Brown stink bug numbers have continued to increase in eastern Virginia from the Northern Neck to the Tidewater region. We have scouted fields in Suffolk and Caroline County with higher than threshold infestations spanning the entire field. Infestations in most fields remain confined to border rows and the majority of infested fields are near where wheat has been recently harvested.
Many growers are facing the decision to treat. Previously I had reported a threshold of 1 bug per 4 plants. In order to be extra protective during ear formation and elongation, treatment at the 1 bug per 10 plants threshold can be justified for heavily infested fields. More information about stink bugs in corn can be found here – NCSU corn stink bug management considerations.
The ability of stink bugs to injure corn depends heavily on corn growth stage. Trials at the Tidewater Research Station have shown that stink bug feeding does not always reach developing ears. The photo below shows a healthy ear developing (VT growth stage) despite multiple feeding lesions to the outside of the stalk. This may be good news for Virginia growers. We cannot determine if yield was effected in these plants until later this season.
This week, we will be rechecking fields that were treated with aerial applications and post updates on the effectiveness of these sprays.
Coinciding with the wheat harvest, brown stink bugs have been moving into pre-tassel corn in the southeastern region of our Virginia. The entomology department has scouted fields over threshold in Chesapeake and Virginia Beach. So far this season, stink bugs are present in low numbers in northern, central, and western regions of the state.
Thresholds for stink bugs in field corn are (From Dominic Reisig at NCSU):
one stink bug per four plants during ear formation, elongation, and pollen shed
one stink bug per two plants nearing the end of pollen shed to the blister stage.
Plant injury from stink bugs may include:
Holes in leaves and, in severe cases, twisted plants.
It is important to remember that this bug typically infests on edges of fields and in spotty locations. It is possible, though unlikely, that stink bugs will infest an entire field. Spray volume is critical if you decide to spray – use a high volume to ensure that sprays penetrate the canopy. Insecticides labeled for stink bugs in corn (e.g., Baythroid XL, Karate Z, Warrior II) must come into direct contact with insects to kill them.
The head of the EPA, Scott Pruitt, signed an order last night denying the petition to ban chlorpyrifos (Lorsban). This decision will allow peanut growers in our area the continued use of this insecticide for the foreseeable future, perhaps until 2022 when the EPA is required to reevaluate safety of this product. The environmental group that filed the 2007 petition to ban chlorpyrifos has announced its plans to appeal the decision. More information can be found here – https://www.epa.gov/newsreleases/epa-administrator-pruitt-denies-petition-ban-widely-used-pesticide-0
Our recent warm weather has done more than wake up your plants – it has signaled to many insects that it is time to start feeding and reproducing. Prompted by a call from ANR agent Mike Parrish in Dinwiddie County, I spoke today with Kathy Flanders at University of Auburn about her recommendations to mitigate insect injury in store grain. Her #1 suggestion – turn on those fans! Your goal should be to keep the temperature inside your bin below 60 degrees. Make sure and leave equipment running long enough to cool the entire structure. If you are unable to keep temperatures below this threshold, or if our nights do not stay cool, make sure to take samples regularly to scout for insect injury. Consult this guide for management recommendations specific to the Southeast: http://www.aces.edu/pubs/docs/I/IPM-0330/IPM-0330.pdf.
The EPA is in the process of reviewing some of our older, broad-spectrum classes of insecticides. The comment period is now open for the preliminary ecological risk assessment of pyrethroids. I strongly support the need for continued availability of these materials because they are relatively safe for mammals and biodegradable. Importantly, pyrethroids are the only option for pest control of certain insect pests in some cropping systems. Entomologists, including myself, at universities throughout the Southeast have expressed their support for pyrethroids in a letter to the EPA. However, the EPA is really looking to hear from people that use these products responsibly. The below link provides a tool to make comments on EPA dockets without looking up each product individually. It also includes the type of information that is most helpful and a template to follow if so desired. Comments from our Virginia growers will be much appreciated!