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.

Current Insects in Cotton at Economic Levels

Today I would like to discuss three insects that are occurring in cotton at economic levels in certain fields. Two of these insects are actually impacting other crops, particularly soybeans and peanuts, as well.

Adult tarnished plant bugs (TPB’s) are being reported at moderate to high levels in some fields statewide. More findings are reported each day and there are likely many fields where they are present but have not been observed yet. At this point, no one has reported high pinhead square loss. This square loss is what we like to base our treatment decisions on. However, based on past experiences, once the adult TPB’s are present it is just a matter of time until some level of square loss is detected. These are all migratory adults that have moved into cotton from wild hosts. They will feed on pinhead squares, which cause abortion, and also deposit eggs in the plant stems. These eggs will hatch in two plus weeks into an immature field generation. The longer the period that adults are allowed to roam in fields, the longer the period of hatching immatures will be in coming weeks. Knowing this, growers can make their own decision as to when controls should be applied.

The second insect I will mention is the tobacco budworm (TBW). An extended flight of budworms has been ongoing in various areas for about two weeks already. This is of no significance to 98% of the states acreage that is planted to Bollgard II or WideStrike varieties. However, this makes a tricky situation in conventional cotton that may need plant bug sprays during this TBW period. This TBW flight is also impacting later planted peanuts that have a limited amount of vegetative growth. Budworm moths seem to be attracted to peanuts with a vegetative width of 3-4 inches. Earlier peanuts that have six of more inch vegetative width do not appear to have as many budworms present. We collected about 250 quarter inch budworms yesterday at Headland, Alabama on about 600 row feet. This was not what I would consider an economic or treatable level. However, up to four budworms per row foot have been reported in some fields and controls, with the newer chemistry, have been applied.

The third insect that is causing widespread concern in cotton at present is the three-cornered alfalfa hopper (3CAH). Numerous fields in the Tennessee Valley area of northern Alabama have had damaging levels of 3CAH reported. This problem has extended as far south as Talladega County. Treatments have been applied. Soybeans are also experiencing a problem with this insect, even more so than cotton, and over a much larger geographical area. 3CAH damage is caused by the girdling of the main stem of both cotton and soybeans by both the adult and immature 3CAH. No good thresholds exist from Alabama research. Usually this problem and damage is greater on field borders but consultants have reported damage field wide in both cotton and soybeans. Treatment thresholds are difficult to develop for 3CAH, just as they are for grasshoppers. Treatments sometimes have to be made based on the risk that certain species present, and not the level of damage observed. Sweep nets are very effective in documenting the number of 3CAH per row foot.

3-Cornered Alfalfa Hoppers Attacking Seedling Soybeans

Three-cornered alfalfa hoppers (3CAH’s) have been found in large numbers in north Alabama soybeans this year and some fields have already been sprayed twice. Numbers of 3CAH’s are comparable to the relatively high numbers observed in 2010. 3CAH girdling of seedling soybeans can result in plants falling over later when strong winds occur. Often plants that have been girdled and do not lodge produce normal yields. The current treatment threshold for soybeans less than 10 inches tall in Alabama is to treat when pests or damage is noted and stands are threatened. The Mississippi seedling soybean treatment recommendation for 3CAH is to apply insecticide from plant emergence to 10 inches in height when the plant stand is reduced below the recommended plant populations. Georgia’s soybean IPM guide recommends treating soybeans up to 12 inches tall when 10% of plants are infested with nymphs and/or adult 3CAH’s. The most common method for sampling soybeans for 3CAH is the sweepnet.  There is no research based threshold for seedling soybeans which states the number of 3CAH’s per sweep for a given row spacing that is needed to trigger an insecticide application. Reports indicate numbers of 3CAH’s per sweep are presently higher in drilled soybeans than in soybeans planted using a 30 inch or greater row spacing.  Soybean insecticide seed treatments to date have provided good control of 3CAH’s for approximately 3 to 4 weeks after planting but with the heavy pressure we are currently seeing even fields that have been planted with insecticide-treated seed should be monitored for damage. 3CAH damage tends to be greater in soybeans planted behind wheat than in full-season soybeans. Seedling soybeans sprayed with an insecticide frequently see 3CAH populations rebound within 2 weeks and another insecticide application may be required.

By: Tim Reed, Extension Entomologist, Auburn University

Tobacco Budworms in Early Season

A tobacco budworm moth flight this week resulted in eggs being deposited in cotton terminals as far north as Prattville, Alabama. On June 5^th, about 40 budworms were collected from 100 tobacco plants at Prattville. All plants had feeding signs but parasites and predators were working on the population. Budworm feeding was also noted on tobacco planted as a sentinel crop at Headland, Alabama yesterday (June 7^th).

A call was received a few minutes ago about what is believed to be budworm larvae on peanuts from the Covington County Alabama-Florida panhandle area. These peanuts were young and had a limited amount of foliage with up to four budworm larvae (3-7 days old) per row foot. This same situation occurred about 3-4 years ago where budworms defoliated some fields of peanuts in June. At this early stage of the season, controls may be necessary due to the limited amount of vegetative growth of the peanuts.

Tarnished Plant Bugs Found

A significant level of adult tarnished plant bugs was found this morning (June 4^th) in nine true leaf cotton in Autauga County Alabama. Levels of up to five adults per 100 plants were reported. No pin head square loss was observed but it is likely just a matter of time until damage is observed. Controls are planned.

In addition to these tarnished plant bugs, eggs, most likely tobacco budworms, were also reported.

Announcing Alabama Scouting Schools

Announcement: Alabama Cotton Scouting Shortcourses Meeting Sites and Dates

• June 12^th (Tuesday) 2012; Autaugaville, Alabama- County Agricultural Center
• June 13^th (Wednesday) 2012; Headland, Alabama- Wiregrass Research Center
• June 19^th (Tuesday) 2012; Belle Mina, Alabama- Tennessee Valley Research Center

All meetings begin at 8:30 AM

Contact Person: Dr. Tim Reed (256-627-3450) or Dr. Ron Smith (334-332-9501)

Note: Dr. Austin Hagan will discuss cotton diseases at the Autaugaville and Headland sites. Dr. Tim Reed will cover soybean insects at all three sites.

Following are thirteen questions that represent the type of information that will be discussed.

1.      Why are grasshoppers easier to control in March/early April than May?

2.      If a foliar is needed for thrips suppression, when is the ideal stage of cotton to apply it?

3.      If you see damage to cotyledon stage cotton (no till) planted behind corn residue, what is the most likely culprit: snails, slugs, or pill bugs?

4.      What is the best method to determine when plant bug controls are needed in pre-bloom cotton?

5.      How would you measure the number of tarnished plant bugs in post bloom cotton?

6.      You are at week four or five of bloom, what would be the threshold for stink bugs?

7.      Under what conditions (situation) would a phosphate insecticide give better control of stink bugs than a pyrethroid?

8.      What new thrips insecticide entered the market this season and does not flare aphids or spider mites?

9.      Suppose you find high numbers of fall armyworms feeding on grass in your cotton field border- should you prepare to spray the cotton?

10.   How old does a green boll need to be to be safe from stink bug damage?

11.   Under what conditions would aphids be more of an economic pest or problem?

12.   At what stage is cotton normally beyond thrips injury?

13.   How long should you wait to evaluate control behind a stink bug spray?