Kudzu Bug Management and Control in Alabama Soybeans

Ron Smith, Extension Entomologist, Auburn University

The Kudzu bug has become a major economic pest of Alabama soybeans in certain fields throughout the state in recent weeks. Populations as high as 50 or more adult bugs per plant were observed in early June. Some of these fields now have 200 or more immature bugs per plant (late June). Calls are being received from growers and field men in recent days from all over the state.

Kudzu bugs are most highly attracted to early planted (April and early May) soybeans. Beans planted later, for example following wheat harvest, are much less attractive.

The primary question asked are when should soybeans be treated and what insecticide should be applied. The second part of the question is the easiest to answer. Most pyrethroid insecticides do a good job of controlling Kudzu bugs. Working thresholds have been previously established by entomologists in Georgia, North Carolina and South Carolina. For pre-flower vegetative beans a treatment threshold of five adults per plant is suggested. After flower, a threshold of one immature per sweep, with a sweep net, is recommended. As an alternative to sweep-net sampling, visual inspections of insect density lower in the canopy will suffice.  If immature kudzu bugs are easily and repeatedly found on the leaf petioles and/or main stems, treatment is likely warranted. However, these threshold guides may be modified slightly based on the number of egg masses that are continuing to hatch.

Kudzu bugs have two generations per season on soybeans. Adults move from Kudzu to early planted soybeans in the spring, deposit egg masses and eventually die. The immatures then hatch and eventually become adults after about six weeks and begin to deposit eggs for the next generation.

A limited number of Kudzu bugs may appear in beans season long. The most efficient and economic use of insecticides occurs when an application is made when the majority of the population in each generation is in the immature stage. Some fields have already exceeded treatment threshold and will likely require two or more sprays during the 2013 season. Fields with lower populations may be able to wait until mid-July or later for a treatment. Only one application may be needed in these fields during the 2013 season. 

Applications made when a high number of unhatched egg masses are present may have to be repeated within one to two weeks. Our goal should be to strategically time these insecticide applications for maximum effectiveness. Treating soybeans repeatedly at close intervals has not resulted in yield increases over fewer well timed applications. The key point is for growers and field men to focus on the peaks of immature Kudzu bugs as we move through the 2013 season.

There will be no way to economically prevent yield losses to Kudzu bugs and minimize inputs without monitoring or scouting soybeans weekly just as we have done in other row crops for decades. Kudzu bugs are not the end of the world for soybean production in Alabama but they do create a new day. Pictures of adult and immatures are available on Ron Smith’s blog http://alabama-insects.blogspot.com/. Basic Kudzu bug information can be found at http://www.clemson.edu/extension/Kudzubugs/index.html. Updates on the Kudzu bug status will be posted on the www.alabamacrops.com website. The Extension Soybean IPM guide has recommendations for Kudzu bugs on page six http://www.aces.edu/pubs/docs/I/IPM-0413/IPM-0413.pdf. Also, there is a podcast now available here http://agfax.com/2013/07/01/first-time-with-kudzu-bugs-listen-up/.

Adults

Egg Mass

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.

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

True Armyworms Spotted in Early April

True Armyworms were reported on April 2^nd feeding on rye near the Wiregrass Research Station (near the Headland, AL airport), in Henry County. This insect had previously been reported from the Coastal Bend of Texas to South Georgia and as far north as Kentucky. The larvae feed mostly at night and may not be found in daylight hours until digging into the soil surface debris. The larvae vary from green to brown with lighter stripes on their sides and back. In some ways they look similar to Fall armyworms.

These caterpillars can cause extensive damage below the crop canopy before they are detected. Controls are suggested when 4 to 5 larvae per square foot are found and feeding is heavy on the lower leaves. It is important to protect the flag leaf.

Most all insecticides labeled for small grains will provide adequate control. They are not as hard to kill as fall armyworms in cotton. However, good coverage is important, especially when making applications by air.