North Carolina Pest News – September 6, 2013 (Field and Forage Crops)
NORTH CAROLINA PEST NEWS
Volume 28, Number 22, September 6, 2013
CAUTION: The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.
FIELD AND FORAGE CROPS
From: Jack Bacheler, Extension Entomologist
Cotton Insect Update
With the exception of some late cotton fields with decent levels of small bolls and a potential top crop given average conditions going forward, additional economic damage from cotton insects should be over for 2013. Additional damage from bollworms, cotton aphids, spider mites and plant bugs should be unlikely.
In late cotton fields that are still only in the 6 to 8th week of bloom, stink bugs could cause economic damage if populations are high. I suggest using an internal boll damage threshold of 15, 30 and 50% for weeks 6, 7 and 8, respectively, in these fields. Be sure to continue to assess only 1-inch or quarter-sized diameter bolls. Inspecting larger bolls will not reflect recent damage. No sense in using late season revenge or recreational sprays. In the past 2 days of conducting our annual damaged boll survey, I have seen almost no stink bugs.
At this early point with only three counties surveyed, very low levels of caterpillar-damaged bolls have been found, while stink bug damage has been relatively high. In one situation I encountered Thursday, close to the Wilson/Wayne county line, three consecutive cotton fields on my preselected route had stink bug damaged to bolls that ranged from 19 to 28% (mean = 23.7%), while just a little way down the road, I encountered three consecutive fields with stink bug damage that ranged from 0 to 4% (mean = 1.3%). Judging from agronomic and other clues, the field groups were likely managed by two different producers. One had apparently responded to potential stink bug damage while the other appeared to ignore stink bug damage. This was not a year to ignore stink bugs on cotton. In the 56 cotton fields assessed so far for stink bug and bollworm damage, bollworms have caused an average of only 0.18% damaged bolls, while stink accounted for an average of 7.4% boll damage.
It has been rewarding to see how far this year’s late, wet cotton crop has come. Some cotton fields I have surveyed appeared to have great yield potential while in others, yields will be modest indeed. Fortunately, I encountered far more of the former.
From: Dominic Reisig, Extension Entomologist
Finishing Up the Season with Kudzu Bugs
Kudzu bug populations are all over the place right now in terms of how they are developing. Believe it or not, this second generation was not as bad as I had predicted (the first generation was worse). However, we are still consistently spraying fields for this insect.
Soybeans are “kudzu-bug safe” once they reach R7 (one mature-colored pod on the plant). This goes also for our defoliating pests that don’t attack the pods or seeds (such as loopers and bean leaf beetle).
Kudzu bug population development is very erratic on a field-to-field basis. Some soybean fields have already finished their second generation of kudzu bugs and some are finishing now. There are only two generations of kudzu bugs a year so if you see adults now, rest assured that they won’t lay eggs. Adults that we see now are going to form our overwintering generation. We’ll see these bugs again next May and June in our early-planted beans.
If you’ve sprayed for kudzu bugs and are noticing adults moving back into the field, this is normal. We get very little, if any residual from any insecticide with this insect. Adults can feed and cause injury, but we don’t have great information on what sort of damage these adults can cause. My gut feeling is that these adults are hanging around in soybeans until they receive the cue to migrate to overwintering sites. We will see this happen soon as the days become shorter. Spraying these adults now is probably not economically justifiable unless populations are really heavy or beans are not near R7. Most of our early beans that are attractive to kudzu bug are mature or close to maturity.
Finally, you might see kudzu bug adults move into double-cropped beans in October like we did last year. These adults moved into fully mature defoliated beans for one last hurrah before overwintering in their favorite spots (behind loose tree bark and underneath leaf litter). We need not worry about these migrating bugs passing through our area, especially since beans should be mature.
From: Jim Dunphy, Extension Soybean Specialist, and Steve Koenning, Extension Plant Pathologist
Soybean Rust Update: September 5, 2013
Asiatic soybean rust was confirmed September 5 in Scotland County, North Carolina. There were pustules on 5 out of 50 leaves examined and these were sporulating. Sentinel plot samples from Lenoir and Cherokee were negative for rust. This is the first find of rust in North Carolina in 2013. This puts rust close enough to much of southern and southeast North Carolina to warrant a fungicide recommendation for soybeans that have started blooming and do not yet have full sized seeds in the top four nodes of the plant. The closest confirmed rust on soybeans to our North Carolina soybeans is now approximately 80 miles from Charlotte, 210 miles from Elizabeth City, 35 miles from Fayetteville, 90 miles from Murphy, 85 miles from Raleigh, 145 miles from Washington, 155 miles from Wilmington and 110 miles from Winston-Salem, North Carolina.
Rust has now been confirmed this year on soybeans in 70 counties/parishes in eight states (Louisiana, Florida, Alabama, Mississippi, Georgia, North Carolina, South Carolina and Arkansas).
Rust has progressed at a faster rate this year than in years past. With a late soybean crop, the odds of needing to apply a fungicide are increased. Now is the time to spray a fungicide in much of the state and to check spray equipment and be sure to have the proper nozzles for applying fungicides in the other parts of the state.
We do not recommend spraying soybeans that have not started blooming with a fungicide to control Asiatic soybean rust. Such pre-bloom applications have seldom improved yields. Once soybeans start blooming, we would recommend spraying if rust has been confirmed within 100 miles of the field.
Resources for Soybean Rust in 2013
Some sources for more detailed information on Asiatic soybean rust are listed below:
USDA soybean rust web site: http://www.sbrusa.net/
North Carolina Agricultural Chemical Manual: http://ipm.ncsu.edu/agchem/
From: Steve Koenning, Extension Plant Pathologist
Physiological Scorch and Disease
Some soybeans exhibit a symptom referred to as “Physiological Scorch”. When there is extensive chlorosis (yellowing) between the veins of the leaf, or necrosis (dead tissue) between the veins, which may occur on the top of the plant or throughout the plant, we refer to this symptom as physiological scorch. It typically occurs when the roots and vascular system aren’t effectively doing their job, such as when root and or stem pathogens restrict the vascular system when soybean is in the reproductive phase. A number of pathogens can cause this symptom. Most commonly, this symptom is associated with “SDS” (sudden death syndrome) or “CBR” (Cylindrocladium black root rot) of soybean. Lab and or visual analysis are needed to distinguish between the two diseases. Other diseases that may occasionally cause these symptoms include Dectes stem borer, Phytophthora root and stem rot, stem canker and charcoal rot. Regardless of which disease is present, fungicides are unlikely to provide a remedy since these are a result of root rots or other vascular disease.
Soybean Stem Canker, Phytopthora Root Rot and Aerial Blight Detected in North Carolina
Soybean stem canker and Phytopthora root rot have been identified in North Carolina in the past week causing symptoms which include dying and physiological scorch. Also, aerial or web blight caused by Rhizoctonia has also been identified (fungal webbing may be seen on pods, stems, and leaves. Proper diagnosis is important, fields infected with aerial blight can be treated with Quadris, but diseases that present the physiological scorch symptom will not respond to fungicides.