Update for the week of July 29th

The dominant question last week was concerning spider mite control. Several calls were received from consultants or agri fieldmen in the southern part of the state. Their question was not so much what to spray with (chemical choice) but instead when to spray. Most were scheduling stink bug sprays within a few days and wanted to know whether to add a miticide or not. Without seeing the fields, that is a difficult decision to make over the phone. My thoughts were that it could depend somewhat on how widespread the mites were in the field, the level of mite infestation and maybe most importantly – what is the weather outlook for the next 7-10 days.

Mite populations seem to hold steady in good rainfall patterns but explode during hot-dry weather. Even though we have had scattered thunderstorms for the past several weeks, there are many places where no rainfall has occurred. Last week was hot, mid 90’s or higher all week, so mites likely increased in number.

My suggestion would be to go ahead and treat mites if the weather outlook is for hot dry weather for the next 5-7 days. Most of our mites controls this season have been with abamectin (Agri Mek) at 8 oz/ac and results have been good.

Stink bug populations are still hanging around, in low numbers in many fields. However, from personal experience in a plant bug trial area in central Alabama that is located adjacent to corn, stink bug numbers have exploded in the past two weeks. Both brown and southern green species are well above the threshold level on the corn-cotton borders. Where cotton yields are promising and quarter diameter 10 day old bolls are still developing, stink bugs should be watched closely and controlled when above threshold. Cotton is at various stages now so our “dynamic threshold” would depend on where we are in the blooming-boll development cycle. Remember that 10% is our suggested threshold from weeks 3 through about 6 of bloom.

One other call was received last week concerning one or more fields in Baldwin County (Gulf Coast) infested with damaging levels of the garden fleahopper. We had several fields in recent seasons with this pest in the Mobile county area. The GFH seems to be primarily a foliage feeder but can damage every leaf in a field.

As of this date the bollworm/budworm complex is almost non-detectable, even in cotton with no caterpillar technology.

Update for the week of July 22nd

The past 7-10 days has been about as quiet insect wise as I ever remember for that time of the season.

Insect wise, we still have a few scattered Tarnished Plant Bug adults and a few immatures in some unsprayed fields – but I am not aware of a single field that has economic or treatable levels. In many instances where I have actually monitored fields, I found that part of the plant bug population is the clouded plant bug species. This species has been present in some fields in Alabama for most of the month of July.

Spider mites are still hanging around but have not exploded in recent weeks. The weather in the form of multiple thunderstorms appears to have slowed mites. Speaking of weather, some areas of the state have received multiple rain events of one to two inches or more while others have received only tenths a few times. Cotton ranges from as good as it has ever looked to knee high and blooming out the top depending on the planting date and the amount of rainfall received. In general, the earlier planted cotton that was stressed due to the heat and drought in May and June offers the least yield potential.

Back to insects now – a few stink bugs, mostly brown, are present in most fields. However, the numbers do not reflect the level we anticipated following a mild winter and the number seen on wheat at harvest time. It appears that the hot dry weather last month took its toll on stink bugs also. Boll damage to stink bugs is less than 10% in many fields. Cotton maturity ranges from the third week of bloom on late planted cotton to probably the sixth or seventh week of bloom on earlier planted fields.

Since we are at least at the third week of bloom, growers might want to consider a clean of spray for subthreshold levels of plant bugs and sink bugs in fields that have not received a foliar insecticide application yet in 2012.

This used to be the time we could also catch some escaped bollworms with this clean up spray. However, at this point, the bollworm flight statewide is very low and escaped worms are almost non detectable. Still the bug complex alone could help justify a clean up spray.

This is the way we see it on July 24, we will be back with an update as the season unfolds and conditions change.

Corynespora Leaf Spot on Cotton

I collected Corynespora leaf spot on cotton at the Plant Breeding Unit.  The cotton, which is just beginning to flower, follows cotton and is irrigated.  Weather patterns for the past week have been favorable for the development of this disease.  Much of the state probably will get a good shower or two sometime in the next 7 days.   Irrigated cotton with a dense canopy that has gotten good rains over the last two weeks is at highest risk for disease.  Given rainfall patterns over the past two weeks, cotton in southwest and west Alabama may be at highest risk for disease.  See the PP-715 Leaf Spot Management in Cotton Timely Information for more information on control procedures and recommended fungicides.  http://www.aces.edu/extcomm/timelyinfo/PlantPathology/2012/May/2012CorynesporaLeafSpotTI.pdf

Bob Kemeriat, the extension plant pathologist found this disease a week ago in a Georgia cotton field.

 By: Austin Hagan, Professor and Extension Plant Pathologist

Department of Entomology and Plant Pathology at Auburn University
149 ALFA Building
961 South Donahue Drive
Auburn, AL 36849
Phone: 334-844-5503
Cell: 334-321-8248
Fax: 334-844-4072

Insect and Weather Update for the week of July 9th 2012

The past 10 days have been characterized by heat, drought, scattered thunderstorms, aphids, and in some cases spider mite decisions. Some areas have received one or more rainfall events of 1 to 3 inches or more while others are still suffering extreme drought. Some of these storms have brought high winds, downed trees, demolished buildings and hail.

Insects have been rather quiet overall. Many field men have made aphid treatment decisions with significant acres treated. In at least one incidence, both aphids and mites were at treatment levels. Other more sporadic fields have needed adult tarnished plant bug controls. In the majority of cases the plant bug population has now shifted to immatures. In these cases field men need to switch from sweep nets to drop cloths to quantify these immature plant bugs. Two or three immatures per drop could be considered a threshold level requiring treatments, especially if “dirty” blooms are present. Pinhead square retention is no longer the best way to look for plant bug damage since they spend more time down in the canopy feeding on larger squares (which later become dirty blooms).

I have not had any calls yet, but field men in the southern areas of the state need to pay attention to stink bugs since our oldest fields are now at week three, four or more of bloom. Weeks three through six of bloom is when stink bugs are most damaging. A good threshold for treatment during this period is 10-15% internal damage to quarter diameter (still soft) 10-12 day old bolls. Look for brown areas near the seed  and warts on the inside boll wall where stink bugs have penetrated in search of a protection source in the form of developing seed. If the population of stink bugs is primarily the southern green species then we have choices of both pyrethroid and phosphates. However, as most likely the case, the population may be predominately brown stink bugs. Here we would need a phosphate such as Bidrin or either a high rate of bifenthrin and get decent suppression.

Reports were just received of an increase of small larvae on peanuts in south-central Alabama. My guess would be that they are tobacco budworms. By July 15, newly hatched larvae will more likely be corn earworms.

Pest Update

The dominant factor in cotton the past one to three weeks has been the drought and heat. The weather has impacted both the crop directly and management decisions for insects. Some localized areas received rainfall on July 1 or 2. However, most cotton remains under stress from lack of moisture.

Aphids are the insect of primary concern since populations have built in many fields, putting additional stress on plants. Most growers delayed treatment decisions for aphids until this week – waiting for either rainfall or natural diseases. However, many are wisely spraying for aphids this week.

In some fields plant bugs are also present. Adults have diminished statewide but immatures have begun to emerge in many fields. I have also noted the presence of fleahoppers (both adults and nymphs) and clouded plant bugs in the mix. Field men have reported a large increase of bollworm moths in southwest Alabama fields this week.

Another significant even in row crop insects occurred during the past week. Kudzu bugs were observed feeding on soybeans in numerous fields in Cherokee County and in other fields in north Cleburne County and near Collinsville in Dekalb County. This pest has the potential to dramatically impact soybean production in Alabama as it already has in Georgia, South Carolina and North Carolina. First of all, soybeans will need to now be “scouted” as cotton has been since the late 1950’s. Mid-season (July) sprays will likely be required which will open the door for greater problems with podworms. Additional later sprays for the Kudzu bug will also be necessary. We will talk later about scouting techniques, thresholds and the selection on appropriate chemistry.

Weather Conditions and Pest Control

First we will give an overview of weather conditions, especially since this may be impacting some of our insect and pest control decisions in the coming days. After a good moisture and rainfall pattern of about 10-14 days ago, our crops have reached a hot-drought stressed condition at present. The situation is worse in the northern area of the state where less rainfall fell during the last thunderstorm period. I saw corn wilted bad in the Tennessee Valley on Tuesday (June 19).

This droughty situation could well impact spray decisions with pests such as aphids and s. mites in the immediate days ahead. Aphids are building state wide and drought stress plants are where I am more suggestive for chemical controls instead of waiting for the natural fungus.

Tarnished Plant Bug adults are also being reported from some fields from the Tennessee line in the north to the Florida line in the south. Square retention is dropping, especially in fields in South Alabama that are a couple of weeks into bloom – these would be early-mid April planted cotton. Also in these some fields, adult brown stink bugs are being reported. We know from past years what stink bugs do to small thumb sized bolls when no larger ones are present.

If present in cotton, stink bugs will feed on small bolls to develop. Knowing this impacts the chemical that we may want to choose for TPB control. It needs to be a product that also controls or highly suppresses Brown Stink Bugs. The best options here would be Bidrin or a high rate of bifenthrin. Aphids in the picture would further complicate the chemical selected. Of the neonic type products, Centric might be the best choice for Tarnished Plant Bug adults, Brown Stink Bugs and aphids.

Three-Cornered Alfalfa Hopper damage is still evident in cotton, in reddish stunted plants that have a girdled and swollen area around the main stem. However, this damage is old now and most plants are too tough for main stem girdling by the Three-Cornered Alfalfa Hopper.

The biggest insect news of the week in Alabama was the finding of the Kudzu bug in soybeans in Cherokee County, Alabama on June 21. The Kudzu bug had been found in about 25 counties on Kudzu but this was the first find on soybeans. Alabama growers will want to lean heavily on recent research conducted in Georgia, South Carolina, and North Carolina on this new envasive pest. We need to beef up our scouting on soybeans for this pest – especially the immature stage.

Kudzu Bug Found Infesting Alabama Soybeans

The kudzu bug was detected this week in 2 soybean fields in Cherokee county which borders on Georgia where the pest was first detected in the Athens/Atlanta area in 2009. The pest has spread rapidly since it was first detected and now has been found in 7 SE states. The kudzu bug had been found previously on kudzu in 25 Alabama counties but this is the first report on soybeans. Economic yield losses by soybeans due to kudzu bug feeding have been reported in Georgia. (The following information was taken from the 2012 Georgia Soybean Production Guide)  Adult kudzu bugs are oval shaped,  about ¼ inch in diameter, and greenish brown in color. Eggs are laid in double-rowed batches of 35-50 eggs and are white in color. Nymphs are also oval shaped and are light green to brown in color and have numerous setae/hairs. Both adults and nymphs are most commonly seen on plant stems using their sucking mouthparts  to feed on plant sap. The effects of kudzu bug feeding on soybeans is similar to drought. Excessive feeding weakens and stresses the plant which can result in fewer pods per plant, fewer seeds per pod, and reduced  seed size.  Overwintering adults survive under pine bark and ground debris . Key reproductive hosts of kudzu bug include kudzu, wisteria , clover and soybeans. Adults begin laying eggs on kudzu shoots in  mid-April and continue laying eggs on kudzu for several weeks. Time required to reach the adult stage is about 6-8 weeks. These new adults then disperse to soybeans and other reproductive hosts beginning in mid-June and continuing thru mid-July. Soybeans become attractive to kudzu bug adults when plants are 8-10 inches tall. Early planted soybeans appear to be at greater risk for kudzu bug infestation compared with later planted soybeans. Adults will begin laying eggs on the underside of soybean leaves and a generation requiring about 6 weeks will be completed on soybeans. Initial field invasions tend to be more concentrated on field margins but will eventually spread throughout the field. In many situations we will begin to see immature kudzu bugs in soybeans at about the R2-R3 stage. Kudzu bugs can be scouted using a 15-inch diameter sweep net. Kudzu bug populations can be extremely high. Georgia entomologists are suggesting a threshold of one immature kudzu bug per sweep. This suggested threshold is based on 2011 field trials where a single properly timed insecticide application preserved soybean yield. If insecticides are applied when adults are still actively migrating from kudzu to soybeans (late June and early-mid July); additional applications may be needed. Research is ongoing to verify and refine management and treatment thresholds for kudzu bugs in soybean. Multiple classes of insecticides have shown activity on kudzu bugs. Insecticide treatments containing bifenthrin, cyhalothrin, zeta-cypermethrin, carbaryl, or acephate provided greater than 80 percent control 2-5 days after treatment.