid populations that have been exposed to pyrethroid sprays have developed resistance to these insecticides. I am not saying this is the case with the sunflower aphids. Control may be very good. However, there is a risk that control would be less than adequate and the aphid population could rebound quickly to the pretreatment levels, especially in the absence of predator insects such as lady beetles and green lacewings.
So, the insecticides to consider if aphids are part of the mix would be Lorsban, methyl parathion and 6-3 ethyl, methyl parathion. These products have performed well at controlling most aphids.